A Practical Treatise on Coal Mining

George G. Andre · 1875 · Coal Mining

19th-century treatise on coal mining — practical geology, shaft-sinking, level driving, getting the coal, haulage, winding, drainage, and ventilation.

Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.

fyxMll nivmii J

Me

Fund

BOUGHT WITH THE INCOl FROM THE

Sage Endowment

The Gift Op

HenrB Sage

...A:3A..A.U

Cornell University Library

3 1924 091 892 491

The original of this book is in the Cornell University Library.

There are no known copyright restrictions in the United States on the use of the text.

://www.archive.org/details/cu31924091892491

y

Mining Engineering.

Practical Treatise

On

Coal Mining.

By

.ASSOC. DJST. C.E. : MINING CIVIL KNGINEER j MEMBtfi OF THE faOCIETY OF ENGINEEES.

Volume Xl

E. & F. N. Spon, 125, Strand, London.

New Yoek: 12, Coetlandt Steeet.

University Ubrarv

Dt

Contents Of Volume Ii

CHAPTER V. — continued. DEIVING OF LEVELS, OK NAEROW WOEK.

The Operations of Driving — Ventilation of the Working Places — Stone Drifts — Machine Boring — Timbering — Walling

Pages 277-304

Chapter Vi.

SYSTEMS OF WOEKING. Post-and-Stall Workings— Long- Wall Workings 305-313

Chapter Vii.

Getting The Coal.

Long-Wall Workinas — Special Methods of Working applicable to Thick Seams — Square Work — Long-Pillar Work — Thin Seams — Material for Stowage — Details of Working by Long WaU — Details of Working by Post and Stall — Coal-outting Machines 314-344

Chapter Viii.

HAULAGE. Tubs — Eoads — Motors— Self-acting Planes — Systems of Haulage— Tail-Eope System — Endless-Chain System — Endless-Eope

Chapter Ix.

Winding.

Guides and Keeps — Cages — Head-Gear — Eopes — The Engine and its Accessories— Winding Drums — Winding Engines — Accessory Arrangements and Precautionary Measures — Cost of Winding . . . . . . . . . . 395-424

Chapter X.

DEAINAGE. Underground Water — Pumping Machinery — Cornish Pumps — Cornish Pumping Engines— Direct-acting Differential Pumping Engine — Erection of Pumps ., .. ,. .. ., .. .. .. .. 425-453

Vi Contents.

Chapter Xl

Ventilation.

Constitution of the Atmosphere of Coal Mines — After-Damp — Diffusion — Volume of the Ventilative Current — Measurement — Thermometer — Barometer — Water Gauge — Anemometer — Eetardation of the Flow of Air — Ventilative Arrangements — The Furnace— The Fan Pages 454-499

Chapter Xii.

INCIDENTAL OPEEATIONS. Lighting the Workings — Boring for Water — Dams — Undergroimd Fires .. .. .. .. .. .. 500-517

Chapter Xiii.

SUEFAOB WOEKS. Pit-head Gear — Engine House — Coke Ovens — Tramways — Miners' Dwelling Houses ,. .. „ ., 518-520

Chapter Xiv-

MANAGEMENT A.ND ACCOUNTS. Duties of the Engineer in Charge of a Colliery — General Eules — Special Eules .. ., .. „. „ 521-531

Chapter Xy.

CHAEACTEEISTICS OF THE COAL FIELDS OF GEEAT BEITAIN AND AMEEICA. The Durham Coal Field— The Cumberland Coal Field— The Yorkshire Coal Field— The Lancashire Coal Field— The Cheshire Coal Field— The North Staffordshire Coal Field— The South Staffordshire Coal Field— The Shropshire Coal Field — The Leicestershire Coal Field — The Warvdckshire Coal Field — The Somersetshire Coal Field — The Forest of Dean Coal Field— The South Wales Coal Field— The North Wales Coal Field— The Coal Fields of Scotland— The Coal Fields of Ireland— The Coal Fields of the United States of America 532-538

List Of Plates.

Plate Figs.

I. — Geological Diageams and Sections 1-3

11.- „ „ „ 4-10

in.— „ „ „ 11-16

Iv.- „ „ „ 17-24

V. „ „ „ 25—29

VI.- „ „ „ 30-34 VII. — Chaeaoteeistio Fossils op the

SiLUEiAN Period 35-63

VIII.— „ „ .. 64-70 Chaeacteristic Fossils of the Devonian and Old Bed Sandstone Periods 71-78

Characteristic Fossils of the

Carbon Period 79-83

Ix.— „ „ .. 84-113

X.— „ „ .. 114-129 XI. — Characteristic Fossils of the

Permian Period 130-144

Labteinthodon Kemains of the

Triassic Period 145-146

XII. — Characteristic Fossils op the

Lias 147-160

XIII.— Boeing Tools 161-177

XIV.— Boring Eods 178-185

Boring Frames 186-191

Xv.— „ 192-195

Xvi.— „ 196-200

XVII.— Boeing Appllancbs 202-215

XIX. — Mather and Platt's Book -boring

Machine 224-225

Xx.- „ „ „ .. 226-233

XXI.— Shovels 234238

Picks 239-252

Wedges 253-256

Sledges 257-268

Pick and Sledge Handles or

Helves 269-274

Plate Figs.

XXII.— Hand Blasting Gear 275-300

XXIIL— EooK Drills— Dubois-Francois .. 301-304

„ Sachs .. .. 305-308

XXIV.— „ Burleigh .. .. 309-312

„ Kainotomon .. .. 313-314

XXV.— „ Ingebsoll .. .. 315-318

XXVI.— „ Darlington .. .. 322-327

„ Warsop 328-329

XXVII. — Strbtchbe Bah for Eock Drills 330 Air Compressors — Sarrbbhuck .. 332-334 XXVni.— „ Coz.LAioN'i .. 335-341 XXIX.— „ Blanzy .. ., 342-344 XXX.— „ EoNOHAMi? ,. 345-349 Air EECBnnEaa ,. ., ,. , 350-351 XXXI. — Sturgeon's High-speed Aie Compressor 352-354

Air Pipes .355-356

Electric Blasting Fuses .. .. 357-367

XXXII. — Bornhardt's Electrical Machine 368-371

XXXIII.— Blasting Diagrams 372-382

XXXIV.— Sinking Bucket and Hooks .. 383-385

Curbing 386-390

XXXV.— Shaft Walling 391-394

Iron Kibble 395

XXXVL— Pit-head Frames 396-398

Iron Kibble 399

Shaft Walling 400

XXX VII.— Blasting Diagrams 401-406

XXXVm.— Curbing 407-411

XXXIX.— Tubbing 412-418

Xl.— „ 419-424

Piling 425-426

XLL— Tubbing 427-430

Xlil— „ 431-432

Kind - Chaudron Shaft - sinking

Apparatus 436-439

List Of Plates.

Plate

Xl Viii.-

Lx.—

Lxi.— Lxii.—

KiND - Chaudbon Shaft - sinking

Apparatits 440

DiAGEAMS OP Shaft Divisions .. 441-445

„ OP Levels 446-447

Blasting Diagrams 452-457

Brain's System op Boeing .. .. 458-459

Walling 474-475

Diagram of Thrust and Cebep .. 476

Workings in Coal — Post and

Stall 477

„ „ Long Wall 479

Effects op Cleat 483-484

Workings in Coal — Long Wall . . 485

„ „ Square Work 488

„ „ Long Wall.. 489

-Means of obtaining Pack .. .. 491-496

Timbering 497-500

Winstanley and Barker's Coal

Cuttee 501-502

Economic Coal Cutter 513-516

-Bails 517-519

Tubs 520-523

Plate Pigs.

LXX.— Tubs 524-529

Tramways 563-565

Lxxil— „ 566-572

LXXIIL— Inclined Planes 573-576

Friction Eollbes, Clip Pulleys,

and Sheaves 577-585

LXXIV.— Diagram of Inclined Planes .. 586

LXXV.— Tail-Eope System 587-593

Endless-Chain System 594-595

LXXVL— Endless-Eope System— No. 1 ,. 596-599

No. 2 .. 600-604 LXXVII. — Diagram showing Position op

Guides 605

Cages 606-613

Diagrams of Strains in Head Gear 614-617

LXXVIIL— Pit-head Frames 618-622

Lxxix.— „ „ 623-630

Diagrams op Curve for Balance

Truck 637

LXXXl.— Balance Bob 638

Angle or V Bob 639

Vibrating Kod 640

Coenish Pump 641-643

Top Nozzle, Coenish Pumping

Engine 645

Bottom Nozzle „ „ 646 Cataract „ ,, 647-648 LXXXII. — Cornish Pumping Engine .. ., 644 LXXXIIL— Davey's Direct- acting Differential Pumping Engine .. .. 649-658

LXXXIV.— Ventilating Furnace 663-665

GuiBAL Fan 666-667

Deiving Of Levels, Oe Naekow Woek. 281

first of these is the necessity for providing for the flow of the water towards the bottom of the shafts from which it is to be raised. This necessity compels the miner to drive his level in a slightly ascending direction. The second circumstance is the desirability of facilitating the bringing out of the trains of loaded tubs. This question is one of great importance, since by adapting the fall of the road to the load to be conveyed over it, a large saving of labour may be effected, an advantage particularly noticeable when horse power is employed as the means of traction. Experiments have shown that an incline of 1 in 130, or a little more than i inch in the yard, gives the maximum of advantageous effect to horse power, in drawing the loaded tubs down and the empty ones back, and therefore, where practicable, this inclination should be adopted. But it will be obvious, on reflection, that in very long levels, such as would be driven when it is desired to gain the greatest possible area from one winning, this degree of inclination would be too great, inasmuch as the extreme end would be too elevated. In such cases the inclination given to the level is usually 1 in 200, or a little less than inch to a yard. Besides this necessary inclination, it is of the highest importance that a level should preserve in every portion of its length a rectilineal character ; that is, it must be driven from one end to the other in a perfectly straight line. Or, if the circumstances are such that this condition cannot be satisfied, it should be driven on a curve with a large radius. It is easy to see that the fulfilment of such a condition, in laying out the principal roads of a mine, is favourable to the transport of the produce, and conducive to economy in every way. When the traction i& effected by steam power, it is essential that the roads be perfectly straight. This will more clearly appear when we come to consider the question of haulage.

The OPERATioisrs of Driving. — When a level is driven singly, it has to be divided by a brattice for the purpose of promoting ventilation, in the same manner as the shaft. Or, instead of the brattice, an air pipe may be laid along the level, and its outer end placed in communication with a furnace or with a fan, by means of which the air is exhausted from the working face, and a current kept up in the way already described for the shaft. The fan is sometimes made to force air up to the working face. But in driving the main levels of a mine this difficulty is generally avoided by driving them in pairs, and cutting, at intervals, a communication between them for the passage of the ventilative current from one to the other. We will, therefore, assume that the levels a b and d e, Fig. 446, are started simultaneously from the shafts D and U, in a direction at right angles to the dip.

Driving in a given Direction and to a given Inclination. — Before commencing the actual operations of driving, it is necessary to make oneself acquainted with the means commonly adopted of preserving the direction of a level, and of giving it its due inclination. The former end is attained by means* of certain fixed points, first determined by an instrument of precision, as the dial or the theodolite, and afterwards preserved, in most cases, by simple expedients. These fixed points consist of two plumb-lines suspended from the roof of the heading in such positions that a straight line passing through them in the same horizontal plane shall either coincide with the axis of the excavation or be everywhere equidistant from that axis ; in other words, that this line shall be in the direction in which the level is to be driven. The plumb-lines are placed from 10 to 20 yards apart, the greater distance giving the more accurate indications. To ascertain the correctness of the driving, the man in charge of the work places himself behind the first line in such a position that the two shall appear to coincide, that is, shall be " in line." If these plumb-lines then divide the " face " of the heading vertically into two equal parts, the driving is progressing in the right direction. When the plumb-lines, or "points," as they are usually called, are fixed to the timber of the roof,

282 Mining Engineeeing.

there is always a risk of error from the shifting of the timber as the rock settles down upon it. To guard against the error arising from this source, the points are sometimes suspended from the solid rock rather than from the timber. If three points are used instead of two, any movement of one makes itself at once apparent.

The mode of procedure in testing the accuracy of the driving is as follows : The line of the point nearest the working face having been chalked to make it reflect the light, a candle or lamp is placed near, to illumine it. The man whose duty it is to attend to this matter then places himself, as before remarked, behind the other point in such a position that the two shall be in line ; at the same time a workman, provided with a light, places himself at one side of the working face. This man moves his light backward and forward across the middle of the face, according to the directions of the observer, until the two lines of the points cut the flame. The point on the face directly behind the flame is then marked, and the distances of the two sides from this point measured, to ascertain if they be equal. If this equality exists, the driving is progressing in a straight line. By suspending lamps from the plumb-lines, the operations of testing may be performed by one man provided with a plumb-line and stationed at the working face.

When the driving has progressed 20 feet, or if preferred 30 feet, beyond the nearest point, a shift must be made to bring the point up nearer. To do this, a candle or lamp is placed at the face in the same vertical plane as the plumb-lines, in the manner already described ; that is, it is made to occupy a position in which the lines cut the flame. Then, while the observer remains at his post behind the distant point, a third plumb-line is held up near the face of the heading, and moved backward and forward until it is seen to be in the same vertical plane as the other two and the light immediately behind which it is held. In this position it is fixed to the roof, and the distant point is removed. These operations, though extremely simple, demand very great care ; for perfect accuracy in their performance is indispensable to prevent the level from deviating from the straight line, or, in miners' language, from getting " loose." To guard against error, it is well to test the accuracy of the points occasionally with the dial.

The means employed for giving the requisite inclination to the floor of the level are also of a simple character, and demand care in their application. As the inclination, or " pitch," as it is commonly termed, is always towards the shaft, that is, away from the working face, the flow of the infiltering water is first made use of as a means of ascertaining the direction and approximately the degree of inclination given to the floor. A small drain is made along the lower side of the level to convey the water back to the sump, and the flow of this water as it enters from the face shows the direction of the dip of the floor at that point, and also indicates, roughly, by the rapidity of its motion, the degree of the dip.

To keep the floor of the level even, all the slight irregularities of the bed must be cut through, whether it be necessary to remove coal or stone. How far this regularity may be observed when faults occur will depend upon their magnitude. Under such conditions, it may become necessary to change the direction of the level in order to catch the coal on the other side of the fault. Such questions as these must be determined by the circumstances of the case. It should also be remarked here that in driving a level with an upward inclination, there is always a tendency to rise too fast, which tendency must be guarded against by frequent checking with the instruments.

The instruments used for this purpose are of a very simple character. In England, an ordinary " T-bob " is commonly employed. The foot of this T-bob is set at an angle with the vertical piece

Deiving Of Levels, Oe Naeeow Woek. 283

from wliicla tbe plummet is suspended, corresponding to the angle of inclination to be given to the floor. Pig, 448 shows the bob as constructed in this manner. It is used by placing it upon the tram plates or rails with which the level is laid. On the Continent, the form of T-bob employed is that represented in Fig. 449. It is usually of iron, and consists of a rule or straight-edge c d, sometimes 12 feet in length, but oftener only about 6 feet, by reason of the difficulty of turning it in narrow headings ; two feet a c and h d ; and a piece i e perpendicular to the straight-edge. The rods fg a and f g b are merely for the purpose of rendering the instrument more rigid. At h, a brass plate is inlaid in the straight-edge, and above it at i is fixed the point from which the plummet is suspended. When the plumb-line coincides with a line engraved upon the brass plate at h, the extremities of the instrument a and 6 are in the same horizontal plane. The mode of determining this line, or of verifying it, is as follows : The two feet at the extremities of the straight-edge are set upon the heads of two spikes driven into the ground, so that the plumb-line may fall to one side of the plate ; this point is marked, and the instrument turned round and again set upon the spikes. The position of the plumb-line on the other side of the plate is marked in like manner, and the space between the two is divided into two equal parts. A vertical line passing through the point of division will be the line required.

To apply this instrument, the miner provides himself with two spikes, and a number of metal discs of known thickness. Having driven the level as nearly to the required inclination as possible by sight and the indications of the water, he drives the spikes into the ground at a distance apart equal to that of the feet of the instrument. We will assume that the length of the instrument is 12 feet, and that the inclination to be given to the floor is a quarter of an inch in the yard. Having driven in the spike that is farthest from the face, the miner places upon the head of this one a sufiicient number of his discs to make up a thickness of one inch, and sets one foot of the instrument upon the discs. The second spike is then driven down, at a distance of 12 feet nearer the face until, the other foot of the instrument having been set upon it, the plumb-line coincides with the line engraved upon the brass plate. The heads of the spikes are then so situate relatively to each other that a line joining them will have an inclination of a quarter of an inch in a yard. Instead of having recourse to the discs, one of the feet may be made to slide through a socket, and capable of being held in any part by means of a thumb-screw provided for that purpose. In such a case, this leg would be graduated, say to sixteenths of an inch, and before being set upon the lower spike it would be made to project beyond the other by one inch, in order to give an inclination of a quarter of an inch in a yard, with the conditions of length previously assumed.

Besides the tests afforded by the comparatively rough means and methods described in the foregoing paragraphs, it will be necessary to check the accuracy of the results obtained, from time to time, with the spirit-level in the ordinary manner.

Driving the Heading. — As before remarked, the two levels constituting the water-level and the rolley-way will be started at the same time, and carried forward at the same rate of progress. This rate will be generally a rapid one, since the driving is mainly in coal. In the example chosen for the purpose of illustration, it is assumed that the seam is of such a thickness and the roof of such a nature that the whole of the coal will have to be removed, without stripping down any of the rock. In this case, therefore, the driving will be wholly in coal.

In driving a level through coal, the first operation is to " hole " or " undercut " the face. This holing or undercutting consists in cutting a groove with the pick between the clay of the floor and

284 Mining Engineering.

the coal above, by removing a portion of the latter so as to undermine the mass. The groove or holing is carried in to a depth of about 30 inches, and the width of the holing is kept as small as possible for the sake of the produce ; for it will be evident on reflection that the coal which is chipped out from the holing will be in so broken a form as to be valueless. In holing the face, the miner lies on his side and swings his pick horizontally. This operation will be more fully described in the chapter devoted to getting the coal. If the coal be of a very weak and tender character, it may be necessary to support portions of the undermined mass during the holing by short wooden props called " sprags " ; but in these narrow workings such supports may be safely dispensed with when the coal is strong. When the undermining has been effected, the mass is shorn away at the sides. This operation is a kind of vertical holing, a vertical groove being cut on each side between the mass to be removed and that which is to remain. The depth of these grooves is, of course, equal to that of the undercutting, and the same reasons exist for limiting the width. When the undercutting and the vertical side shearing have been completed, the mass of coal to be dislodged is left unsupported on three sides, and it only remains to break it away from the fourth side to free it altogether. This operation is called by miners "falling" the coal, and is performed either by means of wedges or by blasting with gunpowder. When wedges are employed, they are driven in between the coal and the roof, and under the conditions which exist, their action is suflScient to break down the whole mass. The wedges are inserted at intervals of a few feet apart, and driven in with sledges. To complete the falling of the mass, the iron bar is made frequent use of. When the coal is very strong, and often when it is not strong, the falling is effected by gunpowder. A few shot holes are rapidly drilled by hand in the upper part of the soft coal, and lightly charged. A light tamping of shale is quickly forced in, the material being always ready at hand, and the blast is fired with but little delay. The effect of the blast is invariably to bring down the mass in the most complete manner ; but the coal is much more broken by this means than by the wedges. The effectiveness of the operation, however, and the ease and rapidity with which it may be performed, are usually sufficient to induce the miner to adopt it in preference to that of wedging, notwithstanding the better condition in which tbe latter leaves the coal.

When the coal has been brought down, it is broken up into blocks as large as can be conveniently handled, and conveyed in tubs to the shaft to be raised to surface. It was remarked in a preceding chapter that coal, like rock, increases largely in bulk when broken up, and this fact is an important one when estimating the cost of a driving and in making provision for the execution of the work. It is impossible to ascertain, without experiment, what the exact increase of bulk will be in any given case, since it depends upon several variable conditions, to be hereafter described. But a general average may be taken which shall be sufficient to constitute a basis of calculation, where only approximative results are required. Such a value is to be attributed to the following proportions :

The increase in the bulk of coal when broken up is, as already stated, in the proportion of 1 to 1 6 ; that is, a cubic yard of coal in the seam will occupy a space of 1 6 cubic yard when removed and broken up. The value of 1 6 cubic yard in feet is 43 2, and if no modifying circumstances exist, a tub

having a capacity of 24 cubic feet will contain -— of this quantity. Hence there will be required

43" 2

-j- 1 8 tub to convey away this quantity ; in other words, one cubic yard of solid coal will

break up into 1 8 tub load. But the size of the tubs employed will materially influence the degree

Driving Of Levels, Or Narrow Work. 285

of increase in bulk, this increase being greater in tubs of small capacity than in those having larger

dimensions. Thus when small tubs are used, a relatively greater number of loads will be obtained

from a cubic yard of coal. Also the increase in bulk will be greater when the coal is strong, and,

consequently, breaks up into large blocks, for the larger the blocks the more spacious are the voids

existing between them. When the excavation is in rock, the distance of the shot-holes apart, and

the strength of the explosive employed, will hence influence the increase in bulk. For when deep

holes widely spaced are adopted, the rock is brought out in larger fragments than when the blasting

is carried out in numerous shallow holes ; and the stronger the explosive, the more shattered is the

rock. In estimating the increase in bulk, therefore, according to the average given, these modifying

circumstances must be taken into account. Grenerally the increase of bulk in the levels of a mine,

where the tubs used for the extraction of the material are small relatively to the trucks employed

in excavations coming out to day, as the heading for a railway tunnel, for example, may be

taken as 1 to 1 75 for coal ; 1 to 1 70 for shale ; and 1 to 1 80 for sandstone. That is, a cubic

yard of these substances will occupy, when broken up, a space of 1 75, 1 70, and 1 80 cubic yard

respectively.

As these substances increase in bulk on being broken up, they of course decrease in weight

in a like proportion under the same conditions. Thus, if we take the average weight of bituminous

coal as 79 lb. the cubic foot 2133 lb. the cubic yard, its weight when broken up will be

YTffR 1219 lb. the cubic yard, or 45 lb. the cubic foot. Hence, a tub having a capacity of

24 cubic feet, will contain 45 x 24 1080 lb. 9 cwt. 2 qrs. 16 lb. In like manner, the weight of shale being 153 lb. the cubic foot, that substance will weigh 90 lb. the cubic foot when broken up; and the weight of sandstone being 158 lb. the cubic foot, this rock will weigh in a broken state 88 lb. the cubic foot. A tub of the same dimensions will, therefore, contain 90 x 24 2160 lb. 19 cwt. 1 qr. 4 lb. of the former; and 88 x 24 2112 lb. 18 cwt. 3 qrs. 12 lb. of the latter.

To facilitate the removal of the coal and rock dislodged from the face of the heading, the floor should be laid with a double line of tram rails. These may be of light weight, and of any form that may be deemed suitable to some of the requirements of the case. When the driving is executed with the aid of machine drills, the floor is frequently laid with only one line, from which sidings are laid off as required. These tramways are only of temporary character, to be replaced by the permanent lines when the excavation is completed.

Ventilation of the Working Places. — It has been remarked that one of the objects in driving two levels simultaneously is to obtain a good ventilation of the working places. By referring to the plan shown in Fig. 446, Plate XLYI., it will be seen that the air from the downcast shaft will make its way up to the heading a 6 in suflScient quantities to keep the atmosphere at the face cool and pure to a certain distance from the entrance. This distance will depend upon the strength of the ventilative current, and the potency of the causes of vitiation. G-enerally the distance allowed will be from 30 to 40 yards. Supposing then each level to have been driven as far as the ventilative conditions will allow, an air passage will be cut through from one to the other at that point. This passage, which is shown on the plan at xy, is in many localities called a "third," and the operation of driving it is called " thirling." When the first thirling has been completed, the direct connection between the shafts is stopped by building a wall of brick or stone in the drift connecting them, as shown at s.

286 Mining Engineeeing.

It may be remarked here that all "stoppings," as these artificial obstructions to the passage of the air current are called, which are situate by the side of the main ways should be well and strongly built, and be further strengthened by a stowing or backing of five or six yards of rubbish behind them. The importance of this will be made apparent in the chapter devoted to the subject of ventilation.

As the air-way directly connecting the two shafts is stopped, the whole of the ventilative current descending the downcast will pass up the heading a b, through the third y, and down the heading d e, to the upcast shaft U, By these means the working faces of both headings will be ventilated by the full current. The air follows this course during the subsequent operations of driving, which are continued until the influence of the current has again become insufficient, say through another 40 yards. A. second thirling x'y' is then made, and a stopping put into the first XT/. The passage through xy being closed, the air will pass up to the new third, and again efficiently ventilate the working faces. These operations of driving and thirling are repeated throughout the length of the levels. When spoken of relatively to the ventilative current, the level which receives its air directly from the downcast shaft and conveys it up to the working places is described as the " intake," and that which receives its air from the working places after passing through the " intake," and conveys it to the upcast shaft, is described as the " return."

If the coal give off much gas, it will be impossible to continue the driving of the level throughout a distance of forty yards under the influence of a ventilative current passing through the third in the manner described. Under such conditions it becomes necessary not only to bring the current up to the working faces at intervals, but to compel it to pass constantly in close proximity to those points. As it is undesirable to third at very frequent intervals in order to meet this requirement, the expedient of the " brattice " is resorted to. This brattice is similar in nature and in construction to that used in the shaft during the process of sinking, but being of a more temporary character, it may be more lightly constructed. The use of the brattice is to divide the level longitudinally into two portions, aud to accomplish this purpose it is erected vertically by being fixed against the floor and the roof of the level. The material employed is chiefly wood ; but the quantity required and the labour of fixing and removing it are, in numerous cases, greatly lessened by the substitution of prepared canvas, called "brattice cloth," for the boarding or " leading " of the wooden brattice. Of course, the character of the brattice and the care bestowed upon its construction will, in some degree, be determined by the nature and the potency of the causes of vitiation in the atmosphere. When much gas is given ofi", a strong current of air must be maintained at the working face and to insure this, the joints of the brattice must be made fairly air-tight. Under all circumstances however, where a brattice is needed, these joints will demand careful attention, for though the amount of leakage through any individual joint may be small, collectively the loss due to that source may be sufficient to reduce the strength of the current passing the face in a very important degree. The position of the brattice is shown in m n, Fig. 446. It will be seen that the air is compelled to pass up to the face of the intake level, and back to the third, from which it is again compelled to pass up to the face of the return level by the brattice there similarly placed. The course of the ventilative current is shown by the arrows on the plan. As the heading advances, the brattice is continued forward until the point for the next thirling is reached, when it is removed and again applied to the next length. If the seam of coal be gassy throughout, the bratticing will have to be repeated from thirling to thirling; but sometimes the seam is foul at certain points only — in the vicinity

Deiving Of Levels, Oe Naeeow Woek. 287

of a fault, for example, in which case, the brattice may be required only when passing these points.

Stone Drifts. — Hitherto we have supposed that the pioneer excavations of the mine have been driven in the coal. But it is often necessary to drive headings of this character through the rock, and in such a case the excavation is called a stone drift. These drifts may be required for many purposes, and they may possess every degree of importance. We have, however, now to consider only those through which the workings, or portions of the workings, are opened up. In the Continental coal-fields pioneer, stone drifts are especially common. When, for example, a seam of coal lies at a high angle, the shafts may be sunk upon or near the outcrop, and carried down vertically to a sufficient depth. From this point, a stone drift is put out and driven horizontally in the direction of the dip to cut the seam. From this point, the levels may be driven out in the coal in a waterlevel direction, and the drift used as a main roadway to the shaft. The drift may be carried to the boundary of the concession or royalty for the purpose of cutting and proving all the seams situate within it, such exploratory work is very frequently performed. These drifts are driven through all the intervening strata, and hence they are described by French and Belgian miners as travers-hands. Frequently a stone drift is required to recover a seam lost by a fault. The coal measures of the Ronchamp district, in France, have been much disturbed, and are crossed by a series of parallel ridges. Against the flanks of these anticlinals, the coal seams die out, or they pass over the crest as a thin carbonaceous band, often less than an inch in thickness. When the workings have been carried up to one of these ridges, a stone drift is driven through to reach the seam, which is found of its full thickness on the other side. Sometimes the stone drift will take the form of a tunnel or adit driven into a hillside for the purpose of proving and working the mineral, or for draining off the water. But whatever the purpose may be for which it is required, the stone drift possesses the peculiarity of passing through the barren rock or " stone " of the measures, and hence is subject to conditions which do not exist for the ordinary workings in the coal.

As stone drifts are excavated in rock of a more or less hard and compact character, the operations of driving will consist wholly of blasting. This work will thus afford a favourable ojjportunity for applying the principles explained in the preceding chapter, so as to execute it with the highest attainable degree of economy. In the execution of this work, indeed, a want of attention to those principles will inevitably lead to an enormous expenditure of labour and material, and it becomes imperatively necessary to exercise in such cases skill, judgment, and supervision, to prevent a ruinous cost of time and money. The operations of blasting have been fully described relatively to hand boring, and it only remains now to consider some of the principles according to which machine labour must be executed. It may be remarked that these principles will apply, with slight modifications in some cases, to shaft-sinking also, under which head they were only briefly explained.

Machine Boring. — The excavation of stone drifts affords peculiarly favourable conditions for the application of machine drills. And as rapidity of execution is here often of paramount importance, the advantages to be derived from the adoption of machine labour are great and manifest. Hence it is that driving by hand is being gradually abandoned in favour of the new system ; and as this system is certainly destined to become general, it behoves us to consider it somewhat in detail.

Preliminary Conditions and Provisions. — When a spacious stone drift is driven by hand, it is usually made narrower at the top than at the bottom, on account of the difficulty of working at that

288 Mining Engineeeing.

part. But when machine labour is employed, the sides are always made vertical. This gives a somewhat larger sectional area for the same base. But to enable the machines to work freely, the width of the driving at the floor is generally made a little greater than when the labour is to be performed by hand. Thus it is requisite to remove a larger cube of rock when machine boring is adopted; but against this disadvantage must be set greater spaciousness and convenience in the finished drift. The dimensions of the drift will be generally those which afford the most favourable conditions to a rapid advance, since these will be amply sufficient for the subsequent prosecutions of the workings. Such dimensions should admit of a man reaching, when standing upright, all the points in the face of the heading, and allow ample space for men to work in on each side of the machine when the latter is set near the centre, that is, when the support of the machine runs upon tram rails. Thus the height must not exceed 7 feet, nor be less than 6 feet 6 inches ; and the breadth should reach 6 feet as a minimum. It is undesirable to increase the breadth beyond the limit required by convenience in working, since to exceed this is to increase the diflSculty and the labour of shifting the machine laterally. The maximum breadth may, therefore, be fixed at 7 feet. A section of 7 X 7 feet is frequently adopted, and found to be very favourable to the exigencies of machine labour.

The choice of a machine drill suitable to the conditions of underground boring ; the design and power of the air-compressing machinery for the supply of the motor fluid ; the capacity of the reservoir in which the compressed air is to be stored ; the material, dimensions, and mode of fixing the pipes through which the air is conveyed from the reservoir to the machines ; and the best form of drill bits for rock of a given character, are matters that have been fully described in the preceding chapter. It now remains, therefore, only to treat of the operations of boring, and those which are immediately dependent on them. A few additional remarks on the air-pipes may, however, not be out of place here. There is a tendency to employ pipes of needlessly large diameter for the purpose of reducing the friction. But this friction occasions only an insignificant loss, provided the diameter be not excessively reduced. This is notably the case in mines, where the length is seldom very great, and where the additional head due to the depth of the shaft nearly compensates the loss incurred. A reduction of one inch in the diameter of a pipe involves a very important diminution in the mass of the metal, and this diminution materially lessens the first cost. And as the first cost of the machinery and its accessories is often the sole obstacle to the adoption of the mechanical system of boring, this is a matter deserving of careful attention. A diameter of 4 inches for the main conduit will be amply sufficient in all cases, and frequently 3 inches may be adopted with advantage. And within certain limits, the diameter of this pipe may be fixed at from 3 inches to 4 inches, irrespective of the quantity to be passed through it in a given time. The intermediate portion of the piping, that is, that portion which takes the air from the main conduit and conveys it to the points from which the several branch pipes take it, should be from 2j to 2f inches in diameter, and those terminal branches which convey the air to the points at which the machines are being applied should be from inch to If inch in diameter. The most economical material for the air-pipes is wrought iron, when the conditions underground are favourable to its durability. To provide for the expansion and contraction due to the changes of temperature, the compensating joint, previously described, should be inserted at surface, and down the shaft ; but it will not be required in the levels of the mine. The simplest and cheapest method of fixing the pipes is to lay them upon the floor of the levels, and in one of the angles ; but it will be found more advantageous to suspend them from

Deiving Of Levels, Oe Naeeow Woek. 289

the roof, or against the sides of the excavation by means of clamps, because when in that position they are visible in every part, and readily accessible for repairs, should a leakage occur. A leakage is also at once detected when the pipes are everywhere exposed. At the Saint Grothard Tunnel, the safety-valve was placed upon the pipes as near as possible to the working faces instead of on the reservoir, for the purpose of utilizing, as a ventilative current, the air which escaped when the pressure became excessive.

Boring the Shot-holes. — It has already been remarked that the exigencies of machine labour render it impracticable to follow closely the principles which lead to economy of labour and material in blasting. In hand boring, economy is gained by reducing to a minimum the number of holes and the quantity of the explosive substance required. But in machine boring, economy is to be sought mainly in the reduction of the time needed to accomplish the driving. Attempts have been made to assimilate the methods of machine boring to those adopted for hand labour, but the results have not been satisfactory. On the contrary, the conditions determining the position and the direction of the holes relatively to the production of the greatest useful effect have been wholly ignored in favour of those which determine the most rapid boring. This system has been attended with more satisfactory results. Another system, partaking of both the preceding, is widely adopted, and hitherto the best results have been obtained from this, which may be regarded as a compromise between conflicting conditions. Thus we have three systems of executing machine boring : one in which a single machine is used upon a support capable of holding it in any position, so as to be able to bore at any angle, and in which the holes are placed according to the lines of least resistance, as in hand boring, A second, in which several machines are fixed upon a heavy support, allowing but little lateral or angular motion, and in which the holes are placed at regular intervals apart, and bored parallel, or nearly parallel, with the axis of the excavation, irrespective of the varying nature of the rock, and the lines of least resistance. And a third, in which it is sought, by the employment of one two, or at most three machines, upon a simple and light support allowing the position and direction of the machine to be readily changed, to satisfy, in some degree, the two sets of conditions determining the two former systems, by placing the shot-holes as far in accordance with the lines of least resistance as the exigencies of a fairly rapid handling of the machine will allow.

In the first of these systems, the necessity for extreme lightness in the machine is unfavourable to its efficient action, and the great length of time consumed in changing the position of the machine, so as to comply with the conditions of resistance in the rock, render it impossible to attain a higher rate of progress than is reached by a well-regulated system of hand boring. With such a result, there is nothing to compensate the first cost of the machinery, or in any way to justify its adoption. In the second system, the time consumed in removing and fixing the machines is reduced to a minimum, and the chief portion of the time during which the machines are at the working face is, consequently, occupied in actual boring, a circumstance that is highly favourable to machine labour. Hence the rate of progress attained by this system is greatly in excess of that accomplished by hand labour ; and this superiority has led to the adoption of the system in several important cases, and has also led many to regard it as the most favourable to the exigencies of machine drilling. But as the holes are bored to suit the requirements of the machine, quite irrespectively of the resistance of the rock, their positions and directions are very unfavourable to the action of the explosive. This circumstance necessitates a much greater number of holes to ensure the fracture of the rock around

2 p

290 Mining Engineeeing.

each charge, and hence the time saved in shifting the machines is in part lost in extra boring ; besides which the consumption of powder is enormously increased. It would, therefore, appear that the full advantages of machine boring are to be obtained from the intermediate system, if carried out in accordance with all the conditions of the case.

Assuming that we have a machine and a support of such dimensions, weight, and construction as to be capable of being readily placed in position, it is evident that we shall still require a much larger number of holes than would be needed if the boring were performed by hand, because they are not placed wholly in accordance with the lines of least resistance. In some parts of the heading, indeed, these lines will have to be wholly neglected, in order to avoid the loss of time involved in shifting the supports ; for the principle upon which an intermediate system is based is to fulfil the requirements of the lines of least resistance, when that can be conveniently done, and to neglect them when such fulfilment would involve a considerable expenditure of labour and time. In this way, the time both of fixing and removing the machines and of boring is reduced to a minimum, and thus two conditions favourable to rapid and economical progress is insured. It is evident that when this system is followed, the face will not require the same number of holes at each blast. Another circumstance operating to increase the number of shot-holes is the desirability of bringing down the face in fragments small enough to be lifted without great difficulty. When the rock is completely broken up, the labour, and, consequently, the time of removing it after each blast, are lessened in an important degree. Hence there will be an advantage in placing the shot-holes sufficiently close together to insure the fracture of the mass between each. These circumstances render it necessary to bore a larger number of holes when the work is done by mechanical means. The boring of the additional holes reduces the superiority of machine over hand labour, and the additional quantity of the explosive required augments the cost of the work. To counterbalance these disadvantages, the shot-holes should be bored deep. It has already been pointed out that when a hole is once started with a machine, the rate of progress is immensely superior to that attained in hand boring, and to profit by this advaTitage the hole should be continued to as great a depth as practicable. This is sufficiently obvious, since it amounts to increasing the proportion of the whole time consumed that is occupied in actual boring ; for as it is in the rapidity of the operation of boring alone that the superiority of machine labour exists, it is plain that the longer the proportion of the time so occupied, the more marked that superiority will be. Thus by increasing the depth of the holes to the farthest practicable limit, we approximate as much as possible to the condition most favourable to machine boring. The intermediate system, therefore, which takes full advantage of this means, will lead to the best results. To recapitulate the main points of such a system, it should follow the lines of least resistance when that can be conveniently done, and neglect them when the fulfilment of their requirements would occasion a considerable expenditure of time. And to counterbalance the disadvantages of machine boring, it should employ shot-holes of as great a depth as is practicable.

Supposing such a system in use, it now remains to consider the operations of boring, and the subsequent operations of charging, firing, and removing the rock dislodged by the blast. Of the method of executing the boring, little remains to be said. It may, however, be well to direct attention to the necessity for keeping the holes clear of the debris. To ensure this, the bits should be chosen of a form suitable to the nature and the structure of the rock, and the hole kept well supplied with water. When the hole becomes deep, it should be cleared out with a scraper during

Deiving Of Levels, Oe Naeeow Woek. 291

the time of changing the bit, and in very argillaceous rock it may become necessary sometimes to withdraw the tool, and to remove the accumiilation with the scraper. When the debris does not work out freely, its escape may be facilitated by giving a slow motion to the tool, and then suddenly changing to a rapid motion. When several machines are employed, the maximum number that can be applied with advantage is one to the square yard of working face. The absolute number of holes required in any case will, of course, depend upon the tenacity of the rock and the development of the jointing planes, and also, in some degree, by the lines of fracture due to the preceding blast. The same circumstances will determine the distribution of the holes. Leaving minor variations out of account, however, the same distribution will be adhered to throughout the driving. The manner of distributing the holes over the face of the heading may be varied according to the judgment of the engineer in charge ; that is, the general features of the distribution to be adopted may be chosen to suit the requirements of the machines and their supports. Also, it should be noted that one method of distributing the shot-holes will require a less number of them than another. Some examples have already been given ; others will be found on Plate XLYIII. Fig. 452 represents the heading of the Mont Cenis Tunnel; Fig. 453, the Goschenen end of the Saint Grothard Tunnel ; Fig. 454, the Airolo end of the same tunnel ; Fig. 455 represents the face of a stone drift driven at Marihaye ; Fig. 456, a similar drift at Anzin ; and Fig. 457, a drift of the same character at Ronchamp ; the latter three examples being typical of the distribution adopted in the French collieries.

Charging and Firing. — The operations of charging the holes and firing the shots demand particular attention when machine labour is employed. It has been pointed out in the foregoing paragraphs that holes bored by machine drills cannot be placed or directed strictly in accordance with the requirements of the lines of least resistance ; but that, on the contrary, these requirements can only be approximately complied with, and in some cases must be wholly neglected. To compensate in some degree this defect of machine labour, the strength of the charges should be varied according to the resistance which they will be required to overcome. That is, the principles of blasting described in a former chapter, which cannot be complied with by the borer, should be strictly followed by the blaster in apportioning his charges. By this means, a great saving of the explosive compound may be effected, and that without difficulty or loss of time, if the blaster be intelligent and understand his work. A glance will be sufficient to show what charge a given hole of a known depth will require, and as cartridges of different sizes are ready at hand, no delay is occasioned m making up the charge. The holes in the centre, which are intended to unkey the face, will of course require the heaviest charge, since the conditions are there most unfavourable to the effects of the explosion. And the more complete the unkeying resulting from this first explosion, and the more fractured and jointed the rock surrounding the cavity thus formed, the more may the charges placed behind these unsupported faces be reduced.

As economy of time is in machine boring the chief end to be attained, the tamping should be done with dried clay pellets previously prepared. This material gives the greatest resistance, and thereby ensures the maximum of usefuleffect ; and if prepared beforehand, in the. manner described in the preceding chapter, the time consumed in tamping will be reduced to a minimum. An abundant supply of such pellets should always be ready at hand. In downward holes, such as are used in shaft-sinking, the plastic clay pellet and sand may be employed. This tamping may be put in very rapidly, and, in all but very shallow holes, it is very effective. When it is desired to

2 p 2

292 Mining Engineeeing.

use sand tamping in horizontal holes, and holes bored in an ascending direction, the sand should be made up in paper cartridges. The tamping employed in the St. Grothard Tunnel consisted of sand prepared in this manner. At the Mont Cenis Tunnel, an argillaceous earth was similarly prepared in paper cartridges for tamping.

Firing the charges also affords an occasion for the exercise of knowledge and judgment. A skilful determination of the order in which the charges are to be fired will in a great measure compensate the ill effects of badly-placed holes. The firing of a shot leaves the surrounding rock more or less unsupported on certain sides ; and it is evident that to profit fully by the existence of these unsupported faces, -the succession of explosions must be regulated so that each shall have the advantage of those formed by the preceding shots. This condition can be wholly fulfilled only by simultaneous firing; but when the firing is to take place successively, the condition may be approximated to by regulating the succession according to the indications observed in a careful inspection of the rock. Before firing the charges, the blaster should consider the relative positions of the holes, the stratification and jointing of the rock, the fissures caused by the preceding blast, and any other circumstances that may influence the results. The charges intended to unkey the face will be fired first, and those in the concentric series will then be fired in the order determined upon, by means of different lengths of fuse. The series will follow each other from the centre outwards. When a large number of shots regularly placed in series have to be fired, a convenient practical means of insuring the successive explosion of the series, in the case of the whole being lighted simultaneously, consists in bringing the fuses from all the shot-holes together in one point at the centre. This method of regulating the length of the fuses was adopted at the St. Gothard Tunnel.

Removing the Dislodged Rock. — As the removal of the rock brought down by the blast consumes a large proportion of the time saved by machine boring, it becomes necessary to provide means for reducing this loss to a minimum. The most important of these means consists in a suitable provision for the rapid removal of the machine to a place of safety, and a conveniently designed and well-laid tramway, upon which the rock may be quickly run out without confusion and its consequent delay. The number of tubs required to remove a given cube of rock may be readily ascertained, in the manner described in a former section ; and suificient provision should be made for the transport of these to " day " in the most rapid succession. The tubs should be of such dimensions as to be handled without great diflSculty ; the importance of this condition will be understood when the frequency of derailments is borne in mind. The shovelling up of the rubbish is greatly facilitated by laying iron plates in front of the face to be brought down previously to the firing of the blast. This expedient is generally adopted in important drivings. It has also been remarked that the dislodged rock can be more rapidly removed when it exists in small blocks. Thus there will be an advantage in placing the charges and in regulating their strength so as to completely break up the rock. Another matter of importance in the arrangements for the rapid removal of the rock brought down by the blast, is the proportioning of the number of hands employed to the requirements of the case. This number will increase with the size of the blocks to be lilted, the distance to be run over, and the want of suitability in the matiriel employed.

Division of Labour. — A proper division of labour is greatly conducive to rapid and economical progress. The operations may be divided into three series, namely, boring the shot-holes, charging and firing, and removing the rock dislodged. Each of these series of operations may be performed by different sets of men, and in several instances this division of labour has been adopted. But it

Dewing Of Levels, Oe Naeeow Woek. 293

does not appear that sucli a division leads to the most satisfactory results. The work of boring occupies a much longer time than either of the other two series of operations, and hence the distribution of the time is unequal. It has been found that generally, where all the arrangements have been well considered, the labour of charging the shot-holes, firing the blast, and removing the rock brought down can be performed in about the same time as that of boring. Thus it would seem to be more conducive to economy of time to divide the men employed into only two sets : one set to bore the holes, the other to perform all the subsequent operations. This division has been adopted in numerous instances with favourable results. Sometimes the whole of the operations have been performed by the same set ; but such an arrangement is not to be recommended. The labour of driving the machines is of too distinct and skilled a character to be confounded with that of blasting the rock and removing the de'bris, without a strong reason for such a proceeding, which does not appear to exist. Besides reserving a set of men specially for this portion of the work, it is desirable to keep the same men to the same machine ; for in such a case each man gets accustomed to the peculiarities of the machine entrusted to him, and besides conceives a kind of affection for it that leads to careful handling and watchful attention. In addition to the men required for the operations referred to above, smiths will be needed to resharpen the bits and to repair the machines. The amount of this labour will obviously depend upon the number of machines employed, and the hardness of the rock to be passed through.

Ventilation and Lighting. — A capital condition of rapid progress is an eflScient ventilation at the working face. The atmosphere in such a situation soon becomes greatly heated, and the fatigue consequent thereon tends to retard the progress of the operations. The sources of heat in a heading are : the rocks, the temperature of which may be greatly above that of the incoming air ; the bodies of the men at work, heated by violent exertions ; and the candles or lamps needed to furnish light to those employed. It is easy to see that these causes are sufficient to rapidly raise the temperature of the atmosphere, and that energetic means will have to be provided for counteracting the influence of these causes. The compressed air exhausted from the machines tends greatly to keep down the temperature of the atmosphere at the working face, especially when the compression has been carried to a high degree ; but it is scarcely sufficient to give the requisite coolness and purity during the operations of boring. All the subsequent operations have, of course, to be performed without this aid to ventilation. It is, therefore, necessary to have recourse to other means for the supply of fresh air. Some of these means have been already described, and others briefly alluded to. The use of the brattice to convey the air up to the face of the workings cannot be resorted to when machine labour is employed, on account of the obstruction which it causes in the roadway, or at least its use would occasion much delay, which it is desirable to avoid. Hence the only suitable means available is the air-pipe, such as has been already described. This pipe may be a wooden air-box, 12 in. x 12 in. in section, or an iron pipe having a sufficient sectional area. Usually it will be suspended from the roof of the drift. The outer end of the air-pipe is placed in communication with a small fan erected for the purpose, which fan may either force the fresh air through the pipe, or exhaust the vitiated air through that conduit. The former is known as the " plenum," the latter as the "vacuum " method, and there are advantao-es attaching to each. The most important cause of vitiation in the atmosphere of the level is the smoke and gases produced by the firing of the blasts. After each blast, it is necessary to wait until these gases and the smoke have cleared away before returning to the face ; and the time thus lost is very great. In machine boring, therefore, it becomes highly desirable to reduce this time to a

294 Mining Engineeeing.

minimum. When the fresh air is forced in through the air-pipe, it is delivered near the workingface, and the fumes due to the explosion are driven back to the mouth of the level or drift. In this way, the whole length of the drift is fouled. When, on the contrary, the vitiated air is exhausted through the air-pipe, the fresh air traverses the whole length of the drift before arriving at the working face ; but the smoke and the noxious gases are at once taken up, and conveyed away without fouling the rest of the drift. It would, therefore, appear that the method of employing the air-pipe as a return rather than as an intake is to be preferred. It should be remarked here that stone drifts are usually driven singly, and that, consequently, the method of ventilation adopted in driving a pair of levels is not applicable.

To ensure the proper execution of the work and the rapid progress of the operations, it is important that a good and constant light be thrown upon the face of the heading, and upon the machines themselves, in order that their action may be distinctly observed. To obtain this favourable condition, two strong lamps provided with reflectors are required, one close up to the face, and the other immediately behind the machines. Where several of the latter are used upon a heavy support running upon tram rails, one of these lamps may be fixed upon the fore part of the support, and the other upon the hinder part. The cost of two such lamps is far more than compensated by the facility afforded in working upon a face well lit up, with tools every part of which is plainly visible without the trouble of directing the light of a hand-lamp or a candle upon it. Besides these, small handlamps and candles will of course be required. Naked lights cannot be used near the machines on account of the blast from the exhaust ports ; lamps will, therefore, be more suitable in such situations. The deafening noise of the machines when at work on the face rendering it impossible for voices to be heard, makes it the more necessary that abundant light should be provided.

Brain s Radial System of Boring. — In the preceding chapter, the principles of a new system of machine boring, introduced by W. B. Brain, were briefly explained. This system is known as the " radial " system, the fundamental principle which constitutes its distinctive character being to make the holes of a series to radiate from a fixed point. The object ot this radiation is twofold, namely, to utilize the face of the heading as an unsupported side, and to reduce to a minimum the time consumed in changing the position of the stretcher-bar. It will be obvious on reflection, that if these ends are attained, without incurring a compensating loss, the merits of the system are beyond question, since their attainment leads to rapidity of progress, which is the main purpose of machine labour. It is evident that if the holes are made to radiate from a fixed point, and the horizontal position be avoided, none of them can be perpendicular to the face of the heading, and, consequently, the lines of fracture from each charge tend to reach this face. The importance of this will be understood if the principles of blasting, explained in the preceding chapter, have been fully comprehended. ' A consequence of this fact is that no unkeying of the face is necessary, since each shot tends to blow outwards. Thus the labour of specially angling the centre holes for this purpose is wholly saved. On the other hand, as all the holes have to be set at regular angles, additional time is consumed in the operation of setting the machine. But if we assume, as it seems just to do, that the gain and the loss in these- directions compensate each other, there still remains in favour of the system the reduction in the time consumed in changing the position of the machine support ; and when it is borne in mind that the time so spent constitutes a large proportion of that devoted to the operations of boring, the importance of the gain will be manifest. Hence it must be acknowledged that the end proposed by the designer has been attained in a degree that gives to the radial system a high

Deiving Of Levels, Oe Naerow Woek.

practical importance. The advantages offered by the system will be best appreciated from a description of the manner in which it is carried out.

Let it be assumed that the drift to be driven is 6 feet 8 inches in height ; the width in this case is immaterial to the operation of the system. The stretcher -bar, which is to serve as a support to the machine, is fixed at a certain height from the floor, and at a certain distance from the face, as shown in Figs. 458 and 459, Plate XLIX. The height of the bar above the floor, with slight modifications to suit existing conditions, will be the same in all cases ; but the distance of the bar from the face will be determined by the length of the machine, or at least by the distance from the centre of the clamp to the end of the piston-rod into which the bit is fixed. It is obviously desirable to reduce the distance between the face of the heading and the stretcher-bar to the least possible, since the angle of the holes will rapidly increase as this distance is diminished. The peculiar design of the clamp used with Darlington's drill renders the latter the most suitable to the system in this respect.

"When the stretcher-bar has been fixed in position, as shown in the drawing, Fig. 459, the boring is commenced, from instructions previously furnished by the engineer in charge. It has already been stated that the number of holes to be bored is determined by him, in accordance with the toughness of the rock and the strength of the explosive to be used, and when once the positions of the holes have been thus determined, they are required to be strictly adhered to, irrespective of joints, fissures due to former shots, irregularities of the face, or any other circumstance that may exist peculiar to the case. Thus the exigencies of machine labour are sought to be complied with rather than those of least resistance in the rock. The instructions furnished to the men respecting the boring of the shot-holes are drawn up in the following manner :

Insteuctions.—

Stretcher-Bar to be fixed

Heading, at

Stretcher-Bar.

Collibet.

1 ft. 8 in. from top.

5 „ bottom.

2 4 ,, face.

I. — 3 in. down from level

Holes.

n.-6f

5)

last hole .

IIL— 7i

)S

)j

v.— 6

Js

VI.— lOJ

Jj

J)

Bottom hole

Top

hole, 4 in.

above level

3 ft. 1 in. deep. 3 3 „

The instructions here show that after the stretcher-bar has been fixed in the position indicated, the top hole is to be started at a point 4 inches above the level of the machine ; that is, 4 inches above the point upon which the bit would strike when the machine is in the horizontal position. This position is shown by the dotted line on the drawing, and the point in which it meets the face is that from which the measurements are taken. The drill is therefore directed upwards until its edge would strike a point situate 4 inches above this, and the hole is bored in that direction to a depth of 3 feet 2 inches, according to the instructions. It will be seen from Fig. 459 that a series of these holes is bored across the face ; this series will thus be all of the same depth and in the same plane.

296 Mining Engineeeing,

The holes marked I. on the key section furnished with the instructions are to be started 3 inches down from level, that is, 3 inches below the point at which the horizontal line meets the face. The machine is therefore directed downward until the bit would strike the face 3 inches below that point, when it is clamped in position. The hole is then bored to a depth of 3 feet 1 inch, according to the instructions, at which depth the bottom of the hole will be in the same vertical plane as that of the holes in the top series. A series of these holes is also bored to the same depth across the face, as shown in the figure, all of which will be in the same plane. The instructions show that the next series of holes, marked II., are to be started from points situate 6f inches below the centre of the holes in the series I. last bored. The machine is therefore directed downward until the bit would strike the rock at the required point ; here it is clamped in position, and the hole is bored to the indicated depth of 3 feet 3 inches. This depth is sufficient to reach the same vertical plane in which those already bored terminate. These holes, being repeated across the face, will form a series all of which will be in the same plane. The holes in the series marked III. are to be bored from points situate inches below the centres of those in series II. last bored. The machine having been directed to these points in the manner described, the holes are bored to the indicated depth of 3 feet 9 inches to make them terminate in the same vertical plane as those above them. In like manner,, all the holes in this series will be in the same plane. The remaining series are bored in the same way ; that is. No. IV. at a distance of 9f inches from No. III., and to a depth of 4 feet 3 inches ; No. V. at a distance of 6 inches below No. IV., and to a depth of 3 feet 3 inches ; and No. VI. at a distance of 10 inches below No. V., and to a depth of 2 feet. It now only remains to bore the horizontal holes at the bottom to a depth of 3 feet.

If now we suppose these holes charged and ready for firing, it will be seen that the charges will have to be fired in the reverse order of the numbering. The series marked VI. being first fired, that portion of the face which is situate in front of these charges will be brought out, because the angling of the holes is such that the lines of fracture will run to the face. The removal of this portion of the rock will leave that, behind which the charges in the series marked V. are situate, unsupported, and hence the explosion of these charges will readily bring out that portion of the rock. In the same manner, the explosion of the charges in No. V. renders the conditions favourable to the action of those in No. IV. By the removal of the rock below the series IV- the whole of that above is left unsupported, and hence the successive firing of the remaining series takes place under very favourable conditions. It is also evident that the same favourable conditions will exist in a still fuller degree, if the whole of the series be fired simultaneously by the aid of electricity. This method of firing, and the use of a strong explosive, are necessary to obtain the full advantages offered by this or by any other system of deep boring.

It can hardly be doubted that the radial system is the best of those which have been designed to comply wholly with the requirements of machine labour. It should be remarked that it is especially applicable in cases where the stretcher-bar is used with one, or at most two, machines.

Timbering.— The levels of a mine cannot long be left without support to the sides and the roof. When the driving is through rock of a weak character, the erection of the supports must follow closely the advance of the excavation, and these supports must be capable of withstanding very severe strains. But even when the rock is strong, some kind ot support will in every case be needed. For if we neglect the enormous forces which tend to crush the rock and to bring down the roof, we have still to provide against the disintegrating action of the atmosphere,

Deiving Op Levels, Oe Naeeow Woek. 297

wliich brings down the exposed faces in detached fragments, and thus renders the roads unsafe to travel in.

Two kinds of support are used in the levels of a mine : one consists of timber arranged in various ways, the other of masonry built in the form of an arch. The latter kind is adopted, as pointed out in a former chapter, in those portions of the excavations which lead from the shaft. It is also frequently required in other parts of the main levels. At those points where a greater width than usual is needed, as, for example, where a pass-by is to be made, masonry is often preferred to timber, because the latter would there be required in lengths too great to offer a sufficient resistance. This is especially the case when the rock is weak. The " walling," as the masonry employed for this purpose is called, usually consists of two upright walls to support the sides, surmounted by an arch to carry the roof. If the rock is of a very weak character, the walls are made to rest upon an invert, and to resist the lateral pressure it is sometimes necessary to give the walling an elliptical section. The material used in walling is generally brick, the rock obtained from the excavations in progress being seldom suitable for that purpose. The first cost of walling is very greatly in excess of that of timbering ; hence the latter is generally employed wherever the conditions are favourable. But in the main roads of a mine, such as the levels we are now considering, which have to remain open for many years, walling may in the end be the more economical. The destructive action of the atmosphere and the thrust of the surrounding rock render repairs frequently necessary, so frequently indeed when the rock is weak that the sum of the repairs, and the delay to the working occasioned by them, become more costly in a few years than a walling which, when once erected, will last till the mine is worked out. When the rock is of such a character as to need support at every point, walling is, of course, indispensable. Generally, however, as previously remarked, the support used in mines consists of timber, and hence the question of timbering is one of very great importance. The cost of the material and of the labour expended upon it enters largely into the cost of working coal, and must, therefore, be taken fully into account when estimating the value of any given seam. At present, however, we are concerned only with that portion of the timbering which is used in the main levels of the mine.

Kinds of Timber, and Forms in which it is used: — The timber employed in mines consists chiefly of pine, fir, and oak. The latter possesses in the highest degree the qualities necessary to strength and durability. It is well known to be highly resistant, and to be but feebly acted upon by a moist atmosphere. But, in many localities, it is not readily procurable, and its cost is everywhere great. Pine must be considered the mining timber par excellence. The nature of this wood renders it fairly resistant and durable, the latter quality being due to the large proportion of resin which it contains, and allows pieces to be obtained lighter and more regular in form, and consequently more easily handled, than can be got from oak. Fir is widely employed for mining purposes ; it is cheaper than pine, and as it possesses all the qualities of the latter, except that of durability, it is especially suitable for use in all situations where that quality is not of primary importance. For it must be borne in mind that the timber of a mine is generally crushed long before decay sets in, and that, consequently, the quality of durability may, in many cases, be altogether neglected. Hence it is that fir constitutes the major portion of the timber employed in mines. Other kinds of timber, except in localities where they abound, are employed only in very small quantities.

Timber is usually supplied to mines in the unhewn state, that is, in the " round," In this state it is also used in the mine, except in certain situations to be hereafter described. Squaring

2 Q

298 Mining Engineeking.

the timber would weaken it unnecessarily. In some cases, however, when the dimensions of the pieces are large relatively to the strain to he thrown upon them, they may be cleaved into two half rounds, the operation of cleaving being preferable to that of sawing, which slightly weakens the piece by dividing the fibres. The dimensions of the timber employed as supports are various, ranging from a diameter of 4 inches to that of 1 2 inches ; a common size is 8 inches in diameter. Young trees are to be preferred to the tops of old trees, which are spongy in texture, and less resisting and durable than the lower portions. Timber is furnished both with and without the bark removed ; the latter state is to be preferred, as being favourable to the preservation of the wood. A s mining timber is generally purchased in considerable qiiantities, it is important to its preservation that it be carefully stored. A covered building should be chosen for this purpose, and means of ventilation should be provided. The larger pieces may be stacked horizontally and crosswise ; but the smaller should be placed on end. It is almost needless to remark that in using from such a store, the oldest pieces should be taken first.

Means of Economizing Timber. — In the employment of so costly a material as timber, it is important that every means should be adopted of reducing the quantity required. It is utterly impossible to proportion the dimensions of the timber to the strains to which it will be subjected, for the reason that these strains are wholly unknown. The pressure which a descending mass of rock will exert cannot be estimated ; all that is known about it is that it may be very great, and hence an excess of material is placed to resist it. But though we are unable to economize timber in this direction, some reduction of the quantity may be obtained by a little attention to the rudiments of the resistance of materials. An observance of fundamental principles will here enable us at least to get from the timber employed the greatest resistance of which it is capable.

The materials oi which the supports in a mine are composed may be subjected to a crushing strain in the direction of their fibres, or to a transverse breaking strain, and it becomes important so to place the pieces, relatively to the strains to be thrown upon them, that they may be capable of offering the maximum resistance. If the strain is one of compression, it will be best resisted when it acts in a direction parallel to the fibres of the wood, and to ensure this condition the support should be placed so that its length may be exactly in the direction of the pressure. Thus in inclined seams, it is desirable to place the props at right angles to the floor, that is, perpendicularly to the planes of stratification. As, however, the roof will sink slightly in spite of the prop, the latter may be made to deviate a very little from the perpendicular in the direction of the vertical. If the pieces are long, it may be necessary to stay them in the middle, to prevent yielding by flexure. When the strain is transverse, the length of the piece should be reduced as much as possible by supporting it at frequent intervals, and care should be taken that it rests evenly on the supports. Provision should also be made for distributing the pressure equally throughout the length of the piece by insertinowedges where the rock does not bear. These are principles which any intelligent and experienced miner may understand and apply. Such a man will see at a glance where the pressure comes from, and determine in a moment the direction in which the axes of his timber should be placed so as to resist it most effectually.

In this matter of economy of timber, there is a point which is often overlooked in cutting up the pieces to the lengths required. These lengths should always be cut from the larger end of the piece, so as to reduce the dimensions of the waste.

Arrangement of the Timbers.— The mode of arranging the timbers which are to form the support

Deiving Of Levels, Oe Naeeow Woek. 299

of an excavation will vary according to the strength of the rock, and the dimensions and character of the excavation itself. For it will be obvious on reflection that the main roadways of the mine, which are to stand open for years, will require supports of a stronger and more permanent nature than those roads or air-ways which are of a temporary character. But there is a general type of arrangement that is more or less closely followed in all cases.

If the sides of a roadway are strong, and the roof alone weak, the latter may be supported by timbers resting upon the former. Such pieces are called headpieces, and they are let into the rock on each side, as beams are let into walls, to obtain a bearing. This arrangement is shown in Fig. 460, Plate L. In thus placing the timbers, care should be taken to give each piece a sufficient and an even bearing at each end, so as to properly distribute the pressure. The distance of these pieces apart will, of course, be determined by the strength of the incumbent rock. To distribute the support of these pieces over the roof, and to prevent the fall of small portions of rock which become detached from the mass by atmospheric and other agencies, slabs or planks are driven in between the headpieces and the roof in a direction at right angles to the former. When slabs are used, the flat side should be turned to the roof, in order to cover as large a surface as possible. Sometimes, especially in France, branches of trees are employed for this purpose, to form a network against the roof. The slabs or planks should be sufficiently long to reach at least from centre to centre of two headpieces ; but it is better that they should rest upon three of these supports. To distribute the pressure equally over the headpieces, wedges should be driven in between them and the roof wherever a space exists. The mode of inserting the headpieces will be understood from a reference to Fig. 461, which is a plan of Fig. 460, with the roof removed. A hole or notch A is cut into the side rock near the roof, to a depth sufficient to give the requisite bearing, and made slightly broader than the timber to be inserted, in order to allow the play required by tVie operation. On the opposite side of the excavation, a similar hole B is cut ; but the fore side of the hole is cut away in the manner shown in the figure, for the purpose of allowing the headpiece to be inserted. The mode of introducing the headpiece is shown by the dotted lines. Before, however, the end b has been thrust into its definitive position, a wedge is placed at n, with its thin end outwards, and against this the headpiece is driven by blows delivered at the point b until a sufficient degree of tension has been given to it.

It may sometimes happen that one side of the excavation, as well as the roof, needs support, [n such a case the method of half timbering, shown in Fig. 462, will be adopted. A hole, similar to that at A, in Fig. 461, is cut into the side rock at A to receive one end of the headpiece, or cap, as it is frequently termed. A shallow hole is also cut in the floor at 0, to receive the end of the timber that is to stand vertically on that side. This vertical piece is variously described as " upright," " leg," or " stanchion." The stanchion is set in an inclined position in this hole, usually with its smaller end downwards, and the headpiece having been placed with one of its ends in the hole in lue rock cut for it, and its other end resting upon the upper end of the stanchion, the latter is driven into the vertical position. By this means sufficient friction is developed to hold the two pieces firmly together. If, however, in consequence of the yielding of the floor, or a miscalculation in the length of the stanchion, this friction is not obtained, wedges must be driven in either beneath or above the stanchion. As it is desirable not to weaken the timber by notches or any unnecessary cuts, care will be required in preparing the bearing surfaces. In most cases these surfaces will be held together by friction alone, and two methods of preparation may then be adopted. In one the lower side of the c£p is cut away with the axe in a slight degree, so as to give it a flat bearing

2 Q 2

300 Mining Engineeeing.

surface. The upper end of the stanchion is in this case cut off square. In the other method, the upper end of the stanchion is hollowed out to receive the round surface of the cap. These methods are shown in Pigs. 463 and 464. "Whatever be the method adopted, it is important to make the cap bear evenly upon the stanchions, so as to avoid any tendency to split the pieces when the pressure comes upon them. Sometimes the lateral pressure from the sides of the excavation will be greater than the downward pressure of the roof, and in such a case there will be a tendency to throw down the stanchions. This tendency must be counteracted by slightly notching both the cap and the stanchion, as shown in Fig. 465. To avoid weakening the timbers, the least possible depth consistent with the requisite degree of resistance should be given to this notching. It will be observed that, in consequence of this notching, there will be a tendency to split the timber when the pressure is thrown upon it. To avoid this tendency, a stay may be placed beneath the cap, as shown in Fig. 466. In such a case the notching will not be required, and the cap and stanchions will be held together by simple friction, in the manner already described. The support of the stanchions will be distributed over the side of the excavation by means of slabs or planks, placed horizontally between them and the rock, in the same way as they were placed between the headpieces and the roof.

When both sides of the excavation as well as the roof are weak, which is the most common case, the form of timbering adopted will be that shown in Fig. 467. In this case we have two stanchions, surmounted by a cap or headpiece, and the timbers are put together by notching or otherwise, according to the circumstances. Grenerally in levels driven by hand labour, the two stanchions are slightly inclined towards the axis of the excavation, so as to give a trapezoidal section, as shown in the figure. In such a case the timbers are not placed normally to the stratification, but their position is favourable to stability. One advantage of this position of the stanchions is the consequent reduction in the length of the headpiece, without a material lessening of the breadth of the excavation. As the headpiece is subjected to a transverse strain, the importance of this advantage will be obvious. When the level is driven by machine labour, the sides, as already pointed out, are vertical, and hence the stanchions will, in such a case, be placed vertically.

Sometimes the floor of the excavation, as well as the sides and the roof, is weak. This happens when the rock of the floor is of a soft nature. Where a soft floor has to be dealt with, two points present themselves for consideration. One is the difficulty of obtaining a support for the stanchions upon such easily yielding rock, and the other is the tendency of the floor to rise in the middle, in consequence of the pressure at the sides. This tendency is very marked in many of the under clays of the coal seams, and it necessitates the adoption of means for its prevention, as otherwise the destruction of the roadways goes on continuously. This means is found in completing the framing of the timbering by placing beneath the stanchions a piece similar to the cap above them. This arrangement is shown in Fig. 468. When the floor is only slightly weak, these pieces may consist of half-round timber, placed with the flat side downwai'ds ; but if the tendency to rise is great, whole timber must be employed. The upper surface is slightly cut down, and in some cases notched with the axe, to receive the lower ends of the stanchions. Slabs or planks will sometimes be required beneath these pieces, j 'laced in the same manner as those above the caps, for the purpose of keeping the floor down.

The distance of the sets, that is, each pair of stanchions with their cap, apart is determined, as before remarked, by the strength of the rock. Grenerally, in fairly strong rock they may be placed at intervals of 3 feet from centre to centre, and in very weak and fissured rock at intervals of

Driving Of Levels, Oe Naeeow Woek. 301

18 inches. In some cases it may be necessary to place them close together. As it is impossible to estimate the strength of rock accurately, it may also become necessary to double the sets, that is, to place a new set between every two existing sets, after the first timbering has been completed. The dimensions of the pieces will likewise be determined by the same condition of strength in the rock. As the pieces furnished are rarely of equal size, the larger and smaller should be made to alternate so as to have the weaker set between two stronger ones. In some cases, economy of timber may be gained by thus alternating sets of different dimensions. It is desirable that the timber should be sent into the mine cut to the requisite length.

The timbering of an excavation should proceed simultaneously with the driving, and follow the miners at the working face as closely as convenient. It is very important to prevent any movement or fracture of the rock from setting in. A bed may appear so strong as not to need immediate support. But the action ol the atmosphere speedily breaks up the exposed surface, and the pressure of the superjacent beds forces this surface outwards into the excavation. The sides and the roof then begin to crack and to fall in larger or smaller blocks, according to the nature of the rock ; and when once this action has fairly set in, the difficulties of arresting it by timbering become immense. It is far easier and less costly to prevent any important movement from taking place, than to stop it when it has once begun. For this reason, the timberings especially of the main levels, should, as before observed, closely follow the driving ; and the timbers should be made, by wedging, to bear firmly against the rock in every part, so as to furnish a support at all points. On account of the importance of the main levels, the timbering of these excavations should receive special attention, and the form employed should be one of those shown in Figs. 467 and 468.

Special Form of Timbering. — A form of timbering is employed in France that is deserving of special attention, inasmuch as it possesses very valuable qualities, and is but little, known in other countries. This form is capable of offering an enormous resistance ; so great, indeed, as frequently to withstand the pressure when walling has been completely crushed. It has been found to last three or four years in situations where the ordinary timbering has been destroyed in two or three months, and to have successfully resisted the destructive action of the " creep " when, in consequence of an accident or a strike, the mine has been closed for some time. These properties render the form peculiarly valuable for the main roadways of a mine, and for use in those parts where the pressure is very great. As- a suitable substitute for walling, the form offers, under such conditions, a very considerable degree of economy.

The two main features of this system are : first, the employment of struts to support the stanchions and the cap at the points where they have a tendency to yield ; and second, the use of longitudinal pieces to bind together the different sets of timbering.

The system will be understood from an inspection of the drawing in Fig. 469, which represents a set as designed for a narrow roadway of a single line ot rails. The principal timbering, it will be observed, is of the ordinary construction, the peculiarity of the system lying wholly in the means employed to strengthen the structure. The timber used for the purpose is round, and of relatively small dimensions, the diameter being about 3 inches for narrow roadways, and about 4 inches for the ways intended for a double line of rails. It will be seen from the drawing that two uprights are placed inside the principal stanchions, and in contact with the latter throughout their length. These uprights are firmly set in the floor at A, and reach to about one-third of the height of the stanchions. Their upper ends are bird-mouthed, to receive the longitudinals B, which are intended

302 Mining Engineeeing.

to bind the sets together. These longitudinals are merely placed end to end, and they are held in position by friction alone, no nails or other means of connection being used. The length of these pieces will be equal to the distance of the sets apart, centre to centre, or some multiple of that distance, and it is important that they be all of the same diameter. A similar longitudinal C, is placed in the middle of the cap, and supported by two struts abutting upon the longitudinals at B. The ends of these struts are bird-mouthed, like the upper ends of the uprights. Thus it will be seen that the stanchions and cap of the principal timbering are supported at those points at which they begin to yield, and that in consequence of the connection furnished by the longitudinals, a pressure occurring at one point is distributed over several sets of timbers. Thus the timber is rendered capable of resisting a very great pressure.

The operations of fixing these bracing pieces are performed in the following manner. The workman first places the longitudinal in position beneath the caps, and fixes it there temporarily with pieces of wire. The length of this piece may be from 9 to 12 feet. The side longitudinals B are placed and held in position in the same way. Two or three of the uprights are then placed at suitable points beneath the side longitudinals, and some of the struts are inserted obliquely and driven gently towards their ultimate positions. The whole of the bracing being thus rendered self-supporting, the wire is removed, and the remaining uprights and struts put in obliquely, and driven firmly into their position with a heavy mallet. If the correct lengths have been given to the several pieces, and the work is executed by an experienced man, a firm and unyielding framing is produced, capable of resisting an enormous pressure. It is obvious that this bracing may be applied to every set of timbers, to each alternate set, or to those portions only of the timbering of a level against which the pressure is, or is likely to be, excessive. Of course, the full advantages of the system are obtained only when every set of timbers is braced.

In the broader roadways of a mine, those in which there are two lines of rails, the arrangements shown in Figs. 471 and 472 are adopted. In the case of a horse-way, the latter arrangement is preferable, as affording more room; but it is more complicated in construction. The arrangement shown in Fig. 471 leaves less free space, but it is very suitable for engine planes, and frequently is adopted, without much inconvenience, for horse-roads. In this case, the increased length of the struts will necessitate a corresponding increase in the diameter, 4 inches instead of 3 inches, as in the narrow ways. It may be remarked here that the wood used for bracing is always pine or fir. When the floor is very weak and apt to rise, the bracing is sometimes arranged as in Fig. 473. This is a somewhat more complicated mode oi construction, but it is capable of offering an enormous resistance. In this case, the bracing is similar in character to the curbing used in shafts.

The cost of this system of timbering is not much greater than that of the ordinary system. When a set is to be braced, the timbers may be of smaller diameter, and thus the additional timber is partly compensated. The labour of fixing is increased, but it is found that the additional cost is only about 20 per cent. When it is borne in mind that timbering so constructed is capable of offering- a resistance equal or even superior to that of walling, and that it will last twenty times as lono- as the ordinary kind, the economy of this system is obviously apparent. It should also be remembered that as only short timbers are required, except for the longitudinal pieces, the waste may be used. Generally mining timber is broken long before it is decayed, and these broken, but sound, pieces may be employed for the bracing. The only new timber required will be for the longitudinals, which, being of small diameter, will possess but little value for other purposes.

Deiving Of Levels, Oe Naeeow Woek. 303

Repairs in the Timbering. — As it is impossible to proportion the resistance accurately to the pressure, the timbers will soon be crushed and broken in some places, and, consequently, require to be replaced by others of larger dimensions, or set at smaller intervals. It is only after the lapse of some time that the direction of the thrust can be perceived. If the cap is forced hard down upon the stanchions, the pressure comes from the roof, and the cap may be expected to yield first. If the pressure comes chiefly from the sides, the stanchions will yield first by bending inwards and breaking near the middle of their length. When these evidences of weakness appear, and the direction of the thrust is thus clearly ascertained, repairs and additions to the timbering must be at once made. The pieces that have yielded must be replaced by others of larger dimensions, or put together in a different manner ; strengthening pieces must be added at the points where an excess of pressure is likely to develop itself, and arrangements adopted conformably to the direction of the pressure. In adding timber, a new set is placed by the side of one which shows signs of yielding ; but the latter is not removed until it has become quite useless. The work of executing repairs involves no great difiSculties provided they be undertaken in time. If, however, the matter be long neglected, a sufficient movement may take place in the rock to cause fracture and slipping of the dislocated blocks, and in such a case it may become very difficult to arrest the further progress of the mischief.

Walling. — It has already been remarked that generally the main levels of a mine are walled, instead of timbered, where they enter the shaft. The walling in this case will be complete, that is, it will consist of two side walls, an arch, and an invert. This complete form of walling is everywhere adopted where a great pressure has to be withstood. Sometimes a drift will pass for a short distance through very weak beds, and it may be found necessary to have recourse to walling throughout that distance. Also where a drift is enlarged to form a pass-by or an air-crossing, or for any other purpose, walling will usually be adopted. The great first cost of walling prevents its being employed generally in the place of timber. It is, however, probable that as mines become deeper and timber dearer, its use will become more extended.

The materials employed in walling are the sandstones of the coal measures and bricks, the latter, on account of their more convenient form, being much more frequently adopted than the former material. In some cases, the side walls are built of stone and the arch of brick. The thickness of the walling will be determined by the circumstances of the case, as ascertained by experience. If the rock is broken and in a disintegrated state throughout a considerable distance, it may be inferred that the pressure comes from a distant point and is great. But it the broken condition of the rock extends throughout a few yards only, the pressure is developed near that point, and is not great. According to these and other indications, the thickness of the walling is determined. It will rarely happen that a greater thickness than two bricks is required in the arch ; in most cases one brick will be sufficient, and sometimes half a brick may be adopted.

It is not desirable to enter here into the details of the work of walling, as this is rather the domain of the builder than of the miner. Some remarks on this subject will be found under the head of walHng in shafts. But a few general observations may not be out of place. The walling in the drifts of a mine should be built before any movement or disintegration has begun in the rocks whose surfaces are exposed. The materials employed should be carefully selected, and the labour should be skilfully executed. The mortar should be hydraulic, have a stiff consistency, and be sparingly applied. No empty spaces should be left between the walling and the rock, but these should be completely

304 Mining Engineeeing.

filled with coarse concrete. All the temporary timbering should be removed, as the decay of this tends to produce hollows between the rock and the masonry ; and care should be taken, in the construction of the masonry, to properly tie the component parts, and to break joint in the successive courses. These precautions are necessary to ensure the stability of the structure.

The methods adopted for walling are similar to those already described for timbering. If the sides and floor of the excavation are strong and the roof weak, a brick arching resting upon the side rock may be sufficient. If the roof and one side are weak, a buttress wall is built against the weak side, and an arch is thrown over from the top of this wall to the firm rock on the other side. The wall in this case will be from 18 inches to 2 feet thick, and set from 4 inches to 6 inches in the floor rock. When both sides and the roof are weak, a wall is built on each side, and an arch thrown over to carry the roof. And when the floor, as well as the sides and roof, need support, the side walls are made to rest upon an invert. If a great lateral pressure is expected, the side walls are curved so as to give an elliptical section ; this form is nearly always adopted when the invert is added. Packwalls, which consist of side walls only, without arch or invert, will be described hereafter. Such walls are constructed of the rock excavated in the mine, and are built without mortar. Examples of walling are given in Figs. 474 and 475.

Walling is built in lengths, determined by the nature of the rock, the side walls being kept a little in advance of the arching. The execution of the work offers but little difficulty beyond that due to the constrained position of the workmen. In some cases, the walling will proceed without the intervention of temporary timbering ; but oftener the latter will have to be set. The removal of this timbering requires precaution. If the rock is not of a very weak character, the whole of this temporary timbering may be removed throughout a length of walling ; but if the rock is incapable of standing without support, only a short length can be taken at a time, and the timber from this length must be removed by degrees. When one piece is taken out, the remainder must be propped or otherwise maintained, so as to continue the support to the rock at those points from which the timber has not yet been withdrawn. The methods of procedure are easily described, but their execution is somewhat difficult and delicate, and requires careful and skilful workmen. The object of the workman is to withdraw as Httle of the temporary timbering at a time as he can, and to do this without reducing the support afforded by that which is left, so that no portion of the rock may be left unsupported till the moment arrives for walling it up. Sometimes it will be necessary to build in portions of the timbering ; but, for reasons already given, such a proceeding should be avoided wherever possible.

The question of supporting the surfaces of an excavation by means of timbering and walling is one of high importance to the mining engineer. In many cases it enters largely into the cost of getting the coal, and in all cases it influences greatly the safety of those employed. And it is probable that, in the future, as mining is carried out at increased depths from surface, the question will assume still higher importance.

Systems Of Woeking. 305

Chapter Yi.

Systems Of Woeking.

When- the shafts of a new winning have been sunk, and the levels driven out in the manner described in the preceding chapters, the question which next presents itself for solution is what system to adopt of working out the coal. This question is one of paramount importance, and its proper solution will call for knowledge, experience, and judgment. In making choice of a system, all the conditions which will aifect the getting of the coal must be taken fully into account, and the mode of carrying out the system chosen must be determined according to the peculiar circumstances of the case. The nature of these conditions and the modifications to which the system may be subjected will be understood from the description of the methods actually in use, and the numerous considerations involved in them, to which the present chapter is devoted.

There are two systems of laying out the workings of a colliery, differing widely from each other

in their general features, but capable of such modification as to be greatly assimilated in certain

circumstances. In one system, a set of excavations is driven through the coal parallel wth one

another and at certain intervals apart, so as to leave a rib of coal between them to afford a support to

the roof. These excavations are made as wide as the strength of the rock will admit, a common

width being from 4 to 5 yards. At right angles to these, another set of excavations is driven, also

parallel with one another. The width of the latter is usually about half that of the former, and their

interval apart is much greater. The effect of these two sets of excavations thus crossing each other

perpendicularly is to leave in the seam rectangular blocks of coal, for the second set is driven

through the ribs left between the excavations constituting the first set. The use of these blocks or

pillars is to hold up the roof. In former times, these pillars were left, and as the coal composing

them was permanently lost, it was sought to reduce their dimensions to the lowest possible limit.

Under the most favourable circumstances, however, fully one-third of the seam was necessarily lost in

these pillars, and very frequently the proportion was as great as two-thirds. In the present day,

these pillars are subsequently removed and the roof let down, so that generally the whole of the coal,

with the exception of a small portion of the pillar which is crushed by the descending roof, is

extracted. When the workings are laid out with a view of finally removing the pillars, the latter

are left of very large dimensions, for the purpose of affording a thoroughly efficient support to the

roof during the first part of the working, that is, during the driving of the excavations. This system

is known in England as that o? pillar and stall, or post and stall, and in Scotland as stoop and room.

The stalls are the excavations which are driven through the coal, the first set of which is known

distinctively as hoards, sometimes written bords ; and the second as headways. In the second system

2 R

306 Mining Engineeeing.

of working, the whole of the coal is removed at once in a long and continuous face, and the roof is allowed to fall behind the workmen. To prevent the roof from falling upon the miners at work, a double row of props is set at a distance of about six feet from the face, and moved forward as the face advances. This system is obviously far more simple than the preceding, and it may be remarked here that it is gradually supplanting the post-and-stall system, wherever the conditions are not altogether unfavourable to its adoption. This system is known as the long wall. The relative merits of the two systems of working coal have been a subject of dispute ever since the long wall was first introduced. Undoubtedly each possesses peculiar advantages, and it will be our endeavour briefly to point these out, and to show how each is affected by various conditions and circumstances.

The ultimate object in every working for coal, whatever the circumstances may be under which it is undertaken, or the method by which it is carried out, is to obtain the greatest possible quantity of coal, in the best possible condition, at the least possible cost. In estimating, therefore, the merits of any system or mode of working, its effects must be considered relatively to this object. The condition of cost must be understood to involve the question of safety of life to those employed in prosecuting the workings. That it is desirable to obtain the greatest possible quantity of coal at the least possible cost is obvious enough, and it was shown in a former chapter that coal is greatly depreciated in value by being brolien up. Thus the produce of a coal seam will be obtained in the best possible condition when it is all extracted and conveyed to bank in blocks of considerable size, or, in technical language, when such produce is obtained as " round coal." If the two systems be cour sidered from this point of view, it will be found that the long wall possesses the important advantage of giving the greatest quantity of coal. When the workings are carried out according to this system, the whole of the seam may be extracted ; whereas, on the post-and-stall system, a portion of the pillars, greater or less according to the circumstances of the case, is necessarily lost. Thus the long wall gives the greatest possible quantity of coal. Also, the coal got by this system is less broken than that obtained by post and stall. It will be obvious, on reflection, that the narrow workings of the latter system must necessarily occasion the making of a large quantity of small coal. This quantity is increased, sometimes very largely increased, by the crushing of the pillars as they are worked away. This breaking up of the coal is inherent in the nature of the system, and, therefore, however skilfully it may be carried out, it must remain inferior to the other system in this respect. Thus the long wall gives the greatest possible quantity of coal in the best possible condition. In the latter system, again, the risk of accident from falls of roof is very materially reduced, the ventilation is rendered far more simple and effective, and the labour of the miner, who works in a cooler and purer atmosphere and a less restricted space, more efficient. It thus appears that the system of long wall is that which gives, what is the ultimate object of every working, the greatest possible quantity of coal, in the best possible condition, at the least possible cost.

It must, however, be borne in mind, that though considered merely as a system, the superiority of long wall over post and stall is manifestly great in any given case, the existing circumstances may so far modify results as to greatly diminish that superiority, or even to render the adoption of post and stall desirable, if not necessary. The system of long wall is peculiarly suitable to the working of thin seams, and hence it will offer its fullest advantages when this condition prevails. The condition is, however, by no means a necessary one, and instances might be given where very thick seams have been successfully worked by long wall. A difficulty in working thick seams by this method lies in obtaining the stone or rubbish needed as stowage behind the workmen, which stowage is

Systems Of Woeking. 307

required to partially fill up the hollow created by the removal of the coal for the purpose of letting the roof down easily, and without causing damage to the surface. In working the thick seams by long wall in France, first the upper half and afterwards the lower half of the seam are removed, and the space occupied by the coal is partially filled up by stone quarried at surface, and lowered in the coal tubs instead of returning them empty. This method has been adopted to some extent in the Staffordshire Ten-yard Seam. It will be evident from this circumstance that when a seam is divided by bands of refuse, or dirt partings, as they are called by miners, it may, considered only from this point of view, be more favourably worked by long wall than by post and stall, since, in the former system, the refuse may be utilized as " pack," while in the latter it must be stowed away against the sides of the excavations, where it serves no useful purpose. A good roof is favourable to long work, but it is by no means an indispensable condition. With good management, the system may be successfully carried out when the roof is of a very weak and jointed character. In such a case, a main point is to push the working face rapidly forward so as to be always beneath a fresh, or, as it is termed by miners, a " green " roof. If the roof contains ironstone, which can be worked with the coal, whereby a large quantity of refuse is produced, the seam can be worked most advantageously by the system of long wall. On the other hand, if the roof contains a large quantity of water, or if the surface is covered with important buildings, or reservoirs of water, or traversed by rivers, streams, canals, or railways, in which cases it is essential that the roof be not let down, the system of post and stall offers superior advantages. In some places, where the workings extend beneath the sea, no other could be adopted. Of course, under such circumstances the pillars are lost, and the workings are laid out accordingly. In post-and-stall workings there is also less difficulty in keeping the roadways in a good state, a circumstance of considerable economical importance. The system is, besides, generally favourable to a large daily output. Thus it appears that the system of long wall, modified in its details to suit the requirements of different seams and different localities, is generally greatly superior to the system of post and stall, and therefore in most cases to be preferred ; but that conditions may prevail which are best dealt with by the system of post and stall.

It will appear from the foregoing remarks that the conditions affecting the choice of a system are of a complicated and varying character, and it will be evident, on reflection, that all the subsequent operations of laying out and working the mine must necessarily continue in accordance with the plan first adopted. When this and the important interests at stake are borne in mind, it will be understood that a serious responsibility attaches to the engineer on whom devolves the duty of determining the system to be adopted in a new winning, and the plan according to which it is to be

carried out.

Post-and-Stall Workings. — If a careful consideration of all the circumstances of the case has led to the determination to adopt the post-and-stall system, the next question that presents itself is, how to lay out the workings in conformity with the existing conditions. We shall assume, as before, in order to have a typical example, that the seam lies at a slight inclination, and that it is unaffected, in the portion of the field under consideration, by faults or derangements of any kind.

Direction of the Workings. — In a former chapter of this work, it was stated that the direction of the cleat in coal in many cases determined that of the workings. In workings on the post-and-stall system, it is sought to drive the bords at right angles to the cleat, for reasons which will more clearly appear in the next chapter. Hence the plan of the workings is always so designed as to Bet off those excavations in that direction ; the bords, it should be remembered, are the principal

2 R 2

308 MINING ENaiNEEEING.

excavations, the headways being intended primarily for ventilation. As the bords are invariably set off perpendicularly to the cleat, that direction is spoken of by the miner as " bordways " ; and as the headways are perpendicular to the bords, the direction parallel to the cleat is described as headways, or " on the ends." Now it is evident that, since the main levels are driven in a water-level direction, that is, along the strike of the seam, they may cut the coal bordways, headways, or obliquely, the latter direction being known as cross-cut; and it is equally evident that, since the bords are to be driven at right angles to the cleat, the direction of the workings relatively to the main levels will depend upon the angle at which these levels cut the cleat.

Let it be assumed, in the first place, that the direction of the main levels is headways, that is, that they have been driven on the ends of the coal. In such a case, the bords will be set away out of the upper level, as shown in Fig. 477 on Plate LIII. A barrier of coal, cut through at intervals to form pillars of large dimensions, is left on the rise side of the upper level, to protect these main ways of the mine from the effects of thrust and creep. The thickness of these pillars will be determined by the considerations which affect the shaft pillars, and which have been already treated of. The importance of such barriers is very great, inasmuch as any injury to the main levels deranges the ventilation, and seriously impedes the traffic. Again, suppose, on the contrary, that the direction of the main levels is bordways, that is, that they have been driven perpendicularly to the cleat. In this case a pair of drifts is set off from the upper level, at a convenient distance from the shaft, say about 80 yards. These drifts, which are called winning headways, will be similar in dimensions and in distance apart to the main levels, to which they are driven at right angles. From these winning headways, the bords may be set off parallel to the main levels, as shown in Fig. 478.

Dimensions of the Pillars and Stalls. — It has been already remarked that when it is intended to leave the pillars, these are laid out to the least dimensions consistent with sufficient strength to support the roof To determine what the dimensions are, it is necessary to consider the effects of what is known as " thrust " and " creep." Both thrust and creep are occasioned by insuflScient dimensions in the pillars, the difference between them being due to the difference of strength in the rock composing the floor and the roof. When the floor and the roof consist of strong unyielding rock, and the pillar of coal left is too small to support the pressure thrown upon it, the pillar cracks, breaks up into prismatic portions, from which large slabs fall off, and finally is crushed and ground into small coal and dust. The yielding of the pillar, of course, lets down the roof, and the workings become in consequence choked up, and the surface is injuriously affected. This action of the downward pressure is known as thrust. When, on the contrary, the rock composing the floor, or both the floor and the roof, is weak and soft, and the pillar of coal too small, the downward pressure upon the latter causes the floor to rise in the excavations, while the roof, if also of a yielding nature, sinks at these unsupported points, as shown in Fig. 476. The creep is insidious in its approach, and irresistible in its progress. It may have originated at some unusually weak point ; but having once set in, it spreads slowly, but surely, over the whole district. No timbering can arrest nor even, when it has fully set in, materially retard its progress. The roadways have to be continually repaired, at an enormous cost, and the airways become choked up, until finally the labour of keeping these ways in order becomes too great to allow the workings to be carried on at a profit, and the district or the colliery is abandoned. In this way, thousands of acres of valuable coal have been lost.

To determine the minimum dimensions of the pillars requisite to withstand the thrust and the creep, it would be necessary to take into account the strength of the rock in the floor and the roof

Systems Op Woeking. 309

the strength of the coal itself, and the pressure of the superincumbent strata. But these are problems susceptible of only an approximative solution and of empirical treatment. Experience gained under similar conditions is alone worthy of confidence, and following this experience will lead, for the sake of safety, to excessive dimensions. Hence it has come to pass that minimum dimensions have been left altogether out of consideration, and another principle of working adopted. Wherever it is important that no surface disturbance should take place, the size of the pillars is calculated in the same way as that of the shaft pillars, the base of the calculation in this case being designed to give security by means of a great surplus of strength. The same remark applies generally to the barriers left to protect the main roads from thrust or creep occasioned by the removal of the pillars beyond. In all other cases, the pillars are regarded, not as supports to the roof, but as masses of coal prepared for subsequent removal. Hence enormous dimensions are given to the pillars, and by this means the evils of thrust and creep are entirely avoided. As there is nothing but convenience to limit the size of the pillars when viewed as masses to be wholly worked away, in deep pits it is customary to take out by the preliminary workings, that is, by the driving of the bords and headways, only from one-fifth to one-fourth of the coal, leaving pillars 30 yards long by 18 or 24 yards broad, and even 40 yards long by 30 yards broad. It may be remarked here that long pillars are to be preferred, that is, a pillar 30 x 16, or 30 x 18 yards, is preferable to one 30 x 24 yards. The bords, as before remarked, are usually driven as wide as they will stand, that is, usually from 3 to 5 yards, and the headways, or " holings," as the lesser excavations demanded by the requirements of ventilation are commonly called, are about half that width.

Removing the Pillars. — It was formerly the custom to open out in bords and headways a whole district, and when the boundary had been reached by the workings of this first stage, to work off the pillars, beginning at the extreme limit, and returning to the point at which the bord workings were commenced, leaving the roof to fall behind the workmen. Sometimes this plan of working was carried out over very large areas, and in such cases, when the first workings had reached the boundary, an extensive tract of " broken mine," that is, the portion supported by pillars, was formed. To this mode of proceeding, there are several serious objections. By leaving the pillars until the boundary has been reached, an immense number of airways and roadways have to be kept up, and this number is constantly increasing until the limits of the area to be worked out have been arrived at. This circumstance renders the ventilation difficult, and thereby augments in a very considerable degree the liability to accidents. Moreover, the length of time during which the broken mine is left, immensely increases the danger of thrust and creep setting in, by which the whole area may in a short time be overrun. Also, by this method, the pillars first formed are last removed, and hence it happens that a large number of them crack and crumble away under the combined action of atmospheric agencies and great pressure. Even if they resist this action well, the quality of the coal is greatly deteriorated by the long exposure.

For the foregoing reasons, it is now generally the practice to carry on the two workings simultaneously, by making the working off of the pillars to follow closely the opening up of the bords into the whole coal. By this means, the length and the mean duration of the ways are reduced, and the coal is obtained from the pillars in a good condition. The broken workings should thus follow the whole workings as closely as convenient, so as .to concentrate the workings as much as possible. This mode of proceeding is shown in Fig. 477, in which the hatched portion represents the part from which the pillars have been removed. This portion of the mine is called the " goaf," and into it, of

310 Mining Engineeeing.

course, the roof falls. Goaves need careful watching, as they offer favourable conditions for fte accumulation of gas, which may be forced out by falls of rock.

Division into Districts.— The area contained within the boundary to be worked is divided into several independent compartments or districts. This improved method of laying out the workmgs is due to Mr. Buddie, who was also the first to introduce the plan of working off the pillars behind the whole workings. Each district is separated from the others by strong barriers of coal, and ventilated by its own current of air, so as practically to constitute separate mines. The advantages of this arrangement are great and numerous. Suppose, for example, that we have an area divided into four districts ; the air entering by the downcast shaft will, on reaching the bottom, be separated into four currents, each of which will be made to pass through one of the districts, and then be conveyed to the upcast shaft. By this means, the miners at the most distant faces of work get the air pure and cool, which would not be the case if it had to pass through the whole area comprising the four districts. Another very important advantage of the system lies in the isolation oi the effects of an explosion. As one district is entirely independent of the others, being enclosed by barriers and ventilated by its own current, the effects of an explosion cannot extend beyond the limits of the district in which it occurs. The importance of this fact will be more fully understood when the subject of ventilation has been treated of. Moreover, by the concentration of the working places in the district, or panel system, the ventilation is greatly simplified and rendered much more efficient, whereby the risk of explosion is very greatly reduced. In Fig. 477 only two districts are shown ; but it is obvious that by driving out drifts from the shafts, at right angles to the main levels and between the districts shown, two other districts may be laid out to the rise of the latter. It is also evident that should the conditions of the case admit of it, workings may be similarly laid out to the dip of the main levels.

Long- Wall Workings. — In the system of working by long wall, the whole of the coal is, as before observed, extracted at one operation, the roof being allowed to come down as the extraction proceeds. This is the principle of long work, and whatever form the system may assume, it is strictly followed throughout. It is evident that the mode of carrying out the system may be made to vary widely, and it is equally evident that wide variations will be frequently called for by the different conditions existing in different localities. Long work is susceptible of far greater modification of detail than post and stall. This feature constitutes one of its great merits, and by enabling the system to adapt itself to the varied requirements of different localities, it has contributed largely to its wide and rapid extension. Into these modifications of form and detail we shall enter later ; at present we are concerned only with the main features of the system, to illustrate which we assume a typical case. There are, however, two different methods of applying the system, known respectively as " working out " and " working home," which it is desirable to describe here.

Working Out. — In long workings, as in post-and-stall workings, it is generally sought to advance across the cleat of the coal. This condition is, however, not considered to be imperatively necessary in the former system, and, as a matter of fact, it is frequently deviated from. There are sometimes circumstances, notably that of inclination of seam, which render it desirable to advance the faces of work in some other direction. In the following chapter we shall endeavour to show that the advantages of working across the cleat are often over-estimated. But at present, as remarked above, it is generally sought to advance in that direction.

Let it be assumed that the main levels have been driven headways in the coal, that is, on the

Systems Of Working. 311

ends. A barrier of coal will be left on the rise side of the levels to protect them from thrust, as in the case of post-and-stall workings, though this precaution is not always observed ; and beyond this the workings will be carried forward as a straight face, a curved face, or in several lengths of face, according to the conditions of the case, the most important of which conditions is the nature of the roof. Fig. 479, Plate LY., represents the face laid out in lengths; these lengths are called " stalls," and they are kept in advance of each other to avoid straining the roof along the same line throughout a long distance. It will be observed that, according to this system and method of working, roadways must be made and maintained through the goaf, or, as the exhausted portion is more frequently called in long work, the goh, for the purpose of rendering the faces accessible, and affording a means of conveying the produce to the main levels, and thence to the shaft. These roads are called " gob roads," and their construction and maintenance are matters of the highest importance, inasmuch as they serve, not only as roads along which all the produce of the seam has to be conveyed, but also as airways through which the ventilative current is passed to the working places.

The number of gob roads required will depend very much upon the manner in which the wall face is laid out. It will be seen from, the drawing that a road is required for each stall when the face is broken up, as there shown. To save labour in dragging or " putting " the coal from the several points along the face to the road, the latter is brought opposite the middle of the working stalls, and for the same reason the stall is limited in breadth usually to about 50 yards, so that the extreme distance over which the coal has to be dragged may not exceed 25 feet. To construct these gob roads through the waste or gob, the stone which is extracted with the coal is built up in walls several feet in thickness, to form the sides of the roads. These walls are called " pack walls," and they must be built up to a height somewhat greater than that ultimately required, to allow for subsidence when the weight of the roof is brought upon them. When the seam is a very thin one, either the roof or the floor, usually the former, must be cut away to give the requisite height in the roads. The material thus obtained will be used for the pack walls in preference to that derived from dirt bands and other partings in the seam, which is generally of a less resistant character. In some instances, a thin rib of coal has been left to form the road wall on each side, but the expedient has not proved sufficiently successful to warrant its adoption.

The maintenance of the roads frequently offers considerable difficulties and entails great expense. When the weight of the superjacent beds of rock is brought to bear upon the pack walls, the floor, if weak, is apt to rise, the action of the pressure producing the creep which has already been described. In such a case, the roads have to be repaired at night, by men set apart for that purpose. Sometimes the walls sink beneath the weight of the overlying rock, and the height is reduced by the descent of the roof. This circumstance renders it necessary to frequently cut away the roof, so that, after a time, the road may be wholly in the roof rock. Thus it is evident that the maintenance of the gob roads constitutes a serious question in the system of long wall.

Working Home. — In order to avoid the difficulties and expense of maintaining the gob roads, which are continually increasing in length as the workings advance, another method of applying the system has been introduced. This method is described as " working home," in contradistinction to that which we have been considering, and which is described as " working out." In this method the roads are kept in the solid coal, so that they are not exposed to the destructive action of a falling roof as the gob roads are. Moreover, instead ot continually increasing in length as the working

312 Mining Engineeeing.

proceeds, they, on the contrary, are continually decreasing as the wall face advances. This is the important advantage which the method of working home was designed to gain.

In laying out workings according to this method, the roads are first driven out through the solid coal to the boundary, and the wall face is then laid out in the manner described for working out. The coal is then worked back towards the shaft, leaving nothing but waste or gob behind. The exhausted portion is in this case entirely abandoned when the coal has been extracted, and the roads, being in solid coal, require but little attention. This method of working by long wall is shown in Fig. 480, Plate LVI. It is evident that when the workings are to be laid out according to this method, the preliminary operations will occupy a longer time than when it is intended to work out. This difficulty often constitutes an insuperable obstacle to the adoption of the method, especially where the proprietary is not well provided with capital.

Direction of the Workings. — In the foregoing examples, it was assumed that the main levels coincided in direction with the cleat of the coal, and that it was desirable to give the same direction to the wall face, that is, to advance across the cleat. The workings were therefore at once laid off from the main levels. But if it be desired to advance in the same direction when the levels are headways or across the cleat, the wall face will have to be set off at right angles to the levels. In this case, a pair of winning headways may be driven out from the main levels in the direction of the face, in the manner described under the head of post-and-stall workings, and from these the workings may be laid out, as shown in Pig. 481, Plate LVII. The inclination of the seam will often render this mode of proceeding desirable or even necessary. In some districts, instead of driving these principal gate roads through the coal, and leaving barriers to protect them, the whole of the coal is extracted, and the roads packed with gob or refuse, as shown in Fig. 482. This method is sometimes applied even to the main levels of the mine, leaving only the shaft pillars as solid or whole ground.

In long-wall, as in post-and-stall workings, the system of division into districts is followed. The advantages to be derived from dividing the area into several distinct and independent portions will obviously be, in the main, identical in both eases. These districts will occupy the same relative positions as in the post-and-stall workings, and they will be served from the shafts in the same manner. It will also be evident from an inspection of the drawings that, provided other conditions be favourable, workings may be laid out to the dip of the main levels similar to those shown to the rise. The coal on this side will, however, have to be hauled up by horse or steam power ; whereas, on the opposite side, it will be brought down by gravity alone. Hence the importance of placing the shafts in the most advantageous position to command the field will be apparent.

In the foregoing considerations and descriptions, it has been sought to give a clear understanding of the two systems of working coal, and a full appreciation of their respective merits and defects. To attain this end, the general and distinctive features of each system have alone been brought forward, and these have been illustrated by typical cases. It has been already pointed out that these features are subject to great modifications, in compliance with the requirements of varying circumstances. Such modifications, however, and the conditions which determine them, have been left out of consideration in the present chapter, in order to avoid confusion. These, and the details of working under each system, will be considered and described in the following chapter, which is devoted to the operations of " getting " the coal.

It must, moreover, be understood that the question ot modifying a system to adapt it to any given case can only be treated of in a general manner. The exact form that the system shall

Systems Of Woeking. 313

assume, and the particular mode in which it shall be applied, are questions that must be left to the judgment of the engineer. Neither the choice of a system, nor that of the method by which it shall be carried out, is to be determined absolutely by general considerations, or by chance or caprice. Besides general considerations, local circumstances must be taken into full account. The chief of these will be : the thickness of the seam, its inclination, the nature of the roof and the floor, the extent of the area to be worked, the existence of faults, the inflections of the seam, its gaseous character, the existence of material for pack, the state of the surface and the depth of the workings below it, the extent of the surface works and the quantity of produce to be dealt with daily, the amount of capital to be invested, and a host of other circumstances too numerous to mention. The importance of each of these circumstances must be accurately appreciated, and a system and a method of applying it chosen in general accordance with them. To do this successfully, the engineer must possess wide and accurate knowledge, keen discernment, and great inventive skill.

2 s

3U MINING ENGINEEEINa.

Chapter Vii.

Getting The Coal.

When- sufficient preparatory work has been done, and the system according to which the coal is to be worked determined on, it remains to consider by what method the system is to be applied, and in what manner the workings are to be laid out. The chief circumstances to be taken into account in such a consideration have been already mentioned ; these will be more fully discussed in the present chapter, and their relative importance estimated. In considering these questions, it will be first assumed that the workings are to be laid out according to the system of long wall, because that system, on account of its superiority, is more generally adopted than post and stall, and because it is susceptible of much greater variation in detail.

Long-Wall Workings. — In laying out workings according to the system of long wall, the general features of the plan adopted will be mainly determined by the thickness of the seam and the degree of its inclination. As, however, the latter condition affects all seams alike, we shall consider it incidentally, and describe the methods of working as determined by the former. Thus we shall have methods applicable to thin seams, to seams of moderate thickness, and to thick seams ; or rather a method proper to thin seams, and modifications of that method for seams of greater thickness. It has been already remarked that thin seams afford the most favourable conditions to working by long wall, and it is only in such a case that the system can be followed in its entirety. It should, moreover, be added that it is only by the long-wall system that very thin seams can be profitably worked.

In dividing seams according to their thickness, we shall denote as thin seams all seams between 1 foot and 3 feet 6 inches in thickness, for below 1 foot a seam becomes unworkable ; as seams of moderate thickness, all seams between 3 feet 6 inches and 7 feet thick ; and as thick seams, all seams of greater thickness than 7 feet. This division is determined by convenience in working. Thus the thin seams do not afford sufficient height to work in without cutting away either the roof or the floor throughout the whole face, or at least in the roadways. The seams of moderate thickness afford generally sufficient height without ripping down the roof, but do not exceed the height that may be conveniently reached from the floor. The thick seams necessitate the adoption of special means for reaching the upper part, and of sustaining the roof. The cutting away of the rock in the thin seams furnishes an abundant quantity of pack, and this abundance enables the system of long wall to be carried out in its entirety, by packing the gob full. It will be readily conceived that with such a supply of strong pack the gob roads may be kept in good condition with comparatively little difficulty. In seams of moderate thickness, not only is the space to be filled up greater, but the

Getting The Coal, 315

pack obtained is limited mainly to the partings, and other refuse contained in the coal. Hence the gob can be only partially filled, and the roof falls into the empty space. Sometimes little more can be done than to pack the sides of the gate roads. In thick seams, the quantity of coal removed IS so great relatively to the quantity of refuse obtained, that it becomes necessary to procure material for pack from some other source. In some cases it is conveyed from another part of the workings to the points required ; in others, it is sent down from surface.

The Wall Face. — The most advanced parts of the excavations in which the miners work are called the " working places." The " wall face " is that surface of the seam which is presented to the miners in the working places, and upon which they work ; this face is constantly receding as the excavation progresses. In the post-and-stall system, this surface is called the " working face," or the " face of work." The wall face is always perpendicular to the direction in which the workings advance, and hence forms a straight line. This, however, is true only of that portion which constitutes a stall, for on the large scale the whole wall face may be either a broken or a curved line. A stall is that portion of the wall face which is included between two vertical cuts kept in advance of those beyond them in the line of the face, or which is carried forward by one set of men. The length, or, as it is sometimes called, the breadth, of a stall is the distance comprised between the vertical cuts which bound such a portion of the wall face.

Stalls vary greatly in length. In short stalls, the length is from 10 yards to 25 yards; commonly the length varies from 25 yards to 50 yards, and in some cases it may be as great as 100 yards, 200 yards, or even 500 yards. The length of a stall is determined by several conditions. If the seam is only slightly inclined and composed of strong coal, and is covered by a strong roof, the stalls may be laid out very long. But if the seam is very thin, highly inclined, and composed of tender coal, and is besides covered by weak rock, great lengths become impracticable. It will be obvious that when these conditions exist, it is undesirable, and even impossible, to leave the roof unsupported throughout a great distance. The roof has a tendency to break along the line formed by the wall face, and if this line be prolonged straight throughout a long distance, this tendency may become dangerous. To obviate this, the line of the face is broken up into stalls, and these stalls are kept in advance one of another. By this means, the line of the wall face is practically limited to the length of the stall, and hence it is evident that this length must be determined by the tendency of the roof to yield. Taking this as the limiting circumstance, the stall is made as long as possible. A great length is favourable to supervision, and it facilitates in a high degree the hewing of the coal, whether the operation be performed by hand or by machine labour ; indeed, for the application of machine labour, a long length of face is indispensable. As the use of machine cutters extends, the length of the stalls will increase, for not only are longer faces needed, but they are rendered possible by a more rapid advance of the workings. A great length of stall is also favourable to the labour of loading and " putting " the coal, inasmuch as it allows a tramway to be laid along the face, which tramway is moved forward every day as the face advances. The question of gob roads will, in some degree, influence the determination of the length of the stalls. It is not often that the conditions are favourable to the adoption of a length suflBcient for a tramway along the face; and when this advantage cannot be had the coal has to be dragged, or " putted," as it is called, in sledges to the nearest road. Hence it is necessary either to have numerous roads, or to drag the coal long distances. The difficulty and the expense of keeping up numerous gob roads have been already pointed out, and it will be obvious, on reflection, that this question may considerably modify previous conclusions

9 a 2

316 Mining Enginefeing.

arrived at from a consideration of other conditions. The cost of maintenance of numerous gob roads, and that of putting the coal long distances, will thus have to be compared, and the length of the stall determined accordingly. It has already been stated that a common length is 50 yards in moderately strong ground which length is served by one road. This gives an extreme distance of 25 yards for putting. Not unfrequently, however, the conditions are unfavourable to so great a length as 50 yards. Sometimes, especially in thin seams highly inclined, the stalls have to be laid out short, in which case several may be served by the same road. Examples of the manner in which the stalls are laid out relatively to the gob roads will be given later. It thus appears that in dividing the wall face into stalls, many circumstances have to be taken into consideration, and some knowledge and skill will have to be exercised in arriving at a right solution of the problem.

Direction of the Wall Face relatively to the Cleat. — It is evident that the wall face may advance in three directions relatively to the cleat of the coal, namely, perpendicularly to the cleat, or " on the face " of the coal ; parallelly to the cleat, or " on the ends ;" and obliquely, at an angle at 45°, or " half on." The angle of obliquity might be varied ; but in practice, all the advantages of an oblique direction are obtained most fully from that which is " half on the ends." It is by no means a matter of indifference which of these three directions shall be adopted in any given case. The question is one that greatly influences the labour expended in breaking down the coal, and the physical condition of the coal when got, and hence it is necessary to take into account this influence and the limiting circumstances of the case when laying out the workings of a colliery. A proper attention to this matter is essential to economy of production, and it is probable that, in the future, as competition grows more keen, it may become also an essential condition of remunerative working in many seams. It is, therefore, desirable that in laying out new workings this question of direction of wall face to the cleat of the coal should receive careful consideration.

The ultimate object of all the methods and expedients adopted in mining is, as before observed, to obtain the greatest possible quantity of coal in the best possible condition, at the least possible cost. And as the question of direction under consideration greatly affects the physical condition of the produce of a seam, and the amount of labour expended thereon, it is obvious that it bears directly and in an important degree upon the attainment of that object. Regarded from the point of view of production only, irrespective of other considerations, the question presents itself in a twofold aspect, relating, on the one hand, to a reduction of the waste, and, on the other, to a reduction of the amount of labour required. In some respects these aims are antagonistic, and it becomes necessary to reconcile them, or at least to effect such a compromise as will give the best results economically. By "waste" is understood the small coal, or "slack," which, being utterly worthless, is left in the mine, or, of little value, is raised and sold at a price insufficient to cover the cost of production. A reference to the Table given in the second chapter of this work will show the value of physical condition in coal. It will be there seen that the small coal must, under ordinary circumstances, be produced at a loss, and that the profit upon the medium quality will be absorbed by this loss. It will not be far from the truth to assume that, under existing methods and conditions of workino-, the produce of any colliery may be divided into three equal portions, namely, large coal, medium coal, and small coal. The small coal is sold at a slight loss, the medium coal is sold at a small profit, which profit is absorbed by the loss upon the small. Thus two-thirds of the produce is disposed of without any advantage accruing to the coal owner. Upon the large coal there will be a considerable, and in many cases a large, profit ; but it must be borne in mind that it is taken upon one-third of the

GETTING THE COAL. 3 If

output only. By neglecting to take this fact fully into account, the estimated! vaiue o/ an output is often exaggerated.

It will appear from the foregoing statements, that in order to attain the object of producing the coal in the best possible condition, every effort must be directed to the altering of these proportions in favour of the large coal, and that reduction is essentially needed in the proportion of small, which is raised at an absolute loss. Even the deficiency of price in the small coal does not represent the whole loss. As before observed, a portion of the coal, and sometimes no inconsiderable portion, is broken so small by the operation of hewing as to be utterly valueless, and is for that reason left in the mine. Hence it is not taken into account when estimating the value of the output ; but it nevertheless represents a serious loss both to the producer and to the consumer, since it cannot be rendered available in any degree.

In the matter of production of waste, the advantages of the system of long wall become strikingly apparent. As a large proportion of the waste is produced by the action of the pick in cutting, it is clear that the more frequent the cuts the greater will be the quantity of waste made ; and as the cutting is far more frequent in the system of post and stall than in long wall, it follows that the former is more productive of waste than the latter. Suppose, for example, a stall 5 yards wide in the former system. Assuming that the holing takes place in the coal, we shall have, for the usual depth of 2 feet 9 inches or 3 feet, a width of 1 foot at bottom for the holing, and the same width at each side for the cutting. This width will diminish inwards, so as to give a mean of about 9 inches. Thus we have a destruction of coal throughout a width of 9 inches on the two sides and at the bottom of the face of work. And if we suppose that the seam is 6 feet thick, we shall have an area of 10 square yards in the face, out of which nearly 3 square yards, or 30 per cent., is taken for the cutting. If the vertical cutting be on one side only, and the coal brought down by blasting, the waste made by this mode of " falling " will be about the same as by double cutting. The proportion of waste here made is very great, because only a small surface is operated upon. But in long work the face is laid out to a much greater length, and the vertical cuttings are, consequently, far less frequent. Hence the quantity of waste produced is proportionately smaller.

In the foregoing considerations, the desirability of reducing the waste and of obtaining as much round coal as possible, and the necessity to that end of laying out the face so as to lessen the amount of cutting required, become clearly apparent. It now remains to consider the influence of the cleat, and how the end desired may be most effectually attained.

Coal, as pointed out in a former chapter, divides very readily along those places of cleavage known as the slynes or cleat, and when the other set of cleavage planes are only slightly developed, as in the coal of some of the midland districts, it is comparatively very resistant in the direction perpendicular to the slynes. Such coal will, therefore, furnish the best example of the influence of the cleat in the operations of extraction from the seams. In workings carried on according to the system of long wall, the roof descends behind the workmen at the wall face. This descent is the result of the bending of the beds above the seam along the line of the wall face, throughout which line they are supported by the coal. The pressure of the superjacent beds is thus resolved into two forces, one vertical, the other horizontal. The force which acts vertically downward tends to crush the coal, and to cause it to cleave in a direction parallel to the wall face on which side it is unsupported. ' But this cleaving action of the force acting vertically downward is greatly assisted by the

318 Mining Engineeeing.

force which acts in a horizontal direction. This latter force, being applied only to the upper surface of the seam, tends to divide the latter, parallellj to the face, into infinitesimally thin laminae. To make this action of the horizontal force clear, suppose the seam divided vertically, and in the direction parallel to the face, into separate slabs of a definite thickness. The horizontal force applied to the upper edge of each of these slabs tends to rotate it upon its lower edge as a centre, by which motion the upper edge will be advanced towards the unsupported side, and the wall face will be inclined, as shown in Fig. 483. But as the force acts more intensely as the wall face is approached, the slabs, from the face inwards, will be less and less inclined, that is, they will have been separated by a less distance towards their upper edges. If these slabs, then, had been previously adhering to each other, they would have been separated by the action of this horizontal force; and if instead of being formed ot distinct slabs adhering to each other, the seams were composed of a solid and perfectly homogeneous mass, the force would break it up into thin sHces or laminae. But as a coal seam is never perfectly homogeneous, and the cleaving force is never applied with the same intensity at every point, the seam has a tendency to break up, under the action of the descending roof, into slabs of irregular thickness, or it may be into prisms of irregular dimensions, in consequence of an unequal resistance. These effects are shown in Fig. 484. It will be seen from this figure that the pressure of the descending roof has split up the seam to a distance of 3 or 4 feet from the face, and that the fissures so caused increase in number and in width towards the face. It IS evident that the degree to which the coal will be broken under such conditions as these will depend upon the strength of the roof, which may bend and drop slowly, or break short off; the nature of the roof, which may consist of hard or soft rock ; the degree of descent in the roof, which descent determines the pressure at the wall face ; the direction of the workings, whether to the rise or to the dip, and the degree of the inclination ; the strength of the coal ; and the direction of the cleat relatively to the wall face. The latter circumstance is that which we have now to consider, but it will be evident that in determining the direction of the face to the cleat, the whole of the foregoing must be taken into account.

Let it now be supposed that the face in the section, Fig. 484, is parallel to the cleat, that is, that the workings are advancing across the cleat. In this case, the direction in which the pressure tends to cleave the coal coincides with the slynes or principal planes of cleavage, and it is, therefore, plainly obvious that the cleaving force will act under the most favourable conditions. If the coal be strong, a few extensive lines of fracture may be caused, which will greatly facilitate the getting of the coal by breaking it up into large blocks or slabs, and thereby saving much labour in felling and in subsequently breaking up the mass into blocks capable of being handled. Moreover, if we suppose the face holed, as shown by the dotted lines, the pressure of the roof, added to the weight of the unsupported coal, tends to produce a fracture along the line a h, and if this line be in a plane of cleavage, the condition will be that which is most favourable to the action of the pressure. In such a case, that portion of a seam which has been undercut will come down readily. Also when down the mass will lie with its principal cleavage planes running in a direction perpendicular to that in which the miner approaches it, a direction which is favourable to the subsequent operations of breaking up.

Thus it will be seen that when the wall face is parallel to the cleat, the labour of getting the coal is reduced to a minimum, and it is for this reason that the workings are generally laid out to advance across the cleat when the other determining conditions render the adoption oi" that direction

Getting The Coal. 319

possible. Tliiis an observance of this condition gives the produce of the seam at the least possible cost, which is one feature in the main object aimed at.

But it has already been shown that another feature in that object, namely, that of obtaining the produce in the best possible physical condition, is of equal importance. And it is plain that if the reduction of labour be obtained at the cost of a notable increase in the quantity of waste and small coal made, the ultimate consequence may appear as a loss rather than a gain. Let it be assumed that the coal is of a weak and tender character. Instead of a few long lines of fracture, as in the former case, we shall have numerous short lines traversing the mass both vertically and horizontally, and dividing it into thin slabs and small prisms. When the mass falls, these slabs and prisms are easily broken across, and the same liability to easy fracture exists during the operations of breaking up and loading into tubs. The final result is a very large proportion of small coal. Besides this, a considerable quantity of the coal is ground into dust by the pressure of the roof, especially along the top of the face wheftliPreatest pressure is exerted. Moreover, the ease with which the coal falls when the undercutting has been effected is a source of danger, which has to be provided against by the employment of sprags to support the coal during the hewing. In such circumstances as these, the advantages gained by advancing across the cleat are more than compensated by the larger proportion of small coal produced.

Let it be supposed now that the wall face is perpendicular to the cleats, that is, that the workings are advancing on the ends. In this case, the pressure of the roof tends to cleave the coal perpendicularly to its slynes or principal cleavage planes, and hence the condition is that which is most unfavourable to the action of the cleaving forces. In other words, in workings on the ends, the coal is in the best possible condition to resist the cleaving and crushing action of the pressure due to the descent of the roof ; consequently the coal will be obtained in large blocks, and the waste will be reduced to a minimum. As a set off against this advantage, the labour of getting is considerably increased, but the improved physical condition of the coal more than compensates the loss in that direction The increased labour, however, often constitutes a serious diflSculty, inasmuch as miners are generally unwilling to undergo greater exertions for the sake of an improved produce. It would appear, therefore, that in tender seams, and in seams of moderate strength where the crushing and cleaving action of the roof is great, the physical condition of the produce requires that the wall face should be laid out perpendicularly to the cleat of the coal, and that in strong seams, and in seams of moderate strength where the crushing and cleaving action of the roof is slight, the conditions of labour require that the wall face should be laid out in the direction parallel to the cleat. These are conclusions arrived at from a consideration of the influence of the cleavage planes alone. But it will be shown hereafter that other conditions, as, for example, a high inclination, may render it inconvenient or even impossible to act in accordance with them. The value of the conclusions, however, is in nowise lessened thereby.

There yet remains the direction of half on, that is, the case in which the direction of the face makes an angle of 45° with that of the cleavage planes. This is a medium case between those already discussed, and it may be often profitably adopted in only moderately strong seams where the pressure of the roof is great. In determining the most suitable direction of the workings under any given conditions, all the circumstances before mentioned affecting the action of the forces which tend to break up the coal at the working face must be taken into full account, and the conclusion arrived at from a consideration of these should be acted upon as far as the given conditions will allow. The

320 Mining Engineeeing.

proper laying out of a mine is dependent upon so many conditions, often of a conflicting nature, that it is only by considering each in detail, and carefully comparing the conclusions arrived at singly that the engineer may hope to obtain the object which he has in view. If he pursue this course earnestly and strictly, he may reckon on achieving all that may reasonably be expected from human fallibility.

Direction of the Wall Face relatively to the Dip. — In laying out workings according to the system of long wall, the direction and degree of the dip of the seam are important circumstances to be taken into account. These circumstances will frequently determine the direction of the workings irrespective of other considerations, and hence it becomes necessary to examine how far in any given case they may modify conclusions previously arrived at from a consideration of other determining conditions. In a seam that lies perfectly horizontal the influence of the dip is, of course, absent, and the direction of the main levels and of the wall face may in such a case be determined solely in accordance with those considerations which relate to the cleat. This is, however a case of rare occurrence, and consequently it will be generally necessary, as a preliminary measure, to estimate the influence of this dip. The manner in which the dip of the seam determines the method of working is by affecting the means and the mode of conveying the coal from the face to the shaft. It is always sought to utilize the force of gravity to bring out the coal from the workings, and it will be plain, on reflection, that this question is one of the highest practical importance. By arranging the workings in such a manner that the coal, from the moment when it is broken from the seam, may gravitate continually towards the shaft, an immense amount of labour is saved. Even in dip workings, where the coal has to be hauled up against gravity in the main roads, the temporary roads and the working places are laid out to take advantage of that force. As the action of gravity is in this matter of haulage dependent upon the degree of the dip, it is easy to understand how the latter will operate to modify the method of working. The following remarks have reference to thin and moderately thick seams ; seams of great thickness require to be wrought by special methods, to be hereafter described.

When the inclination of the seam does not exceed 15° or 20°, the coal may be wrought by either of two methods, in one of which the wall face is perpendicular to the dip, and in the other parallel to that direction. In this case, we have evidently a choice of advancing across the cleat of the coal or on the ends, and this choice will be determined mainly by the considerations to which attention has already been directed. When the wall face is perpendicular to the direction of the dip, the workings ascend the seam in the line of the greatest inclination, and hence the full force of gravity due to the degree of the inclination is exerted in bringing down the coal from the face to the main roads. This circumstance limits the application of the method to seams of moderate inclination. In the other method, in which the wall face is parallel to the direction of the dip, the workings advance along the strike of the seam, and hence the force ot gravity does not come into play until the produce has reached the main roads ; this circumstance renders the method applicable to seams of high inclination as well as to flat seams.

The method of " rise " workings, in which the face is perpendicular to the dip, is represented in Fig. 4=79, and more fully in Fig. 485. On the rise side of the main levels, and parallel to these, a length of face is laid out to form a stall. This stall is carried forward, and the goaf behind is packed with refuse upon which the roof descends. Through this goaf a gate road is left protected by pack walls, for the purpose of forming a means of communication between the working places and

Getting The Coal. 321

the main levels through which the produce is conveyed to the shaft. This road, for reasons already explained, will open on to the middle of the face forming the stall. When this first stall has sufficiently advanced, a second is opened from the upper level, and carried forward in the same manner. This is followed, at an equal distance apart, by a third, to which succeeds a fourth, and so on till the limit of the district is reached. Laid out in this way, the wall face forms a broken line, as shown in the figure. When the gate roads become long, and their maintenance consequently difficult and costly, they are cut by a road laid out parallel to the main levels, and the lower portions of them suppressed throughout a certain interval, as shown in Pig. 485. By this means, the cost of " roading " is kept down to the lowest practicable limit. The coal that is broken down from the face is dragged, from the right and from the left, to the gate road in the middle, down which it is carried by gravitation to the main levels leading to the shafts. In this arrangement, the roads, as before observed, open on to the middle of the face in each stall, a position that greatly facilitates the operation of putting the coal by reducing to a minimum the distance through which it has to be dragged. Also the roads which follow the lines of greatest ascent stand much better than those which run along the strike, because in the latter the beds that are cut into in levelling the floor, and the pack wall on the rise side, have a tendency to yield and to obstruct them. These are advantages belonging to the method of working a seam to the rise.

If it be desirable on account of the requirements of the cleat, or necessary in consequence of a high inclination, to advance in the direction of the strike, the stalls will be opened perpendicularly to the main levels. Assuming the inclination to be considerable, roadways may be carried up in the direction of the dip, and out of these, the stalls will be opened in the manner described for the rise workings. This method is shown in Fig. 481, and also in Fig. 486. It will be observed that in this case the gate roads open on to the face at the lower side of each stall, instead of in the middle, as in the former method. By this arrangement, the coal broken down from the face is made to gravitate towards the road ; the working places, which in the other method were level in the direction of the face, being now inclined in the line of greatest descent. Thus the conditions are reversed, the level direction of the working places in the first method being given to the roads in the second, and the inclined direction of the roads in the former being given to the working places in the latter. The main road carried up the seam in the direction of the dip will have the full inclination of the latter, and this road will be fitted up as a self-acting plane, by means of which all the produce of the seam conveyed to it through the roads opening into it will be let down to the main levels leading to the shafts. Instead of this self-acting plane, however, very frequently inclined or diagonal roads are used to bring down the coal from the parallel roads leading from the working planes. This arrangement is shown in Fig. 486. The inclination given to this road is such that the loaded tubs may be run down with the aid of a brake on the wheels, and pushed or drawn up empty without difficulty. The inclined road is necessarily adopted in seams the dip of which is insufficient to allow the use of a self-acting plane in the line of greatest descent. But it is often preferred to the self-acting plane in seams having a considerable inclination. The reasons for this choice do not clearly appear. The plane is considerably shorter than the diagonal road, and even for the same length is, for reasons already given, more easily kept up. And it is far easier to manage a brake on the wheel or drum upon the top of the plane, than to apply brakes to the wheels of the tubs during the descent and to push up the empty tubs, especially when the increased length of road is taken into account. It should be remarked that the use of the self-acting plane is rapidly extending.

2 T

322 Mining Engineeeing.

It is by no means a matter of indifference whether the workings be made to advance in tl-e direction of the dip, or perpendicularly to that direction. Each method possesses features that may be advantages or defects, according as the circiimstances vary. It has been already shown that in workings which advance in the direction of the dip, the maintenance of the roads offers much less difficulty than in those workings which advance across the dip. Another advantage of this method of working Hes in the fact that, under such conditions, the force of gravity acts most favourably in bringing down the coal at the face. This action, as we have shown, tends to break up the coal, and must therefore be considered relatively to the cleat and the strength of the coal. Moreover, as it is desirable generally to work the main roads by the ordinary means of traction rather than to be dependent upon a long and important self-acting plane, or diagonal road, serving a large number of outlets from the wall face, the method of working to the rise is, from this point of view, preferable. Yet another important advantage of this method lies in the facility which it affords of putting the coal along the working face, and of laying a tramway in that situation, to be moved forward as the face advances. By reason of these advantages, this method of laying out the wall face perpendicularly to the dip is usually chosen where no great difficulty to its adoption exists. Such a difficulty may proceed from the defects inherent in the method. In seams having only a slight inclination, the loaded tubs are run down the gob roads to the main levels very easily under the action of gravity. When the inclination is greater, it becomes necessary to check the descent by means of brakes applied to the wheels. These brakes often consist only of a chock of wood placed between the arms of the wheel, to prevent its revolution. But as the necessity for checking the descent increases, so does the labour of getting the empty tubs up the inclined roads increase, and it is easy to see that a limit must soon be reached. This limit will have been attained when the action of brakes apphed to the wheels has become insufficient to arrest the descent of the tub. The labour of pushing an empty tub up an incline sufficient to produce this result is very great. Thus it appears that the method under consideration becomes inapplicable in steep measures. There is also another disadvantage in this method, deserving of careful attention. If the seam gives off large quantities of gas, this gas will, in virtue of its low specific gravity, tend to accumulate in the working places, that is, at those points where its presence is most to be dreaded.

The method of laying out the wall face parallel to the direction of the dip possesses the advantage of being applicable to seams of high inclination. It involves under such conditions, as before pointed out the establishment of a self-acting plane, or the providing of a diagonal road whereon the coal may be brought down to the main levels. In this method, the conveyance of the coal presents but little difficulty, the gate roads being generally level, and the inclined plane easy to work. But as the roads are necessarily made to open on to the face at the bottom of each stall, the coal has to be " put " over a longer distance. The inclination of the working places in this case, however, facilitates the operation. If the inclination of the seam be very great, between 60° and 90°, the tendency of the coal to slide on the floor of the working places may become inconvenient and even dangerous. In England, such seams are rare ; but in some other parts of the world, they are common. To obviate the danger arising from this source, the stalls are, in these high measures, limited to three or four yards.

There is yet another method of working, intermediate in character between those just described, to which attention must be directed. This method, which is illustrated in Fig. 487, consists in laying out the wall face at an angle of 45° with the direction of the dip. It is applicable to seams the

Getting The Coal. 323

inclination of which is between 20° and 45°, and may ia certain cases be adopted with advantage. The important features of this method will be understood from an inspection of the drawing relatively to the conditions and circumstances already discussed.

Whatever be the method of working adopted, it is important to reduce as much as is possible the length of roads open. It has already been pointed out that the difficulty and the consequent cost of maintaining the gob roads in a good condition is at all times great, and hence a lessening of their number or a reduction in their length may effect a notable economy. The means by which this end is attained varies in form and in details of application according to the method of working, but it is essentially the same in principle in all. It consists in cutting the roads which run parallel with one another, at certain wide intervals by others, either perpendicularly or obliquely, to form a base, and in suppressing those portions of the roads which are situate below the cross road. The manner in which this principle is applied will be understood from Figs. 485 to 487. When the gob roads are perpendicular to the dip of the seam, as in Fig. 486, the self-acting plane, or the diagonal road upon which the loaded tubs are brought down, is shifted from time to time towards the wall face, as the latter advances. This is shown by dotted lines in the drawing.

Special Methods of WoRKiNa applicable to Thick Seams. — When the thickness of a seam is so great that the upper coals are beyond the reach of the miner standing on the floor, special methods of working become necessary. It is obvious that when the thickness of a seam reaches 15, 20, or even 30 feet and more, the mode of laying out the workings, which has been described, is no longer applicable without considerable modification, since the methods of extracting the coal must be different. The manner in which it has been sought to adapt the systems described in the preceding chapter to the requirements of these thick seams varies in different localities ; but in aU cases it may be referred to one of three methods, two of which relate to the system of post and stall, and the third to that of long wall. These methods we have now to consider.

Square Work. — The first of these methods consists in opening out chambers in the seam, enclosed by ribs of solid coal, and containing small pillars for the support of the roof. When one of these chambers is worked out, it is shut off from the rest of the workings, and finally abandoned, most of the coal composing the ribs and pillars being lost. This method is shown in Fig. 488, which represents a typical case of a thick seam, slightly inclined and unaffected by disturbances. The main levels are carried forward in the lower coals of the seam to the boundary, and the workings, called in this case " sides of work," are laid off on the rise or on both sides of the levels. The manner of laying off these sides of work is generally as follows. A narrow hole, called a " bolt-hole," is driven into the coal at A to a distance of 8 or 10 yards. The workings are then extended to the right and to the left to a distance of 25 yards or more, according to the dimension to be given to the chambers. Stalls are next driven forward and across in the lower coals so as to leave square pillars about 10 yards in the side to support the roof Where the roof is unsound, additional pillars, 3 or 4 yards square, called, in Staffordshire, " men of war," are left. The breaking down of the upper portions of the seam offers much difficulty and danger ; it is effected by standing upon the rubbish and coal already cut, or upon light scaffolding erected for the purpose. As the portion of the chamber behind the working faces is encumbered with this rubbish and timber it would be difficult to keep up a road through it to the bolt-hole first opened. To obviate this difficulty, a narrow road is driven up the middle of the rib of coal between two adjacent chambers, and other bolt-holes cut through at intervals, as shown in the drawing. The produce of the workings is then conveyed out through the

2 T 2

324 Mining Engineeeing,

hole nearest the face. This narrow road may also be made use of to ventilate the chamber. When the excavation is completed, the pillars are thinned as much as possible to lessen the waste, and when the roof begins to break down, dams are put into the bolt-holes, and the side of work is abandoned. The dams exclude the air from the large mass of small coal left behind, which coal is very liable, especially if of a " brassy " character, to spontaneous combustion, and the ribs prevent the crush from extending to other portions of the workings. Another side of work is opened, and worked out in the same manner, and the process is repeated until the whole area is mined over, each side of work being securely dammed off and abandoned.

This method of working, which is known as " square" work, is employed, with slight modification to adapt it to the requirements of different localities, in the Staffordshire Ten-yard Seam, and generally in the thick seams of anthracite in the United States of America. A difference of detail is to be observed in these anthracite seams, where the coal is worked from the top of the chamber downwards, that is, from the root towards the floor, instead of upwards from the floor to the roof, as in Staffordshire. The method is exceedingly wasteful of coal, and, as before observed, very dangerous to life. The loss of life from falls o . roof in the localities where the method is adopted is fearfully great. Mathias Dunn, writing some years ago, says, in reference to this method, " The working of so large a seam by a single process is attended with many difficulties ; and although a considerable quantity of roof coal be left on, yet it frequently breaks away, as also huge masses of coal in the course of working, so that there is a continual loss of life due to falls of coal alone. And when the ventilation of so immense a space becomes inadequate, the consequences are obvious, in respect to fires and explosions. In the working of the Ten-yard Seam, the small coal necessarily produced and left below during the process of mining, and the loss in pillars and barriers, amount, in the opinion of well-informed persons in the district, to considerably more than one-half, possibly, in some cases, to two-thirds, of the whole contents of the mine."

Long-Pillar Work. — The other methods of working thick seams, to which allusion has been made, are founded upon a totally different principle. This principle consists in considering a thick seam as composed of several thin seams, each of which is distinct from the others, and requires to be wrought separately. In this way, the difficulty of thickness is ehminated, and the question to be solved is how to work a certain number of seams of a convenient thickness, situate immediately above and in contact with one another. Thus regarded, the problem becomes similar to those already considered relatively to seams of moderate thickness, and it is evident that the several portions of the seam may be worked according to either of the systems of post and stall and long wall. Thus we have two methods of proceeding, one ot which relates to the former, and the other to the latter system. Both have been widely and successfully employed on the Continent, but it appears that the former is gradually giving place to the latter, which in most cases offers superior advantages.

In working a thick seam by the first of these methods, the upper layers of the seam are removed first, the object in this case being to let down the roof by stages. Suppose, for example, a seam 18 feet in thickness, divided for convenience into three portions or layers, each 6 feet thick. The workings will be laid out in the upper layer, and this layer worked out completely, as though it formed a distinct seam. So far there will be nothing peculiar in the method, the circumstances being those of a moderately thick seam. The variety of post and stall, however, which is adopted, is deserving of description, inasmuch as it differs considerably from the method described in the preceding chapter, and is frequently employed, especially in France and in Belgium, in working

Getting The Coal. 325

seams of moderate thickness. In some respects, it resembles the long work of South Wales, but it IS free from the defects belonging to the latter method.

By driving a series of narrow excavations at wide intervals, the district is first divided into masses or pillars of large dimensions, as shown in Fig. 489. The dimensions of these masses are commonly 60 yards on the dip by 120 yards on the strike, and the width of the excavations is usually about 7 or 8 feet. These excavations must be regarded as prehminary work, intended to lead to the convenient removal of the masses which they enclose. As soon as a suflScient number of these pillars has been laid out, the second stage of the working may be commenced by driving stalls through them, the preliminary workings being kept in advance of these pillar workings. The stalls are driven from each end of the pillar to meet in the middle ; they are at first driven narrow for the purpose of leaving suflScient protection for the roads, and then widened out suddenly to the greatest breadth at which the roof will stand. The distance of these stalls apart will also be determined by the conditions of the case, but generally it will be such as to leave the ribs or pillars supporting the roof from 10 to 15 yards thick. A third stage consists in removing these ribs; this operation is begun in the middle of the rib, the latter being thus worked away in opposite directions, as shown in the drawing. The removal of the ribs is commenced on the rise side of the main pillar, and continued downward, allowing the roof to drop as the operation proceeds. The upper and the lower ribs are left as a protection to the level roadways, and a portion of each rib is left to protect in like manner the inclined roads. These barriers, which will be in a more or less crushed condition, are removed when the whole of the district has been worked out. The drawing shows how one stage of the working immediately follows up another. In working off a rib, a heading 4 or 5 yards wide is first driven through the middle of its length, and from its dip side. From this point, the working may proceed in one of two ways, as circumstances may require. A series of stalls, at a greater or less distance in advance of one another, may be set off on each side of the central opening to work from dip to rise, or the rib may be removed by two stalls advancing in the level direction and constantly receding from each other.

The foregoing mode of working is that followed in removing the first or uppermost layer of the thick seam, and it will be observed that it allows the roof to descend upon the lower coal. When the top layer has been worked out, and the roof has settled down, the same process will be repeated in the second or middle layer of 6 feet, and again in the bottom layer, the roof being let down at each working. Thus it will be seen that by this means the roof is let down in three successive stages. It was formerly supposed necessary to allow a considerable interval of time, from two to three years, to elapse between the working out of one layer and the commencement of operations in the one immediately beneath, so as to ensure a complete settling down of the roof. Experience has, however, shown that such a lapse of time is, at least when the roof is good, altogether unnecessary, and that, on the contrary, the workings in the second layer might be proceeded with more regularly and with less danger to the miners beneath a recent fall of roof above it than beneath the sound roof above the first layer, because the descent of the roof could be better regulated, and the excessive pressures avoided which are produced when the descent of the roof does not follow the removal of the coal suflBciently closely. In consequence of this discovery, the workings in all the layers into which the seam is divided are now made to proceed simultaneously, under this condition only, that the working off of the ribs in one layer shall precede by a short distance the same working in the layer next below it. One great advantage of this simultaneous working lies in the prevention of

326 Mining Engineeeing.

spontaneous fires. A considerable quantity of slack is necessarily made by tbis system of extraction, and if tbis were left for a long period of time combustion would develop itself, and tbe fire would tbus be let down upon tbe lower portions of tbe seam. But, by following up tbe workings in tbe several layers at sbort intervals, tbat danger is avoided.

Tbis method must be considered economical and very appropriate to certain circumstances. But it possesses tbe defects inherent in tbe post-and-stall system wben tbe pillars are removed, namely, tbe production of a large quantity of waste, injury to tbe surface, and tbe destruction of any unwrought seams tbat may exist above.

In order to avoid some of these defects, a modification of tbe method bas lately been introduced, and in tbis modified form it is rapidly gaining favour. Tbe modification consists in packing tbe excavation, to prevent tbe descent of tbe roof. As a very large quantity of material for pack is required for tbis purpose, it bas often to be obtained from surface, and bence tbe cost of working is considerably increased. As a set off, bowever, against the additional cost, tbe physical condition of tbe coal is improved, and tbe evils consequent on breaking up tbe overlying strata are avoided. Wben tbe method is adopted in tbis form, tbe seam is often worked from below, tbat is, tbe bottom instead of tbe top layer is extracted first. This order is followed because it is generally more convenient to have tbe gob packing under foot than overhead. But the descending order may be rendered desirable by a tendency to spontaneous combustion in tbe coal ; for as the upper coals become broken up in their descent upon the packing, such a consequence is very likely to ensue.

Method by Long Wall. — The second method referred to as applicable to tbe working out the several layers of a thick seam is, however, generally to be preferred. This method is carried out similarly to those which have already been described ; but it is essential to the method tbat tbe gob be fully packed. To do this, the material for pack, as in the case of the modified form of tbe former method, must be obtained from surface and from other parts of tbe workings. For reasons already given, tbe seam is often worked from below. In a six-yard seam, for example, divided into three layers of two yards each, the bottom layer will be laid out according to tbe system of long wall, and the coal forming the layer extracted, leaving the space behind the workmen fully packed. At a sufficient distance behind to allow the roof to settle down upon the pack, workings are commenced in tbe second layer, and carried out in tbe same manner, by fully packing the gob. Behind these again, at the same interval of distance, the workings in the top layer are laid out. Whether these last shall be packed or not will be determined by circumstances relating to the overlying strata.

Though the ascending order is frequently adopted, it is by no means necessary, and in many cases, as before remarked, it is undesirable. It has been found that in a short time tbe pack or stowage has become sufficiently consolidated to form a fairly good roof, beneath which tbe workings may be driven with safety, provided the face be pushed forward smartly, and plenty of timber be used. The height or thickness of the layers will be determined by tbe condition of easily performing tbe operations of packing. Tbis condition will Hmit tbe height to about 6 feet. Less than tbis height, however, should in general not be taken when the seam is worked upwards, because of the breakage which takes place. In consequence of the yielding of tbe pack, the roof, after each excavation, will descend through a greater or less space, and it follows tbat tbe total space passed through will increase with the number of excavations made. The degree of fracture and crusbins: in tbe seam will, other things being equal, be proportionate to tbe total descent of tbe roof; and

Getting The Coal. 327

hence the greater the number of layers into which the seam is divided, the larger will be the proportion of small coal made. This breaking up of the seam, moreover, is favourable to the development of spontaneous combustion, a circumstance of great importance in some cases. When the coal is of a very hard character, this breaking up, due to the descent of the roof, may give certain advantages in getting, but generally it will diminish the proportion of round coal, and increase the quantity of timbering required. It is also evident that the proportion of waste coal made by hewing will increase as the layers are diminished in thickness.

This method of working thick seams by the system of long wall is obviously preferable, if intelligently carried out, to that of the long-pillar work previously described. In the former method, the coal is produced in the best possible condition, and the labour expended upon its production is considerably less than that required by the latter method. In short, in the one case we have all the advantages of the system of long wall, as compared with that of post and stall, which advantages have been already pointed out in detail.

Tsm Seams. — The profitable working of very thin seams of coal constitutes one of the most important questions with which the mining engineer has to deal. It was formerly believed that seams less than 3 feet in thickness could not be wrought at a profit, and hence it has happened that in some localities where njimerous thin seams exist, immense quantities of coal have been left in the ground as altogether unavailable. In many cases these abandoned treasures may yet be recovered, when engineering skill and commercial enterprise shall have become equal to the demands brought upon them. But some have been so injured by lower workings, carried on without the system of stowage, that they must be considered as irretrievably lost. The question is obviously one of national importance, since it affects in no inconsiderable degree the total available quantity of coal which the nation possesses. Already great progress has been made in this direction, and it is now no uncommon thing, in some districts, to find seams of 18 inches and even less being worked at a profit. This is notably the case in the Bristol coal-field, where the seams generally are numerous and thin. The system by which such seams are worked is that of long wall, and the methods are similar to those described in the foregoing sections, slight modifications only being made to adapt them to the requirements of restricted space. The following remarks on the best methods of working very thin seams are contained in a paper read before the South Wales Institute of Mining Engineers, by Mr. Handel Cossham, than whom no man has a higher claim to be heard on that subject :

"In the Newcastle coal-field there are thin seams under 3 feet thick, at present unworked, sufficient to supply the present yield of that district for above one hundred years. It would be important and interesting to ascertain the lowest possible thickness coal can be worked at a profit ; but the question is associated, and must necessarily be so, with so many other inquiries as to the quality and value of the coal when raised, the nature of the roof and floor of the mine, the value of labour in the district, and many other subjects, that it is almost impossible to pronounce with certainty on this subject. My own impression is, that provided the coal is of tolerable quality, and the market good, all seams above 18 inches thick ought to be worked at a profit; and I should not wonder if at some future time seams 12 inches thick be extensively and profitably worked.

" I have now for some years had the superintendence of a colliery where between 2000 and 3000 tons a week are raised from seams none of which exceed 3 feet thick, and more than half of which quantity is worked from an inferior seam of coal, only 22 inches thick. One district of workings, from which I am raising some hundreds of tons weekly, has during the last two years only

328 Mining Engineeeing.

averaged 15 inches thick. In working these thin seams I have obtained some practical acquaintance with the subject, and it is the result of that practical experience which I now propose to endeavour to embody in this paper.

" First. As to the best method of working such seams, I contend they can only be profitably worked by the long- wall system. I do not mean by this that it is essential to work a long continuous face ; it may often be best to work the coal as shown in Fig. 490, with heads of 15 or 20 yards wide, in advance of each other. But what I contend for is, that all the coal must be worked out, if thin seams are to be profitably wrought. The workings may either be carried on the level pitch of the coal, or to the rise, or half-course, according to the nature of the fracture of the coal. The profitable working of thin, and in fact of all seams, will very largely depend upon due care being exercised as to this important subject. A large quantity of small coal is frequently made when large might be raised provided this point received proper attention. The leaving ot pillars in thin seams is unwise, and will necessitate the working over so extensive a tract of surface in order to obtain quantity, that it will soon cost so much to keep the roads and air-ways in repair, as to render the workings unprofitable, and of course lead to their abandonment. One of the essential features, therefore, of working thin seams I take to be the entire clearance of all the coal ; and my experience leads me to prefer gob walls for roads and air-ways, if well packed and properly spade, rather than pillars of coal left for their support, unless indeed those pillars are left of an enormous size, and in that case the loss of coal would cost more than the advantage gained. My own impression is that all, or nearly all, seams are best worked on the long- wall system ; but without going into a discussion on that point now, I content myself with the observation that in the working of thin seams it must and will prove disastrous and unprofitable unless they are so worked.

" Second. Another important item in the profitable working ol thin seams I take to be the loading the trams at the face, and avoiding the shifting of the coal, if possible, till it gets to bank. The mode in which those seams are too often worked involves shifting the coal several times, and this is sure to entail considerable loss by breakage and fouling the coal. To accomplish this object, I would propose that gob roads be carried to the face every 15 or 20 yards, so that no part of the face worked shall be more than that distance from the tram road. If these roads are carried and maintained 3 feet or 3 feet 6 inches in height, trams holding from 8 to 10 cwt. of coal can be easily brought out, on roads laid with light bridge rails.

" Third. Assuming the seams to be at a considerable angle, it is important to notice the best and cheapest method of working the rise and dip coal, and the following I have found to be a cheap and easy way of working rise coal, where the angle is from 15° to 30°. Eun a road or ' hatching,' as we technically call it, to the rise, say 100 yards ; make this wide enough in the middle for the trams to pass each other ; lay two rails at the bottom, four in the middle, and three at the top, as shown in Fig. 490. At the top of the said rise incline, fix a wheel of a form that is simple and cheap, and capable of being easily removed. A brake must be attached to regulate and control the speed ; and if the angle of dip be great, it will be necessary to fix two wheels and allow the rope to go round each like a figure of 8. I find it best to use single-linked chains for these inclines, as the friction on the ground must necessarily be great from the impossibility of fixing rollers ; the wear of hemp or wire ropes would be too great in consequence.

"It is, of course, important to know how far to the rise it is possible to go with inclines worked in this way. My experience has led me to the conviction that from 250 to 300 yards is about the

Getting The Coal. 329

maximum, and that even then it is better to take it in two lengths, or it will he necessary to put on two or more full tubs to draw the empties and chain up. If the rise coal runs beyond that distance, I would then recommend that a larger and higher road be carried, so that a carriage on higher wheels may be adopted, to allow of several trams being put on at a time. By this means, I have no doubt, rise workings might be profitably carried on in thin seams for 500 or even 1000 yards.

" The working of dip coal on thin seams can be most cheaply effected in the following way. Assuming the angle to be, as previously rated, from 15° to 30°. I think the first 50 or 60 yards below the main road can be most cheaply worked by common reels or turn beams, with fly-wheels on each end, and worked with |-inch ropes. The next 50 or 60 yards can be best worked with gins and |-inch or |-inch round wire ropes. Below 100 or 120 yards, I think it certainly cheapest to adopt engine power, and I recommend small, compact, strong, and well-made high-pressure engines as being best adapted for the purpose ; premising, however, that the application of steam power underground always involves a certain and constant expense and annoyance, in the form of smoke drifts, waste steam, and divers other evils too numerous to mention.

" Two points are worthy of consideration here : first, that the cost for timber and some other items is usually less in thin than in thick seams, which partly compensates for the extra cost of labour ; and, second, the liability to fatal accident and injury is also lessened. The risk and danger in working coal above 5 feet thick are much greater than in seams below that thickness ; I need only refer to the workings in the thick coal in South Staftbrdshire to confirm this."

Material for Stowage. — It will be evident from a consideration of the system of long wall, and of the modified method of pillar work described in the foregoing section, that the stowage of the goaf, gob, or excavated portion of the mine, constitutes one of the most important operations of coal mining. It will also be evident that the importance of this operation will increase with the thickness of the seam to be removed, and that as seams become thick, the employment of a complete system of stowage is absolutely essential to their extraction by any method ol long wall. The adoption of a complete system of stowage is said to lead to an increased cost of production ; but the increase is rather apparent than real. When it is borne in mind that with a complete system of stowage a much larger proportion of round coal is obtained, and that the evils consequent on letting down the roof through a great height are avoided, it will be seen that the additional cost incurred is, in many cases, fully compensated by the resulting gains. Besides, in seams of great thickness, it may often happen that by the employment of such means alone can their contents be rendered available ; and to this fact must be added another of still greater importance, namely, that it is only by the employment of these means that the workings may, under such conditions, be carried on with safety to life. Hence it becomes desirable to consider the question o. stowage more closely than we have hitherto done, and to point out the sources whence the requisite materials may be most cheaply

obtained.

Quantity of Material required for Pack— In estimating the quantity of material required as pack, the increase in bulk which every mineral undergoes on being broken up must be taken into account. It was shown in a former chapter that this increase is very considerable, and hence it follows that to pack an excavation completely, the quantity of material required will be considerably less than that of the coal which has been extracted. In the chapter referred to, it was stated that the increase in bulk was as 1 : 1 75 for coal, 1 : 1 70 for shale, and 1 : 1 80 for sandstone. But these proportions had reference to the cubical contents of the tubs employed to convey the material

330 Miking Engineering.

away, for it was shown that the increase is greatly affected by the capacity of the receptacles into which the broken-up rock is put. When packed in the large spaces of the goaf, however, the increase in bulk is less, and may be taken generally as 1 : 1 60 for shale and sandstone. Thus, for every cubic yard of coal extracted, H of a cubic yard of rock will be required to fill the space occupied by the coal. But the whole of this space is not required to be packed, inasmuch as some portions of it must be left as roads and air- ways. And besides this, it is impracticable to perfectly fill up to the roof those parts which are packed. For these reasons, it is assumed that only 8 of the space is occupied by the coal, and hence the quantity required will be of the coal extracted. That is, for every cubic yard of coal removed from the seam one-half of a cubic yard of rock must be excavated to furnish sufficient material for stowage. If, for example, the material be all obtained from surface, the quantity excavated daily in the quarries will be half that of the coal removed underground, and for every ton of coal brought up, an equal weight of stowage must be sent down, assuming the rock quarried to have a specific gravity twice that of the coal.

Sources whence Material for Pack may he obtained. — In thin seams, suflScient material for pack is obtained from the workings themselves ; for though the quantity derived from that source maj be less than that which we have indicated as requisite for a complete stowage, the defect is of little or no importance, since the height through which the roof has to descend is small. The material so obtained consists of the useless matters accompanying the seams, as partings and impure coal, and the roof and floor rock which are cut away to give a convenient height or a firm bottom to the roads. This material may be said to cost nothing, since it is not excavated solely for the purpose of furnishing g pack, and since, moreover, it may be employed as pack at a less cost than would be incurred by its removal from the workings to surface. Hence, in thin seams, the conditions are most favourable to the system of stowage. There is, however, one disadvantage of an important character to be noted attending the use ot material derived from the workings. The shales and the partings of the seam may be of a bituminous or pyritous nature, and when such substances are heaped up in the goaf, they become liable to heat spontaneously in course of time, and ultimately to take fire.

In thick seams, and also in seams of moderate thickness in which it is desirable to pack completely, the refuse obtained in working is altogether insufficient. In such cases, therefore, it becomes necessary to have recourse to other sources. But when labour has to be expended for the sole purpose of obtaining material for pack, the latter constitutes au item of cost, and it then becomes desirable to seek out the cheapest sources, and to adopt methods of working them that will involve but little expense. It is obvious, other things being the same, that the cheapest sources of material will be those which are situate nearest the working places, since, wherever it may be obtained, it will have to be conveyed to those points. Hence it is often sought, when the circumstances of the case do not preclude the possibility ol following such a course, to open what may be described as a "quarry" in the workings in close proximity to the working places. But as quarrying operations are expensive, it is desirable to adopt measures whereby the material may be obtained without the labour of excavating it, or at least with a very little labour. The means by which this object is accomplished is as follows : As the wall face advances, stout timbers are thickly set at a certain point behind the workmen to securely support the roof. The point selected should generally be about half-way between two gob roads. The timbers are set to cover a circular surface of a sufficient diameter for the purpose to be hereafter indicated, and the gob is built up around them, strono- pack walls being placed next this block of timbers. When the workings have sufficiently progressed to

Getting Tke Coal. 331

allow this timbered spot to be nearly surrounded, a roadway protected by pack walls is left to keep it m communication with tbe working places. The quarry at this stage appears in plan, as represented in Fig. 491, which shows a circular chamber surrounded by pack walls in the midst of the gob, and communicating with the face by a narrow roadway. The timbers are now removed as rapidly as possible, beginning with those farthest I'rom the outlet, and tbe roof falls into the chamber. From this chamber, the material for pack is obtained, and run out in trams to the points at which it is required. Such a quarry is practically inexhaustible, since the upper rocks continue to descend as the lower ones are removed; but considerations of transport and injury to surface limit the time during which it may be used, and, consequently, as the workings advance other quarries will be opened in the same manner, in the place of those that have to be abandoned. This method of obtaining pack is frequently adopted in the Continental coal-fields, where the system of complete packing is more extensively carried out than in England. Fig, 492 shows an elevation, partly in section, of the face of the gob and the overlying rocks behind the miners in the working places ; this elevation corresponds to the plan in the last figure. When the seam is highly inclined, the details of the operations of opening out the quarry are varied somewhat to suit the altered circumstances of the case. Suppose a seam inclined at a high angle, as shown in Fig. 493, at a convenient level, a drift is run out narrow in the roof rock for a distance of a few yards, and beyond this point a chamber ot sufficiently large dimensions is excavated, as shown in the figure last referred to. The material removed from this excavation is, of course, employed as pack as it is brought out. During the progress of the excavation, the roof is supported by timber, and when the chamber has attained sufficiently large dimensions, the timber is drawn, as in the former case, and the roof falls. This position of the quarry is shown also in Fig. 494.

It not unfrequently happens that a seam is traversed by a fault, and in such a case the fault may often be made a source of material for pack. If the fault be filled with broken rock having but little cohesion, large quantities may be extracted with very little labour in the following manner : The end of the drift which has come up to the fault is strongly timbered, and from that point a narrow drift is run up at a high angle in the plane of the fault to a height of a few yards. This drift is then widened from the upper extremity downwards, and on the timbers being withdrawn the broken materials fall and slide down the incline, from the bottom of which they may be removed as wanted. This method of obtaining pack is shown in elevation and in plan, in Figs. 495 and 496.

When none of the afore-described sources are available, quarries must be opened at surface, and the excavated material taken down to the workings. Such quarries should, of course, be situate as near the pits as possible, to lessen the cost of conveyance, and they should be of such a nature as to be capable of being cheaply worked. In some cases, the bituminous and pyritous shales that have to be raised to bank in consequence of their dangerous character, may, after they have been burned by exposure in heaps to the air, be taken down again to form pack. Sand and clay, which are substances easily worked, are sometimes used for this purpose, and it has been proposed to utilize in this way blast-furnace slag. An essential point is that the material, whatever its nature may be, shall be obtained at a low cost.

Conveyance of Material for Pack.— The cost of the material used as pack is affected not only by the labour of excavating it, but also by the labour of conveying it from the points whence it is obtained to those at which it is to be applied. It should be borne in mind that the workings are

2 u 2

332 Mining Engineering,

laid out to profit as mucli as possible by tbe force of gravity in bringing out the coal ; that is, it is sought to so lay out the workings that the coal may descend by its own weight from the point at which it is extracted from the seam to the bottom of the drawing shaft. This circumstance will evidently operate against the carriage of pack, which will generally have to be conveyed in the direction contrary to that in which the coal passes. It is partly for this reason that the quarries in the gob are abandoned, and new ones opened as the workings advance, and the necessity for yielding to this condition will be apparent when it is borne in mind that the weight of the pack required is equal to that of the coal extracted. By the exercise of a little skill in laying out the workings, the pack obtained from underground sources may often be made to descend from a higher to a lower part of the district. Such an arrangement is obviously very favourable to economy, and no pains should be spared to render its adoption possible. The same conditions should be observed at surface in choosing a spot for the quarry situate at a higher level than the mouth of the pit down which it will have to be taken, and every facility should be provided for running the loaded tubs down and the empty tubs back quickly and cheaply.

The method of obtaining pack from surface possesses some serious disadvantages. As the material has to be lowered through the shaft in the tubs which are raised full of coal, the operations of raising and lowering have to be performed simultaneously and at an equal rate. Thus one operation is dependent upon the other, an evident disadvantage, since it is important that the operation of winding the coal should be perfectly independent, so as to be carried out with the greatest possible rapidity. Another disadvantage lies in the fact that as the workings are laid out, as already remarked, to allow the coal to descend from the working places to the bottom of the drawing shaft, the labour of conveying the pack from the bottom of the shaft to the working places is necessarily great. This defect may, however, often be avoided where an air-shaft exists to the rise of the workings, capable of being utilized as a drawing shaft. By lowering the tubs loaded with pack through such a shaft, advantage may be taken of the action of gravity underground . A singularly happy arrangement of this nature may be seen at the mines of La Grand-Combe, Departement du Grard, in France. By taking advantage in a most ingenious manner of local conditions, M. Grraffin has succeeded in so laying out the workings that, from the moment when the tubs leave the working places loaded with coal to that when they return to the same places loaded with pack, they are carried along by the force of gravity alone, with the exception only of the time when they are in the shaft. When the tubs leave the working places they descend by their own weight to the bottom of the winding shaft ; from the top ol this shaft they run down to the point at which they discharge their contents ; from this point again the empty tubs run down by their own weight to the quarries from which the material for pack is obtained ; from these quarries the loaded tubs run on again, still by their own weight, to the pit through which they are lowered ; and as this pit is situate to the rise of the workings, gravity takes them down again to the working places whence they started loaded with coal. Thus the traffic is always in the same direction, a circumstance of great importance, since it allows narrow roads to be used, having an inclination suitable to the descending load. It is easy to see that such an arrangement as this must be highly conducive to economy.

It must be considered an advantage that when the pack is lowered through the same shaft that is used for drawing the coal, as the weights of the two substances are equal, there will be a saving of engine power. But with the powerful engines now used, this advantage will be of very small importance.

Getting The Coal. 333

Details op "Working by Loxg Wall. — In the foregoing sections, the various methods of lajong out the underground workings designed to suit different conditions have heen treated of generally ; the particular modifications of those methods adopted in the different coal districts of this countrywill be described in the last chapter of this work. It now remains to describe the details of the operations of extracting the coal from the seam. These operations, no less than those of laying out the workings, demand careful attention, for unless the actual getting of the coal be skilfully performed, the advantages of well-laid-out workings will be lost. It is easy to see that the physical condition of the coal must largely depend on the methods and manner of breaking it down at the face, and preparing it for conveyance away ; and it is equally apparent that the management of the roof, and of the working places generally, must materially influence the diflScxilties and the danger, and, consequently, the cost of getting.

The methods of extracting the coal from the seam differ but little in principle, which consists in undermining the mass and allowing it to fall by its own weight ; but the manner of applying these methods varies slightly from district to district, and from seam to seam, according as the circumstances differ. These variations of detail will be pointed out incidentally in describing the general features of the methods of getting the coal by the systems of long wall and post and stall.

Hewing. — The first operation in getting the coal is to undercut it so as to remove the support from beneath it. The undercutting consists in cutting a groove along the bottom of the seam to a depth of 2 feet 6 inches or 3 feet. This operation is known as " holing," " kirving," or " benching," and it is performed by the most skilled portion of the miners employed, who are hence described as " hewers." It will become evident on reflection that the degree of skill brought to bear upon the operation of holing will influence very considerably the remunerative character of the workings, by affecting the physical condition of the produce. This fact will become more apparent as the labour of the hewer is described. It is true that the skill required is not of a high order, but it is such as demands experience and thoughtful attention to its teachings. This knowledge is especially requisite in the overlooker who directs the hewers, for it is of the highest importance, economically, that the holing should be made under the most favourable conditions. The operation of holing produces, when most skilfully performed, an excavation about 12 inches in height, and the material excavated is necessarily reduced to a state of fine division. Hence it is obvious that if the holing take place in the coal, the quantity removed by the operation will be rendered utterly useless by being reduced to slack ; and if the seam be a thin one, it will be seen that the quantity so spoiled constitutes a large proportion of the whole contents of the seam. For this reason, it is sought to hole in the under clay, and when this can be done, the circumstance is most favourable to economical production. But to be able to hole in the under clay, the latter must be of a nature that is capable of being easily worked. In some cases it is very hard and tough, and, consequently, necessitates heavy labour to excavate ; and sometimes it is absent, the coal in the latter case resting upon hard rock. Such conditions as these may render it necessary to hole higher up, and then it becomes desirable to seek the most favourable position for the holing, so as to destroy as little of the good coal as possible. It was pointed out in a former chapter that coal seams are rarely homogeneous throughout, but that, on the contrary, they usually consisted of either separate layers divided by shaly deposits, called " dirt partings," or of alternating bands of coal of different quality and degrees of hardness. Moreover, the distinct layers which are separated by partings may be, and usually are, different in quality. These circumstances must be taken into consideration in choosing the best place for the holing, for it is obviously desirable

334 Mining Engineeking.

to hole in that portion of the seam which is least valuable. For this reason, the holing is frequently made in the partings, and in such a case an additional advantage is gained by the removal of f,he valueless material. When the holing is made beneath or in the lower portion of the seam, the layer of shaly or pyritous matter constituting the parting falls with the coal and becomes mixed with it, a circumstance which depreciates the value of the produce. Coal so mixed with dirt is said to be fouled, and it is described as " dirty coal." All of these circumstances, and others of a particular and perhaps local character that may exist, must be taken into full account in determining the place for the holing ; and to estimate accurately the relative values oi such circumstances, it is absolutely necessary that the person who directs shall possess knowledge, and sufficient intelligence to apply it.

Before the operations of hewing are commenced, the wall face is divided into lengths, called " stints," of about 2 yards, and one of these lengths is allotted to each hewer. If the holing is to be at the bottom of the seam, the hewer lies upon his side, a constrained attitude that is assumed in order to cut the kirve or groove as narrow as possible. It is in this direction that the skill of the hewer displays itselt. The best hands will hole to a depth of 3 feet, and sometimes 3 feet 6 inches, without exceeding a height of 12 inches on the face. When the holing is in coal, the importance of this is manifest. In order to have sufficient room to swing the pick in, the height of the holing is kept at 12 inches, or thereabouts, for some distance in, and then gradually reduced to nothing at the full depth. This gives an average height of about 9 inches for the whole holing. The hewer, having cut away the face to begin the holing, and placed himself in the attitude described above, delivers a series of well-directed blows, to chip away the coal or the clay. He then clears out the debris which encumbers the groove, and repeats the blows, working forward in this manner from one end of his stint to the other. As the operation is one of chipping, the chisel edge would appear to be more suitable than the point for the holing pick, yet the latter is frequently used. The labour of holing is very great, whether performed in the recumbent posture or standing as when holing in a parting, and it is to be desired that the speedy introduction of machinery may render such heavy toil unnecessary. In holing to a depth of 3 feet or 3 feet 6 inches, the hewer places himself almost beneath the coal, and as the latter is apt to fall when the support is removed from beneath it, he is exposed to some danger. To guard against this danger, the coal has to be propped or " spragged " at intervals. The tendency of the mass to fall will, of course, depend upon the strength of the coal, the direction and development of the cleat, and the pressure of the roof, but it will seldom be prudent to proceed far without placing supports.

Generally, the coal will require to be detached at the sides as well as at the bottom, to ensure its fall in a mass. In narrow workings, as in the driving of levels, this side cutting is indispensable. The operation, which is called " shearing," consists in cutting a vertical groove similar to the hoHng at the bottom. In narrow places, one side is often sheared and the other broken down by blasting, and the same expedient is resorted to in long-wall wide workings, to avoid the necessity of shearing. The latter operation, however, will have to be adopted at intervals, the frequency of which will increase with the strength of the coal. It may be remarked that the advantage of blasting is merely a gain of time, since as much small coal is made by the blast as by the cutting.

Femoving the Coal. — When the holing and shearing have been completed, it remains to remove the coal from the seams. This involves three operations: "falling," " breaking up," and "loading," w'hich are usually performed by two different sets of men. The hewers are loUowed by a set of men called " getters," whose duty it is to break down, or " fall, the coal that has been undercut. To do

Getting The Coal. 335

this, they first remove the spraggs, and in many cases this is sufficient, as the coal then falls of its own weight, and rolls over in large blocks. This almost invariably happens when the working face is long and parallel to the cleat of the coal. Sometimes, though the mass may not fall, only a slight force is needed to bring it down, and in such a case the application of a bar between the seam and the roof is all that is needed. But when the coal is very resisting, recourse must be had to other means. These means — as stated in a former chapter, when treating of driving levels — are of two kinds, namely, wedges and explosives. The wedges used for this purpose have been already described and illustrated ; they are applied between the seam and the roof rock, and driven in with sledges. The action of these wedges is to break down the undercut mass by a gradually increasing force applied at the most favourable points ; and a consequence of this application of force, of great importance from an economical point of view, is the dislodgment of the coal without producing a quantity of small. Thus the use of wedges for falling leads to getting the coal in the best possible condition. When blasting is resorted to, a few holes are bored in the upper coal with an auger drill, and a light charge of gunpowder is inserted. It is important that the strength of the charge should not be greatly in excess of the work required of it, as otherwise the coal will be much broken. A light tamping of shale is put in upon the charge and the latter is fired. The effect of the blast is to bring down the mass of coal ; but the sudden application of the force breaks up the coal in the immediate neighbourhood of the shot-hole, and produces a quantity of small. It needs hardly to be remarked that blasting in fiery seams is an operation demanding great caution, and is at the best attended with considerable danger.

When the holing takes place in a parting in the seam, the lower portion is broken up by means of bars and wedges, or by blasting. This position of the coal is obviously very unfavourable to the operation of falling, since the action of gravity, instead of assisting, is opposed to the dislodgment of the mass. Thus the labour of breaking up these lower beds is severe, and the coal gets much broken. If, however, the seam be highly inclined, gravity may be turned to account in breaking down the lower coal.

When the getters have completed tbe falling of the coal undercut by the hewers who have preceded them, they are followed by another set of men called " loaders," whose duty it is to break up the coal that has fallen into blocks of a size capable of being handled, and to load them into sledges or trams ; these trams are then dragged or pushed along the face to the nearest gob road. The labour of removing the coal from the face where it has fallen to the roads is in some localities called " putting," and those who perform it are described as " putters." The breaking up of the coal into blocks is effected by means of sledges, and even this simple operation requires some care to observe the direction of the cleavage planes. By a little intelligent attention to this matter the production of a large quantity of small may be avoided.

Packing and Timbering. — When the coal has been removed,. there yet remains to be performed two other important operations, namely, those of packing the gob and timbering the roof. Usually these duties are entrusted to the same set of men, who, on that account, are called " packers and timbermen." These men throw back into the gob the refuse that is left in the working places by those who have preceded them; they obtain the material for stowage from the sources already described, and pack it up to support the roof ; and they build the pack walls for the gob roads. In thin seams, it falls to the duty of the packers to rip or blow down the roof to give height in the roads and in seams of only 2 or 3 feet thick this road cutting forms an important part of their oocu-

i36 MINING ENGINEEBING.

pation. It is obvious that the labour of the packers will increase witb the degree of completeness required in the packing, and the height of the space to be packed. When the seam is of moderate thickness and requires to be fully packed, or when a thick seam is worked out by layers in the manner described in a former section, the operations of packing the gob will demand a numerous and properly organized staff of men. Between the very thin and the very thick seams, every gradation of importance may exist. In some localities, especially in ironstone workings, the packers are called " builders up," because their duty is to build up the refuse in the goaf or gob.

The duty of the timbermen is one of very great importance, inasmuch as the security of the working places is, in a great measure, dependent upon the manner in which it is discharged. It has been already remarked that the roof has a tendency to break along the line of the wall face, and it will be evident that the safety of the men in the working places demands that this tendency should be counteracted. The means adopted to effect this purpose consists of timber placed at a short distance from the face. The timbers usually employed are simple uprights, similar to those used in the levels ; they are placed in two, and in some eases of very weak roof in three, rows parallel to the face, the first row being about 6 feet distant from it, and the second row about 9 feet. The props in these two rows are set so as to alternate with each other, that is, a prop in one row stands over against the middle of the space between two props in the other row. The distance of the props apart varies, according to the pressure of the roof, from 3 to 9 feet. Besides these parallel rows of props, single props may be required here and there in the working places where the roof gives indications of weakness. Sometimes the dangerous masses described as " pot bottoms " are met with, and these require to be securely propped, if by good fortune their presence is discovered before they give way. Whenever the miner observes a doubtful appearance in the roof, he strikes the part with the head of his pick : a dull sound is indicative of danger.

The props used in the working places should be of round timbers, and they should be cut square at each end so as to bear evenly over the whole of the sectional surface. A piece of wood, from 12 to 15 inches in length, called a " cap," " lid," or " tymp," is placed against the roof to afford a good bearing, and the prop, which should be cut to a sufficient length, is placed against it obliquely and driven Mp to the perpendicular position by blows delivered against its lower end. This mode of fixing the prop puts it into a proper state of tension. If the piece is not long enough for this, it must be wedged. Not unfrequently the lower end of the prop is set upon a small heap of slack or rubbish, and tightened by wedging from above. The advantage of setting a prop upon this rubbish lies in the facility which is thereby afforded for removing it when required. The pressure of the descending roof is so great that there is often considerable difficulty in removing a prop when set upon the solid rock ; but when it stands upon a heap of slack, this may be easily picked out with the point of a pick, and the removal of the foundation of course releases the prop. Sometimes a piece of board is laid upon the slack to distribute the pressure, and in some localities a hoop is laid around it to prevent it from spreading. Another advantage in this method of placing the prop is the elasticity due to the loose material beneath it. In places where the pressure of the roof is expected to be very great, " nogs " or chocks " are employed instead of the prop. These consist of pieces of wood about 3 feet in length and 6 inches by 8 inches in section, built up crosswise, two by two, to form a square pillar. The advantages of this kind of support are that it possesses a broad base and summit to receive and distribute the pressure, and that it may be easily removed by knocking- out the pieces. Cast-iron props have been proposed, and in a few instances adopted, but their use is not

Getting The Coal. 337

hkely to become general. In some parts of the Continent, the upper end of the prop is bird-mouthed, and cross pieces are laid from one to the other, similarly to the head pieces used in the levels.

"When the hewers, getters, and loaders have removed the coal which was holed to a depth of 3 feet, the timbermen, having as packers packed the gob, knock or pull down the outer row of props, and reset them to form an inner row next the face. The operation of removing the props is attended with some danger, and therefore requires caution. In resetting the props, the timbermen take care to place them perpendicularly to the stratification, as it is only when in that position that their full strength is utilized. When the props are drawn, the roof falls, sometimes slowly by bending down upon the pack, sometimes suddenly by breaking short off. If the roof is weak and jointed, many of the props will be lost, and great caution must be exercised in attempting to recover them.

The usual methods of setting the props and chocks are illustrated in Figs. 497 to 500.

Details op Working by Post and Stall. — The operations of breaking down the coal at the working face will obviously be the same essentially in both long-wall and post-and-stall workings. The differences of those two systems lie rather in the methods of laying out the workings than in the application of the means for extracting the coal from the seam. Hence there remains but little to add to what has already been given on this subject. In the narrow workings of post and stall, the coal is undercut, sheared, and broken down in the same way and by the same means as that in the wide workings of long wall. It will, however, be evident that the labour of breaking down will be much greater in one case than in the other. In the narrow places, the amount of cutting or blasting is necessarily great, and it is to lessen this labour that the bords or chief workings are almost invariably directed across the cleat of the coal. Perhaps the most important difference of detail lies in the propping of the roof. Of this, it is clear that very little wiU be required till the operations of removing the pillars are commenced. This matter will be again referred to later. The division of labour described in relation to long-wall workings will obviously not be the same in post and stall, since some of the operations performed in the former system are not required in the latter. The division will be generally into hewers and putters, the hewers, in this case, being charged with the duty of holing, shearing, and falling the coal, and the putters with that of breaking up the fallen mass, loading it into the tubs, and conveying it to the nearest horse road.

Removing the Pillars. — The driving of the bords and headways in the solid coal constitutes what is described as working in the whole mine, and such workings are known as " whole workings." The portion of the district which has been cut up into pillars by the first or whole workings is known as the " broken mine," and the removal of the pillars is described as " working in the broken." The operations of working in the broken mine are the most difficult of those which are performed under the system of post and stall, and they demand the exercise of judgment and caution. It will be seen that it is in these operations of removing the pillars that the difficulties of a falling roof are encountered. As the removal of the pillar proceeds, the tendency of the roof to come down increases, and it becomes necessary to support it temporarily with props similar to those already described in relation to the workings by long wall. It is easy to see that the descent of the roof must take place under much less favourable conditions in pillar work than in the more regular operations of long wall. In the latter, the roof descends evenly throughout a long length of face, while in the former it gives way rather in detached portions. Hence the necessity for proceeding cautiously and for timbering strongly. The pillar of chocks or bulkhead, previously described, will

338 Mining Engineeeing.

be found very efficacious, and is of frequent use in working in the broken. When the roof is bad, it falls suddenly on the props being withdrawn, and often it becomes impossible, in such circumstances, to recover all the timber or to work out all the coal. If the roof is strong, it will often stand until several neighbouring pillars have been removed, and then, when the limits of its strength have been reached, it may totter in a threatening manner for some days, and finally fall with a tremendous crash that may cause a violent blast to traverse the workings.

Various methods of working off the pillars are adopted, each of which is more applicable to some circumstances than to others. No general rule can be laid down in this matter ; the adoption of the most suitable method under any given conditions must be left to the judgment of the engineer.

One method of removing a pillar is to work it off in slices parallel to its longer face. When removed in this way, a working face may be set off from the headways on the goaf side to meet in the middle of the pillar. The success of this method is greatly dependent upon the existence of a good roof, as otherwise much timbering would be required.

Instead of slicing the pillar, it may be worked off in a succession of steps, each pillar being a grade more reduced in bulk than that which is next in succession to it.

Another method consists in driving a narrow bord or "jerking" up the middle of the pillar, and then to work back simultaneously the two halves to the bords. This method is called splitting the pillar, and it may be adopted with advantage in certain circumstances. An objection to it on weak floors is that it tends to produce creep, but this may be obviated by making the pillars of large dimensions in opening out the whole workings. The methods of working off the pillars or ribs of coal in long-pillar work have already been described.

It will be seen that the operations of removing the pillars are more or less assimilated to those required by the system of long wall, and hence it will be understood that the details, both of extracting the coal and of dealing with the roof, will also be similar. The men are protected in the working places by rows of props or of chocks, or, in some cases, by pack walls. The props have usually to be thickly set and many of them are inevitably lost. In drawing the outer props, a chain and lever are often employed to give greater security to those engaged in the operation.

Whatever be the method adopted for removing the pillars, it is of the utmost importance that the various operations be carried on briskly. If this condition be not fulfilled, much timber will be consumed and a large proportion of small coal made. It is also important, for the same reasons, that the pillar workings should follow the whole workings closely, so as to extract the coal before it has become much crush,ed by the weight of the roof. It has already been pointed out, as one of the defects of the post-and-stall system, that when the pillars have been largely "robbed," as it is sometimes termed, that is, greatly reduced in bulk by being worked off, the portion left is apt to become crushed and rendered comparatively valueless. The more rapidly the pillar is worked off, the less will it be affected by the crushing action of the descending roof, and the smaller will be the quantity of timber required.

It should be remarked, in conclusion, that workings in the broken mine in fiery seams should be prosecuted with great caution to avoid explosions of gas. When a large surface of coal is exposed, large quantities of gas will be given off, and this will accumulate in any situation favourable to its lodgment. The breaking up of the roof also may bring down the gas from a higher seam, and thereby convert the goaf into a reservoir, from which the gas may issue at any moment.

Getting The Coal, 339

Coal-Cutting Machines.— It will have been remarked from the foregoing description of the operations of hewing coal that the labour is of a very severe character. The necessity for undercutting to a great depth in a narrow groo\'e, and the constrained attitude of the hewer, especially in thin seams, combine to render his occupation the most laborious of any connected with coal getting. It is also evident that the force of the hewer, exerted under such unfavourable conditions, must be very wastefuUy applied, and therefore is not employed according to the requirements of economical production. Besides this, even the proportion of the force which is made effective is improperly utilized, since it is made productive of a large quantity of small coal. It has been shown that when holing to the usual depth of 3 feet, the average height of the cut, even with skilful hewing, is not less than 9 inches, and when it becomes necessary to hole in the seam, such an excavation destroys an important proportion of the coal. These disadvantages of hand hewing have been already pointed out in detail. Hence it becomes desirable to substitute machine for hand labour ; a substitution that will obviate these numerous and great disadvantages, and import into the operations of coal getting other advantages than those possessed by hand labour. Another very important circumstance, that has of late assumed a threatening aspect, is the altered relations of capital and labour. This circumstance was pointed out, and its bearing upon rock drilling estimated, in a former chapter ; but it influences in a far higher degree the actual operations of getting the coal. To lessen the dependence of production upon hand labour, it is highly desirable that machinery should be applied to the undercutting of the seam. Moreover, the same change is called for by the constantly and rapidly increasing demand with which it will be impossible long to keep pace by the means hitherto employed. Vast improvements have been effected in the means of haulage and raising the coal in the shaft. So great, indeed, have been the changes in this respect that it is now possible to raise in a given time quantities of coal that a few years ago would have appeared fabulous. But it must be remarked, as an anomalous circumstance, that while the improvements have been going on, very little change has taken place in the means of actually extracting the coal from the seam. So that we have magnificent machinery and perfect arrangements for raising and disposing of the coal after it has been extracted, while the old methods of hand labour are still in use to supply this machinery with the mineral upon which to operate.

It would seem to be a comparatively easy matter to design and construct machinery capable of performing the work of undercutting the seams effectively and efficiently. Experience has, however, shown that the difficulties are greater than they appear. Numerous attempts have been made to overcome them, and numerous failures have been registered. Some of these attempts have resulted in the attainment of some degree of success, and it is to the improvement of the machines which are constructed on the principles involved in these attempts that we look for a satisfactory solution of the problem. As this question has not yet assumed the definite form possessed by that of rock boring, we shall not discuss it in detail. The time has not yet arrived to speak decisively upon the subject, and we shall therefore limit ourselves to merely pointing out the latest phases which the question has assumed. This will be best accomplished by describing the two most recent machines that have held their ground when put to the test of actual work under ordinary conditions. Of these, one has been in successful operation at several places for some years ; and the other, which is more recent, promises to give equally satisfactory results. These machines, moreover, have been designed according to two different principles, and, therefore, may be regarded as fair representatives of two types, each of which possesses peculiar merits that render it suitable to certain conditions.

Winstanley and Barkers CoaZ- Cer.— Winstanley and Barker's coal-cutting machine possesses

340 Mining Engineeeing.

merits that have gradually brought it into favour. Having stood the test of some years of actual work under different and not always favourable conditions, it is deserving of special attention, and may be spoken of with confidence. Its designers have evidently carefully estimated the circumstances to be provided for and the difficulties to be encountered, and it must be acknowledged that they have succeeded in their efforts to meet those circumstances and difficulties. The following description of the machine and of the work which it has accomplished, is contained in a paper by Mr. Eobert Winstanley, read before the Institution of Mechanical Engineers, in July, 1872. It will be observed that the writer gives some valuable statistics relative to the cost of working, whereby a comparison may be made between the systems of machine and hand labour from an economical point of view. It should, however, be borne in mind that such comparisons are unfavourable to the system of machine cutting, because, first, the novelty of the operations leads inevitably to excessive expenditure, and, second, the workings have not been laid out with a view of adopting machine cutters. The latter circumstance is obviously one that must act very prejudicially against machine holing :

"The Winstanley and Barker coal-cutting machine has been worked daily or nightly for nearly two years at the Piatt Lane Colliery of the Wigan and Whiston Coal Co., in a seam of coal known by the name of the ' Pemberton Little Coal,' or ' Pemberton Yard Mine.' The coal is about 2 feet 4 inches in thickness, and is so hard that it was with the utmost difficulty men were obtained to work it ; on one occasion the seam stood idle at this colliery for some time, because colliers could not be got to work in it, and it has always been necessary to pay a higher price for getting this coal than for any other seam of coal worked by the same proprietors.

" The machine under consideration is illustrated in Figs. 501 to 512. Like most other coal-cutters, it is driven by compressed air, which is conveyed down the pit shaft and along the main roads and drawing roads in iron pipes, and from the end of the drawing road to the machine in an indiarubber hose pipe of 2 inches diameter. The frame of the machine is about 6 feet in length, and is supported on flanged wheels which run on the ordinary tramway ot the mine ; the gauge in this instance is 2 feet, but it can be varied to suit other gauges, as may be required. On the front part of the frame are two oscillating cylinders of 9 inches diameter and 6 inches stroke, provided with ordinary slidevalves. The piston-rods are connected to an upright crank-shaft, on the bottom end of which is a driving pinion, shrouded at the top, and having only five teeth, as shown in the plan, Fig. 505. The teeth of this pinion gear into the teeth of a spur-wheel, which is also the cutting wheel, and is 3 feet 6 inches diameter ; the driving power is thus applied with the greatest mechanical advantage, that is, directly on the circumference of the cutting wheel. The cutters are fixed in the circumference of the wheel, one in every cog or tooth, their points projecting 1 inch beyond the teeth ; the mode of fixing them is shown in the drawings as well as the three patterns of cutter which are arranged successively round the cutting wheel.

" The cutting wheel revolves at the end of an arm consisting of a broad flat plate, at the opposite extremity of which is a toothed segment or quadrant, actuated by a worm and hand-wheel whereby the arm carrying the cutting wheel can be turned partly round in its bearing in the frame of the machine. Before the machine commences to hole in the coal, the cutting wheel is under the back part of the frame, as shown dotted in the plan, almost touching the straight face of coal ; and on starting the engines the attendant, by turning the hand-wheel and worm, causes the cutting wheel gradually to hole its way into the coal, until the arm is at right angles with the frame of the machine, as shown in the plan and the transverse section. In this position, the cutter is holing

Getting The Coal. 341

about 3 feet in depth from the face of the coal ; and it can be placed in any position to hole less than this depth if required.

" As soon as the cutter has worked into the coal to the full depth, the machine is drawn along the face of the coal as it holes or cuts its way, throwing out the small coal or slack between the tram rails upon which the machine runs. The thickness of the holing or groove cut out is 3 inches ; this thickness, however, can be reduced if desired by the use of a thinner cutting wheel. There is no traverse motion on the machine, as it is considered simpler to draw it along the face by means of a small crab turned by a lad at the end of the working face. When the holing of the entire length of the face is completed, the cutting wheel is brought back to its original position underneath the frame of the machine, by means of the worm and hand-wheel, and is ready for beginning to hole at the commencement of the new face as soon as the coal already holed has been removed.

" The chief advantages in this machine are, that the swivelling movement of the arm carrying the cutter enables it to cut or hole its own way into the coal, the depth of cut increasing from nothing up to about 3 feet ; and by the same movement the cutter is brought back underneath the frame of the machine when not at work. It will also be perceived that when the cutter is in this position, drawn back underneath the frame, it can be taken through any narrow roads or parts of the mine, without the necessity of removing the cutter from the machine, the space required for the machine to pass being only the width or diameter of the cutting wheel, which with the cutters is 3 feet 8 inches. Again, were it not for this arrangement a portion of the coal would have to be cut out by hand labour, for the purpose of inserting the cutting wheel, unless the machine were started at the corner of a pillar, or what is called a ' loose end.' An important advantage in this machine is, that the power to drive the cutting wheel is applied direct on the circumference of the wheel ; this mode of gearing also allows the small pieces of coal or slack to fall through to the bottom, so as not to lock or clog up the teeth of the machine.

" The average rate of holing is from 25 to 30 yards advance per hour, according to the nature of the coal the machine is holing ; but the rate is not practically a matter of much importance, as the great points to be considered are the amount of work a machine will do regularly, and the way in which it does it. This machine has frequently cut the whole length of the face of 120 yards in a night, or between 7 p.m. and 4 A.M., including all stoppages for meal times and changing cutters, &c. In the same mine, 5 yards per day, or f yard per hour, is much above the average work for one man with the pick ; and, under ordinary circumstances, it is considered that the work done by the machine is equal to that of thirty men.

" The machine works in the night, the coal being removed by ordinary manual labour in the day. No blasting is used in this mine, the coal falling by its own weight after it has been holed by the machine ; this, however, would not probably be tbe case if the face were short, and if the holing were not made of the same width for the full depth. The roof of the mine is ordinary laminated shale, and the underlying stratum very hard fire-clay, nearly approaching rock ; the dip ot the strata is about 1 in 6, and the machine holes up bank. The average pressure of air at the machine is 25 lb. per square inch.

" For more than six months the machine has had little or no repairs, and the practical advantages found in its working are as follows :

" First, that without the machine men could only with great difficulty be obtained to hole this particular coal, on account of its hardness.

Mining Engineeeing.

" Secondly, that when the seam was worked by hand labour, the proportion of lump coal and slack was as 3 of coal to 1 of slack, whilst with the machine it is 8 of coal to 1 of slack.

" Thirdly, that the work is done independently of the men, who cannot be got to work regularly ; consequently the production is more certain with the machine.

" The actual cost of getting the coal by the machine and by hand labour has been found, from the payments made during a period of six weeks at the Piatt Lane Colliery, to be as follows :

Hand labour Machine

3s. 6d. per ton.

3s. lid.

showing a saving of 5d. per ton by the machine. This saving is considered to be absorbed by the expense of compressing the air for the machine, and by interest on outlay, and wear and tear.

" The increased value of the produce, in consequence of less slack being made by the machine than by hand labour, is as follows :

s. d. Hand labour 3 tons of coal at lis. .. .. ., .. 33

1 ton of slack at 7. 3d. ., ,. ,. 7 3

Total 4 tons got

Machine 8 tons of coal at lis. ..

1 ton of slack at 7s. 3d,

Average Value.

40 3 10s. Ofd. per ton.

88

Total 9 tons got

— Average Value.

95 8 10s. Id. per ton.

showing an increase of Qd. per ton in the value of the coal when -the machine is employed. In a seam of coal a few inches thicker, and under more favourable circumstances, it is considered there would be a saving over manual labour of from 25 to 30 per cent.

" The cost of getting the coal by the machine has been given above as 3s. per ton ; but this cannot be taken as a correct representation of the cost by the machine in ordinary cases of working ; the machine at Piatt Lane Colliery being the first that was put to work, and for a commencement a liberal rate of pay was given to the collier attending it, as an inducement to give it a fair trial. The same man has now been working it on contract for the last fourteen or fifteen months, and he now earns more than three times as much per day with the machine as previously with the pick."

The Economic Coal- Cutter. — The other machine to which attention has been directed is known as the " Economic," and is the invention of George Warsop and Henry W. Hill. It is simple, compact, and light, qualities ol essential importance in a coal-cutter, and is capable of being effectively driven with an air pressure as low as 25 lb. to the inch. This latter quahty it has in common with the machine already described. The inventors of the " Economic " coal-cutter give the following description of their machine, which will be found illustrated in Figs. 513 to 516.

" For the purpose of undercutting the coal, a round cutter bar is employed, having a spiral groove or thread in the form of a screw running from end to end. In the raised parts of the bar left after the groove is cut, are fixed, at regular intervals round the periphery, a number of suitable cutters projecting above the surface of the bar and firmly fixed in longitudinal slots or grooves in the same by wedges or screws. These cutters are so arranged in the bar as to form a continuous line of cutters always presented to the surface of the coal or other mineral to be cut, the dust and cuttings from which fall into the spiral groove or thread cut in the bar, and, by the rotation of this latter, are

Getting The Coal. 343

drawn away from tte cutters, leaving them clean and not liable to clog. To further assist the dust being drawn away, a semicircular shield or casing is fixed behind the cutter bar and extending its frill length ; this shield is carried with the bar, but is so arranged as to remain stationary while the bar rotates.

" The cutter bar may be in one with or connected to a crank shaft supported in suitable bearings. On the crank shaft are discs acting in place of a fly-wheel. The whole of the bearings carrying the cutter bar and shaft are fixed on a circular frame, on which is mounted one or more cylinders, capable of rotating the aforesaid cutter bar by means of the usual pistons and connecting rods, the pistons being actuated ia the before-mentioned cylinder or cylinders by steam, air, or other motive fluid.

" The circular frame carrying the cutter bar, cylinder, and connections is in turn carried within another frame or trolly mounted on tram wheels, arranged for running on rails. The circidar inner frame carrying the cutter bar, cylinder, and connections is so made as to be capable of being canted to a position other than horizontal, irrespective of the outer frame or trolly, and of being turned round in a circle after the manner of a turntable, by means of a hand-wheel and worm fixed on the main carrying frame or trolly gearing into a suitable wheel, or into teeth attached to the inner frame carrying the cutter bar.

" The cutter bar is so made that when it is at right angles with the side of the main carrying frame or trolly it projects from three to four feet, or any length at which it is desired to cut the coal ; and the whole machine is so made as to be either self-propelling along the rails as the coal is cut away, or it can be arranged to be propelled by hand, rope, or other suitable means.

" Figs. 513 and 514 of the accompanying drawings represent respectively end and side elevations of the Economic machine, and Figs. 615 and 516 show the details of the cutter bar. The cutter bar is shown having the spiral groove in the form of a screw running from end to end. At regular intervals round the periphery are fixed a number of suitable cutters projecting above the surface of the bar and firmly fixed therein. "When the cutter bar is made to rotate and is pressed against the coal, the cutters cut it away, and the dust and cuttings fall into the spiral groove, and by the rotation of the bar are drawn away from the cutters, leaving them clean and not liable to clog. The whole of the bearings carrying the cutter bar and shaft are fixed on the circular frame. The cutter bar and shaft are rotated by means of a steam or air engine, as shown in the drawing. The circular frame carrying the cutter bar is in turn carried within another frame or trolly mounted on tram wheels arranged for running on rails. The circular inner frame is capable of being canted, as before remarked, to a position other than horizontal irrespective of the outer frame by means of slots and ear pieces, and is fixed in position by means bolts and nuts. The frame is also capable of being turned round in a circle after the manner of a turntable by means of a hand-wheel and worm fixed on the frame or trolly gearing into a suitable wheel attached to the frame carrying the cutter bar."

Besides the machines described in the foregoing paragraphs, several others are in existence, and some of them have been in successful operation for several years. Among those are the machines of W. and S. Frith, and Gr. E. Donisthorpe. In the former, the principle of hand labour has been followed by adopting the action of the pick. The pick is fixed in a socket in one of the arms of a bell-crank lever, the other arm of which is worked directly by the piston-rod of a horizontal cylinder. The machine is mounted upon four wheels which run upon the ordinary rails of the colliery, and it is

344 Mining Engineeeing.

advanced through the requisite distance between each blow of the pick by means of a hand-wheel connected by gearing with the hinder pair of carrying wheels. The two pairs of wheels are coupled together in order to render the full adhesion available for the forward motion of the machine ; it is found that by this means sufficient adhesion is obtained without the necessity of laying down a special rack-rail for the feed motion. The amount of feed between each blow is regulated by the attendant according to the hardness of the coal,

Donisthorpe's machine may be described as a horizontal traversing slotting machine, the material to be operated upon remaining stationary while the machine traverses along the working face of the coal and cuts out a horizontal slot or groove in the bottom of the seam or in a parting in the thickness of the seam itself, as required. The cutter bar, which consists of a cast-steel rod provided with six sockets to hold the cutters, works with a reciprocating motion, and is attached to the upper side of the cylinder, the piston and rod of which are stationary. The object of this arrangement is to economize space, and to give greater stiffness and a better attachment of the cutter bar.

These machines and those which have been previously described may be regarded as types of the four systems that have been hitherto adopted.

Haulage. 345

Chapter Viii.

Haulage.

The conveyance of the produce of a seam from the working places to the shaft constitutes one of the most important questions of mining engineering. Upon this question, indeed, the profitable working of a seam may mainly depend. It is plainly evident that the labour of conveying the produce from the various points at which it is obtained to the point from which it is to be raised to surface must, under the most favourable circumstances, form a considerable proportion of that involved in the whole process of getting the coal, and, therefore, may become a very large proportion if the circumstances are unfavourable. Both the cost of production and the value of the produce are largely dependent upon the suitability of the means employed and of the methods adopted for conveying that produce to surface. This will become more obviously apparent as we proceed, and the great importance of the subject to be passed under consideration will make itself fully felt. It is to be observed, that in no branch of mining engineering has such rapid and great progress been effected as in this. The improvements introduced within the last few years have revolutionized the systems of underground conveyance, and rendered the operations that were formerly difficult and costly, comparatively easy and cheap. The value of these improvements will be appreciated when it is borne in mind that they have not only materially lessened the cost of production, and thereby made some seams available which must otherwise have been neglected, but have also removed the necessity for much severe and degrading toil. It does not fall within the scope of this work to describe abandoned methods ; but the student will find it an extremely interesting and a highly instructive study to trace, by any means that he may have within his reach, these improvements through their successive stages of progress.

The term " haulage " is applied to the operations of conveying the coal from the working places to the shaft, and this term will be understood to include the loading of the coal into the sledges or tubs, and the dragging of these to the nearest horse-road ; labour which is described as " putting " in some districts, and as " carting " in others. So understood, haulage comprises three series or sets of operations, in a great measure separate and distinct from one another, namely, putting the coal to the road, conveying it along the road to the main levels, and conveying it again along these levels to the shaft. These are the three stages of transit through which the coal passes on its way to the point from which it is to be raised to surface, and in each of these stages different conditions will be encountered and different means employed. The nature of the means applied, and the character of the methods adopted, have now to be considered in detail.

Before, however, these considerations are entered upon, it is necessary to point out the conditions

2 T

346 Mining Engineeeing.

which are sought to be fulfilled in any system of haulage. Here, as elsewhere, the ultimate end of mining must be kept constantly in view, namely, the obtaining of the largest possible quantity of coal, in the best possible condition, at the least possible cost. With the first of these requirements, that is, the procuring the largest possible quantity of produce, haulage has nothing whatever to do ; but it affects in a very important degree both the state in which the produce is delivered and the cost of procuring it. A cardinal principle to be observed is to avoid all unnecessary shifting of the coal. It is easy to see that if the coal be frequently removed from one receptacle to another during its transit to the market a large amount of labour must be expended upon it, to the increase of its cost of production, and its quality will be seriously affected by breakage, to the depreciation of its commercial value. If the coal be of a friable character, this depreciation will be very great, and it is clearly obvious that in such cases, as the depreciation of value is produced by labour of a costly nature, in other words, as money has to be expended on the additional labour which causes the deterioration in the quality of the produce, the margin between the cost of production and the selling price must necessarily be small, and may dwindle to nothing, thus rendering a seam of coal unavailable that, with a more favourable system of haulage, might have been worked with a moderate profit. Hence it is desirable that when the coal is once loaded into the tub at the working face, it should not be again touched until it is shot out at surface, and this is the point aimed at in the improved systems. It may, at first sight, appear undesirable to have to raise in the shaft the dead weight of the tubs ; but the advantage of running the same tub through without shifting its load must be considered to preponderate, especially when it is borne in mind that, by the use of drawing cages and guides, and the employment of powerful engines, the facilities for raising and lowering the tubs are great.

Assuming the foregoing principle to have been complied with, it yet remains to adopt such arrangements as will facilitate the transit of the tub with its contents over the distance included between the working place and the shaft. It will obviously be important that the labour involved in the operations necessary to this transit should be reduced to a minimum, since it must tend to increase as the workings are developed, and the distances become in consequence lono-er. The question affects the state of the roads over which the tubs travel, and it involves numerous conditions relative to that state. These conditions are mainly: the inclination of the roads, which inclination may be in favour of or against the load ; — and in connection herewith it must be borne in mind that the empty tubs will have to be conveyed back to the working places, a circumstance that necessitates a consideration of the traffic in opposite directions ; — the regularity of the inclination and the direction for it is clear that a succession of elevations and depressions in the surface of the roads and the existence of curves, which change their direction, must be unfavourable to the traffic ; the state of the surfaces over which the wheels of the tubs run, a question that comprises the even and firm laying of the tram-rails, and their preservation in a state of efficiency ; and the provision of suitable and convenient means whereby the tubs may be made to pass readily from one road to another with which it is in communication. Hence it will be desirable, in order to obtain a clear and comprehensive view of the matter, to consider the subject of haulage in a threefold aspect ; first relatively to the rolling stock or " vehicles " employed ; second, relatively to the roads upon which these vehicles run ; and third, relatively to the means adopted for communicating motion to these vehicles.

Putting the Coal along the iace.— The operations of putting the coal along the working face claim attention in this place, since they constitute the first stage of the labour of haulao-e and

Haulage, 347

introduce to ns the vehicles in which the coal is conveyed, which vehicles have heen set down for primary consideration. In the descriptions contained in the foregoing chapter, putting was incidentally mentioned, and the operations involved in it briefly alluded to ; but it is necessary here to review them somewhat more in detail.

The mass of coal thrown down at the working face by the getters engaged in that service is, as previously remarked, broken up with sledge hammers by the loaders into blocks of a size capable of being handled. In performing this operation, care should be exercised to make as Httle small coal as possible. The blocks are lifted by hand and placed in the vehicle brought up to receive them, and the small coal is loaded into the vehicle by means of a shovel, the form of which was described and illustrated in a former chapter. It will appear, from the character of this operation of loading, that the height of the sides of the vehicle above the floor will materially affect the amount of labour requisite, and that the less the height, the more favourable is the condition under which it has to be performed. This circumstance will be again referred to. It is the duty of the loader to reject all the impurities accompanying the coal ; these matters he throws aside as waste or pack. As, however, he gains an advantage by including the impurities with the coal, inasmuch as his labour is thereby rendered more productive, supervision and checks are needed to prevent a depreciation of the value ot the produce by raising it to bank in a fouled state. The supervision must be exercised in the working places, and the checks applied at surface. These checks may be obtained from the methods adopted ascertaining the amount of work done by each man or set of men, in the manner to be presently described. When the seam is composed partly oi valueless coal, or when it is divided by dirt partings, the labour of separating the good coal from the useless material is considerable, and the necessity for its performance imperative. In some localities, the miners are more careful in this matter than in others, and in such localities a dirty seam may be worked at a profit, though the same seam would be utterly valueless elsewhere. The impure matters that have been separated should be thrown back into the gob, or heaped up by the side ot the heading, and when holing in the underclay or in a parting, the refuse excavated should be shovelled back previously to the falling of the coal, to avoid fouling the latter. In the north of France, it is not uncommon to see the floors swept with a broom after the holing has been completed. But whatever precautions may have been taken by the getters to ensure the purity ot the coal raised, a necessity for sorting will always exist, and the duty of sorting will be incumbent upon the loaders. Colliers, that is, those of them who are immediately engaged in getting the coal, are usually paid according to the weight of the produce which they send up. To render such an arrangement practicable, the loaders place a number or a metal ticket, called a " token," upon each load sent away. On arriving at bank, the load is weighed, and entered in a book according to the number it bears. If refuse is mixed with the coal, the fact may be noted, and, in making up the accounts, a deduction may be made accordingly.

When the coal has been loaded into the vehicle prepared to receive it, the latter has to be dragged or pushed along the face, or " put," as it is termed, to the nearest road. The manner of performing this operation will depend upon the height of the seam, and the nature of the vehicle employed. It was formerly the custom to use " sledges " for this purpose, and in many places, both in England and abroad, the sledge is still in common use. The form of the sledge varies widely, but, whatever the form may be, it consists essentially of a wooden box set upon two pieces of wood set edgewise similar to the steel edge of a skate. The use of the latter is to enable the sledge to slide

2 T 2

348 Mining Engineeeing.

readily along the floor. The box is generally rectangular, but sometimes it is circular in form, and made up of staves and hoops like a tub ; it is. bound by iron straps to the wooden piece beneath. At each end, a hook is fixed to enable the sledge to be dragged along by means of a chain. The capacity of a sledge varies from cwt. to cwt., and its weight from cwt. to 1 cwt. As a vehicle for the conveyance of coal, the sledge possesses some advantages and numerous defects. It may be made very low to suit the requirements of thin seams, it costs but little to make, and hardly anything to maintain in repair, and it may be used without making provision of a specially prepared road. But it absorbs a large amount of force in being dragged over even a tolerably smooth floor, and its small capacity necessitates the employment of a great number of putters.

Instead of the sledge, the " tub " is now generally adopted as a more suitable vehicle for the conveyance of the coal. It consists of a rectangular box or " body," built up on a stout oak framing, and carried upon axles and wheels. It is, indeed, a small railway mineral waggon, difi'ering from those employed at surface in no essential particular. The introduction of the tub into coal mines was a great step in advance in the matter ot conveyance, and the improvements of recent years have been directed to the development of the railway system of which it forms a part. Tubs vary but little in ibrm ; usually the material employed is wood, but tubs are now made either wholly of iron or of an iron body set upon a wooden framing. Their capacity varies generally from 5 cwt. to 8 cwt. ; but in some cases tubs of smaller and of greater dimensions than these have been adopted. The questions which determine the capacity of a tub will be hereafter discussed. Tubs of the dimensions given above weigh from 3 cwt. to 4 cwt. ; some of the large tubs used in the north of England which have a capacity of 11 cwt. weigh only cwt. The wheels are flanged to run upon bridge or T rails, and vary in diameter from inches to 15 inches, according to the requirements of the seam and other circumstances. In some instances, wheels of a greater diameter than 15 inches have been adopted. In the design and construction of a coal tub, it should be sought to combine lightness with strength, so as to lessen the dead weight while retaining sufficient resistance in the material to withstand the rough usage to which it will be subjected.

One great advantage afforded by the tub is the conveyance of the coal from the working places to the shaft, without the inconvenience and delay of shifting the load during any stage of the transit. But another advantage, of no less importance, lies in the facility with which it may be conveyed from point to point. Thus, it appears, that the tub fulfils, as a vehicle of conveyance, the conditions pointed out as essential to a perfect system of haulage, namely, to transport the coal from point to point without shifting it from one receptacle to another, and with a minimum expenditure of labour. The comparatively small force required to set and to keep the tub in motion, besides being of importance to the system of haulage generally, is especially so to the putter, for as the proportion of the motive force absorbed by the friction of the wheels, and the other resistances opposed to their revolution, is much less than that taken -up by the friction of the sliding supports of the sledge, he is enabled, with the same expenditure of labour, to put a much heavier load, and thereby to greatly lessen the total requisite amount of work. The manner of putting the tub along the face is in the main identical with that adopted for the sledge, the load being dragged or pushed over the fl(.)or. The labour of putting the tub to the nearest road is often performed by boys, who are thus introduced to the arduous occupation of a collier. In those seams where the height is insufficient to allow a man to stand erect, the operations of putting become difficult and toilsome. In these low places,- it is sometimes necessary to go on all fours, and it is easy to see that under such conditions the cost ot

Haulage. 349

putting, or "carting" as it is called in Somersetshire, must be very great. When it becomes needful to assume the posture indicated above, the tub is pushed along by the feet, the putter moving backwards, or if a sledge is used, it is drawn along by means of a chain affixed to the waist of the putter and passed between his legs. Formerly this mode of putting was common in England, and it is still followed in the thin seams of G-ermany. Where there is sufficient height, horses may be applied to this work with advantage. The horses employed for this purpose are Shetland and other ponies standing from 3 to 4 feet in height ; usually they are driven by boys, who may be of younger age than those required for the more severe labour of putting by hand. In the collieries of the northern districts, large numbers of these ponies are thus employed.

Wherever the circumstances are favourable, tram-rails should be laid along the face. The friction of the wheels upon the rails being far less than that of the wheels upon the floor, even where the expedient of laying tram-plates is adopted, the transport of the load is greatly facilitated, and consequently the labour of putting reduced, by the adoption of this system. A tramway in such a situation is obviously of a temporary character, since, the face being daily pushed forward, the tramway must be advanced in like manner. The simplest methods of laying the rails are therefore desirable ; and of such methods, those are the most suitable which allow the rails to be readily fixed and removed. One of the simplest tramways fulfilling these requirements consists of half-round fir sleepers, provided with two notches at the requisite distance apart, into which the rails are laid. The latter are held in their places with sufficient firmness by means of wedges driven in on the inside of the rail to reduce the length of the sleeper. Such a tramway may be quickly laid or taken up, and is therefore suitable to the requirements of a working place. Instead of the notch and wedge, iron spikes may be used to fix the rails to the sleepers. It is almost needless to add that very light rails should be used in such a situation. The tramway is laid along the working places between the face and the timbers next the gob, and as the face is advanced by 3 feet at each holing, the rails will have to be shifted through an equal distance each day before the timbermen draw and reset the props. The labour of doing this, however, is far more than compensated by the increased facilities for putting the coal to the horse-roads or the inclined planes. Where the output is to be large, this advantage will obviously be an important one.

Tubs. — We have now to consider the question of haulage relatively to the vehicles employed for the conveyance of the coal. It has been already pointed out that the vehicles now used for that purpose are tubs, or small waggons, consisting essentially of a rectangular body to contain the load, and of axles and wheels to support the body. These two divisions, or parts, of the tub will influence the system of haulage differently, the former having reference to the conditions affecting capacity, the labour of loading and thickness of seam, and the latter relating more directly to the force of traction to be exerted upon the load. As these are matters of great and essential importance in any system of haulage, it is desirable to consider them carefully and in detail, in order fully to appreciate their influence and to be able to modify their consequences as occasion may require. To this end, we shall examine separately the design and construction of the two essential parts of which a tub consists, pointing out the conditions which determine them, and their influence upon the general question of haulage. It must be premised, however, that this examination, and the conclusions arrived at from it, must necessarily be of an approximative character, which character is, indeed required by the exigencies of practice, for exact mathematical investigations are here unnecessary and undesirable.

350 Mining Engineering.

JVJieels and Axles. — The form and construction of the wheels and axles of a tub, and their arrangement relatively to each other, influence in no small degree the question of haulage considered with respect to the requisite force of traction. The principal points to be taken into account, in a consideration of this nature, are the kind of connection made between the wheels and the axles, and the diameter and the form of the rim of the wheels adopted. There are two kinds of connection made between the wheels and the axles of vehicles ; in the one kind, we have the wheels fixed upon the axles in an invariable manner, so that the latter are compelled to revolve with the former ; and in the other kind, the axles are fixed and the wheels revolve freely upon their extremities, which, in such a case, receive a particular form, and are described by the term "journals." When the connection is of the first kind, the wheels are mutually dependent, that is, the angular motion of each must be equal and take place in the same direction, or, in other words, they must turn in the same direction and with the same velocity. When the connection is of the second kind, the wheels are completely independent of each other, that is, they may revolve with different velocities and in contrary directions. Thus it is evident that the nature of the connection will, under certain conditions, operate to facilitate or to impede the work of traction.

It will have been observed that the system of fixed wheels is invariably adopted upon railways, and that the system of free wheels is as invariably applied to vehicles running upon common roads. The reasons for this are plain and easy to be understood. On a railway, the motion is in a straight line, and the surfaces over which the wheels of the vehicles roll are perfectly even. These are the conditions always sought; in practice it becomes necessary to modify them frequently, as, for example, when curves are adopted, but curves are avoided whenever possible, and when circumstances compel their adoption, they are made of the largest possible radius in order to approximate to the straight line. On common roads, on the contrary, the motion of a vehicle is continually in a curved line. It is impossible that it should be otherwise, when the wheels are not guided. But irrespective of this, road vehicles have to be very frequently directed out of their course to avoid other vehicles and obstacles of various kinds, and to be turned off at a sharp angle, or completely round in a small space. And again, the surface of a common road is very far from possessing that regularity which is characteristic of the railway. Thus the conditions of motion upon a railway and upon a common road are essentially different, and these conditions determine the kind of connection between the wheels and the axles.

Two wheels invariably fixed to their axle practically constitute, as a writer observes, "two parallel sections of the same right cylinder with a circular base, which, rolling upon two parallel rails, tends to remain upon the line with a high degree of stability." This tendency, where great weights are moved at high rates of speed, is obviously of paramount importance. Another advantage of the invariable connection lies in the fact that the wheels are always kept normal to the axle, that is, perpendicular to the surface upon which they roll, a position that is soon deviated from in free wheels in consequence of the wear of the rubbing parts. There is moreover another point of some importance to be noted, namely, that when the wheels are thus made mutually dependent, the vehicle has a tendency to advance in a straight line, even when the tractive or propelling force is not applied at a point in the plane passing through its centre of gravity, as, for example, when a railway carriage is pushed along by one of its buffers. It may also be desirable to point out, that with an invariable connection between the wheels and the axles, the vehicle is supported upon the extremities of the latter passing beyond the wheels, which are thus within the points of support.

Haulage. 351

For a given width of road, this arrangement gives greater stabiHty to the body of the vehicle, by increasing the breadth of its base. On the other hand, it must be conceded that the framing is less firmly bound together than when the axle is made to take part in the connection.

When the motion of the vehicle takes place on a curve, as in the case of a common road, the arcs passed over by the two wheels are unequal, and the degree of the inequality will obviously increase with the distance of the wheels apart. One of the arcs will be reduced to nothing, if the vehicle be made to turn upon one of its wheels as a point of support ; or they may be equal, but the motions contrary in direction, if it be made to turn about its centre of gravity. If the wheels were mutually dependent, as one would be required to revolve more rapidly than another, or the two be required to revolve in contrary directions, it is evident that one or both of the wheels must slide, and the same result will follow from one wheel passing over an irregularity in the road. But when the wheels are independent of each other, the requisite inequality of motion presents no difficulty whatever, since each wheel is free to move with the velocity and in the direction needed. Hence it appears that the adoption of the fixed wheel on the railway and of the loose wheel on the common road may be perfectly justified.

Having ascertained the conditions peculiar to each case, and the influence of the mode of connecting the wheels and axles upon the work of traction under those different conditions, it now remains to examine those which prevail upon the underground roads of a mine in order to determine the class to which they belong. Such an examination will show us that in these roads both of these classes or sets of conditions exist, and that consequently the question is here greatly complicated. Hence it has happened that opinions are divided respecting the most suitable kind of connection, and we find in some collieries tubs with wheels upon revolving axles, and in others, tubs with wheels upon fixed axles. And we shall find, when we have taken into full account all the circumstances of the case, that both of these systems may be justified. In these, as in other matters relating to mining, we have to deal with conflicting requirements, and in order to effect the best attainable compromise, we must carefully consider and accurately appreciate all the determining conditions.

It is altogether impracticable to construct the tramways of a mine with the accuracy of direction and the solidity attained upon ordinary railways. Such tramways are characterized, and necessarily so, by irregularity in all their features. The irregularity will be more or less developed, according to circumstances, but it will always exist, even upon the best constructed engine planes. A primary point to be noticed is, that on underground lines the principle of motion in a straight line, which, as before remarked, is the ruling principle on ordinary railroads, has to be subordinated to other requirements. Hence it happens that curves ai'e of frequent occurrence, and these curves are of comparatively very small radius ; in other words, the straight line is often and widely deviated from. But even upon those portions of the line in the horse-roads, and, in a less degree, on the engine planes, which are not marked by any decided curvature, irregularities of direction occur that assimilate the track of a tub to that of an ordinary vehicle upon a common road. In consequence of these irregularities, the motion of the tub takes place in a sinuous direction, a circumstance obviously unfavourable to the system of fixed wheels. Another source of irregularity is the lack of stability in the roads, whereby inequalities are produced that tend to increase the sliding of the wheels when they are mutually dependent in respect of their motion. But a circumstance of greater importance relatively to the system of wheels and xles is the abruptness of the junction

352 Mining Engineering.

of the brancli lines with one another, and of these again with the main hnes. On common railways, junctions are effected very gradually, the conditions being such that the angle may be reduced as much as desired. But underground the conditions are very different. Here the junction must be made at a considerable angle, often one of 90°, and when it is borne in mind that numerous junctions are required, it will be seen that the question is one of great importance in its bearing upon the subject of haulage. It will be evident, on reflection, that when one line enters another at an angle of 90°, means must be provided for turning the vehicle; such means may consist of turntables, but though these are suitable for the purpose on heavy surface railroads, they are undesirable, and, indeed, almost impracticable underground. Instead, therefore, of the turntable, a kind of fixed table, or platform, is used, upon which the tub is turned by being dragged, or pushed, round into the desired direction. If the wheels are fixed upon the axle, they are compelled to slide during this operation. There yet remains to be taken into account one other circumstance that may largely influence the question of fixed or loose wheels. In some parts of the mine, notably in the working places, the tubs may have to run upon the floor where it is unprovided with rails, and in such a case the conditions are, of course, wholly unfavourable to the system of fixed wheels. Thus it will be seen, that though the use of the rail and the flanged wheel confers the nature of the railroad upon the underground tramroad, yet the existence of the foregoing conditions, which determine the requirements of the common road, must greatly modify that nature, and that such modification may proceed so far as to render it extremely difiScult to pronounce which requirements are paramount. Grenerally, however, it will be found, notwithstanding the examples to be met with in many well laid-out collieries, that those of the common road claim the primary consideration, and that, consequently, loose wheels are more suitable than fixed wheels for underground tramways.

Since numerous and sharp curves are inevitable, it becomes desirable to examine here more closely their influence upon the traction, and to point out some of the means employed to lessen that influence. In running over a curve, the wheel upon the outer rail has to run through a longer distance than that upon the inner rail, and therefore must revolve with a higher velocity. But when the wheels are fixed upon the axle, both are compelled to revolve with the same velocity, and consequently, as the distances to be passed over are unequal, one of the wheels must slide upon the rail. The extent of the sliding will obviously be the difierence of the distances passed through by the two wheels, and it is easy to calculate its effects upon the traction. If we denote the angle at the centre of the curve by a, the mean radius of the curve by r, and the breadth of the road by 2 b, the length of the outer arc will be + b) a, that of the inner arc (r — b) a, and the extent of the sliding 2b a; hence, for a given angle, the latter quantity increases with the breadth of the road, a fact that is almost self-evident. The ratio of this sliding to the mean space passed through ra is

— . And this quantity, multiplied by the ratio of the coefficients of friction between the

r a r ± j.

wheel and the rail, and between the axle and its bearings, is the measure of the increase of the work of friction due to the existence of the curve.

Another circumstance to be noted in reference to the curve is the obliquity of the axle relatively to the rails. When the line is straight, the axle is normal to the rails, and the wheels tend therefore to roll upon the latter ; but as soon as a curve is entered upon, the force of inertia, which tends to keep the tub moving in a straight line, produces an obliquity between the axle and the rails, and a consequent tendency in the wheels to run off the rails on the upper side of the curve. This tendency

i

Haulage. 353

brings tlie flange of the outer wheel in contact with the inner side of the outer rail, and thus occasions friction. The force of the contact between these surfaces, and, consequently, the work of the friction, will clearly depend upon the radius of the curve, the weight of the tub, and the velocity with which the latter is moving, leaving out of consideration the state of the surfaces in contact. A large proportion of the tractive force is absorbed by this kind of friction, which may be regarded as one of the chief resistances to be overcome.

It will appear from the foregoing considerations that the system of loose wheels is generally more applicable to the conditions prevailing upon underground railways than that of fixed wheels, and that, consequently, its adoption is desirable wherever it is impracticable to lay out the roads with great regularity. It is, however, possible to combine the two systems so as to obtain some of the advantages of each, and various devices have been adopted to render the combination as advantageous as possible. The most obvious mode of combining the two systems, and one that has been extensively adopted, consists in fixing one wheel to the axle, and leaving the other loose upon a journal, the arrangement being such as to have one fixed and one loose wheel upon each side of the tub. So long as the line is straight, this system acts similarly to that in which both wheels are fixed ; but as soon as a curve is entered upon, the loose wheel takes the velocity necessary to prevent slipping. In order to assimilate this system as much as possible to that of fixed wheels, the loose wheel is made to turn with a moderate friction. Another method, adopted in Silesia, and more recently in some of the French collieries, consists in having as many axles as wheels. In this method each wheel is fixed upon its axle, and a pair of wheels corresponds to two revolving axles parallel to each other. Such a system solves the problem satisfactorily ; but it possesses the disadvantage of complication.

Besides these combinations of the two principal systems, other expedients are resorted to for the purpose of rendering fixed wheels capable of running over curves without occasioning a great increase of resistance. Some of these expedients have reference to the road, and will therefore claim consideration in another place. One device consists in making the wheel conical towards the flanges. This form of the wheels is favourable to the stability of the tub on a straight Kne, and also greatly facilitates its motion over a curve. It is easy to see how these results are obtained from conical wheels invariably fixed upon their axles. If we suppose the tub moving upon a straight piece of line, and driven by some cause to one side, the radius of the wheel on that side will be increased, and that of the wheel on the other side diminished. The tendency of the larger wheel to progress more rapidly than the smaller will immediately restore the tub to its normal position upon the rails. If we suppose, again, the tub to be entering upon a curve, it will be evident that the force of inertia will throw the tub against the outer rail, and bring the flange of the wheel on that side into contact with the inside of that rail, as already pointed out. But this shifting of the tub in the direction of the outer rail has the effect of increasing the radius of the wheel on that side, and of diminishing, in the same proportion, that of the wheel on the other side ; and hence it is clear that the outer wheel will, at each revolution, advance through a greater distance than the inner wheel, as required by the greater length of the arc on that side. On curves of a large radius, this expedient gives very satisfactory results.

A means of lessening the degree of obliquity of the axles relatively to the rails upon curves, and thereby of reducing the resistance of fixed wheels, consists in placing the axles as near to

2 z

354 Mining Engineering.

each other as practicable. The limit in this direction is obviously the diameter of the wheels, and this limit is approached as nearly as the stability of the tub in the direction of its length will allow. An advantage of a different character, due to the near proximity of the axles to each other, lies in the facility afforded by that arrangement for replacing the tub upon the rails when it has run off the line. The operation is performed by lifting the tub by one of its ends, and it is evident that the difficulty of replacing it will diminish as the axles are fixed nearer the centre of gravity. Another expedient sometimes resorted to for obviating the obliquity of the axles altogether consists in pivoting them upon their centres, a system commonly adopted on American railways. This system, however, though it satisfactorily fulfils the purpose required, is wanting in stability.

In consequence of the relative obliquity of the axles and rails upon curves, it becomes necessary to allow the wheels a certain amount of play, that is, to space the rails wider apart than upon those portions of the line which are straight. The shorter the radius of the curve, the larger is the amount of play required, but generally it will be about three-quarters of an inch, or the double of that allowed in the straight. This play will necessitate the adoption of wheels of considerable breadth, as otherwise a lateral movement, such as occurs during motion round a curve, would cause derailment. A moderate breadth of wheel is also favourable to haulage along the working face, and in other situations not provided with rails. The form of the flange is a question of some importance, since the facility with which derailment takes place depends in a great measure upon it. The section adopted upon ordinary railways is shown in Fig. 517; but the curve is somewhat too short for coal tubs. A form commonly adopted on underground tramways is represented in Fig. 518, which, in consequence of the absence of all curvature, offers great resistance to derailment. An objection to tliis form, however, lies in the fact that should the flange get upon the rail it has no tendency to slip off, and to thereby restore the wheel to its proper position. A section formed of two lines, one straight, the other curved, and joined to the former by a small circular arc, has been proposed as fulfilling all the conditions required. This section, which is shown in Fig. 519, offers almost as great resistance to derailment as that represented in the last figure, and it possesses besides a tendency to return to its position, if it should from any cause get upon the rail. This quality is very important in a flange, for not only does it prevent the delays consequent on getting off the line, but it greatly facilitates the placing of a tub upon the rails. The material of coal-tub wheels is generally cast iron, to increase their durability. Mr. N. Wood's observations showed that the relative durability of unchilled and chilled wheels was as 39 to 63. Lately, steel has been adopted for colliery wheels, with very good results.

The resistances to traction on a straight line in good condition are due to the friction of the periphery of the wheel upon the rail and of the friction of the wheel upon the axle, or of the axle upon its bearings. The latter friction varies directly as the load and the diameter of the axle, and inversely as the diameter of the wheel. This fact is clearly apparent, for if the diameter of the axle remain the same while that of the wheel is doubled, the space passed through by the circumference of the latter will be twice what it was at first, and as the same amount of friction will be developed, its value will be only half what it was with the smaller wheel ; and if, on the contrary, the diameter of the wheel remain unaltered, while that of the axle is doubled, the friction will also be doubled, since, for the same effect obtained, twice the rubbing surface is acted upon. If we represent the pressure upon the axles, that is, the weight of the insistent load, by W, the

Haulage. 355

coefficient of friction by /, and the diameters of the wheel and axle by D and d respectively, we shall

have as the value of the resistance,

The value of / may be taken, for unlubricated surfaces, as 25, so that if we have a tub weighing, exclusively of the wheels, 2 cwt., and containing a load of 8 cwt., the diameters of the wheels and axles being 8 inches and 2 inches respectively, the resistance due to the friction under consideration will 1,

o

If the diameter of the wheels were doubled, this resistance would be reduced by one half, that is,

to -jr- 35 lb. ; and if the diameter of the axles were doubled, the resistance would be increased to

70 X 2 140 lb. Thus it appears that the diameter of the axles should be reduced and that of the wheels increased to the utmost practicable limits. The limiting condition relatively to the axle is that of sufficient strength to resist the shocks and sudden strains to which it is continually subjected, and it will be apparent from the nature of this condition that the minimum theoretical dimensions cannot be reached. It is better to incur a slightly increased loss of force by friction than to be exposed to the risk of breakage. Commonly the diameter varies between inch and 1|- inch. The dimensions of the wheels are limited by two circumstances, the height of the roads and the working places, which is itself determined by the thickness of the seam, and the desirability of reducing the height through which the coal has to be lifted in the operations of loading. The construction of the tub has some determining influence upon the diameter of the wheels, as we shall see later; but the foregoing circumstances are the chief, and of these the first is the more important. Hence it happens that tub wheels vary widely in dimensions from one locality to another, and also from one seam to another in the same locality. Generally the extremes may be taken as 7i inches and 15 inches, though in some instances wheels of a larger diameter have been adopted.

The resistance to traction due to the friction of the periphery of the wheel upon the rail has never been satisfactorily determined by experiment. In a remarkable work by Oeynhausen, the value of this friction upon straight surface tramways, as found by a long series of carefullyconducted experiments, is given as 0'07. But this value must be too great for well-laid ways. Mr, Nicholas Wood has shown that the resistance of tubs having axles 1*37 inch and wheels 7*50 inches in diameter, is under ordinary conditions of road and lubrication, of the insistent load. If we calculate the value of the friction upon the axles according to the formula already given, we shall find that, according to these results, the value of the friction between the periphery of the wheel and the rail will be about 0*008, taking the coefficient of friction /at 0*07 for lubricated surfaces; for the value 0*25 already given relates to smooth unlubricated surfaces. This value of the work of friction between the wheel and the rail very nearly corresponds with that which we have determined elsewhere.

Bodies of Coal Tubs. — That portion of a coal tub which is known as the " body " is also deserving of careful consideration, inasmuch as its influence on the question of haulage, though less than that of the wheels and axles, is yet great. The body or box part of a tub commonly consists of oak, threequarters of an inch or an inch in thickness, set upon an oak framing below, and bound with iron to

2 z 2

356 Mining Engineeeing.

give it strength. Sometimes the body is constructed wholly of iron. Such tubs are very durable, but they are not easily repaired ; their weight is about the same as that of wooden tubs.

Lightness is a desirable quality in a tub, since it is important that the dead weight should be reduced as much as possible. Hence that form should be adopted which, with a given weight of material, affords the greatest carrying power. The form which best fulfils these requirements is the rectangular box, and this is therefore generally adopted.

lu the design of a tub, there are two features that demand particular consideration, namely, its capacity and its height. Obviously the conditions which determine the latter will have some influence on the former; but besides these, there are others which relate to capacity alone. In order to diminish the proportion of the dead weight to be moved, it is desirable that the tubs should be of large capacity, and the same quality is required by other circumstances connected with the matter of haulage. But a limit in this direction is fixed by the necessity for having tubs capable of being readily handled. It must be borne in mind that the tubs have to be dragged or pushed along the working face ; that they have to be lifted and turned at the junction of lines that run in directions perpendicular to each other ; and that, in consequence of the imperfections of the road, they frequently get off the line, and have to be lifted on again with little delay. Also, the onsetter and the banksman are required to drag and push the tubs over the tram-plates at the bottom and the top of the shaft, and to quickly run them on or pull them off the cage. Hence it is highly important that the weight should not be too great for one man to deal with. This condition will limit the capacity of a tub, irrespective of other considerations. Moreover, as economy requires that the operations of haulage should be performed or conducted chiefly by boys, the weight to be dealt with should be kept within the limits of their strength. For these reasons, a capacity of 8 cwt. is not often exceeded. Another circumstance that tends to keep down the capacity of a tub is the narrowness of the roads in a mine, for as the dimensions can be increased only in one direction, the limits of convenience are soon reached.

The height of a coal tub is limited mainly by three circumstances, namely, the stability of the vehicle in transit, the difficulty of loading it at the working face, and the thickness of the seam. It has been shown that to comply with the conditions prevailing underground, tubs have to be made narrow, and that, moreover, the curves there existing are very sharp ; hence it will be evident on reflection that height is inconsistent with that degree of stability which is requisite. Also, it will clearly appear that height in a tub is unfavourable to the operations of loading, since the coal has to be lifted into it. This is a question of very considerable economical importance, and it is deserving of more attention than has hitherto been given to it. But irrespective of these limiting circumstances, that of thickness of seam may operate to compel the adoption of tubs of low height. It is easy to see that when a seam of coal is thin, it becomes highly desirable, if not absolutely necessary, to use vehicles of such dimensions as will not require the expenditure of additional labour in ripping down the roof in order to give sufficient height ; and it will plainly appear that, as this circumstance limits the height, it will also influence in some degree the capacity of the tub and the diameter of the wheels. Thus numerous conditions combine to limit the dimensions of coal tubs, and it will be prudent to keep within the limits imposed in designing the rolling stock of a colliery. In some instances, tubs having a capacity of 11 cwt. have been adopted, but it must be obvious that the disadvantages incurred by the adoption of such cumbrous vehicles more than compensate the gain.

The following examples of tubs exhibit the forms actually in use, and show the various devices

Haulage. 357

adopted for obtaining the greatest possible capacity for given dimensions and for satisfying the other requirements of underground haulage. Figs. 520 to 523 represent wooden tubs used in England. It will be seen that they are strongly built, and experience has proved that when constructed in this way the cost of maintenance is very little. Three forms are illustrated. In those shown in Figs. 520 and 521 the body is prismatic, and extends over the wheels ; in Fig. 522, the body is pyramidal in form, and is brought down to the level of the axle. The latter form is very commonly adopted ior coal and other mineral tubs. In different parts of the country, the design and construction of tubs vary somewhat from those illustrated, but in all essential particulars they resemble one of these types. Even when iron is employed as the material for the body, the same forms are adhered to as best fulfilling the requirements of underground carriage.

In Continental countries, the question has received greater attention than in England, in consequence of the greater irregularity of the seams and the increased difficulties of haulage, and hence we find greater variety in the form of the tubs employed. Many of these have been designed to suit special conditions, and are, therefore, not generally applicable. Others however, have been carefully considered, and constructed to comply with ordinary requirements, and these are deserving of the attention of all practical men. A few years ago, a commission of engineers was appointed by the proprietors of the great Anzin Collieries, to examine and report on the coal tubs employed in France, Belgium, England, 'and Grermany, for the purpose of obtaining the best possible design for the new rolling stock. The result of the labours of this commission was the adoption of the design shown iji Figs. 524 and 525. The body, which is of iron, is rectangular in form, and slightly bellied. Its length is about 3 feet Y inches, its breadth 2 feet 6 inches, and its depth 1 foot 10 inches. These dimensions must, for ordinary circumstances, be considered as somewhat excessive. The axles, which are of the finest quality iron, turn upon steel bearings, which allow considerable play in all directions. One wheel is fixed upon the axle, and the other is loose, and the pairs are arranged so that there is one fixed and one loose wheel on each side. The construction of these tubs will be readily understood from the drawings. Another form of iron tub is in use at the Blanzy mines, and it appears to have satisfactorily fulfilled the requirements for which it was chosen. This type of tub, which is illustrated in Figs. 526 and 527, is also the outcome of a careful study of the conditions to which it must be subjected. The body in this case, as in the preceding, is rectangular, and is slightly narrowed towards the bottom, where it passes between the wheels, as shown in the drawings. The wheels are loose, and, besides this arrangement, the axles themselves are allowed to rotate, so that upon curves, or in case of a defective state of lubrication, the resistance to traction due to friction cannot be great. The oval form of the journal box, shown in the details given in Figs. 528 and 529, allows the wheels to remain upon the rails, whatever the irregularities of the road may be. The distance of the wheels apart is maintained by means of loose washers, well greased, as shown in Fig. 528. This arrangement allows a certain degree of elasticity. Many years of experience at Blanzy has shown that, in consequence of these several devices, the tubs rarely get off the rails, though the roads are in many parts very undulated and irregular. An arrangement, proposed by M. Cabany, and adopted in the collieries at Anzin, is shown in Figs. 560 to 562. The object of the arrangement is to reduce the height of the tub while retaining the same capacity. This result is obtained by elbowing the axles, as shown in the drawings. By adopting this form of axle, the bottom of the tub may be brought as low as desired. The construction of the axles will be readily understood from the detailed drawing. Fig. 562. The body of the tub is very similar to that described

358 Mining Engineeeing,

as tlie result of the labours of the commissioners appointed by the proprietors of those extensive collieries.

The cost of coal tubs varies from 3. to 41, each.

Resistance of Tubs to Traction. — The sources of resistance to traction were pointed out and described in a former section relating to the question of wheels and axles, and the value of some of these sources was determined for certain conditions. It now remains to bring together the results of those investigations, and to determine the value of the several resistances in a general manner.

It has been shown that the resistance due to the friction of the wheels upon their axles, or of the

axles upon their bearings, is expressed by the formula W, in which/ is the coefficient of friction,

r the radius of the axle, R the radius of the wheel, and W the insistent weight, which is composed of the weight of the load W, and that of the body of the tub W". When the wheels are loose upon the axles the weight of the latter will be included in W". It will be seen, from an inspection of this formula, and it was shown in the section already referred to, that it is highly important to the question of haulage that the values of / and r should be reduced, and that of R increased, to their utmost practicable limits. We have shown what these limiting circumstances are in the cases of r and R ; and it may be stated here that the value of/ will be determined by the state of the surfaces in rubbing contact. Exhaustive experiments have shown that, assuming these surfaces to be of iron and perfectly smooth, the value of / may be made to vary, by means of lubrication, within the limits 0"25 and 0-06. Hence the importance of lubrication is manifest. Upon ordinary surface railways, the axle-boxes may be kept well provided with grease or oil without difficulty, but on underground tramroads, the operation cannot be so readily performed, and, consequently, the surfaces are not kept in so perfect a state of lubrication. Moreover, upon these latter roads, the axles, being very near the ground, are exposed to dust and to mud, the latter of which is being continually splashed over them. Hence it becomes impracticable to reduce the value of the coefficient of friction f to the lower limit. Experiments have shown that if we take a train of tubs, in what may be termed their normal working state, that is, if we take any train of tubs as they arrive, without special preparation, at the shaft, we shall find that the average value of / will be about 10, and

this value, therefore, may be assumed for/ generally. Thus the formula becomes 0-10 — W. This

R

formula may be made general by assuming that the ratio O'lO, and that the weight of the body

of the tub W" is equal to 3 W', the weight of the load. And these values will be found to represent a true mean of any number of well-designed tubs. With these values, the formula assumes the form 0-01 (W -I- 3 W) 013 W ; W m this case being the weight ot the load of coal. To illustrate the application of this formula, suppose a tub containing 8 cwt. of coal. The value of the resistance to traction, due to the cause under consideration, will be (0-013 x 8) 104, that is, one hundredth part of the insistent weight, which is assumed to be equal to the load plus of the load. When it becomes necessary, in other calculations, to take the weight of the wheels into account, it may be assumed to be equal to 1 W

The friction between the wheels and the rails upon a straight line, as already remarked, has not been made the subject of exhaustive experiments. The value of the friction will, of course, vary with the state of the road ; and as this state may itself vary within wide limits, it is difficult to obtain

Haulage. 359

anything like a general value for the resistance. In a mine, the rails get covered with dust in some parts, and with mud in others, while other parts again may be comparatively clean. Also the irregularities, which always occur at the joints, but which vary considerably in degree, tend to complicate the question. If, however, the whole of these circumstances were taken into account, and the resistance due to them measured over a long piece of road in a fairly good condition, we believe, from investigations we ourselves have made, that the average of the sum of these resistances, determined by a series of experiments, would be about 0*007 of the weight of the tub, that is, 0'007 (W + W" + W") 0-007 (1-4 W) 0-0098W',say, 0-01 W, that is, one hundredth part of the weight of the load of coal. Thus the resistance to traction due to these forms of friction is

expressed by

0-013 W + 0-010 "W" 0-023 W;

W being the weight of the contained load. According to this expression, the resistance is about of

the weight of the coal carried, when the ratio O'lO. When the motion takes place upon a

curve, we have, in addition to the resistances comprised in the foregoing, that due to the friction of the flanges of the wheels against the rails, and, in the case of fixed wheels, that due to the slipping of the wheels upon the rails. The value of these resistances may vary within wide limits, so that it is impossible to assign a general value. But in most cases it will be sufficient to double that given by the foregoing formula, and it may increase that value in a still higher degree. A sinuous piece of road may occasion similar results by bringing the same causes of resistance into action. Hence it is of the highest importance, economically, that the roads should be well laid out and maintained in a good condition.

Hitherto we have considered the resistance to traction on a level road ; it now remains to estimate that which has to be overcome on inclines. The action of gravity upon an inclined road is expressed by the following formula :

G (W + W" + W") sin. % ;

i being the angle of inclination. Or, taking the values previously assigned to W" and W", and representing the weight of the load by "W,

G (1 4 W) sin. i.

This force will always be exerted in the direction of the descent, and therefore must be added to or subtracted from the resistances already determined, according as the tub has to ascend or to descend the gradients. Thus the total resistance, irrespective of the influence of curves, will be : upon a

rising gradient,

0-023 W+ (1-4W) sin. z; and, upon a falling gradient,

- 023 W - (1 4 W) sin. i.

These formulae may be made applicable to empty tubs by substituting the weight of the tub for 1 4 W in the second member, and f of that weight for W in the first member. To illustrate the application of these results, suppose a tub containing 8 cwt. of coal ascending an inclination of 2°, or about 1 in 28. Here we have as the resistance, 0-023 x 8 + (1 - 4 x 8) 035 576, or about -- part of the load. If the tub ascend this gradient empty, the resistance will be - 023 x 2 - 4 + (3-2 x - 035) - 167, or about part of the weight of the tub. Again, if the loaded tub descend

360 Mining Engineeeing.

the gradient, the resistance to traction will he 023 x 8 — (1 4 x 8) 035 — 208, or ahoi.it — part of the load. The resistance in this case is negative, and shows that the tub must he held back by a retarding force equal to part of the contained load. Thus, if a reel be placed at the top of the incline, and a rope passed round it and connected to the loaded tub at the top, and to an empty tub at the bottom, the loaded tub will exert upon the empty tub a tractive force equal to part of its load, neglecting the friction of the reel and the rope ; and it will be easy to calculate what number of loaded tubs will be required to drag up the empty one on such an incline.

Roads. — The subject that claims consideration after that of the vehicles in which the coal is conveyed is that of the roads upon which these vehicles run. It is easy to see that this subject of roads is at least equal in importance to that which we have just considered, since by the adoption of a false principle in laying them out, or by the occurrence of imperfections in their construction, all the advantages gained by a compliance with the principles explained in the preceding section may be lost. Hence it becomes necessary to investigate the influence of the roads upon the force of traction, and to point out the way in which that influence may be rendered favourable to the economical application of the force expended in the several operations of haulage. It is also desirable in this place to describe the various methods of construction adopted, and the means employed for maintaining the roads in a proper state of efficiency.

In laying out railways underground we have to deal with conditions very diff"erent from those prevailing at surface. The roads in the former situation have to be driven mainly in accordance with the requirements of the seam, while in the case of surface railways the roads are cut mainly in accordance with the requirements of the traction. Thus underground lines partake rather of the nature of street tramways where the way has to be adapted to the existing street, than of ordinary railways where the road is created to suit known conditions. Hence it happens that the conditions of road so favourable to traction which prevail upon surface railways cannot be attained underground ; and instead of creating the circumstances desired, we are compelled to deal as best we can with those already in existence. This is only true generally, and in some cases we may make our own circumstances, as at surface, and in others we may more or less modify those existing. Thus the main levels may be driven in most cases with the inclination and the degree of regularity we choose, and as these are the main roads of the mine, the circumstance is one of manifestly great importance. Also the secondary roads may often be laid out to suit the requirements of the traction, and in all cases irregularities may be lessened by the exercise of skill and care. Hence the importance of adopting a well-considered plan in laying out the workings of a new coUiery is obvious. For these reasons it is desirable and necessary to investigate some of the questions relating to the influence of gradients and curves, for the purpose of determining with precision its degree, and the extent to which it may be rendered usefully available.

Influence of the Road on the Force of Traction. — It has been shown that a narrow gauge of railway is imposed by the conditions prevailing on underground roads, and it will be evident from the investigations of the preceding section, that, other things remaining the same, the resistance to traction will diminish upon curved and sinuous roads with the gauge of the way. In constructinoan underground railway, therefore, it should be sought to reduce the width to the lowest limit consistent with the requisite degree of stability in the tubs. A cardinal principle to be observed on underground as well as on surface railways, is to avoid curves wherever possible, and to give to those which cannot be avoided the largest possible radius. There is an objection to curves upon

Haulage. 361

engine planes which does not hold in other situations, namely, the consequent diflficulty of hauling by means of a rope, which necessarily tends to assume the straight line. This difficulty compels the adoption of guides and friction rollers, the use of which introduces complication and impediments into the operations of haulage. When, however, the exigencies of the case render a curve inevitable, it becomes desirable to employ means to lessen its resistant influence upon the traction of the tubs. The most important of these means have relation to the tubs themselves, and have been described already ; others relate to the road, and have now to be considered. Besides the reduction of the width throughout for the sake of the curved portions, an expedient is often resorted to and applied on those portions alone. This expedient consists in laying the inner and the outer rails in different horizontal planes ; in other words, in giving to the outer rail a suitable degree of elevation above the inner. It will be seen that this elevation of the rail places the tub upon an inclined plane transverse to the road, the effect of which is to produce in the tub a tendency to descend towards the inner side of the curve, and thereby to reduce or prevent altogether the friction of the flanges of the outer wheels against the outer rail. A little reflection will show that the mode of communicating motion to the tub will influence this friction, and, through it, the expedient of raising one of the rails. Evidently a force of traction exerted at the entrance of a curve of small radius will produce in the tub a tendency to overrun the inner rail, and thereby to cause friction between that rail and the flanges of the inner wheels, while a force of propulsion, exerted under the same conditions, will produce like results in the direction of the outer rail. It would, therefore, seem desirable to raise the inner rail when the tubs are to be drawn by horses or by engine power, and the outer rail on those roads upon which the tubs are pushed by men. But there is another force in operation upon curves to be taken into account, namely, inertia, sometimes inappropriately called, under such conditions, centrifugal force. Inertia, as we have already shown, tends to cause the tub to overrun the outer rail, and when the velocity is great, this tendency becomes strong. In consequence of this, there will never be occasion to raise the inner rail, for the influence of inertia will always be sufficient to counterbalance that due to the oblique traction. Hence, when the velocity is low, and the curve not very sharp, the two rails may be laid level, if the tubs are to be moved by traction ; but when the velocity is high, and the curve sharp, it will be desirable to raise the outer rail. The degree of the elevation will evidently be dependent upon the weight' W, the velocity V, and the mean radius of curvature r, and it will be determined by the equation :

W

h 2 r

25 W

whence we deduce : h, -7— x — ,

r

h being the elevation of the rail, and 2 h the breadth of the line. Thus it will be seen that h is the

generating height of the velocity V reduced in the ratio of twice the breadth of the line to the length

of the radius of curvature. To illustrate the application of the formula, suppose a velocity of 3 feet

a second, a breadth of line equal to 2 feet 3 inches, and a radius of curvature equal to 10 feet. In

C3V 2C2*25')

this case, J. x ' 0-063 foot inch. If the velocity were doubled, the

requisite elevation would be 3 inches.

3 A

362 Mining Engineeeing.

The influence of the inclination of the road on the work of traction is very great, and claims, therefore, attentive consideration. The value of this influence was determined in prosecuting our investigations concerning the resistance of tubs ; it now remains to consider the results there arrived at relatively to the laying out of underground tramways. It will be evident that in working to the dip the inclination of the roads is unfavourable to the traction, and under such conditions the work of haulage is necessarily great. But in rise workings, the inclination is favourable to the load, and in laying out such workings it becomes desirable to ascertain how far the inclination may be modified so as to reduce the work of haulage to a minimum. In many cases, as previously pointed out, circumstances exist which preclude the possibility of modifying the inclination at all ; but in other cases, as in the diagonal roads, for example, considerable modifications may be made, and often in driving the main levels, we may adopt what inclination we please. Hence it becomes necessary to determine what is that degree of inclination which will reduce the work of haulage to a minimum, in order that it may be adopted in such cases. The importance of this question will be manifest when it is borne in mind that the main levels are the principal roadways of the mine.

"When the circumstances permit the choice of a gradient, the question for consideration is, shall it be such as will allow the loaded tubs to descend of their own weight, so as to reduce the force of traction in that direction to zero ? or, taking into account the necessity for hauling the empty tubs back, shall the inclination be such as will make the force of traction equal in both directions ? The latter arrangement will reduce the work of traction to a minimum ; but the former may ofier advantages under some circumstances.

The inclination upon which a tub will just stand, and down which it will run of its own weight

if set in motion, is called the gradient or angle of equilibrium, and if we take the resistances as

already determined, it will be given by the equation : 0"023W (I'4 W) sin. i,

0'023 whence sin. i — 0*0164, the angle corresponding to which is 0° 57'. Thus the inclination

sought is rHli'j 1 i'l 61. Upon a road having this gradient, the influence of the inclination is equal to the sum of the resistances due to the several sources of friction, and hence the force of traction will be reduced to zero.

The inclination upon which the force of traction is equal upon the descending loaded tubs and the ascending empty tubs is called the gradient or angle of equal resistance, and is given by the equation 0-023 W - (1-4 W) sin. i 0-0069 W + (0-4 W) sin. i;

whence sin. z — 5 - 009, the angle corresponding to which is 0° 31'. Thus the inclina-

tion sought is, in this case, ytitj, or 1 in 111. With this inclination, the traction upon a straight line will be equal in both directions, and the condition of minimum work will have been fulfilled.

Construction of Roads. — We have now to consider the practical application of the principles investigated in the preceding section, and to describe the operations of constructing the underground tramways. These operations are of a very simple character, such indeed as may be performed altogether without the aid of skilled labour; but those to whom the supervision of the work is intrusted will do well to bear in mind that the more carefully it is executed, the more will the cost of haulage be reduced. The accuracy obtained upon surface railways is neither possible nor desirable on underground lines, but great irregularities should be avoided, and a degree of stability o-iven to the way sufficient to preserve it in the requisite state of efficiency. These remarks apply rather

Haulage. 363

to the horse-roads than to the engine planes, where greater solidity and accuracy are indispensable ; indeed, on these latter, too much care cannot be bestowed. The great influence which the state of the roads exerts upon the work of traction having been already pointed out and estimated, this point need not further be insisted on.

In driving the roadways, it is very desirable to avoid undulations in the floor, as these undulations are highly unfavourable to the subsequent operations of haulage, and where the road possesses these irregularities, it is well to reduce them as much as possible when preparing the floor for the reception of the rails. The labour expended upon this preliminary work will be far more than compensated by the increased facilities thereby afforded to the transport of the produce of the mine.

An underground railway, like those existing at surface, consists essentially of two parallel lines of iron rails supported upon transverse or upon longitudinal timbers called sleepers. The form of the rails, and nature of the means employed for connecting the rails to the sleepers, are also the same upon important underground engine planes and upon surface railways, the only difference being in the dimensions of the material used. But on the less important ways, simpler means of connection, and sometimes simpler forms of rail, are adopted. As the roads underground do not possess the permanent character of those at surface, it is essential to economy that the material of which the lines consist should be light, and that the methods of laying them should be such as will allow them to be quickly taken up and relaid. These conditions are most completely fulfilled in the edge-rail tramway, to which attention has already been directed relatively to the operations of haulage along the face. As this simple railway can be made to answer all the requirements of the secondary ways of a mine, and as, moreover, it is extensively adopted in many localities, notably on the Continent, it is desirable to describe it somewhat more fully in this place.

The rail used in this system is simply a flat iron bar, from I5 inch x inch, to 2f inches X f inch in section, according to the weight of the traffic, upon the edge of which rail the wheels of the tubs run. The rail is fixed to the sleepers by means of a wedge of a suitable form to prevent its being forced out in the upward direction. Notches, the cross and longitudinal sections of which are trapeziums cut in the sleepers at such a distance apart that the outer sides shall correspond with the gauge of the line, measured from outside to outside of the rails, and in these notches the rails are laid. Wedges, of a form to fit the notch, are then driven in on the inside of each rail, which is thereby supported in and held firmly down to the sleeper. The distance of the sleepers apart should be such, relatively to the length of the rails, as to bring the ends of the latter together in one of the notches. This arrangement by which the ends of two successive rails are brought together upon one of the sleepers is generally adopted, irrespective of the form of the rail ; for the method of effecting a junction by means of fish-plates is rarely adopted on underground lines. The mode of laying a Hne according to this system is shown in Figs. 563 and 564.

A common form of rail laid in the main ways is the double-headed rail so generally adopted upon surface railways. This form probably most fully satisfies the requirements of underground lines, since it is of light weight, is laid upon transverse sleepers, and may be easily fixed in position. When the line partakes of an important and permanent character, it is laid with cast-iron chairs in the manner adopted upon ordinary railways ; but in less important ways, the rails may be spiked down to the sleepers. Bridge rails are not unfrequently used ; they possess the advantage of being the lightest form obtainable, but they require longitudinal sleepers, which in a mine are, for several

3 A 2

364 Mining Engineeeing.

reasons, more objectionable than at surface. In some instances, bridge rails have been laid upon transverse sleepers, but their section is unsuitable for that kind of support. The Yignoles rail has also been adopted on underground lines with satisfactory results. The details of the operations of laying a line with any of these forms of rails are so simple and so well understood that no description of them is needed here. It may, however, be desirable to remark that when the floor is of a weak character, a circumstance which necessitates frequent repairs in the roads, short rails should be used for the purpose of reducing as much as possible the length of line which it becomes necessary to pull up and relay. In places where the floor is very soft, it will be well to distribute the pressure by placing longitudinal timbers beneath the cross sleepers. The weight of the rails used of any given section will vary with the capacity of the tubs, and also with the distance of the sleepers apart. Grenerally this distance will be about 2 feet, or 2 feet 3 inches ; if they be spaced more or less widely than this, the weight of the rail for a given load must be increased or diminished in a proportionate degree. On the principal engine planes, the weight of the rails will vary generally between 18 lb. and 24 lb. to the yard ; on the secondary roads, a considerably less weight will be found to be sufficient.

In the construction of underground railways, the points which claim special attention are the junctions of the various lines with each other. These junctions are far more numerous than on surface railways, and, as we have already pointed out, take place at far sharper angles. When one line enters another at a small angle, the mode of efi"ecting the junction is similar to that adopted on surface lines, slight differences of detail only being made in favour of simplicity ; but when the angle of junction is great, other means are used which partake of the character of the turntable. These two methods now present themselves for consideration.

In a junction of the character shown in the diagram, F'ig. 565, three points. A, B, and C, have to be considered. The question to be solved is, how to arrange these points so that tubs arriving from the portion X of the principal way, or from the branch Y, may of their own accord enter the portion Z, and also so that tubs arriving from the portion Z of the main line may be made to keep the direction Z X, or to enter the branch Y as desired. It will be observed that at the point C two lines of rails cross each other, and this point will therefore have to be treated in a manner different from that adopted for the others A and B, where no such crossing occurs. The object to be attained in this case is to arrange this point so that the flange of the wheel on the inside of the corresponding line of rails shall not come into contact with the other rail. To arrive at this result, both rails must evidently be notched to a. sufficient depth and breadth to allow the flange to pass through freely. Suppose a line consisting of the edge rails previously described ; in such a case, a horizontal cut will be made in the ends of the rails meeting at that point at the level of the surface of the sleeper, and the upper portion bent round, as shown in Fig. 566. The other ends are brought to a point, or cut off square and set in a triangular piece of cast iron, which has the same effect. With this arrangement, the rails may be fixed in the usual manner with wedges. The same principle is observed when other sections of rail are used ; but in such cases, the whole of the portion shown in Fig. 566 is usually cast in one piece, into which the rails run.

At the points A and B, the outer rails, that is, the rail of the main line at A and the rail of the branch at B, are continuous, whilst the other rail of each line is made to turn about one of its ends so as to establish the continuity of both rails in each line as desired. These movable ends of the rails are called points, and they are made to thin off towards the extremity which is brought into contact

Haulage. 365

with the fixed rail. The motion of the points is effected by means of a lever fixed by the side of the line and connected to the points by means of an iron rod passing beneath the rails. This arrangement of the junction is shown in Fig. 567, from which the action of the points will be readily understood. If the tub is approaching the points from Z and is required to pass on to X, the point a A must be opened and the point h B closed ; but if the tub be required to enter the branch T, the position of the points must be that shown in the drawing. If the tub is approaching from the contrary direction, either from X or from Y, the flange of the wheel will force the points into the requisite position, if they are not already there.

The foregoing method of effecting the junction is very simple and effective ; but it may be simplified still further by suppressing the movable points, as in the arrangement shown in Pig. 568. In this arrangement, the portions of rail a A, 6 B, which were movable in the former, are fixed, and a sufficient space is left between their extremities and the rails which they approach to allow he free passage of the flange of the wheel. When the junction is effected in this manner, the motion of the tub in the direction of Z takes place without any difficulty ; but when the tub is approaching the junction from the opposite direction, it has to be pushed to one side or to the other, according as it is required to keep on the main line, or to enter the branch. This is a more simple operation than moving the points, and it may be readily performed upon single tubs ; but with a train of tubs, the points are preferable, the driver in such a case being thereby enabled to perform the shunting with greater ease and certainty. The more simple method will thus be adopted on the ways of less importance. A double branch, forming a junction with the main line at the same point, is shown in Fig. 569 ; and Fig. 570 represents the method of doubling the line to form a pass-by where the road is laid with only a single line of rail. The manner of laying out the curves necessary to this mode of junction will be described in a subsequent chapter devoted to surface works.

The roads of a mine frequently intersect each other at a great angle, in numerous cases perpendicularly, and when the junction has to be effected under such conditions, other means than those already described have to be adopted. Upon ordinary railways the problem would be solved by means of the turntable ; but upon underground lines their cost and somewhat complicated construction render them impracticable by reason of the great number that would be required and the frequent occasion for their use. The means employed, however, are similar in principle, though the details have been varied to obviate the disadvantages alluded to. They may be said to consist of a fixed table, upon which the tubs are turned, by being lifted at one end and carried, or by being dragged round by the men or boys in charge of them. The table or platform is constructed of stout planking, carefully laid, and usually covered with iron plates, to diminish the friction and to lessen the wear and tear. The construction may be varied to suit the requirements of the case ; but it will always be of an extremely simple character. The chief points requiring attention are to lay the floor evenly, and to give the structure sufficient stability to resist the somewhat violent strains thrown upon it. The ends of the rails are brought upon the flooring and made to curve outwards, and between these curved portions ribs or raised guides, curved in the contrary direction and brought together in a point, are placed ; the object of this arrangement is to facilitate tlie entrance of the tubs. Fig. 571 represents a junction at right angles of two branch lines with one of the secondary main lines, and shows the application of the system to the case represented in Fig. 569. The whole of the arrangements will be readily understood from this drawing. It will be observed that the space in the centre is clear to allow the tub to be turned round and directed as required. If the same

366 Mining Engineeeing.

direction is to be continued, the tub is simply drawn or pushed across the floors. Sometimes a circular rib or guide is placed in the middle of the floor, as shown in Fig. 572. The diameter of this guide is slightly less than the gauge of the line, the object of the arrangement being to keep the tub in the middle of the flooring, and hence opposite the entrance to each of the lines, while it is being turned round. The system is applicable to the junctions of the lesser roads, the pass-bys, and the points where trains of tubs are made up and distributed. It will be observed that it is unfavourable to the use of fixed wheels.

Motors. — In the preceding sections, the vehicles in which the coal is transported from the working places to the shaft, and the roads over which it is conveyed, were described, and the influence of their mode of construction upon the force of traction was investigated. It now remains to consider the sources whence the motive force is derived, and the manner in which it may be applied. The subject is one of those which claim the careful attention of mining engineers at this time, especially when strict economy is necessary to remunerative working. As we have already remarked, partial measures are of little value, and if knowledge and skill have been applied in the production of vehicles and roads that shall satisfy all the requirements of underground traffic, the same degree of attention must be directed to the motors through which these means are utilized. It is therefore desirable to consider the characters and values of each motor separately, and in connection with the means through which its force is applied.

Gravity. — The force of gravity possesses a special claim to attention in any consideration of the motive forces employed to effect the transport of coal underground, inasmuch as it is the cheapest obtainable, and is, moreover, very generally applicable. It has already been pointed out that all the principal roadways of a mine are laid out to utilize, as much as circumstances will permit, the force of gravity, and it has been shown by what means and in what manner that object is attained. In the chief roadways to the shaft it is not desirable to render the force of gravity sufficient to effect the transit of the loaded tubs, since the adoption of such an arrangement would involve difficulties of another kind. Hence it is sought to lay out these ways in a manner that shall reduce to a minimum the force of traction that has to be supplied. But though this condition is imposed on the main levels which follow the strike of the bed, no such restriction exists for the secondary ways, which are driven in the direction of the dip., These ways, which thus coincide with the line of greatest descent, have the inclination of the seam, and they extend the workings in the direction of the dip, as the main levels extend them in the direction of the strike. Thus the former may be considered complementary to the latter, and their inclination is obviously determined by the dip of the seam. If, therefore, this inclination is sufficient to effect, with suitable arrangements, the transit of the loaded tubs in one direction and of the empty tubs in the other, it is clearly desirable to employ this force in preference to another of a more or less costly nature. A road upon which the traffic is effected by this means is called a self-acting plane, and in consequence of this self-acting character, it possesses numerous and great advantages. Being directed in the line of greatest descent, it is the shortest way from the main level to the point to be reached ; the rapidity with which the descent is made largely compensates for any delays that may occur at the top or at the bottom of the incline ; and as the labour is reduced to that of one man at the brake, instead of that of several men and horses required upon diagonal roads, the economy is manifest. The additional expense of keeping the road in repair, and the rapid wear of the ropes, are defects to be remembered against the inclined plane ; but these are far outweighed by the advantages enumerated.

Haulage. 367

In estimating the influence of gradients on tlie traction of tubs, it was shown how the angle or inclination of equal resistance might be calculated. By means of the formula there given, the minimum inclination necessary to a self-acting plane may be readily determined. But in this determination it must be borne in mind that other resistances have to be taken into account, namely, the friction of the rope and that of the sheave or reel. Moreover, as a certain velocity will be required, the time of the descent must be included. It is not desirable here to do more than allude to this calculation, since it has been well ascertained in practice that an inclination of 1 in 36 is the limit below which the plane ceases to be self-acting, and to attain so low an inclination as this, the road and the tubs, as well as the apparatus employed therewith, must be maintained in a perfect condition. Practically it may be considered that 1 in 30, or a little more than one inch in a yard, is the least inclination that will render a plane self-acting. As the inclination becomes greater than this a brake will be required to absorb the excess c f force acting on the descending load.

In laying out a self-acting plane, the section should receive some attention, especially when the plane is to be of an important and a permanent character. To render the action of the plane in all respects satisfactory, certain conditions of varied inclination have to be fulfilled. In some cases it would be difficult, and therefore undesirable, to satisfy these requirements ; but when the circumstances are favourable, the opportunity of attaining a higher degree of perfection in the working of the plane should not be neglected. It will clearly appear on reflection that if the upper portion of the plane on which the tubs are started be laid out with a sharper inclination than the main portion, and if the lower portion be also laid out with a less inclination than the main portion, the force of gravity will operate more regularly, and will be more easily controlled than if the plane have the same inclination throughout. Let AD, Fig. 573, represent a diagrammatic section of a self-acting plane, the portions A B and C D of which have respectively a greater and a less inclination than the main portion B 0. Also suppose a loaded tub in the position X, the starting point, and an empty tub in the position Y, the lower extremity of the plane. It must be remembered, that to set a body in motion a certain amount of force is required to overcome its vis inertias ; this is provided for by the arrangement shown in the diagram. Let us now observe the action of the force of gravity upon this plane. As the loaded tub stands upon a gradient sharper than that allowed in the main portion by the general inclination of the seam, the action of gravity is greatest at the point from which the tub is to start ; this additional force is required to overcome the vis inertia of the loaded tub, that is, to set it in motion. But this tub is connected, through the medium of a rope, with the empty tub at Y, and before the former can start down the plane, it must overcome the vis inertige, the resistance of friction, and the action of gravity in the latter. Here we have another reason for increasing the inclination of the plane at the starting point of the loaded tub ; but the same reason renders it desirable to reduce the inclination at the starting point of the empty tub. Thus it will be seen that on a plane having the section shown in the diagram, the value of the force of gravity acting upon the tub is greatest for the loaded tub, and least for the empty tub, when each is at its respective starting point, which is the condition required. Suppose now the loaded tub to descend until it has reached the point X', which is near its stopping point. The condition required now is the contrary of that needed at starting, since the motion of the tub has to be arrested. To arrest the motion of this loaded tub, its vis viva, and the action of gravity which is still urging it forward, must be overcome, and it will be evident that the value of the latter will be reduced by lessening the inclination throughout the portion C D. But when the loaded tub has reached the position X',

368 Mining Engineeeing.

the empty tub will be at Y', and during tlie time that the former is passing over the diminished gradient C D, the latter will be ascending the augmented gradient B A. The increased resistance of the empty tub acting against the diminished force urging the loaded tub forward, tends to bring the latter gradually to rest. There is yet another reason to justify this arrangement of the plane. When the loaded tub starts from the position X, it has to overcome the resistance of the whole length of rope X Y, the weight of which is considerable. This resistance, which acts energetically in opposing the motion of the tub at starting, will operate but feebly in arresting its motion after it has reached the point X', because the ascending rope has been transformed into a descending one. It will be easily understood that when the inclination of the plane is greater and the force of gravity, consequently, abundantly sufficient to start the loaded tub with the requisite velocity, it will not be advisable to increase it on the upper portion AB, but there will still be an advantage in lessening the inclination over the lower portion C D.

In plan, a self-acting plane differs but little from the ordinary roads ; it requires, however, to be somewhat more strongly constructed. Gi-enerally a double line is laid throughout the length of the plane, and each line receives alternately the loaded tub. But not unfrequently the advantages of the double line are obtained by the arrangement shown in Fig. 574. In this arrangement, three rails are laid on the upper portion of the plane, four rails in the middle where a pass-by is required, and two rails at the bottom. At a and b are two points, which are operated by the descending tub. The arrangement by which the descending tub is made to open a way for itself, and to set the points for the ascending tub, is shown in Fig. 575. In this drawing, a a' are points which turn upon vertical axes c c' ; these points are rigidly connected by the iron rod /. On the outside of the line are two studs gg', to limit the movements of the points. Counter or guard rails are placed, as shown, to keep the tub upon the line. The loaded tub in its descent forces the points back, and the empty tub thus finds the way prepared for the ascent. This mode of laying out the line allows the breadth of the road to be reduced. In some cases, when it is required to still further diminish the breadth of the road, the whole length is laid with a single line, and a counter weight is used to draw up the empty tub. This counter weight may be a partially -loaded tub running on a road parallel to the plane, a narrow and very low truck running between the rails of the plane, and capable of passing beneath the tub, or a weight suspended in a well, the depth of which is determined by the value of the counterweight. The use of the single line, whilst involving serious difficulties, possesses no other advantage than that of diminishing the breadth of the road.

The top of the incline should be laid out so that the loaded tubs arriving may be readily run on to the line which is clear to receive them. The simplest means of effecting such an arrangement is by means of tramplates laid in the manner described for junctions. In numerous cases, the incline is extended as the workings progress, the wheel being shifted higher up the plane as occasion requires. Under such conditions as these, it is, of course, impossible to have an increased inclination at the starting point of the full tubs ; indeed, it will seldom be practicable to adopt that expedient underground. Moreover it frequently becomes necessary to adopt measures for receiving the loaded tubs from roads opening on to the plane at various levels. When the inclination is slight, the arrangement offers no difficulty ; but if the inclination is sharp, some modification of the road at those points has to be made. One method adopted in such a case is shown in Fig. 576. The level of the road is here continued across the plane, and the hollow thus formed is bridged over by movable rails. When the loaded tubs are to be despatched from this point, and the empty ones received at the same level,

Haulage. 369

the rails are removed, and they are restored to their positions when the service at that point is completed. When the inclination of the plane is very great, a large proportion of the contents of the tub would be spilled during the transit from the top to the bottom if they were run down in the usual manner. In such cases, a trolly provided with a level floor may be used. The tubs are run upon the trolly, to which they are fixed by some simple means, and let down the incline, the empty tubs being hauled up in the same manner. The floor of the trolly is level with the line on reaching the bottom of the incline, so that they may be run ofi" and on without difficulty. Also the floor of the trolly is in a position to receive the tubs from the roads opening on to the plane at various levels — a circumstance of considerable importance.

The only mechanism required to work a self-acting plane consists simply of a reel, sheave, or drum, around which a rope or chain is passed, and upon which is set a brake to control its motion. The apparatus may be made to revolve about either a vertical or a horizontal axis ; the latter arrangement being the more common. In the former case, only one rope is used, which is passed round the sheave, one end being attached to a tub at the bottom of the plane, and the other end to a tub at the top of the plane. In the latter case, either two ropes coiling in contrary directions may be used, or a single rope sufficiently long to be passed several times round the reel. In some instances, an endless rope has been employed, which is made to pass over a pulley at the bottom of the incline, and kept in a state of sufficient tension by means of a counterweight connected to the pulley with the endless rope, which requires the tubs to succeed each other with great regularity ; the full tubs descend on one line of rails and the empty ones ascend on the other. Whatever the arrangement adopted may be, a powerful brake must always be provided. This brake may be of very simple construction, consisting merely of a segment of wood fixed to a lever, and arranged to be readily brought into contact with the periphery of the sheave. To obtain greater power, compound levers may be employed, and the same object may be attained by means of an iron band enclosing the whole of the periphery and worked by a system of jointed levers. The mode of applying a brake is a matter of some importance. It is evident that the brake may be so arranged that when left to itself it shall be in operation, or the arrangement may be such that the brake shall cease to act when left to itself. In the former case, the force is applied by means of a weight attached to the end of the lever ; in the latter, the force is applied by hand. The former method of arranging the brake is generally the best to adopt, as it offers the greatest security against the negligence of the brakesman. It is well to adopt the principle that the apparatus of a self-acting plane should be incapable of setting itself in motion without the intervention of the brakesman. The latter, to start the tubs, releases the brake, and holds it wholly or partially released during the time of the descent of the load. In this way, he is able to regulate the motion, and to arrest it easily at the proper moment.

In order that the brake may be capable of controlling the motion of the load, as well as that of the sheave or reel, it is necessary to arrange the rope in such a way that it cannot slip. With the horizontal reel, this may easily be effected by passing the rope a few times round it : three or four times being abundantly sufficient. But with a sheave turning about an axis that is perpendicular to the plane, this expedient cannot be so readily adopted. One turn round a sheave having the ordinary kind of groove would be insufficient to prevent slipping. In such a case, the groove may be made conical, so as to grip the rope, or one of Fowler's clip pulleys may be used. Another method consists in passing the rope several times round tho heave, and providing an arrangement by which the

S B

370 Mining Engineeeing.

friction of the several turns of the rope against each other isa voided. The arrang ement is merely the addition of one or more parallel grooves to the sheave, which is then put in relation with another sheave, of any diameter, provided with one groove less. The rope is wound and unwound upon this sheave regularly, as upon one of the ordinary kind. A diagrammatic representation of this arrangement is shown in Pigs. 577 and 578.

The friction of the rope upon a self-acting plane is, as we have already remarked, considerable ; and as this friction not only absorbs the motive power, but causes a rapid wear of the rope, it is very important that it should be reduced as much as possible. This is accomplished by means of friction rollers, placed at suflSciently short intervals apart throughout the plane to prevent the sag of the rope from causing contact with the ground. These friction rollers should be of a considerable diameter relatively to their gudgeons, which should be kept well greased, for otherwise they will not turn, but constitute fixed points- of support to the rope. Two forms of friction rollers, with the method of fixing them, are shown in Figs. 579 to 581. The latter form is used on those portions of the road where the rope has a tendency to oscillate.

The reels and sheaves used upon self-acting planes should be of a simple character, and fixed in a manner that renders them capable of being easily shifted from point to point as the workings progress. Common forms are shown in Figs. 582 to 584. In the former of these, a sheave is fixed in the middle, upon which the brake acts. The reel turns in bearings fixed upon two props securely set in the roof and floor rock, and the posterior end of the brake may be fixed upon a prop, or in any other manner that may seem more suitable. The other end of the brake will be handled by the brakesman ; or by compounding the leverage, as shown in the drawings, will be connected to a second smaller iron lever, an arrangement that gives greater control of the apparatus. The segment embracing a portion of the circumference of the sheave is bolted on to the lever, so as to allow of its being readily replaced by a new one when it is worn out. Soft wood should be used for these blocks. In Fig. 584 the sheave, which is provided with a conical or Y groove, has its axis perpendicular to the plane. The rope in this case passes once round the sheave, upon which a brake may be made to press by any convenient arrangement. The wooden framing carrying the sheave is fixed down to the floor by means of stout iron cramps, driven into holes bored in the rock. An apparatus of this nature, like the preceding, may be quickly removed to a higher point, as the workings progress : this is a quality of considerable importance in such apparatus, which has frequently — sometimes every two or three days — to be shifted higher up the plane. When the inclination becomes great. Fowler's clip pulley, with which a single turn of the rope will be suificient, may be used. This pulley, represented in Fig. 585, is constructed to grip the rope with a force proportionate to the tension upon it — an object which is completely attained by the mechanism shown in the drawing.

The details of the method of working a self-acting plane vary somewhat according to the inclination of the plane, the number of the points at which it receives the tubs, and the number of tubs let down at one time. When the inclination is moderate, and the tubs are despatched from the top of the plane, the operations are of an extremely simple character. Each man, as he arrives with his loaded tub, immediately attaches it to the rope and runs it on to the rails of the plane. The brakesman, however, does not allow it to descend until he has received a signal from the bottom informing him that an empty tub has been attached to the other end of the rope, when he releases the brake and the load descends, bringing up the empty tub to the man or boy who is waiting to receive it.

Haulage. 371

As the tub approaches the landing, the brakesman appHes his brake, increasing the force progressively, so as to bring the tubs gradually to rest. On moderate inclinations, several tubs may be sent down at once, and when the plane is long, there will obviously be a great advantage in sending down long trains of tubs. The foregoing is the simplest case of the inclined plane ; but it may be required to despatch tubs from some intermediate point on the plane. In the former case, the length of the rope is regulated once for all, and in such a way that when one end is at the top of the plane, the other is at the bottom. In the latter case, the length of the rope has to be regulated according to the position of the point from which the tubs are to be despatched. The arrangement adopted will depend upon the manner of serving the different levels whether simultaneously or successively. If these several points are served successively, the rope may be lengthened as the distance to be run on the plane becomes shorter. For example, suppose a plane that has been worked for a certain time from the top, when it becomes necessary to detach a number of tubs from a point lower down. To allow this point to be served by the plane, the rope must be lengthened so that the empty tub shall stand there when the loaded tub is at the bottom landing. This lengthening may be accomplished by inserting a piece into the main rope ; for which insertion, provision must be made in order that the operation may be performed with the least possible loss of time. If after this it becomes necessary to serve a yet lower point, another length of rope may be inserted. Sometimes the length of the rope is regulated by making one half of the barrel upon which it is wound movable at pleasure on its axis. If the several points are to be served simultaneously, which is generally desirable in order to keep them clear, either the system of the endless rope, or that of the single line and counterweight, must be adopted. When the endless rope is used, the putter or driver on arriving at the plane, signals the brakesman to stop : he then attaches his loaded tub to the rope by means of a short piece of chain, or other means, and pushes it on to the rails. The apparatus is again set in motion, and as soon as an empty tub arrives at his level, he again signals the brakesman to stop, detaches the tub, and having notified the fact to the brakesman, departs with it into the workings. In this case, the rope is suspended near the roof, so that one may pass freely with a tub from one side of the plane to the other. When the plane is single and worked by means of a counterweight, the empty tub is stopped by signal on arriving at the point from which a loaded one is to be detached, and having been removed and the loaded tub substituted for it, the brakesman is signalled to let it descend to the landing place. This arrangement is suitable to short planes of secondary importance. In the greater number of cases, self-acting planes are worked only from the top, and if it be well laid out and properly managed, a very large quantity of coal may be let down in the course of a single shift, particularly if a considerable number of tubs be let down at once. For a busy plane, a speed of 6 feet a second may be allowed with safety, provided the road be kept in a good condition ; and the time occupied in changing need not exceed a few seconds. The advantages of a system which thus utilizes the force of gravity in the performance of work of an otherwise costly character, are too plainly manifest to leave it desirable to insist on them further.

In concluding our considerations on self-acting planes, it may be well to direct attention to the laying out of a new colliery with a view of utilizing to the utmost the force of gravity. We have seen that the inclination which reduces the labour of traction to a minimum upon horse-roads is one of 0°31' or 1 in 111. Also it was shown that an inclination of 1°55', or 1 in 30, was practically the limit 'below which a self-acting plane will not work. In laying out a new colliery with a view of utilizing the force of gravity to the utmost, therefore, we shall have to take these facts into account,

3 B 2

Q

72 Mining Engineeeing.

aud to plan tlie workings in accordance with them. This will be most clearly understood from the diagram shown in Fig. 586. In this diagram, let S represent the shaft, which has been sunk on the deep side of a royalty in which the seams dip at an angle of 5°. Here we may obviously have three principal planes — one S C in the line of the dip, and two others S B and S B' at such an angle with it as will give an inclination of 1°" 55', or 1 in 30. This angle may be readily determined by means of the formula for the oblique section, given in the first chapter of this work. With planes laid out in this manner, it is evident that all the coal above B S B' may be brought down to the shaft by gravitation upon the main self-acting planes S B, S 0, S B', The remaining portion, comprised in the triangles A S B, A' S B', may be brought down by gravitation to the principal horse-roads S A and S A'. These horse-roads, or main levels, will be driven with an inclination of 0° 31', or 1 in 111, which, as shown in a former section, is that which makes the resistance to traction equal in both directions, and reduces the work of haulage on these roads to a minimum. If the dip of the seam were greater, say 10° instead of 5°, the extreme self-acting planes and the main horse-roads would be driven in the directions shown by the dotted lines, and a considerably larger portion of the field will be commanded by the self-acting planes. In a colliery laid out according to these principles, the force of gravity will be fully utilized, and consequently the cost of haulage reduced to a minimum.

Men and Horses. — In former days, the labour of men was largely employed in conveying the coal from the working places to the main roads and even to the shaft. Now, however, this work is performed chiefly by horses, so that if we except the putting of the coa,l along the working face, the work of men is not applied to the operations of haulage. In conveying the coal to the main roads, small ponies driven by boys are used, and when the inclination is moderate, the work is easily performed. When, however, the inclination is against the load, as in dip workings, the labour becomes great. In such cases, stronger horses must be used, and shorter trains of tubs dealt with. Upon the main roads, which are laid out to favour this means of traction, more powerful horses may be employed and longer trains of tubs drawn. As a large proportion of the work of haulage is performed by horses, it becomes important to know what amount of work a horse, subjected to the conditions prevailing in a mine, is capable of performing, in order to be able to properly proportion their number to the work to be done. This determination of the power of a horse is not readily effected, since the conditions vary greatly from one part of the mine to another. Thus the circumstances existing in one place where a horse is employed may be unfavourable to the full utilization of its strength, while in another place conditions have to be submitted to which materially diminish its available power. Among these, an insufficient ventilation is the most potent. A horse is soon and greatly affected by a want of air, and therefore, in those places where a brisk ventilation cannot be maintained, its capacity for work is seriously lessened. Also it is evident that the state of the roads must materially affect the weight of the load which a horse is capable of transporting through a given space in a given time. All these circumstances combine to render it impossible to determine with anything like accuracy the power of a horse when employed underground. But assuming average conditions, an approximate general value may be assigned to it which shall be of service in estimating the requirements of a colliery. Mr. Nicholas Wood ascertained, as the result of numerous experiments, that on railways at surface a horse is capable of exertino- a force of 120 lb. when travelling at the rate of about 3 miles an hour, and that moreover it is capable of continuing that exertion for ten hours, say, including necessary stoppages, 20 miles a day, when the resistance is

Haulage, 373

equal in both directions. But from similar experiments made on underground lines, he found that the useful work of a horse could not be estimated at more than one-third of that obtained upon surface colliery lines. Thus, instead of 120 lb., we have 40 lb. as the maximum effect which a horse is capable of exerting under the conditions given ; and as the force which a horse is required to exert becomes greater than this, the distance travelled will have to be proportionally shortened. If, for example, it be required that a horse shall exert a force of 120 lb. 40 x 3, when travelling at the rate of 3 miles an hour upon a road having the inclination assumed in the preceding case, the time during which the work can be continued will have to be reduced in a like proportion, namely, 3|- hours. This value is founded upon results actually obtained, and therefore takes account of the delays incurred at passing places, where the roads are laid with only a single line of rails, as well as the greater defects existing on underground railways. These are circumstances susceptible of improvement, and hence it is clear that where double lines are provided and laid with some degree of care, and where, moreover, the ventilation is good, the maximum effect may be assumed to be 60 lb. instead of 40 lb., a value that in the above case would make the time five hours instead of only three hours and twenty minutes. But even with this increased value, it will be seen that horse-power underground is far from economical, and that it is of the highest importance to substitute a more suitable motor to do the work of haulage upon these railways. In this direction, there is a wide field open to engineering ingenuity, and it is one in which ample reward is to be obtained in a material reduction of the cost of haulage. "We have shown how the force of gravity may be made to perform a large proportion of the work of conveying the coal to the shaft ; in those parts where this force cannot be utilized, engine power may be applied upon all the main roads.

Steam Engines. — In any consideration on motors, steam naturally suggests itself as the most fitting substitute for horse-power underground. It is independent of the conditions which operate to render tbe latter unavailable ; and as the principal cost of the engine is fiiel, and as, moreover, suitable fuel may be obtained at a comparatively trifling cost, it would seem that steam power is particularly applicable to the requirements of underground haulage. In raising coal from the dip workings, the employment of steam obviously affords great advantages, for it is especially in such portions of a mine that the conditions are unfavourable to the utilization of horse-power, and the cost of haulage consequently becomes very great. Accordingly, we find that steam engines are gradually taking the place of horses, and that the results of this substitution of an inanimate for an animate motor are everywhere of a highly satisfactory character.

The question of the application of steam to the operations of underground haulage has thus become a very important one, and it is consequently desirable to investigate the conditions under which that motor may be applied most advantageously. It would be beyond the scope of the present work to consider this subject relatively to the engine itself; our limits will confine us to an investigation of those circumstances and questions which relate exclusively to the application of an engine of any given design and construction. Of these circumstances and questions, some relate directly to the motor, and others to the means through which its force is utilized. These two classes of subjects demand separate consideration. The former obviously belong to the present section; but the latter will be best treated of in another division devoted to the description of Systems of

haulage.

When considering the advantages of an application of steam power to the work of haulage, the first question that presents itself is, What proportion of the force developed may be utilized ? In other

374 Mining Engineeeing.

words, What is the maximum useful effect obtainable from a hauling engine working under the generally unfavourable conditions prevailing upon underground railways ? It is obviously impossible to determine this question in a general manner, since it involves conditions of a very variable character, to be hereafter considered ; and even by assuming conditions in order to assign a particular value to the useful effect, the question can only be determined by direct experiments. Such experiments have, however, been made for some cases, and from those undertaken with great care by Nicholas Wood we learn that where no special source of loss exists, underground hauling engines are capable of realizing an efficient performance varying from 40 to 50 per cent, of the pressure of the steam upon the piston. With the improved engines of the present day, this value may be safely increased 10 per cent., so that we may assume the efficiency of a hauling en9:ine to be from 50 to 60 per cent, estimated in coal conveyed. This value, which compares very favourably with that determined for horse-power, may be taken as a basis upon which to found any calculations relating to the performance of hauling engines.

The direct employment of steam in the operations of haulage is, however, not without disadvantages. . If the boilers are placed underground, their position is by no means arbitrary ; for it is necessary so to place them that the products of combustion may pass as directly as possible to the upcast without traversing drifts used as a travelling road, and that there may be no danger of an explosion from firedamp reaching the furnaces. These are disadvantages attending the direct employment of steam of a somewhat grave character, which cannot be entirely got rid of when the boilers are placed underground, and in order to avoid the danger as far as is possible, it may become necessary to adopt a position but ill suited to the requirements of the engines. It is easy to conceive how this condition may operate to determine in some degree the position of the engines, which ought to be chosen solely to satisfy the requirements of the traction. One means, not unfrequently adopted, of obviating these difficulties consists in erecting the boilers at surface, and in conducting the steam down the shaft, and to the points were the engines are fixed, through iron pipes. But this expedient introduces difficulties of another kind. To prevent the condensation of the steam by the radiation of heat from the pipes, the latter have to be well coated with a suitable non-conducting material. But whatever expense may be incurred in providing this protective covering, the remedy is but partially effectual ; in all cases a large amount of condensation inevitably takes place, and the evil thus caused will obviously become more serious as the distance of the engines from the boilers increases. But besides these drawbacks, there is in every case the disadvantage arising from the heating of the atmosphere underground by the exhaust steam. It is true that this objection to the direct use of steam may be to some extent removed by the adoption of suitable arrangements ; but such arrangements have to be adopted, and the evil even then admits of only partial remedy.

It is easy to see that if a complete system of mechanical haulage is to be established in the place of the horses now largely employed, it must be possible to fix an engine in the most favourable position for the traction, and in any part of the workings, for such a system would involve the use of small engines, capable of being readily moved from place to place, to serve the less important points, as the workings advance. The requirements of the haulage are partially fulfilled by -the system of erecting both boilers and engines at surface, and in transmitting the force down the shaft by means of an endless rope. This system, however, though it gives good results in some cases, leads to complication, and is limited in its application. Perfect efficiency and completeness can only be attained by the use of several independent engines, situate at various points in the workings.

Haulage. 375

and designed and proportioned in their dimensions to the work they have to perform, and the conditions under which they are to operate. It is obviously apparent that in such a system of haulage the direct application of steam is altogether impracticable, and it becomes therefore desirable to find a means through which its force may be conveniently transmitted. The only satisfactory solution of this problem appears to lie in the adoption of compressed air. It has already been shown that when air-compressing machinery is erected at surface, the compressed fluid can be conducted without difficulty, and with only a trifling degree of waste, down the shaft, and thence to the most remote part of the workings. The discharge of this air into the atmosphere of the mine, so far from occasioning inconvenience, as in the case of steam, tends to reduce the temperature and to promote the ventilation. In this respect also it possesses an advantage over water, the presence of which, after its discharge from the engines, is more or less seriously objectionable. Compressed air, as we have already shown, may be easily and cheaply conveyed to any part of the workings through branch pipes of small diameter, laid from the primary and secondary mains in the principal roads ; hence, not only may the hauling engines be placed in positions most favourable to the traction, but the rock-boring and coal-cutting machines may be supplied from the same system of pipes as the hauling engines. This is a matter of no small importance, since the general adoption of machine drills and coal-cutters is inevitable. With a well-laid-out system of air-pipes and small and compact hauling engines suitably placed, the operations of haulage might be performed with a rapidity suited to the requirements of the present large outputs, and at a cost far below that now incurred even by the improved means in use in many places. Probably in no department of mining engineering is there such an opportunity for the exercise of inventive skill, and for the application of recent discoveries in mechanical science, as in this of haulage by means of compressed air ; and it may be confidently believed that, as the cost of manual labour continues to increase, the necessity for the use of such means will become greater. The only objection to the employment of compressed air lies in the loss of the motive force which it occasions ; but this loss is far more than compensated by the advantages afforded in other directions. The value of the loss due to the compression of the air and to its use inexpensively was shown in a former chapter, whence it will appear that generally the power of the steam engine will have to be doubled when its force is to be applied through the medium of compressed air. The theory of the transmission of force through this medium having been fully considered in the chapter referred to, and the construction of the compressing engines minutely described, it is unnecessary to treat these subjects in this place.

Systems of Haulage. — It now remains to consider the means interposed between the motor and the load, and the methods according to which those means are applied. The means are in every case either a rope or a chain ; but the methods or systems of applying it vary. Thus our considerations will be limited to that of the systems, the means being treated of only incidentally.

Eegarded solely from the point of view of difference in principle, there are but two systems : one in which two distinct ropes are used — a main rope attached to the fore part oi the tub to draw the load towards the shaft, and a tail rope, of smaller diameter, attached to the hinder part of the tub, to draw it back towards the working places when empty ; and another, in which an endless rope is used, passing round pulleys at each end of the plane, and bringing out the loaded tubs on one side and carrying back the empty tubs on the . other. The former is known as the tail-rope system, and the latter as the endless-rope system. It is easy to conceive that these systems are susceptible of considerable variation in the details of their application, and that some modification will be rendered

376 Mining Engineeeing.

necessary by the substitution of a chain for the rope. Hence we have in practice a fourfold division or classification, distinguished respectively by the appellations of the tail-rope system, the endlesschain system, the endless-rope system No. 1, and the endless-rope system No. 2,

The characteristic features of these several systems are briefly as follows : In the tail-rope system, the hauling engine is placed near the bottom of the drawing shaft, where it actuates two drums, either of which may be thrown into or out of gear at will. These drums are each provided with a separate brake, and they receive, one the main and the other the tail rope. The former rope passes down from the drum under a friction roller or pulley, placed to bring the rope near to the ground and into the axis of the way, and is attached to the fore end of the first tub ; the latter rope is carried along in one of the angles of the roof to the sheave at the farther end of the plane, passed round this sheave, and attached to the hinder end of the last tub in the train. Both ropes are made to run upon friction rollers, to lessen the friction and the consequent wear, and are led round angles by pulleys suitably fixed. To illustrate the action of these drums and ropes, suppose a train of loaded tubs standing at the starting station. The drum upon which the tail rope is wound is first thrown out of gear, and its brake lightly applied to keep a sufficient tension upon the rope. The brake upon the drum which receives the main rope is then released, and that drum thrown into gear. The train of loaded tubs is thus drawn towards the shaft by the main rope, which at the same time pulls out the tail rope from the other drum. When the loaded tubs have arrived at the shaft, the ropes are detached, and the tubs run out of the way, their place being taken by a train of empty tubs, to which the ropes are attached in the same manner. The main-rope drum is then thrown out of gear, and the brake lightly applied to keep the rope in tension, and the tail-rope drum is put into gear. The empty tubs are thus drawn back to the starting station by the tail rope, which at the same time drags out the main rope. Arrived at this end of the plane, the empty tubs are run away into the workings, and their places are filled with full tubs that have been brought down from the working places.

It will be seen that this system requires only one line of rails, and that the engine may be made to drive four drums as well as two. Thus we may evidently have two principal planes in different directions, from which branches may be laid off as required to serve a point in any district to which the loaded tubs may be brought by men or horses. Besides these branches, there may be stations on the plane, at which tubs may be taken up or left, sidings being laid at such points for that purpose. If will be remarked that this system necessitates the adoption of high speeds in order that the time of a return journey may correspond with that required to raise in the shaft the load conveyed. These high speeds, which may be from 12 to 16 feet a second, require powerful engines and a welllaid way.

In hauling from the dip workings, the tail rope may sometimes be dispensed with, the action of gravitation being sufficient to take back the empty tubs and to drag out the main rope. The least inclination upon which these effects are produced with certainty has been found by experiment to be 1 in 28. This, it will be observed, is a slightly greater inclination than the minimum upon which a plane will self-act.

The system of the endless chain or rope differs altogether in principle from that of the tail rope. In the former, the engine, erected near the drawing shaft, drives by means of suitable gearing a sheave or pulley around which passes an endless chain. To prevent the chain from sHpping, it is passed twice round the pulley, or some other expedient is employed to hold the chain, such as providing the pulley with iron studs upon which the links catch. At the other end of the plane, the

Haulage. 377

chain passes once round another pulley, both this and the driving pulley being at such a height above the floor as will cause the chain to clear the top of the tubs. In the interval between the two ends of the plane, the chain is not supported upon friction rollers, but upon the tops of the tubs distributed along the lines of rails beneath it. This system, it will be observed, requires a double line of rails, one for the loaded tubs running to the shaft, and another for the empty tubs returning to the workings. The motion f;f the endless chain being continually towards the shaft upon one line and towards the workings upon the other, a much lower speed than that necessary in the tailrope system will obviously be sufficient. Usually the speed varies between 2 feet and 5 feet a second, according to the requirements of the output. The method of attaching the tub to the chain is exceedingly simple. As already stated, the pulleys around which the chain winds are fixed at a sufficient height to allow the chain in its immediate neighbourhood to clear the tops of the tubs ; but the sag brings it down in a short distance near enough to the floor to catch the edge of tubs arriving at that point. The loaded tubs are, therefore, simply run on to the line and pushed forward till caught by the chain. In some cases, friction alone is trusted to, in others the connection is made more secure by means of some arrangement upon the ends of the tubs to catch in the links of the chain. Upon the other line of rails, the chain of course leaves the empty tub at this point ; at the other end of the plane, the same action takes place in the contrary order, the loaded tub leaving the chain and the empty tub being caught by it. On leaving the chain, the loaded tub continues its course towards the point to be reached, in virtue of its acquired velocity, assisted sometimes by a slight inclination given to the tram-plates upon which they arrive. Thus the chain connects itself with and disconnects itself from the tubs at the required moment. The same artifice is adopted at curves. At such points, an inclined pulley lifts the chain from the tub, which, in virtue of its acquired velocity, continues its course round the curve till the chain again descends upon it. Though these operations take place automatically, a boy is usually stationed at these points as a precaution against the disorder that would result from the occurrence of any irregularity. This expedient of raising the chain by means of a pulley is also adopted at the intermediate stations along the line, at which it is required to run a loaded tub in or to take an empty tub out of the train in motion. The arrangements adopted at the junctions of branch lines will be illustrated hereafter. As the chain is supported upon the tubs, too great an interval must not be allowed between these ; generally, 30 yards should not be exceeded, and it will obviously be desirable not only to diminish this distance, but to distribute the tubs as equally as practicable. It will also be evident that in estimating the resistance due to friction in the tubs, account must be taken of the weight of the chain resting upon them. An important advantage of the endless-chain over the tail-rope system to be noted here is, that with a given velocity the former allows a much larger number of tubs to be conveyed over a given distance in a given time. Hence it is possible to perform the sam3 work with a much smaller expenditure of motive force. The motive force is further economized by the regular distribution of the full and the empty tubs along the chain, whereby their dead weight is neutralized. Also it is evident that upon an undulating line, the action of gravity will be compensatory, so that the work of the motor will be greatly reduced. The plane might indeed become self-acting if the station at the lower end were sufficiently below the starting points. This property of the system which makes the principal resistance to be overcome constant and to depend only upon the relative levels of the extreme points renders it particularly applicable to districts where the conditions encountered render the roads very irregular in level, since it allows a succession of rising and falling gradients to be run

378 Mining Engineering.

over without, a great expenditure of force. The same property renders the system very suitable for surface tramways which it is either impracticable or undesirable to work with locomotives or horses.

The endless-rope systems being merely modifications of the foregoing, possess but few characteristic features. By the substitution of a wire rope for the chain, some differences in the details of construction are required, and some advantages are gained which will be pointed out later. In the endless-rope system No. l,the engine, having a fly-wheel provided with a brake, is generally made to drive a pulley or sheave having several grooves to prevent the slipping of the rope, as described in a former section. The rope, after passing over this pulley and that which is conjugate with it, passes round a pulley at the head of the plane, runs throughout the whole length of this plane, and returns to the driving pulley by the engine, after having in its course passed round a large pulley fixed upon a movable framing held in position by a counter weight. The object of this latter arrangement is to keep the rope in a state of sufficient tension to prevent its slipping on the driving pulley. In this system, the tubs are dragged along in trains, at the head of which is a special tub in which the conductor rides. By means of a kind of clamp, the conductor fixes his tub to the rope, and the whole train is thereby set in motion. On approaching the station, be releases the clamp, and applies a brake to the wheels of his tub, in order to bring the train to rest at the point desired. It is evident that there may be several trains of loaded tubs and several trains of empty tubs in motion upon the lines at the same time, so that the system is capable of satisfying the requirements of a large output. It will be observed that in this system a shorter length of rope is needed than in the tail-rope system in the proportion of 2 to 3. G-enerally the endless rope is applied to a double line of rails, in which case the motion of the rope is continuous and in the same direction. But it may be used upon a single line by making the motion intermittent and to take place in contrary directions. Applied in this manner, the system partakes of the character of that of the tail rope already described. When the motion of the rope is in this way intermittent, the mode of attaching the trains of tubs is by means of a hook on a piece of chain fixed in the fore part of the first tub. This hook is dropped into rings or loops placed at intervals along the rope for that purpose. If the plane consists of a succession of rising and falling gradients, the train must be attached to the rope at both ends. A similar expedient and mode of attachment is adopted, under the same conditions, when the line is double and the motion continuous in one direction.

The endless-rope system No. 2, beyond the substitution of the rope for the chain, differs in no essential particular from the endless-chain system. The use of the rope necessitates the adoption of different means for attaching the tubs. That usually employed consists of the hook and chain described above, which is attached to the rope by giving it a turn or two round it. The operation may be performed very quickly while the rope is in motion. The tabs may be made to travel singly or in trains consisting of five or six tubs. If a succession of rising and falling gradients has to be passed over, the tub, or the train of tubs, must be attached to the rope at both ends. The rope employed in this system is of much less weight than the endless chain, an advantage of some importance ; but, on the other hand, the latter is much more durable than the former.

The foregoing descriptions treat generally of the distinctive features of each of the several systems of haulage actually in use. It now remains to describe these systems in detail, and to show their application to particular cases. It would be a difficult task to select examples for this purpose, and to deduce from them information concerning their relative merits of a sufficiently trustworthy character to be confidently acted upon in practice. Fortunately, however, the assumption of this task

Haulage.

has been rendered unnecessary by tbe labours of others whose ability and judgment claim the highest respect. A few years since, the North of England Institute of Mining Engineers appointed a commission, composed of men eminent in their profession, to examine and report upon the several systems of haulage in use in this country, with a view of obtaining definite and reliable information concerning them, and of arriving at some just estimation of their relative merits. The Report of this commission was published in the year 1868, and as it minutely describes the systems and points out clearly their merits and defects, we shall reproduce portions of it rather thaa adduce information and arguments of our own, such a course being certainly justified by the authoritative and exhaustive character of that report. The following description and remarks, therefore, are those of the members of the commission in question :

" The Tail-Rope System.--lu order to give a general idea of the extent to which the tail-rope system can be applied in leading coals underground along an engine plane with numerous curves and branches, the following description is given of the arrangement of waggon way, and the method of working the tail rope at North Hetton Colliery, which affords one of the best examples of the many applications of this system in the district. It will be seen by reference to Fig. 587 that there are two main waggon roads in this pit, lying at right angles to each other. No. 1 plane being driven east, and No. 2 north. The following are some of the particulars of the engine and waggon way :

"Engine. — Number of cylinders, two; diameter of cylinders, 12 inches; length of stroke, 24 inches ; number of drums, four ; diameter of drums, 4 feet ; circumference of rope, inches. The boilers are at surface.

" Engine Plane. — Rails, 22 lb. per yard ; gauge of way, 2 feet 4 inches ; diameter and weight of rollers, main 5 inches, 26 lb., tail inches, 32 lb. ; distance of rollers apart, 21 feet ; diameter of sheaves at curves, 10} inches ; tail sheaves, 4 feet.

" When the ratio of the piston to the spur wheel was as 1 to 2, the engine was found rather too weak for its work, and the proportion was, therefore, made as 1 to 3. It now goes at a speed varying from 150 to 250 strokes per minute, the usual speed being about 180 strokes a minute. This makes the power exerted to be about 100 h.p., and thus presents the rare example of a tail-rope engine working to the utmost of its power. One end of the shaft of each set of drums is placed on a movable carriage, by means of which they are put into gear with the driving pinion. The drums are connected to the shaft by means of clutch gear. The engine and drums are placed beneath the waggon way, and the wheels W and W which direct the course of the ropes for No. 2 plane, as well as several other fourfeet wheels upon these planes, are also placed under the way. The ropes for the No. 2 plane come to the surface of the waggon way about the point P.

Description of Planes. — No. 1 Plane.

Distance from shaft .. .. ..

Eise or fall from shaft

Time from leaving the shaft to returning

Heaviest gradient rising out-bye

Tubs in set

Speed of set

Wats.

1st North.

2nd North.

Cross-Cut. Ibt South.

2nd South.

yards.

yards.

yards.

yards.

yards.

fall

fall

fall fall

fall

10 min.

9 min.

.. Ab(

8 min. 1 1 for eac or each way 3ut 10 miles

10 min. b way.

per hour.

9 J min.

Mining Engineering.

" It wil] be seen from the above that none of the branches are of very great length, and that all the ways rise towards the shaft.

No. 2 Plane.

Ways.

1st West.

2nd West.

3rd West.

yards.

yards.

yards.

Distance from shaft ., .,

Eise or fall from shaft

rise

rise

rise

Time from leaving the shaft to returning .. „

6 min.

15 min.

17 min.

Heaviest gradient rising out-bye

1 in 15 for each way.

Tubs in set

35 for each way.

Speed of set

About 10 miles per hour.

" No. 1 plane consists of a main road, with two branches on each side ; at the end of the main road is another way, which after going in a cross-cut direction for a short distance, turns to the north. These five 'branches are all worked by two of the drums, the other two drums working No. 2 plane and its branches. In the plan which is uot drawn to scale, and which is in many places out of proportion, owing to the difficulty of showing clearly the arrangement of rails, the ropes are shown by dotted lines. In the second west way and the cross-cut way there are two stations ; a description of the arrangement of which is given hereafter. The four curves leading from the main way to the branches have each a radius of about 22 yards; the radius of the curve in the first south way is 4 chains, and of that in the cross-cut way about 5 chains.

" No. 2 plane has one main road and three branches, two to the west and the other in a cross-cut direction. The curves to the branches are about 3 chains radius, and the curve upon the main road about 4 chains.

" At the far end of each of the branches there is a siding, one way for the full and the other for the empty tubs. At the in-bye end of the first west way there are three putting stations, from which the tubs are led in short sets by ponies to the siding at the end of the engine plane. The full way of the shaft siding is raised several feet to form a ' kep,' or incline ; and when the set of full tubs has been drawn on to the top of the kep, the tubs are let down to the shaft as they are required.

" Arrangement of Ropes. — In the working of this and all other tail-rope planes, two ropes are necessary, which are called main and tail ropes, the former being used for drawing the set of full tubs out-bye, and the latter for taking the empty set in-bye. When the main rope is bringing the full set out-bye, the tail-rope drum runs loosely upon the shaft, and by applying the brake the tail rope is made to run steadily oS the drum ; when the tail rope is taking the empty set in-bye, the main-rope drum is put out of gear, and the main rope is drawn in-bye behind the set. It will be seen on referring to Fig. 587 that the ropes for No. 1 plane have a direct lead from the drums, whilst those for the No. 2 plane are taken round pulleys at a right angle not far from the engine. On No. 1 plane, the ropes connected to the engine are those of the cross-cut way, and the set is supposed to have just arrived at the shaft ; thus the main rope is nearly all wound upon the drum. At the points A and B there are shackle joints, of the description shown in Fig. 588, on both the main and tail ropes. This shackle is secured by the pin a. When the rope ends to which the set is attached are at the shaft, these joints are always at the points A and B, no matter from which way the last set came.

Haulage. 381

Most of the sheaves used in taking the ropes round the curves are fixed horizontally in walling built for the purpose, as shown in Pig. 589. At and C both the ropes are taken round the curves by small sheaves ; but at most of the curves only one rope goes round the curve, the tail rope passing round a 4- feet sheave ; this arrangement is much to be preferred. Both main and tail ropes are 2 J inches in circumference. The large sheaves at the curves, and the tail sheaves at the in-bye end of each of the branches, are 4 feet in diameter ; these wheels arfe placed under the way and the rails are laid over them. Where the ropes are shown to cross the waggon way they are arranged to pass under the road. The total length of main rope on the plane is 2520 yards, and of tail rope 9636 yards; and there are altogether 1390 small sheaves, and fourteen 4-feet sheaves upon the planes.

" Method of Working the Plane. — No. 1 Plane. — On referring to the plan it will be seen that the ropes connected to the engine are those of the cross-cut way, and that the ends of all the other branch ropes are lying at the branch ends. Supposing that the next empty set has to go into the second south way, whilst the rope ends at the shaft are being disconnected from the full set and attached to the empty set, the boy attending the switches at B is disconnecting the shackles S S, and connecting them to T T. This is done in about two minutes, and is generally finished before the set at the shaft is ready to come away. The boy then opens the switches for the second south way, and everything is ready for the set going in. The set of empty tubs is taken into the branch, and the full set returns to the shaft before the ropes are altered again. Should the first north way next be ready, the ends E E are replaced by P P, the switches are put right, and the empty set goes in and the full set comes out. If the cross-cut way be next ready, it will be seen that, to put the ropes right for this way, four rope ends will have to be connected, two at the station A and two at B.

" No. 2 Plane. — It will be seen that the ropes in this plane connected to the engine are those of the third west way, and here also the set is supposed to be at the shaft. All the branches on the plane No. 1 are to the dip ; on the contrary, all the branches from the main road, on No. 2 plane, are to the rise from the shaft. The branch ropes on the latter plane are connected in the same way as on No. 1 plane, and here also it is necessary to connect four rope ends when the third west way has to be worked, if the second and then the first west ways have been worked before it. In the first west way, on No. 2 plane, there is an adaptation of the tail rope which is worthy of notice. The gradient of this way is found heavy enough to cause the outcoming full tubs to pull the tail rope after them ; in taking the empty set in-bye, the main rope is knocked off at the point R, and the set is pulled in by the tail rope ; the full set is afterwards let down the incline by the single tail rope to R, at which point the main rope, which is necessary to pull the set on to the kep, is attached. The drum man sometimes brings the set out of this way by the brake whilst the engine is working another way_ The gradient on the second west way is not heavy enough to allow this method to be adopted.

" On the No. 1 plane there are two stations by the side of the main way, to which sets are taken several times during the day. One of these stations, Fig. 590, is in the cross-cut way, and the other. Pig. 591, is in the second south way. When a set is intended for the station in the latter way it is taken to II, and there the ropes are knocked ofi"; the full set stands at mm; and in order to get the ropes to this point, a piece of rope of the length of the set is attached to the two ends, which are then pulled by the engine opposite to the ends of the full set. Thus, eight connections and disconnections are necessary for each set led from this station. The arrangement of the station on tne cross-cut way, which was made some time after the station just described, is much better. Here the 'vay from x to z is made to dip gently in-bye, and when the empty set is brought in-bye both ropes

Mining Engineeeing.

are knocked off at x x, and the set runs forward by itself to ; the ropes are then connected to the full set standing at y y. The ropes are connected to the set by means of the link shown in Fig. 592, the fastening of which is secured by the cotter c. Fig. 593 represents another kind of knock-off link used with the tail-rope system. When it is equired to disconnect the rope from the set the cotter at d is removed, and the link e is pushed off by the foot.

" Duration of Ropes. — It is not known how long the ropes last, as a rope is first a main and then a tail rope, and is afterwards used as a tail rope on a lighter plane. The general duration of the rope is supposed to be from two to three years.

" The Endless-Chain Si/stem. — The following are the chief peculiarities in the application of the endless-chain system:

" 1. A double line of tramway is always requisite, one line being used for the full and the other for the empty tubs.

" 2. The chain which moves the tubs rests upon them, and is driven by a pulley at the higher end of the ginney road, there being much more friction upon this wheel than upon that at the lower end of the road, owing to the weight of the fall and empty tubs upon the incline.

" 3. The speed at which the endless chain is worked varies from 2 to 4 miles an hour.

" 4. The tubs are always put on singly, and at distances apart varying from 10 to 40 yards.

" 5. The tubs are attached to the chain by means of a ' fork,' which forms one piece with the strap encircling the upper part of the tub. The end of the tub on which the fork is placed is made to go last in starting up hill, but in going down hill it is placed first.

" 6. In working branch ways, motion is transmitted to the chain in three different ways : by shafting and bevel or mitre gearing ; by a short endless chain ; or by a continuous application of the same chain.

" 7. Unlike the tail-rope and No. 1 endless-rope systems, little care is needed in laying the waggon way, since, owing to the low speed at which the tubs travel, slight irregularities are not felt.

" 8. This system should only be worked in perfectly straight lines, that is, without any gradual curve in the road ; angles being worked by disconnecting and connecting the tubs again, and for this the attention of a man or boy is required. When a self-acting curve is employed, its safe and regular working cannot be depended upon, and it is found necessary to keep a man near to it, who may, however, be employed at other work,

" The Hapton Valley Colliery presents several examples of the various methods of applying the endless-chain system. Here two revolving screens are placed close to the terminus of the ginney road at A, Fig. 549, and the full tubs, when disconnected from the chain, run, with only a slight guidance, to the screens. In the formation of the termini of the ginneys, one rule is always observed, viz. on the ' coming off ' side the way is made to rise a few yards from the terminus, in order to obtain such a fall as will enable the tub on leaving the chain to acquire an impetus sufficient to take it off the ginney road, and on the 'going on ' side the way is made to dip from the terminus, so that the tub may run to the chain without the aid of manual labour. The methods adopted for disconnecting and attaching the full and the empty tubs at either end of a ginney road are as follows : To attach the empty tub a vertical link of the chain is placed in the fork at the end of the tub ; if left alone the tub would generally attach itself, but it is usual for the ' ginney tenter,' who puts the tub into the ginney road, to connect it to the chain ; this can be done when it is at a distance of five or

Haulage, 383

six yards from the 'ginney tenter,' and is the work of a second. The disconnection of the fuU tub IS effected by the declination of the way referred to, and by the chain being raised by a small pulley, which also guides the chain to its proper position on the main sheave. The chain also at this point passes between iron rods, which, in the event of the fork of the tub being affixed in any way to the chain, push the tub off, and thus prevent it reaching the pulleys.

"Description of Engine and Plane. — Engine. — Vertical, with two cylinders 12| inches diameter ; length of stroke, 24 inches; diameter of driving pinion, 30 inches; diameter of followers, 65 inches; diameter of fly-wheel, 84 inches ; distance between centres of cylinders, 70 inches,

"Chain, — Length, 6414 yards; diameter of iron, inch; weight per yard, 131b.; general duration, twelve years.

" Sheaves. — Two of 48 inches diameter and 848 lb, weight ; two of 36 inches and 560 lb, ; and four of 36 inches and 448 lb.

" Rails. — Weight per yard, 28 lb. ; number of lines, 4 ; gauge of way, 22 inches.

" Tubs. — Average weight empty, 246 lb. ; ditto of coal contained, 360 lb. ; height above rails, 27 inches; diameter of wheels, 1 Of inches ; total number on ginney roads and in the pit, 980; number required for working ginney roads, 518,

" Work Done. — 370 tons per day of hours.

" The greater part of the main ginney road is on the surface ; the underground part is arched to the station, and is 4 feet 6 inches high. Two ginney lines underground are worked by the main ginney, motion being transmitted by shafting and mitre gearing, working iinderneath the flat sheets at the station. Fig. 595. The main road rises from the engine at a gradient of 1 in 20 for 337 yards, and then falls towards the underground station at 1 in 17 for a distance of 286 yards. No. 1 ginney is 1524 yards long, with a rise of 1 in 381 out-bye; and No. 2 ginney is 1060 yards long, with an average gradient of 1 in 48 dipping out-bye. The roads are made 6 feet 2 inches wide, the average height of the roof above the surface of rails being 2 feet 6 inches. A separate travelling road is made for the men, about ten yards from the ginney road, which, with the travelling road, forms a double intake for the air.

" Method of Working the Ginney Eoads. — At each end of every ginney road a man or a boy according to the quantity of coals coming out, attends both to the full and the empty sets. He takes care that every tub is attached to the chain, that a regular distance is kept between the tubs, and that the coming-off tub is turned, on becoming detached from the chain, in the right direction. He also has charge of the rapper, with which he can signal to the brakesman when necessary. The tubs on the main ginney road are ten yards apart ; on No. 1 ginney twelve yards apart ; and on No. 2 fourteen yards apart ; these two latter distances being just suitable for their own general work ; and for feeding the main ginney with tubs, ten yards apart. The tubs are kept the regular distance apart by means of a catch, which the ingoing empty tub strikes when it reaches a certain fixed distance from the point of starting ; this catch raps to the station and another tub is then attached. The station is laid with flat sheets. When the empty tubs come down the main ginney some pass from a to h, Fig. 594, and the rest are taken by the boy attending No. 1 ginney. The full tubs from No, 2 ginney are brought into the station by a curved rail with a slight fall. The man attending the main ginney just puts on the tubs as they come to hand from either branch, and when no coals are out he pulls round the incoming empty tub, and sends it back on to the full side ; this is not of frequent occurrence, since, when the coals continue to come out slowly, the speed of the engine is

384 Mining Engineeeing.

reduced. The driving pulley for the chain is worked on the third motion, and is so arranged that when the engine is going at from 100 to 130 strokes per minute, the tubs upon the ginnej roads are moving at a speed of two to four miles an hour. In order to gain sufficient friction on the driving pulleys, to prevent the chain from slipping, it is passed two and a half times round the driving wheel at one end of the ginney road, and half a turn round the wheel at the other end. These driving wheels on the main ginney road are four feet in diameter, whilst on the other roads they are only three feet. Levers are attached to the driving wheels of the two branches by which they can be put out of gear, and rapper wires are laid to the in-bye end of each of the ginneys. When there is slackness of coals at either of the ginneys, they can have them put out of gear by rapping to the station,

" The station at the in-bye end of the main ginney road at Hapton Valley, see Figs. 594 and 595, affords a very good example of the method of working branch roads by the endless-chain system. In these figures the method of transmitting motion will be easily seen. There are two self-acting endless-chain roads at work at this colliery : one on No. 1 ginney, and the other on No. 2 ginney. The chief objection to these self-acting roads is that a boy is constantly required to attend to the brake, since, unless the tubs are attached to the train with perfect regularity, they are apt at one time to remain stationary, and at another to run amain. These self-acting planes, when worked on a heavy gradient, are frequently made to work a level plane at the upper end.

" The Endless-Rope System, No. 1. — The following are the chief characteristics of the No. 1 endless-rope system, which is in operation at the Shireoaks Colliery :

1. The rope, as the name implies, is endless.

"2. To give motion to the rope a single wheel is used, and friction for driving the rope is supplied either by clip pulleys or by taking the rope over several wheels.

'"3. As only one driving wheel is used, the rope has to be kept constantly tight ; this is effected by passing it round a pulley fixed upon a tram, to which a hanging weight is attached,

" 4. Either one or two lines of rails are used. When a single line is adopted, the rope works backward and forward, only one part of it being on the waggon way, and the other running by the side of the way. When two lines are used, the rope moves always in one direction, and the full tubs come out on one line, the empties go in on the other.

"5. The set of tubs is connected to the rope either by means of a clamp, as shown in Figs. 596 and 597, or by sockets in the rope, to which the set is attached by a short chain.

" 6. The working of curves and branches by this system has not been much attempted ; but where curves have been tried they have been found to work very well.

" Description of Engine and Plane. — Engine. — Number of cylinders, 2 ; diameter of cylinders, 12 inches; length of stroke, 24 inches ; diameter of driving pinion, friction gear, 32 inches; diameter of followers, 48 inches ; diameter of clip wheel, 48 inches ; distance between centres of cylinders, 29 inches ; no fly-wheel.

"Rope. — Length, 1590 yards; circumference, inches; weight, 25 cwt. 2 qrs. 21 lb.; general duration, eighteen months.

"Sheaves, wood. — Number, 106; weight per sheave, 141b.; diameter, 5 inches x 16 inches; distance apart, 45 feet.

" Rails. — Weight per yard, 18 lb. ; number of lines, 4 ; gauge of way, 24 inches.

"Tubs, — Average weight, empty, 3361b.; ditto, of coal contained, 6611b.; height above rails,

Haulage, 385

28 inches; diameter of wheels, inches; total number in pit, 450; number required to work endless rope, 256 ; number in a set, 31.

- " Work done.— 320 tons per day of 11 hours.

" The engine plane is laid with a double way ; the empty sets going in on one side, and the full sets coming out on the other. It was originally intended to have sets coming out and going in at the same time, but the limited quantity of coals now being drawn renders this unnecessary.

" The plane, worked by the endless rope, is 750 yards long, with an average rise towards the shaft of 1 in 48, the heaviest gradient being 1 in 29. The same engine also draws coals along a single-rope plane 737 yards long, the average rise of which towards the shaft is 1 in 15. One of Fowler's clip pulleys, 4 feet in diameter, is used to give motion to the endless rope. This wheel is in a horizontal position, Fig. 598, and is connected by mitre gearing to the friction gearing by which it is worked. The pinion friction-wheel is 2 feet 8 inches in diameter, and drives two spur wheels of 4 feet diameter, one for the clip pulley, and the other for the single-rope drum. The friction gearing is found to answer exceedingly well, and is very convenient for putting out of gear, a movement of inch being suflScient to disconnect the wheels ; this is effected by the shafts of the spur wheels being placed in eccentrics. As it was found desirable, in the adoption of the clip wheel, to cause the rope to pass round as large a circumference of the wheel as possible, in order to get as much of the grasping effect of the clips as practicable, the ropes at a short distance from the clip wheel are crossed, as shown at a, Fig. 598. In working the endless rope by the clip pulley, it is necessary to keep it very tight, as otherwise it is apt to slip out of the clips ; this is effected by having the wheel in-bye placed on a carriage moving on wheels, and tightened by a chain passing down a small staple, Fig. 599, to which a weight of about 15 cwt. is suspended. The weight descends as the rope stretches, and thus keeps the rope at the same tension. Wrought-iron sounding bars, I inch diameter, are used for signalling to the engineman ; the run-rider carries a piece of iron with which he strikes the sounding bar ; the signal is heard very distinctly when the engine is standing, but when in motion the brakesman has to stand near the termination of the bar.

" Method of Working the Plane. — The rope in passing from the clip pulley on the out-bye end, and to the tail wheel at the in-bye end, goes under the roUey-way for about 80 yards, as shown by the shaded portions in Fig. 598 ; the tubs can thus pass over the rope in coming from the shaft. In taking the set in-bye, the tubs are coupled together at the bank-head, and the run-rider, who rides in the first tub at the front end of the set, first hooks the chain aflSxed to the clamp. Fig. 596, on to the iron loop at the end of the centre bar of the tub, and then fixes the clamp upon the rope, which is always upon the middle of the way ; this clamp is closed by a handle lever passing over the curved end, and, by the insertion of the pin p, is kept firmly fixed without the pressure of the hand. The clamp has such a strong hold upon the rope, that in a case of the set being stopped by some obstruction, the rope has been found to break rather than slip through the clamp. The clamp having been fixed to the rope, the run-rider strikes the sounding bar, and the rope moves forward, the man pressing upon the handles of the clamp to keep it perpendicular, and the tubs being pulled forward by the chain on the clamp. The set at the start is about 45 yards from the engine, and is on a falling gradient of 1 in 520; the next or middle gradient is 1 in 47. As the set is found to overrun the clamps in going in-bye at this latter gradient, six ' spraggs ' are placed in the wheels of the tubs at the end of the set to prevent the tubs getting together and becoming uncoupled. At a distance of 364 yards from the engine, and about the middle of the 1 in 47 gradient, the clamp is taken off the

3 D

386 Mining Engineeeing.

rope whilst in motion, and the set runs forward by itself. When the clamp is disconnected, the runrider raps to the engine, and the rope is stopped, the engine then being free to work the single-rope way.

" There are two stations from which coal is being drawn at present ; the first being 640 and the second about 795 yards from the engine. When the ' gang' or ' set ' has to go to ' No. 15,' or the first station, the points are placed for this, and the set, then disconnected from the rope, runs round the curve into the station ; the rope at this curve passes under the rolley-way, so that with this arrangement the clamps could not pass this point. When the set is intended for the far-off station, or 'No. 13,' it runs down by itself from the 'knock-off' point, the 'spraggs' being taken out, when necessary, by a boy who rides with the set for the purpose. In coming out-bye, the clamp is also placed at the front end of the full set, which is pulled out to within 140 yards of the engine, when the clamp is removed, and the tubs run forward to a point from which they are taken to the shaft by horses. When bringing the full tubs out, the strain of the full set upon the clamp chain raises the rope a little and prevents the clamp from striking the rollers ; but in going in-bye, where there is much less strain, the clamp, in passing over the rollers, touches them slightly. The engine cannot pull coals out from the endless-rope way and the single-rope way together ; and if this were possible, it would be hardly worth while, since it never goes for more than three and a half minutes at a time in working the endless rope.

" The Endless-Rope System, No. 2. — -The following are the chief peculiarities in the working of the No. 2 endless-rope system, as applied at the Bridge Pit, near Wigan ; the principle of which is very similar to that of the endless-chain system.

" 1. A double line of rails is used.

" 2. The rope rests upon the tubs, which are attached to the rope either singly or in sets of tubs varying in number from two to twelve.

"3. The connection between the tubs and the rope is effected by a short chain, which is secured to the rope in a way hereafter described.

" 4. As with the endless chain, the tubs are placed at a ' regular distance apart, and the rope is driven at a slow speed.

" 5. Motion is given to the rope by large driving pulley's, and friction is obtained by taking the rope several times round the driving pulley.

" 6. Curves can be worked by this system ; and branches also could very easily be arranged for.

" Description of Engine and Plane. — Engine. — Number of cylinders, 2 ; diameter of cylinders, 20 inches ; length of stroke, 42 inches ; diameter of driving pinion, 46 inches ; diameter of follower, 89 inches; diameter of fly-wheel, 123 inches; diameter of driving wheel, 168 inches ; distance between centres of cylinders, 94| inches.

"Eope. — Length — main, 787 yards, tail, 4730 yards; circumference — main, 3*9 inches, tail, 3-14 inches; weight — main, 48 cwt. 22 lb., tail, 175 cwt. 2 qr. 26 lb.; general duration — main, 24 months, tail, 84 months.

" Sheaves. — Number between main pulley at engine and tightening pulleys — on main rope, 34, and on tail rope, 35; diameter, 14 inches.

"Return Sheaves. — Weight, 672 lb,; diameter, 60 inches.

"Rails. — Weight per yard, 18 lb.; number of lines, 4; guge of way, 22| inches.

"Tubs. — Average weight, empty, 224 lb.; ditto of coal contained 616 lb. ; height above rails, -'29 inches ; diameter of wheels, 8 inches ; total number in pit, 450 ; number required to work endlessrope roads, 350.

Haulage. 387

" Work done. — 400 tons per day of 11| hours.

" These planes are laid with round-top bridge rails, the general size of the waggon way being 10 feet by 4 feet, it having been originally made this size. The avc"age gradient of all the ways together is a rise towards the shaft of 1 in 62, the chain brow-way being a rise to the shaft of 1 in 54, the slant way a fall towards the shaft of 1 in 47, and the main road a rise to the shaft of 1 in 18, part of it at the in-bye end rising towards the shaft at a gradient of 1 in 5' 5. With the exception of the curve on the chain brow-way, all the planes at this colliery are straight,

" Arrangement of Ropes. — The main driving rope passes two and a half times round the driving pulley at the engine, and the outgoing rope goes past the shaft to the tightening pulley A, Fig. 600. This pulley is placed on a strong tram, and the rope is tightened by means of a screw attached to the tram, the other end being secured to a piece of fixed timber. There are two sets of pulleys near the shaft ; one, B, for working the main way and the slant way connected with it ; and the other, 0, for working the chain brow-way. The driving rope, in coming from the tightening pulley, passes once round the pulley C and twice round B, there being a much greater load on the plane worked by the pulley at B. These two pulleys and the tightening pulley are 9 feet in diameter. The tightening pulleys are usually 5 feet in diameter ; but it was expected, when this was erected, that it would have to work another engine plane. The smaller sheave on the shaft B is 6 feet in diameter ; and that on C 5 feet. They are put in and out of gear by an apparatus very similar to that used in the working of the endless-chain system. The rope working the main road is of steel, 1 inch in diameter, and that on the chain brow-way the same diameter of iron. The mainroad rope passes round a tightening pulley D, at about 690 yards from B, and it then passes twice round the pulley E. There are two pulleys on this shaft, that for the driving rope being 6 feet diameter, and that working the slant way 5 feet diameter. The slant-way rope, 1-inch iron, is tightened at the out-bye end by the apparatus at F. The chain brow-way is not straight like the main and slant ways, but has a curve at H, round which the rope passes by means of two 4 feet 6 inch pulleys placed horizontally. This curve is at an angle of about 118°, and the rails are laid at a radius of only 5 yards. The rope passes round the tail sheave J, which, as is usual in working a single way by this system, also acts as a tightening pulley ; the tram on which the pulley is placed being fixed as before described. The ropes have just half a turn round the tightening pulleys, and two and a half turns round the 6-feet and 5-feet driving pulleys at C and B.

" Method of Working the Plane. — The tubs on the main road are taken in and out-bye in gangs of two at a time, twenty yards apart, the heavy gradient at the in-bye end preventing a greater number than this from being together. On the chain brow-way the tubs are brought out and taken in one at a time, twenty yards apart ; and on the slant way, where most of the coals are coming out, from two to twelve tubs at a time are brought out, no regular distance being observed. The tubs are connected to the rope by means of chains. If the gradient be regular either way, only one chain is put on at the end of the tub going to the rise ; at the Bridge Pit, however, owing to the way for some distance from the shaft being nearly level, it is necessary to attach chains at both ends. At the point H, Fig. 600, on the chain brow-way, the gradient becomes a heavier dip in-bye, and a boy stationed here takes the fore chain off the ingoing empty tub, and lays it on the top of the full tub, which comes out with a chain attached to the fore end only. On the slant way only one chain is put on to the ingoing empty tubs, but an irregularity in the way makes a chain at each end of the

full tubs requisite.

3 D 2

388 Mining Engineeeing.

" The chains by which the tubs are attached to the rope are of |-inch iron, 6 feet long, with a hook at each end. They are connected to the tub in the following manner : The fore end of the tub is first connected to the rope ; this is done by attaching one end of the chain to the second link of the coupling chain of the tub, and throwing the other end over the rope, which is constantly in motion. The chain is then passed twice over the rope, the hand being introduced under the rope to receive the coils. Fig. 601, in order to let the chain slide loosely on the moving rope till the hook is secured. When the right number of coils of chain, two in this case, has been passed over the ropes, the hand is withdrawn, the point a is brought over the hook, and the chain is pulled tight ; it is not until the chain is securely fixed that the weight of the tub is allowed to come upon the chain. When the full weight of the tub is upon the chain the coils get quite close together, and form a very compact and secure fastening. An expert 'hooker-on' does not need to put his hand between the coils, but passes the chain round the rope, and secures it before the rope has time to move on. The chain .it the back end of the tub is attached in a similar manner, but with three coils instead of two ; this is necessary, owing to the heavy weight of the tub upon the chain for a short distance in going in-bye. When two or more tubs are put on the planes together, chains are fixed on to the fore and back ends of the ' gang,' or at one end only, as the case may be. The chain is disconnected from the outcoming tubs at the back end by unhooking the chain from the tub ; it is then easily loosened from the rope. At the fore end the chain is tight, and the foot is placed upon it, pressing it down, and making it loose enough to admit of disconnection. Thus there is more labour required in the disconnecting than in the attaching. This description has reference to the taking off of the full tubs at the end of the main road, and here there is a rise towai ils the shaft. At some other places the terminus of the full way is made to dip slightly, and the chains are removed just when the tub, passing over the brow, loosens the chain at the fore end. On the other hand, the labour required for attaching the empty tubs is less than at other places ; here the empty way is made to rise slightly, and the fore chain is put on first, and one boy is able to manage both ; where the empty way at the start falls in-bye, both chains have to be put on together, thus requiring two boys. At the top of the main roadway, a boy stands at about twenty yards from the place to which the full tubs come, and removes the back chain, leaving it hanging on the rope by the hook ; it is taken off by the man who disconnects the chain at the fore end, and, together with the other chain, is thrown over by him to the place where the empties are hooked on. The usual time for attaching both chains to the empty tub is about twelve seconds, the minimum time being six seconds, and the time for disconnecting is rather more. Sometimes a stoppage is caused by the fastening of the chain being difficult to disentangle, and the man disconnecting has then to rap to stop the engine, to prevent the tub from reaching the pulley. The chain is very seldom known to slip on the rope ; when it does the damage done is often rather heavy, since, should the fore chain slip, the tub going on to the back chain is generally upset, or, in the absence of the back chain, it may rest on the plane till the next tub comes up to it, the chain of which not only often knocks the tub off" the way, but is sometimes broken itself, and as it is difficult to tell at the engine when such an occurrence takes place, there is much damage done before the engine is stopped. The chief accidents to tubs usually occur at the heavy gradient on the main way at this pit, for should a weak link in the connecting chain break whilst the tub is on this gradient, the tub getting loose generally breaks several other chains and tubs below it. The slow speed at which the tubs go, being 1 35 miles an hour on the main road, and 1 126 miles an hour on the other ways, is necessary to prevent accidents to the tubs. The rope rests upon the tubs, and unless the way is laid perfectly

Haulage. 389

straight it is a slight distance from the centre of the tub ; a small angle at the joint of the rails is sufScient to cause this deviation, and should the rope catch any irregularity on the top of the tub, it will sometimes overturn it; to avoid this much attention is paid to keeping the tubs in good repair.

"In the vsrorking of the endless rope at this colliery, the apparatus for putting the driving wheels in and out of gear is found to be indispensable ; such an apparatus is at both the driving wheels B and 0, Fig. 600, and at E, at the bottom of the main road. Thus the chain brow, the main road, and the main road with the slant way, can each be worked separately. The workings at the in-bye end of the main road serve to keep t' main way supplied for a short time, when it is necessary to put the slant way out of gear. The lower driving-wheel, at the points B, C, and E, is fixed, and the upper, loose on the shaft, being put in gear by a catch-box worked by a lever ; the pulleys can be put into gear whilst the driving wheel is in motion, but the engine is usually stopped in taking out of gear, as the edge of the catch-box is liable to get chipped by striking against the fixed part of the boss.

" There are two curves on the engine plane at this colliery, one at the bottom of the main road, worked by disconnecting and reconnecting the tubs ; and the other which self-acts on the chain browway. At the former, which turns round an angle of 72°, the motion is transmitted from one pulley to another on the same shaft, as shown at E, Fig. 600, and to a larger scale in Fig. 602. The road is laid round the curve at such an inclination that the full and the empty tubs, when disconnected, run by themselves to the place where they are again attached to the rope. There are five hands required here : four boys and one man. This curve might probably be made to self-act, like the curve at the chain brow-way by means of four or more pulleys ; but when it was originally arranged, it was intended to draw a large quantity of coals from other districts besides the slant way. The curve on the chain brow-way is, as before described, of about 5 yards radius, and at an angle of 118°. The ropes are taken round by two 4 feet 6 inch pulleys, H, Figs. 600 and 603, each inclining slightly towards the ' coming on ' side. The way for the full tubs is laid nearly level, and for the empty a slight rise from the shaft, this arrangement, after many experiments, having been found to act most efficiently. The pulley wheels are made with a large flange on the lower side, to prevent the rope slipping off, and to enable the knot of the chain, connecting the tub to the rope, to pass easily into the trod of the wheels. The use of four pulleys instead of two at a curve of this description would enlarge the radius of the curve and cause a smaller part of the surface of each wheel to be touched by the rope. Slow speed appears to be very necessary for working a curve by this system, for the jerk which occurs when the tub, in passing round a curve, starts away after being stationary for a moment, would probably not fail to cause an accident if taken round at a much higher speed. A boy, placed near this curve for the purpose of taking off the chains at the fore end of the ingoing tubs, also attends to the curve when necessary. Near the in-bye end of the slant way there is a ' flat ' at which the tubs are taken off and put on, whilst the tubs passing to and from the terminus are in motion. The place is laid with flat sheets for a few yards, nearly on a level witli the rails. The empty tubs are disconnected and brought under the rope between two outcoming sets of full tubs. Points are laid on to the full way, and a full set or gang of two or more full tubs is put on, when the slackness of the rope indicates a long distance between two full sets.

" The tightening pulleys, as used in this system of conveying small sets of one or more tubs by the endless rope, are fixed, and not similar to those used for the No, 1 endless rope, where the

Mining Engineeking.

varying strain upon the rope, owing to the set of tubs being at different parts of the plane, makes it desirable to have the tightening apparatus movable. The pulley, Fig. 604, is fixed on a strong timber frame, to which a screw is attached. The screw is secured by a chain to a balk placed upright, as shown. The waggon-way men, or ' pushers on,' regulate these screws according to the state of tension in which they find the rope. The method of splicing the ropes, to make them endless, is the same as that usually adopted. The length of the splicing depends upon the size of the driving wheel, and the number of times made round it by the rope ; thus the main-way rope is spliced for 18 yards, this being rather more than two and a half times round the driving wheel.

" The engine only having been at work about three years, the duration of the ropes can only be approximately obtained. It is found that the main driving rope is soonest worn, it being finished in about two years. The other ropes are worn in two ways — first, by the friction of the coils of ropes upon the pulleys ; and second, by the moving of the rope upon the tubs. Judging from their present appearance, they are estimated to last seven years.

" Comparative Merits of the Several Systems. — As the preceding summary is chiefly of a descriptive character, the following remarks are added in order to show more fully the relative merits of the several systems. In the adoption of a system of underground haulage, the following are the chief considerations to be kept in view : I. First cost of driving drifts for waggon way ; II. First cost of engine, boilers, and waggon- way plant ; III. Cost of labour required for conveying a given quantity of coal a given distance ; and IV. Greneral cost of maintenance, divisible into : 1, ropes, or chains ; 2, maintenance of plant ; and 3, horse-power required.

" To illustrate the remarks to be made on each of these heads, the following Table is given, which shows average values obtained from the numerous cases reported on :

Average

Cost per Ton per Mile.

First Cost.

Coals

Average

Gradient

Horse-

Cost of

First

(S*f'q°!fp-

System.

led per

Distance

Else for

Power

Labour

Eopes

Main-

Cost of

Day.

led.

full

Exerted.

per Day.

or

taining

Coals.

Labour.

Total.

Waggon Engines lt'i'L"!

Tubs.

Chains.

Plant.

Way Plant.

tons.

yards.

liu

£ s. d.

d.

d.

d.

d.

d.

£

£

£

Tail-rope

(15 p. 0.) (24 p. 0.) (30 p. c.) (31 p. c.)

Endless-cliain

-083 1 -468 1 -256 -572 (6 p. 0.) (34 p. 0.) (19 p, c.) (41 p. c.)

No. 1 Endless-rope

-263 1 -541 1 -237 11-020

;(13 p. c.) (26 p. c.) (12 p. c.) (49 p. c.)'

No. 2 Endless-rope

-252 -726 1 -323 1 1-692 '2-993

(9 p. 0.) (24 p. c.) (11 p. c.) (56 p. c.)

" I. In the working of the tail-rope and endless-rope systems, it is customary tomake the waggon way the travelling road for men and horses, and to effect this, the ways have usually a width of 9 to 12 feet, by 6 to 7 feet in height. In the working of the tail-rope and No. 1 endless-rope systems, the quick speed at which the tubs run makes it desirable to have regular gradients at not too great an inclination, and to attain this object, considerable expense is incurred in driving stone drifts through faults, in taking stone from the top and bottom of the road, and in giving constant attention to the condition of the waggon way. With the two other systems, where the ropes do not touch the ground, and where a slow speed is adopted, no such expense is necessary, since heavy gradients are

Haulage. 391

worked witli ease, and slight irregularities in the way cause no inconvenience. The method in operation in some collieries, which consists in making the tram-roads at no greater cost than an ordinary coal place, and in having a separate travelling road, which forms, with the tramway, a double intake for the air, must be recommended both for economy and safety. In this case, the waggon ways may be only from 2 feet 9 inches to 3 feet 3 inches in height, and as a tub seldom gets off the way, little attention to the road, which is accessible from the travelling road by numerous holings, is required. With all the other systems the greater frequency of accidents to tubs makes it necessary to have the waggon way higher.

" II. It will be seen that as regards the cost per mile of waggon-way plant, the cost of endlesschain system is highest, owing to the use of the chain and of a double way, and that the tail-rope is less than the No. I endless-rope system, owing to the former being worked by a single way. Taking this endless-rope system as worked with a single way, which is its most economical adaptation, the cost per mile of tail-rope plant will be the greater, since three miles of rope are necessary for the latter as compared with two miles for the former. With a single rope, the cost per mile of the No. 1 endless-rope way, as adopted at Shireoaks, would be only about 520. The cost of rollers on the waggon way for the tail-rope and No. 1 endless-rope systems is an expense not borne by the other systems. The heavy cost per mile of the No. 2 endless-rope system is chiefly due to the large size of rope used.

"As regards the cost of machinery, the average amount of 1105. for the engine drums, and boilers required for the tail-rope system, contrasts forcibly with 276. for the endless-chain, this being due partly to the difference of power required to be exerted, and partly to a single driving wheel supplying the place of the drums used for the tail rope ; this item of economy applies also to the two endless-rope systems. The cost for the No. 1 endless-rope is very low, for reasons hereafter explained ; whilst the high cost for the No. 2 endless-rope system is chiefly due to a larger engine being employed than is at present necessary. On the question of primary cost of engines, it may be stated that the high-pressure engines, known as Fowler's engines, are found very economical, both on account of their compactness and small first cost, and of the small expense of maintenance,, fuel, and labour required.

" III. It will be seen that the cost of labour varies from 3 2 per cent, of the total cost with the tailrope system, to 57 per cent, with the No. 2 endless-rope system. These proportions indicate the high cost in the former and the low cost in the latter, of the other items of cost. Constituting as it does on an average nearly one-half of the total working expenditure, the cost of labour is one of the chief questions in the consideration of the comparative merits of the different systems of haulage. It should be remarked generally as to the comparative cost of the tail-rope with the other systems, that the tabular summary does not present a fair comparison, since the quantities of coals led, and the distances traversed are much greater, in the instances given, with the tail-rope than with the other systems ; and this is partly the cause of the high cost of the labour charge for the endless-chain, which otherwise would show a more favourable contrast with the tail-rope and other systems. The heavy cost of labour in the working of the No. 1 endless-rope system, which also exhibits the economy of the other charges, may be said to be partly due to the peculiar condition of the Shireoaks waggon way. The cost of labour by this system, as hitherto developed, is actually less than by the tail-rope ; and this is due, firstly, to the labour of attaching the ends of the rope to the set of tuDS being much less, since with the endless rope the two points of connection are always relatively

392 Mining Engineeeing.

in the same position ; and, secondly, to tte extra labour consequent on the difference in the amount of power expended. The high cost of the No. 2 endless-rope labour charge is simply an evil of the system, being due to the laborious method of connecting the tubs to the rope, and this suggests the advisability of applying this system only where the adoption of any of the other systems is not convenient.

" Regarding the labour required to work the tail-rope, the cost, as a rule, will be found to exceed that of the other systems from the following causes, namely : 1. The amount of power expended causing more labour to be necessary. 2. A boy being required to attend to the drums. 3. The employment of a run-rider, and of hands to form the tubs into sets.

" In regard to the labour required for connecting the tubs together, this also applies to the No. 1 endless-rope. With the endless chain, it is altogether avoided ; but whilst with the endless chain only one tub can be attached to the chain at once, with the No. 2 endless-rope system the tubs can, with one connection to the rope, be attached in sets of one to twelve tubs. This would be an advantage where the tubs are taken in sets from the end of the engine plane to the putting stations ; but, as in the laying out of an engine plane, it is desirable to avoid all horse driving — that is, to arrange for the coals to be *put' from the end of the plane, and this is accomplished at North Hetton by the tail rope, and at the Burnley Collieries by the endless chain — it is an advantage only to be made use of when circumstances limit the extension of the engine plane. A run-rider for the tail-rope and No. 2 endless-rope systems, is only necessary where there are branches or curves, and when danger is consequently more to be feared.

" With reference to the methods of connecting the tubs to the rope in the No. 1 endless-rope system, the plan of attaching tlie set to sockets in the rope is to be preferred to the use of the clamp, which always requires an attendant, and which, besides, is only applicable to a limited strain. It is probably only when a number of branches are worked that the labour charge of the tail-rope system contrasts favourably with the endless-chain and No. 1 endless-rope systems.

" IV. — 1. This item of cost constitutes, of the cost per ton per mile, from 6 per cent, with the endless-chain system, to 15 per cent, with the tail-rope system. It will be seen that the cost of the former system is less than one-third of the cost of any of the other systems, and this shows very clearly the economy of the endless-chain system, as far as this charge is concerned. The chief comparison lies between the tail-rope and the No. 1 endless-rope systems. The duration of ropes with the tail-rope is quoted at eight, nine, twelve, twenty-four, and thirty months, and with the endlessrope at eighteen, thirty, and thirty-six months ; and as steel ropes are used for the latter system, so far the comparison is slightly in favour of the endless-rope; but, in addition to this, the greater length of rope required for the tail-rope system increases the cost of maintenance. On the other hand the extra wear of the rope due to its tightness in the working of the No. 1 endless-rope system should be considered. The cost of ropes with the No. 2 endless-rope system is almost as low as the endlesschain, since the rope lasts seven years ; but this cost appears high in the table, partlv for the reason before assigned, that the quantity of coals, and the average distance led, are so small, and partly because so great a length of waggon way is worked at one of the pits.

" 2. This charge varies from 24 per cent, of the total cost with the tail-rope system, to 34 per cent, with the endless-chain. It will be seen that the cost per ton per mile for this item is almost exactly the same for the endless-chain as for the tail-rope system. In regard to the cost of maintaining tubs, the endless-chain is shown to be more than the tail-rope, owing to more tubs being required upon the

Haulage, 393

engine plane. The cost of maintaining tubs is actually much less with the endless-chain, since it is totally free from the accidents which occur with the tail-rope, frequently causing considerable damage to the tubs. The cost of upholding tubs with the No. 1 endless-rope system is about the same as the tailrope cost, whilst the cost of the No. 2 endless-rope system, owing to its irregular action, and to the large number of tubs used, is rather greater. The cost of upholding engine and boilers, and maintaining way, is nearly the same in each system, the former generally being highest where most power is expended, and the latter greatest with the tail-rope and No. 1 endless-rope systems, the quick speed of which necessitates a carefully-laid way. The cost of grease, &c., will be observed to be highest for the tail-rope and No. 1 endless-rope systems, where sheaves upon the waggon way are used.

" 3. Introducing as it does the question of consumption of fuel, and thus to some extent of the cost of labour, this item of economy is very important. It will be seen that the cost of coals varies from 11 per cent, for the No. 2 endless-rope system to 30 per cent, for the tail-rope. The low cost of the former is partly due to the fact that with this system and with the endless-chain no power is wasted, as with the tail-rope, in overcoming the friction of drums and the brake pressure on the loose drum. The cause of the heavy expense for fuel in the working of the tail-rope system is obvious. The average power expended is about 112 horse-power, as compared with 20, 29, and 62 horse-power for the endless-chain, No. 2 endless-rope, and No. 1 endless-rope respectively.

"As to the proportion of power expended upon ropes in the working of the tail-rope and No. 1 endless-rope systems, it will be seen that with the former on the average 42 per cent, of the power expended is utilized in the set of tubs, 45 per cent, being required for the rope, while with the latter 68 per cent, is utihzed, and 23 per cent, expended on the rope. The percentage of power utilized in drawing the set of tubs depends chiefly on the inclination of the waggon way, being lowest where the gradient is light, and greatest where the gradient is heavy.

" With the endless-chain and No. 2 endless-rope systems the power expended in moving the chains or rope is simply in the proportion of the weight of the chain or rope to the total weight moved, and amounts in the former system to about 25 per cent, of the total power exerted, and to about 8 per cent, in the latter. The most important point of this comparison is between the power required in the working of the endless-chain and No. 2 endless-rope systems, 20 and 29 horse-power, and that required for the tail-rope and No. 1 endless-rope systems, 62 and 112 horse-power. This is due, firstly, to the avoidance of the friction of the rope or chain on rollers and sheaves, and secondly, to the reciprocal motion of the two former systems, this movement, which distributes a counterbalancing effect over the whole of an engine plane, being one of the chief characteristics to be observed in the consideration of economy of power."

" The conclusion arrived at by the Committee is that, as far as the cost of maintenance and the working charges are concerned, the endless-chain system can be applied, with but few exceptions, to every condition of waggon way with greater economy than any of the other systems, these exceptions being the cases, 1st, of the tail-rope system, where numerous branches are worked ; and 2nd, of the No. 2 endless-rope system, where the plane rises in one direction, and has one or more sharp curves. The fact which led to this conclusion is that in each of the three chief items of working expenditure, namely, economy of power, maintenance of ropes or chains, and cost of labour, the cost of the endless-chain is less than of the other systems. In the application of this system to

3 E

394 Mining Engineeeing.

curves underground, a man or a boy will have to be placed at eacb curve ; but the additional cost thus occasioned will be more than compensated by the saving effected in the power exerted.

" The No. 1 endless-rope system is to be preferred to the tail-rope when the plane is undulating, has neither stations nor branches from the main way, and has only slight curves, if any. The No. 2 endless-rope system is only to be economically applied under the conditions stated above, and it cannot be advantageously adopted where the planes are undulating. The tail-rope system is preferable to the endless-rope systems whenever any stations by the side of the plane, or branches from the main way, have to be worked."

Winding. 395

Chaptek Ix.

Winding.

The work of underground conveyance is not ended when the coal has been brought to the bottom of the shaft ; but the subsequent operations are of a character entirely different from those included under the term " haulage," to the consideration of which the foregoing chapter was devoted. In conveying the coal to the shaft, the load is dragged in wheeled vehicles running upon more or less even roads through the distance which separates the pit eye from the working places, and the force of traction required is never more than a small fraction of the load ; but from the pit eye to the pit mouth, or as it is technically termed " to bank," the whole load has to be lifted vertically through a height represented by the depth of the shaft. Moreover this load is augmented, for reasons already given, by the weight of the tubs, and also by that of the cages in which the tubs are raised. Hence, not only are different means and arrangements required to effect the transport of the coal throughout this portion of the distance over which it has to be conveyed, but an immensely greater force is needed, involving the use of powerful and costly motors. A moment's consideration of these facts will render it clearly evident that the subject of " winding," as the operations of raising the coal in the shaft are called, is one of very weighty importance.

Probably in none of the operations of mining have such great changes taken place during the past fifty years as in those of winding the mineral in the shaft ; ahd these changes have not consisted merely in the increased magnitude of the means adopted, as greater depths were attained, and larger outputs became necessary, but they have brought improvements of detail in the methods of applying those means by which the eflSciency of the latter has been materially increased. The introduction of cages moving between guides, combined with the adoption of steam engines of great power, have rendered it possible to attain a speed in the shaft at which the miners of the past generation would have felt astounded, and, as a consequence, to raise quantities of coal in a given time that to them would have seemed fabulous.

Before entering upon the study of the means employed in winding, it will be well to point out the necessity which exists for making ample provision for the demands likely to be made upon them. It will be observed that the entire output of a colHery will be limited by the means available for raising the produce through the shaft. When once the winding machinery has been erected, it is clear that whatever the demand may become, the quantity of coal raised daily cannot exceed its capabilities, and if this obvious fact be borne in mind, the desirability of providing for future contingencies will be readily acknowledged. The additional cost incurred by the provision of what at

O E J

396 Mining Engineeeing.

the time may appear superfluous power, is of small importance when compared with the immense advantage of being able, in case of need, to largely increase the output.

It was formerly the custom to tip the coal as it arrived at the shaft, into vessels of various forms, in which it was raised to bank. This vessel, being allowed to swing loose in the shaft, rendered it impossible to wind at a high speed. Moreover it was necessary to adopt some arrangement whereby the ascending vessel was prevented from coming into contact with the descending one, when two were used in the same shaft. This system of winding was very slow and insecure, and in consequence of the jolting occasioned by the vessel striking against the sides of the shaft, both it and the rope were speedily destroyed. Another disadvantage of this system was the delay and the injury to the coal occasioned by tipping it into the vessel at the bottom of the shaft and by tipping it out again at surface. The system is still in use in Belgium, where the vessel in which the coal is raised is called a cuffat, and partially in Staffordshire, where the coal is raised upon skips, to be hereafter described. The necessity for raising a larger quantity of coal in a given time, for obtaining that quantity in a better condition, and for providing a system of winding more secure to life and limb, led to the adoption of cages moving between guides, as already remarked. These so-called cages are iron constructions, made to contain one or two or more tubs, which are in this way raised through the shaft with their contents. The tub is run on to the floor of the cage at the bottom of the shaft, and off again when the cage has arrived at surface. Thus the objections to the transfer of the load from one receptacle to another are altogether obviated. Also, as the cages are made to run between guides, they may be raised and lowered at a high speed with perfect safety. In some pits, the load is raised with a velocity of 20 feet a second. The introduction of the cage, which is due to Mr. Ourr, of Sheffield, must be regarded as the greatest improvement ever effected in the operation of winding. One serious disadvantage attending this system is the great increase of the dead weight to be raised in the shaft. But this disadvantage is much more than compensated by the gain in the directions already pointed out. This additional dead weight remains, however, an important matter to be dealt with by mining engineers, the question being how to reduce this weight to a minimum. This question will come incidentally under review later.

Guides and Keeps. — The guides or conductors in general use are of wood, and these may be arranged and fixed in various ways. Essentially they consist of lengths of timber, usually of Memel pine, placed vertically against the sides of the shaft, to which they are affixed by means of crosspieces or buntons, set at intervals throughout the shaft. These buntons are also of pine, and they are fixed into the masonry of the shaft in the manner already described for bratticing. The intervals apart at which these buntons are set are usually 6 feet, and the sectional dimensions of the pieces are 9 inches by 3 inches. The guides are 4 inches by 3 inches in section, and are firmly bolted to the buntons. Generally only two guides are used, one on each side of the cage, which is rectangular, and these guides are fixed in the middle of the shorter sides to give greater stability to the cage. But other arrangements may be adopted, as shown in Fig. 605. The system of guides practically divides the sliaft, or that portion of it which is set apart for drawing purposes, into two compartments, in one of which the loaded cage ascends, while in the other the empty cage descends. It is obvious that the arrangement of the guides may be varied in many ways, according to the requirements of the case and the judgment of the engineer. The guides must, of course, extend throughout the distance traversed by the cage ; they will reach down to the floor of the levels entering the pit eye, and rise to the distance of a few feet above the mouth of the shaft. Wheu the

Winding. 397

guides are fixed in the middle of the shorter sides of the rectangular space in which the cage moves, and when, as is usually the case, the tubs are run off and on at those sides, it becomes necessary to suppress the guides at those points, and to provide some arrangement by which the cage may be guided on the other sides. It is evident that this is a matter of easy accomplishment, and it needs therefore no further notice.

In some instances, bridge rails, and in others, angle iron are used instead of wood for the guides. Whatever the material employed may be, it is essential that these guides be regular in section, and that the joints between the lengths be evenly and firmly male. Iron, in consequence of its comparative want of elasticity, causes a greater jolting in the cage than wood, a matter of some importance in rapid winding. The slides or cheeks upon the cage, by means of which it is guided, are of thin wrought iron, and are constructed to clasp the guide loosely on three sides, as will be seen in the drawings. They are slightly bell-mouthed both upwards and downwards to allow them to pass freely over any inequalities that may exist.

Sometimes, as in Lancashire, the guides, or conductors, as they are more commonly called, consist of continuous round bars of iron, fixed at the bottom of the shaft in stout balks of timber and screwed up to other balks upon the head frame at the top. The cage, in these cases, is provided with rings which run upon the rods. The transition from these rods to the wire rope similarly stretched down the shaft was easy, and hence we find the latter plan adopted in many places. When the wire-rope conductors are used, they are fixed, like the rods, to wooden balks at the shaft bottom and to the framing of the head gear at the top, where they are tightened by means of screws. Another mode of tightening these conductors is to fix them at the top, and to suspend heavy weights from their lower extremities beneath the balks. This mode of attachment possesses the advantage of keeping the conductors constantly taut. By reason of the want of rigidity in these conductors, two are insufficient ; in no case should there be fewer than three, and generally four will be required. This absence of rigidity, by allowing lateral motion to the cages, renders it necessary to have considerable space between the ascending and descending cages. To ensure safety, they should not be allowed to pass each other more nearly than 9 inches, when moving in straight lines. Wire-rope conductors pass through rings provided upon the cages for that purpose. The relative merits of rigid and flexible conductors constitute a disputed question among mining men. The principal defect of the latter lies in the swaying motion which is set up in them and in the cage, especially when the velocity of the latter is high and the depth of the shaft great. This swaying motion is, however, in a great degree neutralized by the employment of four ropes or lines of conductors, an expedient now generally adopted. Thus applied, wire-rope conductors are now very commonly used.

When the cage has been raised to the mouth of the shaft, some means are needed for supporting it in that position. These means usually consist of a system of levers called, from their use, " keeps," which are raised by the cage as it ascends, and which, by being weighted, drop back into their positions as soon as the cage has passed. With this arrangement, the cage is drawn up sufficiently far above the shaft mouth to allow the keeps to fall back into their position, in which their extremities project slightly over the shaft, and then lowered upon these projecting keeps, which are incapable of further downward motion. The cage rests upon these keeps while the loaded tubs are being run off and the empty tubs on. When these operations are finished, the cage is again raised out of the way of the keeps, which are drawn back by the lander, and held by him clear of the shaft until the cae has descended below them. For this purpose they are connected to a lever, and

398 Mining Engineeeing.

worked after the manner of a railway switch. In some instances, the levers are arranged to be worked by the foot. It is obvious that a system of keeps may be contrived in a variety of ways, so that it is wholly unnecessary to describe any one in particular. Simplicity of construction and strength of parts are the only essential conditions to be satisfied in a design of this nature. It may be remarked here, that when the cage is two-decked the operations of raising and lowering upon the keeps have to be repeated for the second level, and that the arrangements at the bottom of the shaft are similar to those at the top. To avoid this repetition, however, the arrangements sometimes include a staging, by means of which the loading and the unloading of the cages may be carried on at the different levels at once. This is notably the case in Belgium, where four-decked cages are not uncommon. With such an arrangement, and a two-decked cage, when the lower deck of the cage at surface is on a level with the shaft mouth, the upper deck of the cage at the bottom of the shaft is on a level with the floor of the roads entering the shaft ; the lower deck is here reached by means of an inclined plane. When the cage is single-decked, the arrangement of the on-setting and the landing places, as well as the operations of loading and unloading, are greatly simplified.

Cages. — Cages are merely receptacles for the tubs, or vehicles in which the loaded tubs are transported to surface and the empty tubs returned from surface to the workings. Their use being merely to travel up and down the shaft, they are not subject to any of the conditions which determine the construction of the rolling stock, as considered in the preceding chapter. But the conditions prevailing in this case become obvious on reflection. Thus it is clearly apparent that the requirements of a drawing cage are : 1, that its form and capacity shall be such as will allow a sufiicient number of tubs to be readily placed in it and removed from it ; 2, that its form and mode of construction shall be such as will allow it to run easily along its guided path in the shaft ; and 3, that its mode of construction and material shall be such as will allow the greatest carrying capacity with the least weight of cage.

It will be seen that the form of a drawing cage is determined, first, by that of the division in the shaft in which it has. to travel ; and second, by that of the tubs which it has to contain. Those divisions are always rectangular, and the tubs, as already shown, possess the same form. Hence it has happened that the rectangular form has been universally adopted for the drawing cage. Its capacity is determined chiefly by the requirements of the output. In many cases, it has but one floor, and it is then described as " single-decked." This floor may be constructed to carry either one tub, or, what is a more frequent arrangement, two tubs standing end to end. The floor is laid with rails, to facilitate the introduction and withdrawal of the tubs. To keep the latter in their position during their transit to surface, or from surface to the shaft bottom, some kind of catch is used, often a simple latch which, when hanging vertically of its own weight, projects over the opening into the cage. This opening is left in both of the shorter sides of the rectangle, in order that the loaded tubs may be pulled off on one side, and the empty tubs pushed on on the other. In the two, three, and four decked cages we have merely a repetition of this floor at different levels. The top of the cage is provided with an iron bonnet or roof for the protection of persons riding in the cage. In the middle of the shorter sides, are fixed the guide cheeks, when rigid wooden or iron conductors are used. The form of these has already been described. With the flexible wire-rope conductors, rings are provided at each of the angles. The cage is suspended from the rope by four short chains at each of the upper corners, and, in the case of heavy cages, from the middle of the larger sides as well.

Drawing cages are generally constructed of wrought iron, and, as a wide margin of strength

Winding. 399

must be allowed, the parts are necessarily excessive in section, and strongly put together. These conditions make the dead weight of the cage great, and it is sought, by adopting suitable forms of section and modes of assemblage, to reduce this weight to the lowest practicable limits. As at present constructed, wrought-iron cages weigh from 5 to 6 cwt. when designed to carry a single tub, and from 9 to 10 cwt. when the carrying capacity is two tubs, whether the cage be a single or a two-decker. A two-decker cage, constructed to carry four tubs, may weigh from a ton to a ton and a quarter, or even more. Thus it will be seen that the dead weight of the drawing cage constitutes a very important item in the load to be raised. Eecently successful attempts have been made to reduce this dead weight by substituting steel for wrought iron, and it is probable that this material will ultimately be generally adopted. The cost of drawing cages varies, of course, with the price of iron ; but taking an average, it may be said to range from about 35Z. a ton for wrought iron, to about 45. a ton for steel. The construction of these cages is shown in Figs. 606 to 612. The design shown in Pigs. 606 and 607 is for a wrought-iron singledecked cage to hold two tubs ; that shown in Figs. 608 and 609 is for a steel two-decked cage to contain four tubs ; and that represented in Figs. 610 to 612 is for a steel two-decked cage to carry two tubs, and to be used with wire-rope conductors.

Sometimes drawing cages are provided with an attachment for arresting their descent in. the shaft in the event of the rope breaking. Such cages are called safety cages, and it is true that they have in some instances prevented the occurrence of fatal accidents. The attachment usually consists of a contrivance for gripping the conductors on the strain of suspension being taken off. Many contrivances of this nature have been adopted at various pits at different times, but no one of them appears to have given complete satisfaction. Some of them, by their liability to come into action when not required, introduce a new source of accidents. Others possess defects of different kinds that have led to their abandonment. Up to the present time, no safety attachment has been devised possessing suflScient merits to justify its general adoption. So long as a device of this nature is seriously imperfect, its use tends rather to occasion than to prevent accidents, by causing a relaxation of vigilance in the persons employed. It is, however, ardently to be hoped that the efforts of inventors in this direction will soon be crowned with success, so that miners may obtain comparative security against those appalling accidents to which they are now exposed. Some other contrivances of a similar character, but designed solely to prevent the descent of the cage when severed from the rope by overwinding, have given more satisfactory results. Among these may be mentioned as worthy of the attention of mining engineers, Ormerod's Safety Link, and Walker's Self-detaching Hook, which have been adopted at many collieries, and which already in some instances of overwinding have prevented the occurrence of fatal accidents. The object sought to be accomplished in these safety appliances is to cause the hook or link by which the cage is suspended from the rope, to release its hold of the rope, and to take hold upon a portion of the framework of the head gear arranged and placed at a certain height for that purpose. In this way, the rope is saved from rupture, and no injury can occur to any part of the structure. The only objection to safety appliances of this nature lies in their apparent liability to release their hold of the rope when not required to do so, as the effect of a sudden shock brought upon them. It is, however, but just to remark that hitherto no accident of this kind has occurred.

In Staffordshire, a system, of winding still prevails similar in character to that of the corves generally in use in former times. Instead of using cages in which to raise the receptacles containing

400 Mining Engineeeing.

the coal, these receptacles are themselves suspended directly from the rope and raised in that manner in the shaft. They differ also entirely in their construction from tubs, being composed, as shown in Fig. 613, of a platform carried upon wheels and of two or three large iron hoops. To load these " skips," as they are called, a quantity of coal is stacked upon the platform and the largest hoop is then placed over it to keep it in position. A second quantity is then stacked up, and a second hoop of a somewhat smaller diameter placed over it. These operations are repeated with hoops of smaller size, until the pyramid of coal has attained the limit of height allowed. The mass is further held together by the four chains by which the skip is suspended from the drawing chain. The load is then drawn by a horse to the bottom of the shaft, where it is attached to the drawing chain. On arriving at surface, it is simply drawn by the banksman from over the shaft mouth by means of a hook and lowered upon the landing, or he pushes a platform over the mouth of the shaft beneath the load, upon which platform the load is then lowered. The loaded skip having been run off and its place supplied by an empty one, the latter is raised suflSciently to allow the platform to be withdrawn, and then lowered into the shaft. In this system, the winding is necessarily slow.

Head Gear. — The head gear constitutes a very important part of the fittings of a shaft. It consists essentially of a pulley frame, constructed either of wood or of wrought iron, carrying a pulley, or more frequently two pulleys, over which the rope suspended in the shaft is passed and led thence to the drum of the winding engine. These pulleys are provided with a round or a flat groove, according to the form of the rope used, and are made of a large diameter in order to avoid giving a quick bend to the rope. The design and construction of these pulley frames, or head stocks, demand careful consideration, inasmuch as they are extremely important structures and are required to fulfil various conditions. The two essential features which these structures must possess are height and strength. It is obviously necessary to safety that the pulleys over which the ropes pass should be placed at a considerable height above the mouth of the shaft, since by this means alone can a margin of safety be allowed to the engineman. If it be borne in mind that with the winding drums of large diameter now in use, a single stroke of the engine is sufficient to raise the cage 50 or 60 feet in the shaft, the necessity for such a margin will be apparent. For this reason, the height of pulley frames is made to vary from 30 to 60 feet according to the speed of winding. The security of human life, however, demands that in all cases the greater rather than the lesser height should be approached. The condition of strength in the pulley frame is equally or even more important, since it is evident that a yielding of this structure must inevitably lead to disastrous consequences. The necessity for a great height renders this condition difficult of fulfilment, since height in any structure is opposed to its stability. Hence arises the importance of carefully and fully considering the character and the directions of the strains to which the pulley frame is subjected, and of so designing and constructing it that it may possess ample strength to resist them. This subject was briefly discussed in a former chapter, but it is desirable, by reason of its importance, to investigate it more fully in the present section.

The essential parts of a pit-head frame are the legs or uprights, upon which the pulleys rest, and the spurs or inclined supports which are set on the side of the legs next the engine. All other parts of the frame are auxiliary to these, or to some other appendage of the frame. The uprights are intended to resist the vertical strains, and the spurs the oblique strains which tend to overthrow the former in the direction of the source of power, that is, the spurs are intended to prevent the legs

Winding. 401

carrying the pulleys from being pulled over towards the engine. Thus, in designing a pit-head frame, we have to consider these two parts relatively to the strains to be thrown upon them ; and in this consideration we have, first, to determine the direction of the strains, next, the value of these strains, then the best relative position of the parts of the frame, and lastly, the dimensions necessary to enable these parts to resist the strains thrown upon them. Each of these questions demands thoughtful attention.

The direction of the strains, as well as their value, may be readily ascertained graphically by means of the parallelogram of forces. To show the application of this method, it will be well to consider some examples. Suppose a vertical support carrying a pulley over which a rope is passed in such a way that the two portions are parallel with each other and with the support, as shown in Fig. 614; and suppose a weight W attached to one portion of this rope, and a force P applied to the other portion, sufficient in intensity to produce equilibrium. The weight W may be assumed to be that of the cage with its contained load, and the force P, that exerted by the engine. In this case, the tension of the rope is obviously equal in both portions, since the forces are in equilibrium, and these forces are W + w in one portion of the rope, and P + w' in the other, w and w' being the weights of the respective portions of the rope. Now it is evident that the strain upon the support is the sum of these forces, that is, 8 W + w + "P -i- w', or, if we make W the total weight, S 2 W. And it is also evident that this strain will be a vertical one, that is, it will be exerted along the axis of the support.

Suppose again that one portion of the rope is inclined to the other at an angle of 45°, as shown in Fig. 615. In this case, it is plain that the strain upon the support will be changed, both in direction and in intensity. To determine the direction and the value of the strain, lay off S A, SB equal to a unit on any scale, say one inch, and from the points A and B, draw A E parallel to S B and BE, parallel to S A ; S A E B will then be a parallelogram, the diagonal S E of which will represent the strain both in direction and in intensity. The value of the latter may be found by measuring the resultant S E upon the scale adopted. Such a measurement will show that when the sides of the parallelogram are each equal to 1, as in the example, the diagonal representing the resultant of the forces will be 1 85. Thus, if we assume W 10 tons, the value of the strain will bel0xl"85 18"5 tons, instead of 10 X 2 20 tons, as in the preceding example. If the line SE representing the direction of the strain be produced, it will meet the ground line at the point 0, and as this point is without the base of the vertical support, the latter will be pulled over in the direction of this point. Hence it becomes necessary to add a spur, and to place this spur in a favourable position to resist the strain. It will be observed that the effect of adding the spur is to widen the base of the support, and it is obvious that the greater the inclination of the spur, the wider the base will be. The question now is, What, under the conditions supposed, shoud be the inclination of the spur ? The condition of stability is satisfied so long as the resultant S E falls, when produced, within the base of the structure ; hence the least inclination will be that of the line S 0, which, it will be observed, is half that of the inclined portion of the rope. The angle of this portion being 45°, that of the spur will be 22°, and with this inclination, the structure, under the conditions assumed, will be perfectly stable, since the resultant of the forces to which it is subjected will coincide with the axis of the spur. But as in practice it is possible that the force P may exceed the weight W in consequence of some hitch occurring, as, for example, in the case of the cage being drawn up against the pulley, it is prudent to give the spur a somewhat greater inclmation.

3 F

402 Mining Engineeeing.

If the inclination of the rope be increased to 60°, as in Fig. 616, the strain will he again altered in direction and in intensity. Determining this strain, as before, by means of the parallelogram S A B B, we find it represented by the diagonal S R, which, being produced, will meet the ground line at 0. The value of the strain SR measured on the scale will be found in this case to be 1 73, and, assuming the same weight as before, this value will give 10 x 1 73 17 3 tons. The minimum inclination of the spur will be that of the line S 0, which is equal to half that of the inclined portion of the rope, or 30°.

Suppose again an extreme case in which the two portions of the rope are at an angle of 90° with each other, as shown in Fig. 617. The strain upon the supports is represented by the resultant SR, which, being produced, will meet the ground line at the point 0. The value of this strain, measured as before, will be found to be 1'41, which, with the same value for W, will give 10 x 1*41 14' 1 tons, as the intensity of the strain to be resisted. In this case, the minimum inclination of the spur will be that of the line S 0, or 45°, which is half that of the inclined portion of the rope. It must be borne in mind that these inclinations are measured from the vertical, and not from the horizontal.

Instead of laying off the distances S A, S B to some scale, we may merely make them equal, and

then find the value of the resultant S R by calculation, from the formula r . ' , , a being the

angle S A R, 6 the angle S R A, and r the side S R of the triangle S R A. Thus in the second

example in which the inclined portion of the rope is at an angle of 45° with the vertical portion, the

value of the resultant representing the strain will be r . ' „„, 5 ;rzr- 1 '85.

It will be seen from the foregoing considerations, that the condition of stability is that the line representing the strain due to the two forces shall fall within the base of the structure, and that this base is the distance comprised between the lower ends of the uprights and of the spurs. In order to ensure that the resultant shall fall well within this base, the minimum inclination of the spurs should, as already pointed out, be slightly exceeded. In many of the pit-head frames at present in existence, the minimum inclination is greatly exceeded ; but inasmuch as this circumstance reduces the strength of the spur by increasing its length, the practice is to be condemned as wrong in principle. There is clearly nothing to be gained by increasing the base of the structure beyond the limits required by the condition of stability.

In estimating the value of the weight W, account must be taken of all the resistances that have to be overcome. Thus at the moment of starting the engine, when the resistance is greatest, we have to consider the weight of the tubs with their contained load of coal, which may be regarded as the useful weight, that of the cage with its attachment of chains, and also that of the drawing rope. Representing the useful weight by w, that of the cage by w' and that of the rope per yard by w", we have W w + w' + w"'H,'B. being the height in yards of the pulley above the shaft bottom. But besides these weights, it is also necessary to take account of the friction of the cheeks against the guides, and other slight resistances which may be opposed to the motion of the cage. These resistances ought not to be estimated at less than of the total weight. This value will give us, W 1 1 (i<; + w" H). As an illustration of the application of the foregoing, we will take a case in which the weight of the two-decker cage with its attachments is ton, that of the four tubs with their contained loads,

Winding. 403

3 tons, and that of the chain per yard 10 Ih., the height of the pulley above the bottom of the shaft being 400 yards. The value of W or the total weight will in such a case be,

W 1-1 (3 + 1-5 + 2) 7-15 tons.

If now we suppose that the inclined portion of the rope makes an angle of 60° with the vertical portion, and calculate the strain upon the pulley frame in the manner already described, we shall find that this value of W will give 7-15 x 1-73 12-37 tons, as the intensity of that strain. Thus the structure will be subjected to a strain of 12-37 tons in the direction shown by the resultant of the component forces.

Having determined the direction and the value of the strains to which the pulley frame is subjected, and the inclination to be given to the spurs to ensure stability, it becomes necessary to ascertain what dimensions the parts should have to enable them to withstand these strains. The wood usually employed for piilley frames is pitch or Memel pine, and as the parts may be considered to resist after the manner of columns, we shall have to calculate the strength of that material when applied in that

form. The breaking weight P for solid long square columns of dry Memel pine is, P — yt~'

B being the breadth of the side in inches, and L the length of the column in feet. As, however, the

strength of timber is considerably reduced when exposed to a moist atmosphere, the coefficient 7 8 is

too great, and ought to be taken at 6. With this value, the formula becomes P -j-r> from which

4 /p T 2

we deduce B V . When the side of the column has this value, it will yield beneath the load

or pressure P, since P here represents the breaking strain. The value of B, therefore, thus found will

have to be increased according to the factor of safety determined upon. In a structure of the nature

of a pulley frame, which is constantly being subjected to shocks, and which may be excessively strained

in consequence of a hitch occurring during winding, the factor of safety should be taken as j, that

is, the normal or ordinary strain should not exceed the breaking strain. Arranging the formula

/P 1/ according to this proportion, we have, B ——, in which B the side of the square timbers

which are to form the pulley frame.

In the case supposed we have the strain equal to 12*37 tons. Substituting this value for P, and assuming the length of the spurs to be 40 feet, we have as the requisite breadth of these pieces,

/ 12- 37x40 23.47 inches. Thus, under the conditions assumed, the section of the spurs

should be 13*47 inches square in the middle of their length. In practice, the legs or uprights are usually made equal in section to the spurs. With these dimensions, we obtain a sufficient, but not a superfluous degree of strength. If it be intended to strongly brace the structure, however, the dimensions of these essential parts of the pulley frame may be slightly reduced. The systems of bracing will be described hereafter when treating of the details of constructing pit-head pulley frames. In determining the dimensions in this way, we have considered the support as consisting of only one leg and one spur. But in practice, a pulley frame is composed of two legs and two spurs, between which the load is suspended. Thus only half the load is borne by each pair of supports, and,

3 F 2

404 Mining Engineeeing.

22*37 therefore, the total weight must be halved in making the calculation. If — - — 6 '18 be substi-

tuted for W in the formula, we shall find the value of B to be 11 33 inches. Hence in designing a Memel pine pulley frame to support the load assumed, the principal timbers should not be less than 11 inches on the side in the middle of their length.

The kind of wood used in the construction of pit-head frames is usually, as before remarked, pitch or Memel pine. Though preference is generally accorded to the former, the latter will be found to be very suitable for the purpose, provided it be chosen sound and free from knots and cracks. There are various ways of arranging the several parts of a pulley frame, and also of connecting these pieces one to another ; two designs slightly differing in details, are shown in the accompanying drawings. It is essential to stability that all the chief component parts of the structure should be set upon the same wooden framing by which those parts are securely held together at their bases. This wooden framing consists of sills strongly jointed and bound together, upon which the legs and spurs are set by means of cast-iron sockets bolted down to the sill. Grood workmanship is an essential requisite in the construction of pulley frames, since it is important that all the joints should be accurately fitted, and the parts made to abut evenly one upon another. The double tenon joint is generally the most suitable in such structures, and it may be rendered secure by an iron bolt passing through each tenon. Over the more important joints, wrought-iron straps will be required. After the joints have been properly fitted, they should be well covered with red-lead. These details of construction are shown in the drawings. The legs of the frame are slightly inclined to each other towards their summits, and are braced together. The spurs are also in some instances braced to the legs. These spurs, or back-stays, as they are frequently called, are sometimes made to abut against the engine house, instead of being set upon a sill. This practice is, however, to be strongly condemned, as being inconsistent with the requisite degree of stability. In order to obtain the greatest height possible with timber of a given length, the cap or framing carrying the pulley is placed above the uprights and back-stays, as shown in the drawings ; these drawings also show the details of the construction of this portion of the framing. As it is necessary that ready access should be had to the pulley, it is usual to provide one of the back-stays with steps, whereby the top of the framing may be reached without difficulty. For the convenience and safety of the person to whom this duty is entrusted, a hand-rail should be added ; this arrangement is shown in one of the designs illustrated.

The pulleys used on pit-head frames are of iron, and they vary in diameter from 10 to 20 feet. It has already been pointed out that when wire ropes are used, the pulley must be of a large diameter to avoid straining the metal by too sharp a bend. A common diameter is 16 feet. Formerly pithead pulleys were constructed wholly of cast iron, and this material is still used in the South Staffordshire district, where heavy drawing chains are employed with pulleys of small diameter. But generally this system has been abandoned for the compound system, in which the central boss and the rim are of cast iron, and the arms of \.rought iron. The mode of arranging the arms is shown in the drawings. The rim of the pulley is grooved to receive the rope, and the bottom of the groove, known as the " face " of the pulley, is made either circular or flat, according as round or flat ropes are to be used. It is important that the face of the pulley for flat ropes should be perfectly flat, since otherwise the rope is unduly strained. The groove in the pulley should be sufiiciently broad and deep to allow the rope some degree of play. This play is desirable when flat ropes are used, to prevent any ill effects of inaccuracy in the fixing of the pulley, in consequence of which

Winding. 405

inaccuracy the vertical medial planes of the pulley and of the drum would not be perfectly coincident. But with round ropes, the play is indispensable, since the rope, as it is being wound upon the drum, is constantly changing its position relatively to the vertical plane of the pulley.

The drawings illustrative of the foregoing remarks on pit-head frames are those numbered from 618 to 630. These drawings show some of the modes of construction that may be followed, and also some of the details of forming the joints.

Wrought iron has in some instances been substituted for wood in the construction of pit-head frames, and it appears probable that this material will be extensively employed in the future. The increasing difficulty of obtaining timber of a sufficient length to meet the requirements of the present day has, indeed, rendered the adoption of some other material than wood necessary in many cases where great height is desirable. It is evident that with an iron structure the height is practically unlimited by the material employed ; and hence we may obtain an elevation of the pulley above the mouth of the shaft, of 70 or even 80 feet, without difficulty. We have already pointed out the advantage of height in the pulley frame, and it is probable that these lofty structures will become more and more common as the necessity for raising a greater number of tubs at one time increases.

In the construction of iron pulley frames, the T section is generally adopted in the principal parts, and these parts are braced together by flat or by angle bars, somewhat after the manner of a lattice girder. This construction is shown in the drawings numbered from 631 to 636. It is to be regretted that hitherto no experimental tests have been made for the purpose of ascertaining the strength of iron when placed and strained in this manner. The subject forms an interesting one for the investigation of engineers, and it is to be hoped that it will be soon taken up, and that such results will be arrived at that we shall be able, as in the case of other framed structures, to calculate with accuracy the dimensions required to resist a given strain, and also to determine the most suitable form of section. The drawings referred to above being self-explanatory, need no further description. Of course the design of such a structure admits of endless variation.

Ropes. — The pit rope constitutes the means through which the force developed by the engine is transmitted to the load, and is therefore an object of the first importance. The two essential requirements in a rope are flexibility and strength, and it is desirable to obtain these qualities with the least possible weight. The desirability for a light weight in the rope rests upon two different grounds. In the first place, it is important that the dead weight to be dealt with should be as little as possible ; and in the second place, the strength of the rope is, in some degree, dependent upon its weight, inasmuch as the weight of the suspended portion must be subtracted from that of the useful load. Thus, if the distance between the pulley and the pit bottom be 300 yards, and the weight of the rope be 4 lb. a yard, the strain upon that portion of the rope which is upon the pulley will be equal to 300 x 4 1200 lb. when the rope is unloaded. Hence its efiective strength will be reduced by that amount.

In order to obtain these qualities in winding ropes most fully, various materials have from time to time been chosen, and more or less extensively adopted. Hemp was a few years ago the only material employed in the manufacture of ropes ; later, aloe fibre was adopted, and these two materials are still commonly used in many places. In Belgium, aloe fibre is very generally employed. The strength of ropes made of this material is slightly greater than that of hempen ropes, and their durability is notably superior. But, on the other hand, they are heavier per unit of length, so that

406 Mining Engineeeing,

their superiority remains on the side of durability alone. One defect in hempen and aloe-fibre ropes is their liability to absorb moisture, whereby their weight per unit of length is considerably increased. The defect is probably greater in aloe-fibre than in hempen rope. More recently, iron wire has been adopted as a material for ropes, and the results have proved eminently satisfactory. These ropes consist of several wires of the toughest iron twisted together in the same manner as the strands of the vegetable ropes, but the degree of the twist is less in the former than in the latter. Theoretically a wire rope will best resist the strains brought to bear upon it when all the wires of which it is composed are parallel to one another ; but practically, by reason of the flexibility and extensibility required, the strength of a wire drawing rope is found to be greatest when the strands are arranged spirally as in the hempen rope. In the wire rope, the weight per unit of length is, for a given strength, considerably less than in the hempen and aloe-fibre ropes, and the diameter is also reduced in a like degree. The flexibility however is less, and for that reason, pulleys of a larger diameter have to be employed. The transition from iron to steel was an obvious step, and hence we find the most recent ropes made of this material. The greater tensile strength of steel allows the diameter of the rope to be still further reduced, so that the weight per unit of length has again been notably lessened. The advantages obtained by the successive changes in the material employed in the manufacture of ropes are clearly set forth in the table given hereafter.

It is desirable to point out here a change in form which has been made with a view of augmenting the efiective strength, and of attaining other ends, which will be explained later. In the new form, the rope, instead of being cylindrical, is flat, and it was supposed that when arranged in this manner, the several fibres or wires of which the rope is composed would be more evenly strained than when they were all arranged spirally. This result may, however, be regarded as more than doubtful. For we have, in the first place, the fact that the fibres or wires are still arranged spirally, inasmuch as the flat rope consists merely of several small round ropes stitched together, the material forming the stitches adding to the weight without in the smallest degree increasing the strength ; and, in the second place, it does not seem probable that the separate strands are in practice more evenly loaded than they would be in the round rope. It is easy to see that even if the strain be uniformly distributed upon a new rope, that uniformity may be quickly destroyed by numerous causes. One portion of the rope may not offer the same resistance as another part, and this part by becoming more extended than the rest will render the strains upon the whole irregular. Also it is evident that if the face of the pulley be not perfectly flat, the rope must be irregularly strained. To prevent as far as possible these accidents, each strand is made as nearly as may be identical, and they are used in even numbers. Also the direction of the twist is contrary in each pair, to counteract the tendency of the twist to come out under the action of the load. In winding, the flat rope is made to lap over itself upon the drum, so that the diameter of the latter is practically increasing or decreasing during the operation of winding. The advantages of this circumstance will be pointed out later. One obvious advantage of this overlap of the rope is that the latter is kept constantly in the same vertical plane. The flat rope has not been regarded very favourably by mining engineers generally, and hence it has not been very widely adopted.

The quality of a rope of course greatly depends upon the method of its manufacture and the care bestowed upon the operations. It would be foreign to our purpose, however, to describe and to discuss questions of manufacture ; in this place, we have to deal exclusively with the application of ropes to the work of raising the produce of the mine. A primary consideration is the strength of ropes ; but

Winding

his IS a question that can be dealt with only approximately. It has been the custom to assimilate tbe resistance of a wire rope to that of an iron rod of the same effective section. But it is obvious that the whole section of the rope cannot be so uniformly strained as that of the rod. Moreover as already remarked, the operations of manufacture introduce elements of uncertainty in the rope which either do not exist at all in the case of the rod, or exert a much less important influence. Besides, the rupture of a wire rope is due rather to the bending strains to which it is constantly subjected, than to the tensile strains occasioned by the load suspended from it. Hence it happens that we are compelled to have recourse to empirical methods of calculation, and to content ourselves with results of a very approximative character. The following formulae and table will be found practically useful m determining the dimensions of a rope of a given material required to bear a given strain. If C the circumference of the rope in inches and W the breaking weight in tons, then for hempen ropes W 0-2 C, for iron wire ropes W 1-5 and for steel wire ropes W 2-5 C. The safe working load may be taken at from i to j of the ultimate strength, according to the speed at which it is to run and the vibration to which it is to be subjected. Thus for iron wire rope, the safe

working load L will be L

1-5 C'

L

or

L

-, according as the speed of winding is

to be moderate, high, or very high. Assuming the circumference to be 4 inches, the values of L will be 4f tons, 4 tons, and tons respectively. The weight of the rope hanging over the pulley is of course included in the working load. A sufficiently close approximation to the safe working load of round wire ropes moving at high speeds may be found by multiplying the weight of the rope per fathom in pounds by 5 for iron wire and by 8 for steel wire, the product being taken as representing hundredweights. Thus the weight of a 4-inch rope being 14 lb. a fathom, we have 14 x 5 70 cwt, and X 14 8 112 cwt. respectively for iron and steel wire. As before remarked, all of these results must be regarded as rough approximations, and therefore it is necessary, in determining the dimensions of a rope, to allow a wide margin of safety, which should never be less than i. Taking it generally at we may find the circumference of the rope by transposing the preceding formulse in the following manner: C '\/4L for iron wire, and C V'2-4L for steel wire. Thus if the working load is to be 4 tons, the requisite circumference of an iron rope will be 4 X 4 4 inches, and of a steel rope v 2-4 x 4 3"1 inches. The following is a comparative table of the weights and strengths of hempen and of wire ropes, as given by the manufacturers :

Flat Eopes.

Hemp.

Size in Inches.

4 +li

5 -f If 5*+ If

5i +

6 +11

7 +H

+ 2i

9 -J- 2i

Weight per Fathom.

lb.

Iron.

Size in Inches.

2i + +

+

3 + 3i + +

+

4 +

H + U +

4f +

"S" ff 'S B "B"

a

¥

¥

Weight per Fathom.

lb.

Steel.

Size in Inches.

Weight per Fathom.

2 +i 2i + i 2-i + 2f + 1

3 +f 3i+l 3i + f

lb.

Equivalent Strength.

Working Load.

Load.

cwt.

tons.

Mining Engineeeing.

Eound Eopes.

Hemp.

Circumference.

incliea.

f s'

li' 12'

Weight per Fathom.

lb.

'4

'5

"7

"9

si

Iron Wire.

Circumference.

inches.

Q3

3f 3f

Weight per Fathom.

lb.

H

Steel Wire.

Circumference.

inches. l'

1 '

i3

Si

Woifcht per Fathom.

lb.

2'

s'

9"

16'

Equivalent Strength,

Working Load.

owt.

Breaking Load.

tons.

In estimating the strains upon a rope, we must take account of that which is exerted upon it at starting. While the rope is moving at a uniform speed, the strain upon it will be evidently that of the working load. But as the load starts from a state of rest, the velocity is an accelerated one from the moment of starting till that in which the maximum speed of ascent is attained, and during this time, the strain upon the rope will be greater than that due to the load, since a portion of the force exerted is expended in giving velocity to the load. The strain upon the rope during the time of

Ws

accelerated motion is given by the following formula : L W + , in which L is the load

required, W the weight of the working load, s the full speed in feet a second, and t the time in seconds during which the accelerated motion takes place. Thus if the working load be 2 tons and

20 , 2 + — tons,

the full velocity 10 feet a second, the strains upon the rope will be 2 +

ij n' X

assuming that five seconds are occupied in getting up the speed.

One disadvantage of wire ropes is that in passing over the pulley and in coiling round the drum they raise the load by a series of short vertical jumps, and thereby occasion a jerky strain which tends to cause a rupture of the wires. This jerky motion, which is greatest in flat ropes, is diminished by increasing the diameter of the drum. Another serious disadvantage to be guarded against in using wire ropes is their liability to break suddenly without having previously exhibited any indications of weakness.

It is impossible to give a close approximation to the time that a rope will last, since its

Winding. 409

durability depends, not only upon the quality of the material of which it is composed and the care bestowed upon its manufacture, and upon the value of the work done; but also upon the nature of the atmosphere in the shaft in which it has to work. Moisture is an active agent in the destruction of rope, especially of hempen or aloe-fibre rope. The water in shafts is commonly impregnated with mineral acids that promote a rapid oxidation of wire ropes, and the same effects may be caused by the gases which ascend the upcast shaft. Thus it has been ascertained that a rope which in some situations will last three years, will in others be destroyed in less than half that length of time with the same work. The average life of round hempen rope varies, according to size, from six to twelve months, and of flat ropes, or bands, from one and a half to two years. Of wire ropes, the average life may be taken as varying from one and a half to two years for round ropes, and about two-thirds of that time for flat ropes. Steel is somewhat more durable than iron. Experience has shown that the wear of ropes increases with the speed more rapidly than with the load, so that, from the point of view of durability in the rope, it is better to increase the load than the speed of winding.

To preserve rope from the action of atmospheric and other destructive agencies, they should be coated with some protective substance. Tar is applied to hempen and aloe-fibre rope, but care should be taken not to apply it in too great a quantity, as any excess not only adds unnecessarily to the weight of the rope, but is in itself a source of weakness. Hempen rope is saturated with about 17 per cent, of its own weight of tar, and aloe-fibre with about 13 per cent. The quantity of tar applied should be slightly less than that required for saturation. Wire ropes are usually coated with raw linseed oil, or with a mixture in equal proportions of Spanish brown and lampblack with linseed oil. When the rope is to be exposed to the action of water, it may be saturated with a boiling mixture of tar and lime, in the proportions of one bushel of the latter to one barrel of the former. The lime is added to neutralize the acid.

In some places, chains are used instead of ropes for winding the load in the shaft. This is notably the case in the South Staffordshire districts, where flat chains are still employed. The extremely ponderous character of these chains, however, constitutes a serious disadvantage, which is not compensated by the greater facility with which the chain coils upon the drum, a circumstance that renders it possible to employ drums and pulleys of smaller diameter than those required by the wire rope. The use of chains for winding is being everywhere gradually abandoned.

The Engine and its Accessories. — It would be beyond the scope of the present work to enter upon a detailed discussion of the numerous questions relating to the use of steam, and to the construction of winding engines which shall most fully satisfy the requirements of practice. Such a study would be an extremely interesting one, and of the highest importance to mining engineers. But its wide demands would require a volume to do it justice, and such subjects should be dealt with in special treatises. It is, however, desirable to point out the essential qualities required in a winding engine, and to describe briefly the means by which those qualities may be obtained. These points will, therefore, receive consideration. Of the accessories of the winding engine, only those which are essential to the operations of raising the mineral in the shaft, and particularly applicable to those operations, will be dealt with. These accessories are the winding drum and the brake. In treating of these subjects, it will conduce to clearness to give priority of place to the drum, as coming in natural sequence for consideration after the winding rope, to which attention was last directed.

The Winding Drum. — The drawing rope, alter passing over the pulley at the top of the headstocks, is led to the winding drum, upon which it is coiled. This drum may be either cylindrical or

3 G

410 Mining Engineeeing.

conical in form, and it may be made to revolve either upon a horizontal or upon a vertical axis. The latter arrangement is now, however, rarely adopted, and we shall therefore consider only the case of horizontal drums. A drum consists of a barrel, upon which the rope is wound, and two side pieces or cheeks, called flanges, the use of which is to prevent the rope from slipping off the barrel. These two portions are carried upon arms connected to a central boss, through which the shaft passes. The material used in the construction of winding drums is most frequently iron, a combination of both cast and wrought iron being usually adopted. The barrel is cast in segments and put together by being bolted through flanges provided for that purpose. The arms are also of cast iron, and are bolted to the side flanges of the barrel, a portion of the rim being cast upon each arm, in some cases. The inner ends of the arms are fitted into a cast-iron boss and secured in position by turned bolts in bored holes. The shaft is of wrought iron, and should be forged from the best scrap ; to secure the bosses, which should be bored out to the exact diameter of the shaft, the latter is turned and provided with key-beds cut into it. A similar mode of construction is adopted when the drum is conical in form, in so far as its essential component parts are concerned. With this form, the drum presents the appearance of a double cone, or of two cones, or frusta of cones placed base to base, and the rope is fixed so as to be ascending upon one cone while it is descending upon the other. The principal object of this arrangement of the drum and the rope is to ensure the regular coiling of the latter ; but the arrangement contributes, in a manner to be pointed out hereafter, to equalize the resistance to be overcome by the engine.

The diameter of a winding drum is determined mainly by the nature of the rope to be used, a much larger diameter being required for wire ropes than hempen ropes. But it should also bear some proportion to the diameter of the rope of a given material, since it is obvious that the thicker the rope, the less readily it will coil upon a cylinder of a given diameter. A suitable diameter of the drum may be obtained in the following manner. Assuming 10 feet to be the minimum diameter for a wire rope 1 inch in circumference, add 6 inches to the diameter of the drum for every increase of a qiiarter of an inch in the circumference of the rope. Thus a rope inches in circumference will require a drum 10 + 4 5 14 feet 6 inches in diameter, and a rope of inches will require a drum of 10 + 7*5 17 feet 6 inches. It has already been pointed out that as the diameter of the pulley and of the drum is increased, the life of the rope is lengthened, and it is obvious that, determined by the conditions of wear in the rope, the diameters of the pulley and of the drum should be equal.

Round rope is wound upon the drum in parallel coils, and in some instances it is made to rise and return upon itself on cylindrical drums for the purpose of diminishing the length of the latter ; the arrangement is, however, unfavourable to the durability of the rope. When the drums are conical, the overlap is, of course, impossible, and the same necessity for it does not exist. A flat rope is always wound upon itself, so that its coils are all in the same vertical plane. Hence, practically, the diameter of the drum is constantly increasing or decreasing, and the velocity of the load consequently accelerated or retarded. This variation tends, of itself, to render the work of the engine unequal during the raising of the load. But it will be observed that this tendency is counteracted by a variation in the value of the load during the same time, and that, consequently, this overlap of the rope results in an equalization of the work of the engine. When the load starts from the bottom of the shaft, it has its maximum value, for at that moment the weight of the whole length of rope is added to that of the cage with its contained load ; and it has been shown that the resistance due to the inertia of the mass must also be overcome at the moment of starting. But when the load has

Winding. 411

thus its maximum value, the diameter of the drum is at its minimum value, since the rope is then wholly uncoiled, and hence the leverage in favour of the load will also have reached its lowest limit. Moreover, as the other portion of the rope- will, at the same moment he wholly coiled upon the drum, the latter will, relatively to this portion, have attained its greatest diameter, and consequently the leverage in favour of the descending load, consisting of the empty cage, its highest value. These circumstances are evidently favourable to the equalization of the work of the engine, and it will be seen that these circumstances continue throughout the time of winding. For, as the one portion of the rope ascends and diminishes in weight, the leverage in favour of it increases in a like degree ; and as the other portion descends and increases in weight, the leverage in favour of it is diminished in like manner. The same advantages are obtained with round ropes, though under less favourable conditions, by making the drum conical. When the drum has this form, there is a liability of the rope slipping if any hitch should occur to slacken it, and such a slipping would probably cause rupture of the rope. The length, or as it is sometimes described, the breadth of the drum is obviously least with the flat rope.

When both portions of a round rope are wound upon the same drum, the length of the latter will be that required by a single rope, since one portion is being unwound while the other is being coiled upon the drum, so that the sum of the lengths coiled at any given moment is equal to the length of one portion of the rope. In such a case, one portion of the rope is wound over the drum, and the other portion under the drum. As both portions are wound over the pulley, one is thus wound in contrary directions, a circumstance unfavourable to its durability. The evil is removed by the use of two drums revolving in contrary directions, an arrangement which allows both portions of the rope to be passed over the drum. The details of fixing the rope to the drum are very simple. Usually a notch or a groove is provided on the drum to receive the end of the rope which is held in by wedging. To avoid bringing the strain of the load upon this fastened end of the rope, the length is always regulated to leave two or three coils upon the drum when the cage is at the bottom of +he shaft.

In arranging the length of the rope, the two portions are so proportioned that when one cage is resting at the bottom of the shaft, the other is resting upon the keeps at the top. A slight excess of length is given in order that the operation of raising the top cage a little above, and the lowering it upon the keeps may not affect the bottom cage. In determining the length for a new rope, a little allowance should be made for stretching. It may happen that in consequence of the working being directed to a higher seam, or from some other cause, the rope is found to be too long ; or in consequence of a defect having to be cut away, it may become too short. In such cases, as in that of putting up a new rope, it becomes necessary to proportion the lengths as required, that is, a number of coils will have to be takeji up or let out from the drums. One method of doing this is the following : the end of one rope is let down to the level of the pit mouth and the excess of the other is measured in the shaft; the former is then taken off the pulley and wholly wound upon the drum, and the end attached to it, after which the drum is turned until a sufficient length of the latter has been removed to equal the excess of length in the shaft. The first having then been replaced upon the pulley, the two ends will arrive simultaneous at the points required. If one of the two ropes requires to be lengthened, these operations will, of course, have to be reversed. By reason, however, of the great weight of the rope, its removal from the pulley offers considerable difficulties ; to escape these difficulties, where two drums are used, another method has been adopted, which consists in providing

8 a 2

412 Mining Engineering.

ail arrangement by means of which one' of the drums may be made loose. With this arrangement, the relative lengths of the ropes may be readily adjusted.

The position of the drums is a matter of importance. Eelatively to the engine, they may be placed with their axes in the horizontal plane passing through the piston rod, or they may be placed above the cylinders with their axes in the vertical plane passing through the piston rod. Each of these positions possesses some advantages to be noticed hereafter ; the former appears, however, to be preferable, and it is more commonly adopted. Eelatively to the pulleys, the level of the drums should, where easily practicable, be so adjusted that the inclined portion of the rope shall not make a very acute angle with the vertical portion ; hence the higher the pulleys, the greater should be the interval between the drums and the pit mouth. Too great a distance is, however, objectionable, by reason of the sagging and swaying of the rope. The best arrangement, where it can be adopted without difficulty, consists in erecting the drums at a higher level than the pit mouth. This is one of the advantages obtained by placing the drums over the steam cylinders. An essential condition to be observed is to place the drum and its corresponding pulley in the same vertical plane, and strictly perpendicular to their axes of rotation. A slight irregularity in this respect, by forcing the rope to deviate from one side to the other, gives rise to considerable lateral friction, which tends to rapidly destroy the rope.

The question of regulating the load to be lifted is one of the most important relating to the operations of winding. The variation in the value of the load is due, as we have seen, to the constantly diminishing length of the ascending rope, and the constantly increasing length of the des3ending rope. As the weight of the rope is great relatively to that of the useful load, it is obvious that this variation must be great also. To take an example, suppose a depth of shaft equal to 340 yards, a useful load of 16 cwt. of coal, and wire rope weighing 10 lb. a fathom, or 5 lb. a yard. As the cages are equal in weight, they may be left out of the question. At starting, the load to be Hfted is 16 X 112 1792 lb. of coal + 340 x 5 1700 lb. of rope, 3492 lb. We are not now considering the strain upon the engine, which question would involve the taking into account of the inertia of the mass, but only directing attention to the variation which takes place in the value of the load during the time of ascent. Now it will be observed that as the length of the ascending rope is constantly diminishing, its weight is constantly decreasing from 1700 lb. at starting, to zero at the lauding place at the mouth of the shaft. And as the length of the descending rope is constantly increasing, its weight is being constantly augmented, from zero at starting, to 1700 lb. at the moment of stopping at the bottom of the shaft. Moreover, as this weight acts as a counterbalance to the ascending load, the latter, on arriving at surface, will be reduced to 3492 — (1700 x 2) 92 lb. Thus during the time of ascent, the value of the load has been diminishing from 3492 lb. to 92 lb. It is easy to see that this value may become negative. Suppose the depth of the shaft to be 360 yards, instead of 340 yards. In such a case, the weight of the load, on arriving at surface, will be 3592 — 3600 — 8 lb. ; that is, the descending load will have over-run the ascending load, and the engine will have to oppose a retarding force of 8 lb.

This great variation in the load to be raised is manifestly very unfavourable to the work of a steam engine, and hence it becomes necessary to provide means for regulating the load. It has been suggested that this end might be attained by employing a variable degree of expansion. But a moment's consideration will show such means to be utterly inefficient. If it were a question merely of equalizing the speed of the engine, a skilfully contrived and carefully managed expansion would

Winding. 413

doubtless effect the purpose required. But what is needed is an equalizing of the work developed at each revolution. A high degree of expansion is demanded by the exigencies of economy in the consumption of fuel. But a high degree of expansion presupposes, not only a nearly uniform speed, but also dynamical equilibrium among the various forces exerted upon the engine. Hence it is evident that the requirements will not be satisfied by the adoption of a variable expansion. Other means of regulating the load had, therefore, to be sought, and they have been found in the counterweight, and the conical drum. It has been already pointed out that the regulating effect of the conical drum is more or less fully obtained, when a flat rope is used, by coiling the rope upon itself, whereby the virtual diameter of the drum is made to vary. We shall, therefore, consider the counterbalancing of the load and the coning of the drum relatively to the case of round rope. These means solve the problem in a satisfactory manner ; and it may be remarked that the former is more common in England, where it was first employed, and the latter on the Continent, where it has received the most attention.

The counterweight usually consists of a number of excessively heavy iron links, suspended in a pit or well from 30 to 50 yards deep, provided for that purpose. To these links is attached a rope, which is fixed to the drum shaft. The length of the balance chain is equal to the depth of the pit in which it hangs, and it is connected to the drum shaft in such a manner, relatively to its length, that when the drawing ropes are at the starting point, that is, when one cage is at surface and the other at the bottom of the shaft, its whole length is hanging in the pit. The rope by which it is wound up is also arranged so that the whole of the balance chain may rest upon the bottom of the pit when the ascending and the descending cages arrive at the same point in the shaft. This rope is made to pass over the drum shaft in a direction contrary to that of the drawing rope which it is intended to counterbalance. The action of the counterbalance will now be readily understood. At the moment of starting the engine, the whole of the links are suspended, and these, by their great weight, hold the drawing rope in equilibrium. As the latter ascends and is diminished in weight, both, by reason of the reduction going on in its own length, and of the increase taking place, at the same time, in that of the descending rope, the links are being deposited at the bottom of the pit, and, as previously pointed out, the whole of the links will be resting upon the bottom when the cages meet in the shaft, at which moment, the ascending and the descending ropes balance each other. From the time when the cages pass each other, the weight of the descending rope preponderates, and this preponderance goes on increasing until the bottom of the shaft is reached. But from the moment when the descending cage passed the ascending one, the counterbalance chain is again being wound up, this time in the contrary direction, and as it is raised link by link, its weight counteracts the preponderating weight of the descending rope. Thus it will be seen that this system of counterbalancing, if it does not give perfect uniformity, yet solves the problem of regulating the load with sufficient completeness for practical purposes. The weight of the balance links must, of course, be proportioned to that of the rope, account being taken in the calculation of the diameter of the pulley or drum upon which it is wound. This diameter, it will be observed, is related to the depth of the pit or well in which the chain hangs. The pit is generally situate on the side of the drum farthest from the shaft. Sometimes, instead of the chain, a heavily loaded tub, or truck, is used as a counterweight. In this case, the tub is made to run upon rails suitably inchned. The inclination of the road is made to vary so as to be sharp near the upper end and flat at the lower end, for the purpose of obtaining a constantly increasing or diminishing resistance. During the time of drawing a load,

414 Mining Engineeeing.

the tub runs twice over the road, first descending and then ascending. Thus the force of traction exerted by the tub upon the rope to which it is attached is greatest at the moment of starting, null at the end of its course when the cages are at the same point in the shaft, and greatest again when the cages have reached the landing place ; whence it will be seen~that the action of the tub is precisely that of the balance chain in the pit. By carefully determining the curve required, the counterbalancing of the rope may be, in this way, very counpletely accomplished, and often more easily, and at a less cost than by means of the chain. To determine with rigorous accuracy the curvature of the line upon which the tub is to run, would require the application of the higher mathematics. But in practice, rigorous accuracy is not needed, and even if arrived at by calculation, it could not be obtained upon the ground. The curve may, however, be determined approximately in a ready manner by the following method, which simply involves the use of a table of sines.

The influence of gravity, or rather the value of the force of gravity in causing a body to descend an inclined plane is represented by P W x sin. a, where F is the force sought, W the

F

weight of the body, and a the angle of the inclination. Hence sin. a , that is, by dividing the

force by the weight, we obtain the angle of the inclination. Now suppose that, to balance the weight of the rope when that weight is at its maximum value, a tractive force of 1000 lb. must be exerted by the tub upon the rope by which it is attached to the drum shaft, and that the weight of

the tub with its contained load is 1 ton. In this case, sin. a -9777 ' 0446, which the table will

show to be the sine of the angle of 26° 30'. Draw a horizontal line AB, Fig. 637, and from the extremity A lay off A at an angle of 14° 20' ; which inclination is the mean of those given below. Upon the line A 0, lay off, to some convenient scale, the length A X of the road upon which the balance tub is to run, say, for example, 50 yards ; and from the point X let fall a vertical line to meet A B at the point Y. Divide A Y into a number of equal parts, say ten, and from the points of division, erecting perpendiculars, parallel to X Y to meet A X, as shown in the diagram. Now it will be observed that as the force F is to diminish regularly from 1000 lb. at the upper end of the incline to zero at the lower end, it must have diminished by at each of ihe successive points at which the ordinates or vertical lines meet the line AX; that is, at X the force will be 1000 lb., at the next ordinate 900 lb., at the next following, 800 lb., and so on in succession until it becomes zero at the point A. The problem now is to find a curve which shall vary so as to give these results, and to do this, we must determine the angle of inclination at each of these points. Thus

4014 sine of 23° 40' ; 3568 sine of 20° 54' , and in the same way, we find 2240 ZJiW

the angles at the other points to be in succession, 18° 12', 15° 31', 12° 54', 10° 17', 7° 42', 5° 7', 2° 30'

and 0. From the point A, at which the inclination is zero, draw a line at an angle of 2° 30' with

A B till it meets the first ordinate ; from this point, draw a line at an angle 5° 7' with the horizontal

A B till it meets the second ordinate ; from this point again, draw a line at an angle of 7° 42' till it

meets the third ordinate, and continue these operations with all the angles found. The points in the

ordinates determined by these inclined lines will be points in the curve required, which may now be

drawn in ; and the distances from the base line to these points will b. the heights of the ordinates,

which may be set off on the ground.

Winding, 415

In the foregoing example, the total length of 50 yards is divided into only ten parts ; it is evident that greater accuracy will be obtained by making the intervals smaller. The curve found in this way will not be exact, as already pointed out, either in length, or in degree of curvature ; but the approximation is sufficiently close for all practical purposes.

The other means of regulating the load by means of a conical drum solves the problem less completely than the counterweight ; but it possesses the advantage of leading to less complication ; for every additional piece of machinery needing constant inspection increases the risk of failure. The question to be determined relatively to the conical drum is, what, under the given conditions, shall be the value of its mean diameter ? This question, however, practically resolves itself into another, namely, what, under these conditions, can be its initial or least diameter ? Here we have to deal with considerations of a conflicting character. The initial diameter most favourable to the durability of the ropes is the largest possible, for reasons already given. But the initial diameter most favourable to an equalizing of the moments of resistance in a deep shaft is the smallest possible, the number of coils upon the drum increasing as the diameter diminishes. It is evident that when wire ropes are used, the wear of the ropes will require a large initial diameter, since that wear will be determined by the least, and not by the mean diameter. The initial diameter should be proportioned to the thickness of the rope, in the manner already described for cylindrical drums, and the mean determined according to the conditions of the case. Thus it will be seen that the limits of variation are very narrow, and hence it results that the regulating effect is more or less imperfect. In practice, a common size of conical drum is 16 feet at the smaller end and 20 feet at the other.

Large conical drums are sometimes provided with a spiral channel for the reception of the rope, the object of this arrangement being to prevent the rope from slipping. The slipping of the rope is a danger to be feared with conical drums ; but if due care be taken to wind the rope on very tightly at first, this danger is not great upon drums having the inclination usually adopted. Of course, cheeks or side rims are required, as in the case of cylindrical drums, to guide the rope from slipping off the drum altogether. This matter has been made the subject of legislative control, and it is enacted that there shall be on the drum of every machine used for lowering or raising persons, such flanges or horns, and also, when the drum is conical, such other appliances as may be sufficient to prevent the rope from slipping. It is hardly necessary to add that the component parts of a winding drum should possess ample dimensions and be strongly connected together, and that the foundations upon which the bearings of the shaft rest should be massive and securely placed, so as to render the drum capable of resisting, not only the ordinary, but accidental shocks, and of serving as a protective medium interposed between the force and the engine.

Winding Engines. — In order to understand the requirements of a winding engine, it is necessary to consider carefully the work demanded of it. Such a consideration will at once show us that an engine used for winding purposes is required to work under conditions differing widely from those to which an engine employed in driving machinery is subjected. In lifting a loaded cage from its resting place at the bottom of the shaft, the engine must start slowly, at first in one direction for the purpose of lifting the cage at surface off the keeps, and then in the contrary direction to lower the empty cage in the shaft, and to raise the loaded one. But it is to be observed that during the time that the empty cage is being lifted off the keeps, the loaded cage is resting at the bottom of the shaft, and that, consequently, the latter does not, during that operation, exert its counterbalancing effect upon the former. When the empty cage has descended below the keeps, the force is applied to the

416 Mining Engineering.

loaded cage at the bottom, which is then lifted, and which, during a time, moves with an accelerated velocity. During this time, as already shown, the resistance is greatest. After the full velocity has been attained, it remains uniform for a few seconds ; it is then retarded, and when the cage has arrived within a certain distance of the surface, a signal warns the engineman to cut off' the steam. From this point, the ascent is made by the vis viva of the mass in motion. As soon as the cage has ascended above the shaft mouth, the engineman reverses his engine, and thereby brings the whole instantly to a stand. The cage having been stopped above the level of the keeps, a slight movement to allow the steam in the cylinder to escape, gently drops the load upon the keeps. And here it is to be again remarked that during the time of raising the loaded cage above the keeps and lowering it upon them, it is not counterbalanced by the other cage, which is then resting at the bottom of the shaft.

Now if these operations be carefully viewed, it will be clearly perceived that to ensure their regular performance, two conditions will have to be satisfied ; first, the engine must possess a considerable excess of power to give it complete control over the load, and, second, it must be constructed and regulated that the engineman may have it completely under his control. Moreover, as it is of the utmost imjoortance that the engine be always capable of performing the work required of it, and that, consequently, no failure to raise the load at any moment should be liable to occur, another condition to be satisfied is that the design and the construction of the engine should be such as to reduce the chances of derangement to a minimum. These three conditions Iiave acted to determine the type of engine employed for winding purposes.

The most approved design of winding engine consists of two coupled cylinders, and is provided with a light fly-wheel. The use of this wheel is rather to furnish a means of controlling the motion by a brake than to regulate the motion, which is sufficiently effected by the mass of the winding drum, pulley, rope, and load. With an engine so constructed and controlled, the attendant has the force at his disposal sufficiently well in hand to enable him to perform promptly the operations we have described, without having to deal with the difficulties of the dead point.

To satisfy the third condition, to which attention has been directed, the number and the importance of the parts of the engine must be reduced to a minimum, especially those which are not constantly in sight, such as the valves, pistons, and stuffing boxes. To obtain the desired simplicity, it has been the custom to construct the engine to work at high pressure, without a greater degree of expansion than is to be given by the lead of the slide valve, and without, of course, condensation. These conditions, however, though favourable to simplicity, are unfavourable to economy of fuel, and as the cost of the latter has greatly increased of late, attention is being directed to the advantages of expansion. With the improved mechanical arrangements of the present day, suitable expansion gear may be applied without adding much to the complexity of the whole, and accordingly we find the more recent engines designed to work with a variable expansion. For the same purpose of gaining simplicity, the piston rods are usually connected directly to the fly-wheel shaft, upon which the winding drums are fixed, so as to avoid the intervention of gearing. One advantage of this arrangement is that, inasmuch as there is but one revolving shaft, one brake is sufficient. The reversing gear adopted is similar in character to that employed on locomotives.

The cylinders may be placed either horizontally or vertically, the latter position being common in the north of England. Each of these positions possesses certain advantages. One advantage claimed for the vertical cylinder is that the wear of the parts in rubbing contact is less, and more

Winding. 417

equal m that than in the horizontal position. But the objection to the latter on this ground must be regarded rather as theoretical than practical. It is also urged against the horizontal cylinder that, m consequence of the mode of connection adopted between it and the bed-plate, the parts are strained by unequal expansion and contraction due to varying temperatures, and that it occupies more space than the vertical cylinder. This latter objection is, however, of very little value, and as an equivalent set-off to the former, it may be urged that the horizontal position of the cyhnder gives greater stability than the vertical, and is besides more convenient. In favour of the vertical position it IS also claimed that, with such an arrangement of the cylinders, the winding drums are placed at a higher level, and that, in consequence, the angle made by the oblique with the vertical portion of the rope is increased, whereby the wear of the latter is lessened. This advantage is indisputable, but it must be borne in mind that by increasing this angle the resultant is thrown farther out of the vertical, the consequences of which have already been noted. The chief gain derived from the higher level appears to be that it places the engineman nearer the shaft, and allows him to obtain a better view of the shaft mouth.

Power of Engines and Boilers. — A pound of coal consumed in the furnace of a steam engine will produce a certain mechanical effect, and the amount or quantity of mechanical effect thus produced may be measured in foot-pounds, that is, by the number of pounds raised 1 foot high. This effect is called the duty of the fuel, or more usually, the duty of the engine. The duty of an engine is therefore not the amount of work developed by the fuel in producing evaporation, but only that portion of the total work developed by the steam which is available for the work to which the engine is applied, the difference being absorbed by the engine itself. The duty of engines varies within very wide limits. In some instances in which expansion and condensation are carefully and intelligently carried out, we find a consumption of 1 5 lb. of coal to the horse-power an hour ; in others the consumption is as much as 7 or 8 lb. The duty of a Cornish pumping engine is usually estimated in pounds of water lifted 1 foot high by the consumption of a bushel of coals. As high a duty as 125 millions of pounds has been reached by this class of engines. Such results must, however, be regarded as altogether exceptional. The more common duty obtained from a well-managed engine used in the mining districts is from 65 to 75 millions. The duty of an engine is not to be confounded with its power. The duty, as we have seen, is the work developed by a given weight of coals without reference to time. Thus, whether a bushel of coal raise 70 millions of pounds a foot high in one hour or in twelve hours, the duty of the engine is the same. But the power of the engine is quite different, being estimated by the work it is capable of performing in a given time. Hence, while the duty of the engine is measured by the number of pounds raised 1 foot high, its power is measured by the number of pounds raised 1 foot high in one minute. To avoid the large numbers involved in this mode of estimating the power of an engine, it is customary to express it in terms of the higher unit horse-power, which represents the power requisite to raise 33,000 lb. 1 foot high in one minute. Thus an engine of 10 horse-power is capable of raising 330,000 lb. 1 foot in a minute, or about 20 millions of pounds an hour. This is known as effective horse-power, to distinguish it from nominal horsepower, the latter being a term somewhat capriciously employed by makers to express certain cylinder capacities and dimensions. In determining the dimensions of a boiler for a stationary engine other than the Cornish engine, it is customary to assume that for every effective horse-power to be exerted by the engine, 1 cubic foot of water an hour must be evaporated by the boiler. This allows a very large percentage of waste in the engine, greater probably than ever takes place ; but the error is on

3 H

418 Mining Engineering.

the safe side, and the rule may be considered as sufficiently accurate in practice. When, therefore, the term horse-power is applied to boilers, it is to be understood as indicating their capability of evaporation at the rate of a cubic foot of water an hour. Thus a boiler of 50 horse-power is one capable of evaporating 50 cubic feet of water an hour, the furnaces being worked in the ordinary way. The dimensions of the grate and the extent of heating surface necessary to produce this rate of evaporation vary more or less according to the practice of different engineers ; but generally it is agreed that 1 square foot of grate surface is requisite for every horse-power in the boiler. Thus it follows that as much fuel is consumed an hour upon a square foot of grate surface as is necessary and sufficient to evaporate a cubic foot of water. The extent of heating surface in the boiler is generally estimated at the rate of 15 square feet to the horse-power. Thus a boiler of 50 horse-power requires a heating surface of 750 square feet. In the Cornish boiler, on account of the slow combustion maintained on the grates, 2 square feet of the latter are allowed to the horse-power, and the extent of heating surface is increased four or five times.

In proportioning the dimensions of the cylinder, it is a common practice in all stationary land engines to make the diameter equal to half the stroke of the piston. With respect to the absolute dimensions, it is obvious that the magnitude of the cylinder and the piston necessary to produce a given power must depend upon the pressure of the steam after it has entered the cylinder and the velocity with which the piston moves, the degree of vacuum on the other side of the piston, if any, and the grade of expansion carried out. When the piston and the other reciprocating parts of the machinery change the direction of their motion at the end of each stroke, they will be, for a short interval, before and after the change, accelerated and retarded. This acceleration and retardation is still greater when the steam is used expansively, since, in that case, the impelling power varies in intensity. In practice, however, the irregularity is effaced by the momentum of the fly-wheel, and we may assume for the purposes of calculation that the motion of the piston is uniform. The question which then remains is, what determines the rate of this uniform speed ? In other words, what are the conditions that determine whether the piston shall have a velocity of 100 or 200 feet a minute ? The velocity of the piston will depend upon the rate at which the boiler is capable of supplying steam of the requisite tension to the cylinder. Suppose, for example, that the resistance on the piston is equal to a pressure of 20 lb. to the square inch of its surface. To drive the piston at any given rate, the boiler must be capable of supplying steam at a tension of 20 lb. in sufficient quantity to fill the space swept through by the piston in a given time. As an illustration, let us assume that the required speed is 200 feet a minute and that the area of the piston is 78 5 square inches, corresponding to a diameter of 10 inches, which, expressed in square feet "545. Then to enable the piston to advance through a space of 200 feet, it must be followed by a column of steam 200 feet in length and 545 square foot in section, which equals 109 cubic feet of steam. But the relative volume of steam at a pressure of 20 lb. as compared with the water from which it is produced, is that of 1222 to 1. Dividing, therefore, we have

'089. The boiler must thus be capable of evaporating 089 x 60 5"34 cubic feet of

water an hour. That is, allowing a margin for the increased resistance due to the speed, the boiler must be of 6 horse-power.

Eelative

Eelative

Belative

Total

Volume, or

Total

Volume, or

Total

Volume, or

Pressure

in lb. per sqjiare

Corresponding Temperature.

cuVjic inches of Steam produced by a

Pressure

in lb. per square

Corresponding Temperature.

cubic inches of Steam produced by a

Pressure

in lb. per square

Corresponding Temperature.

cubic inches of Steam produced by a

inch.

cubic inch of Water.

inch.

cubic inch of

"Water.

inch.

cubic inch of Water.

By means of the foregoing Table, many practical problems, similar to the preceding and of great, utility, may be solved with the aid of common arithmetic alone. The temperatures corresponding to the pressures have been carefully calculated. They will be found to vary somewhat from those of similar tables that have been published ; but it is believed that they are more accurate, the formulae by which they were calculated being fully confirmed by the elaborate calculations of Zeuner and Eankine respecting the relation existing between the latent heat of evaporation, the temperature, and the specific volume of steam.

The following examples illustrate the use of the preceding Table :

1. A boiler is capable of evaporating 20 cubic feet of water an hour. The pressure of steam in the cylinder being 20 lb., what must be the diameter of the cylinder to give a piston speed of

200 feet a minute ?

By referring to the Table, we find the relative volume for 20 lb. to be 1222. Hence

=407-3 is the number of cubic feet of steam that will pass through a cylinder a minute,

and 407-3 X 144 293-2 square inches the area of the piston. A table of areas will at once

o-ive the diameter,

420 Mining Engineeeing.

2. A piston 20 inches in diameter is required to move with a velocity of 200 feet a minute against a gross resistance of 10,000 lb. ; it is required to find the requisite boiler power.

A table of areas gives 314*1 square inches for a diameter of 20 inches. As the resistance is

10,000 lb., the pressure to the square inch will be 31 '8 lb. The next greater pressure to

this in the Table is 32, the relative volume corresponding to which is 786. The area of the piston

in square feet being 2*181, the power of the boiler 31*77, say 32 horse-

power.

3. Given a piston 30 inches in diameter, supplied by a boiler of 50 horse-power, it is required to find the pressure to the square inch that can be given to the piston when the latter has a velocity of 200 feet a minute.

The area of the piston is 706*8 square inches 908 square feet. Hence —

1177*9, the number of cubic inches of steam that would be produced by a cubic inch of water. The nearest number to this in the Table is 1167, and the pressure corresponding to this number is 21 lb. We may therefore assume that the required pressure is 20| lb.

4. Griven a piston 40 inches in diameter, and a boiler of 50 horse-power ; it is required to find at what velocity the piston may be driven against a resistance of 20 lb. to the square inch. For a pressure of 20 lb. the Table gives 1222 as the relative volume. Hence 1222 x 50 61100 is the number of the cubic feet of steam that passes through the cylinder an hour. The area of the piston

in square feet being 8*72, we have 116*8, say 116 feet a minute.

In calculating the power requisite in a winding engine to perform a given work, we must bear in mind, first, that a considerable excess of power is required to give the engine complete control over the load, and, second, that the engine must possess sufficient power to enable it to lift the load under the most unfavourable circumstances. It has already been pointed out that the loaded cage at surface is being raised and lowered while the other cage is resting at the bottom of the shaft, so that the former is deprived of the counterbalancing effect of the latter. Thus it will be seen that the engine may be, and at every winding is, required to work with only one rope ; and, consequently, it must possess sufficient power to do this, and still to have that excess which is needed to give it full control over the load. But it may also be required to lift the load under the unfavourable conditions when one of the pistons is at the dead point and the other at half centre, conditions most unfavourable to the engine. And hence it will be necessary to give the piston such a diameter as will enable it to do this easily. The diameter will be determined by the resistance to be overcome ; and as account must be taken of the obliquity of the connecting rod, the area of the piston will have to be multiplied by the effective pressure of the steam and by the coefficient 0*95. When the second piston begins to act, the force will not be doubled, because the connecting rods are in oblique positions, but the total force exerted will be expressed by the area of the piston multiplied by the pressure of the steam in the cylinders and by the coefficient 1 40. To take an example for the purpose of illustration, suppose the weight of the cage and its attachments to be 12 cwt., that of two tubs to be 6 cwt., and that of their contained load 16 cwt. ; total 34 cwt. To this must be added 5 per cent, for the resistance due to inertia and friction, giving thus a total resistance of 35*7 cwt.

Winding. 421

3998-4 lb., say 4000 lb. to be overcome by the pressure in one cylinder when the piston is in the middle of its stroke. Assuming an effective pressure of 45 lb. to the inch, we have, as the expression of the force utilized, a; x 95 x 45 42 75 a; being the area of the piston. But as the engine is to have an excess of power, we shall have to take a lower value for the coefficient than 0-95, say 0-80. With this value, we have a; x 0-8 x 45 36 as the expression of the force required to overcome the resistance. As the value of the resistance was 4000 lb., we have 36 x 4000,

whence x -j lUi inches. A table of areas will show that to obtain this surface, the piston

must have a diameter of 12 inches. Hence the engine required must have two 12-inch cylinders. The boiler power for such an engine may be calculated in the manner already described.

Acoessori/ Arrangements and Precautionary Measures.— It is of essential importance that the engineman should at all times and under all circumstances have complete control over his engine, so that he may be able to promptly accelerate or to retard the speed, and to stop the motion within a space of time corresponding to a small fraction of a revolution of the winding drum. To do this, he will, under ordinary circumstances, set in action only the starting and the reversing gear. But as a safeguard against accidents in unusual circumstances, he must have under his control, and ready for instant application, a brake of sufficient power to instantly stop the engine with full steam on. This brake is applied, as previously remarked, to the fly-wheel, the circumference of which it nearly surrounds ; and it is worked either by some such means as a weighted lever, or by steam, the latter system being by much the best. The brake should be always on while the engine is standing, to prevent the occurrence of accidents ; it should be taken off by the engineman at the moment of starting, and again applied by him the moment the engine has stopped, unless some unusual occurrence requires it to be brought into operation for the purpose of instantly stopping the engine. In the case of the steam brake, during the time that the brake is on, its cylinder should be in communication with the boiler, in order to keep it nearly of the same temperature as the latter, so as to avoid condensation of the steam on admission, for it is essential that the pressure should act instantly. As a safeguard against an accidental releasing of the brake, an arrangement is frequently added, consisting of a screw worked by a hand wheel, by means of which the brake is held down. Before starting, the screw has to be withdrawn sufSciently to allow the brake to be released. When the engine is not connected directly to the drum shaft, two brakes are needed, one upon the fly-wheel of the engine, and the other upon the drum shaft. The latter, which will be worked by a weighted lever, should be always off, its application being reserved for the case of fracture of one of the geared wheels.

It is obviously necessary to the satisfactory performance of the operations of raising and lowering the cages that the engineman should at all times know exactly the position of the latter in the shaft. He should be able to watch the descent and the ascent of the cages from the moment of starting to the moment of stopping. As, however, the cages themselves cannot be seen, means must be provided for rendering their position visible in the engine house. Some of the means adopted fulfil the purpose completely, others in a less perfect degree. The most simple means consists in painting a white mark upon the winding rope at a certain height above the cage. When this mark appears at surface, the engineman knows that the cage is near, and he prepares accordingly to land it. At night, it is necessary to have a strong lamp placed so as to render the rope at the shaft mouth clearly visible. It will be observed that this means shows only one position of the cage, and is, therefore, far from

422 Mining Engineering.

fulfilling the requirements of an indicator. It is useless when the cage has to be stopped at different levels in the shaft. Another means, fulfilling all the requirements, consists of the following arrangement. A representation to scale of the shaft is drawn upon the wall of the engine house in front of the engineman as he stands at his post, and in such a place that he can see the whole of it clearly. Two weights, to represent the cages, are suspended from cords, against the wall and within the lines representing the sides of the shaft, which, of course, is shown in section ; the cords pass over pulleys at the top, and are led to a shaft driven by gearing from the drum shaft, which gearing is adapted to give to the indicator shaft the number of revolutions which, relatively to those of the drum shaft, are required by the scale of the shaft drawing. The weights, having been adjusted to the positions of the cages in the shaft, the engineman is able to watch the course of the latter with as much certainty as if they were visible. Instead of a sectional representation of the shaft, it will obviously be sufficient to draw a line and to mark upon it points corresponding to the landing places ; in such a case, the weights would slide up and down, one on each side of the line preferably. But the sectional drawing possesses the advantage of removing all necessity for reflection on the part of the engineman by showing the position of the cages instead of merely indicating them. To call the attention of the engineman, a bell may be added, to be sounded by the ascending weight when it has arrived within a certain distance of the surface line. Yarious other devices for the same purpose have been adopted, one of which is an endless screw, driven from the engine shaft, upon which screw a block is made to travel backward and forward, and to sound a bell at a certain point ; but it is unnecessary to describe them all.

As the rupture of the winding rope entails very serious consequences, it is desirable that every possible precaution should be taken to prevent the occurrence of such an accident. It has already been pointed out that for this reason the working load should be such as will allow a wide margin of strength. But when this precaution has been taken, frequent and careful inspection is needed to guard against the dangers arising from wear and tear, and it is desirable to adopt such arrangements and expedients as will prevent the occurrence of excessive strains. The engineman should avoid sudden variations in speed, and he should be especially careful to start gently. As the empty cage descends below the keeps at the mouth of the shaft, the strain of the load at the bottom of the shaft is brought suddenly to bear upon the other rope, and it has been shown that the strain due to the load is greatest at that moment. To prevent a shock, the speed of the rope should be very low at the moment when the strain of the load is brought to bear upon it, and until the load is fully lifted, the engine should not be started. The shock, which in some degree must inevitably occur, may be greatly lessened by the interposition of some elastic medium through which the force will be applied gradually. The rope itself is such a medium, but it is a very imperfect one. "When the descending cage comes to rest at the bottom of the shaft, the rope contracts a little in consequence of the strain due to the weight of the cage and tubs being removed. After the cage has received the loaded tubs, and when the engine begins to wind up the rope, the latter stretches to the extent of the previous contraction, and this extension is increased in a degree proportional to the weight of the coal. But the total amount of extension is not sufficient to wholly prevent a shock, even when the engine is skilfully handled. To effect that highly desirable object, a spring is sometimes interposed with very good results. The spring used is in most cases a coach spring, and it is attached to the chains from which the cage is suspended. It has been found that the durability of wire ropes is considerably increased by the interposition of this elastic medium. Another expedient of the same character is

Winding. 423

the elastic support for the pit-head pulleys proposed by M. Gruibal, and adopted at several mines in Belgium. One advantage of this arrangement lies in the protection from shocks which it affords to the pulley frame.

Security against overwinding, over and above that afforded by the brake, is sometimes sought to be obtained by various contrivances designed to act upon the cage. Allusion has already been made to the safety links and hooks invented for this purpose. One arrangement consists in continuing the wooden guides up to the top of the pulley frame, and in providing at a certain height a set of lever keeps similar to those used at the mouth of the shaft. These keeps are counterweighted and set to be lifted out of the way by the ascending cage, and to drop back into their position as soon as the cage has passed. The object of the arrangement is to arrest the descent of the cage should the rope be ruptured when the cage is brought into contact with the upper portion of the headstocks, and is thus to prevent rather the disastrous effects of overwinding than overwinding itself. The latter object may be effected by means of some arrangement which will set the brake in action when the cage ascends to a certain height up the headstocks. Such an arrangement may be devised in many ways. Probably the best is to have some attachment upon the indicator shaft, already described, which, when a certain point is reached, corresponding to a dangerous position of the cage, shall admit steam into the brake cylinder. An arrangement of this nature, in combination with the set of keeps described, would give almost perfect security against the appalling accidents occasioned by overwinding.

The engineman should be stationed in such a position that he can see clearly the ropes at the mouth of the shaft, and have his governing levers conveniently at hand. He ought not to obey a signal to set the engine in motion until, by a glance at the mouth of the shaft, he has assured himself that all is right. The engine room should be an object of special attention ; it should be so well lighted, and everything in it so arranged, that any imperfection in the parts of the machinery, or any derangement of those parts, may be at once seen. The external moving parts of the engine should be kept perfectly clean and bright, and to this end means should be employed to protect them from the water brought in upon the ropes. Rules also should be made and strictly enforced to prevent unauthorized persons from entering the engine room ; where so much depends upon the care of the engineman, no precautions should be neglected to avoid occurrences whereby his attention is distracted and his motions impeded. A properly regulated engine room affords the greatest security against accidents and delays in winding.

Cost of Winding. — It is very difficult, if not impossible, to give such data concerning the cost of winding as will enable one to form even a rough approximate estimate for any given conditions. It will be perceived on reflection, that the cost must tend to diminish for a given tonnage as the depth increases, and that the same tendency of the cost to diminish will exist when, for a given depth, the tonnage increases. For some of the elements of the total cost increase proportionally, or nearly proportionally, with the depth, or with the tonnage ; others increase in a much less degree, and others, again, are almost independent of depth and tonnage. Hence it becomes necessary to estimate every individual case on its own merits. The cost of labour is a variable quantity respecting which nothing determinate can be laid down. The same may be said of the cost of the fuel consumed. It has been pointed out that the conditions of economy of fuel are necessarily far from being satisfied in a winding engine, and hence the consumption will be great and variable, the quality of the fuel being usually very low.

424 Mining Engineeeing.

The following example of a case in practice may serve as an indication of what, under similar conditions, the cost of winding may be expected to attain to. The depth being 340 yards, and the output 600 tons a day, it was found that the cost of winding per ton was 21 of a shilling, or 2d., made up in the following manner :

s. Labour (wages of engineman, stokers, onsetter and banksman, and assistants) ,, .. ., 0'09

Fuel (slack and inferior qualities of coal) .. .. .. .. .. .. .. ., 0*06

Eope (wire rope exposed to average conditions of wear) .. .. .. .. .. ,. O'Oi

Maintenance of engine, drums, and pulleys .. .. .. .. ,. .. .. ,, 0*02

In this estimate of the cost, no account is taken of the depreciation of the machinery. For this 5 per cent, should be allowed, and also 5 per cent, for interest on the capital sunk. Taking the cost of the machinery and shaft fittings as follows :

£ Winding engine complete, with boilers .. .. ., .. ., „ ,, ,, ., 2700

Pulley frames, and its accessories .. .. .. .. „ .. ., „ ,. 200

Shaft fittings .. .. .. .. .. .. .. ., .. .. ,. .. 320

Laying out pit eye and pit bank .. .. ., .. .. .. ., ,. ,. ,, 40O

Total 3700

We have 10 per cent, upon this sum 3701, and assuming winding during 300 days in the year, this will give 04 of a shilling as the cost per ton. Thus the total cost of winding is 0*21 + 04 3d. a ton.

The following information concerning the winding engines at some of the best known collieries in this country is indicative of what may be met with in practice :

Kippan Colliery, Leeds, Yorkshire: Depth of shaft, 108 yards; daily output, 350 tons, in eight hours ; engine of two horizontal cylinders, connected directly to the drum shaft ; distance of engine from shaft, about 15 yards.

South Brancepeth Colliery, Brancepeth, Durham : Depth of shaft, 88 yards ; daily output, 700 tons, in twelve hours ; vertical beam engine.

Clifton Hall, Clifton, Lancashire : Depth of shaft, 526 yards ; daily output, 800 tons, in thirteen hours ; engine of one vertical cylinder, directly connected to the drum shaft.

California Pit, Wigan, Lancashire : Depth of shaft, 306 yards ; daily output, 600 tons, in ten hours ; engine of two vertical cylinders, connected directly to the drum shaft.

Porster and Richard Pits, at Seaton-Delaval, Durham : Depth of shafts, each 220 yards; daily output, 1200 and 400 tons respectively, in ten hours; engines of two horizontal cylinders, directly connected to the drum shaft ; diameter of cylinders at Porster Pit, 36 inches; diameter of cylinders at Eichard Pit, 20 inches ; length of stroke, 6 feet and 3 feet 6 inches respectively.

Monk-Wearmouth Colliery, Sunderland: Depth of shafts, each 568 yards; daily output, 1100 and 500 tons, in twelve hours ; engines of one vertical cylinder, connected directly to the drum shaft ; diameter of cylinders, 67} inches ; length of stroke, 7 feet.

Drainage. 425

Chapter X.

Deainage.

The foregoing chapters deal with those operations which lead directly to the extraction of the coal from the earth. But there are others of a subsidiary character which, though they do not tend directly to the same end, must be carried on at the same time. Of these, the two most important are drainage and ventilation, and these it now remains to consider.

To obtain a full knowledge of the important subject of drainage, it is necessary first to have a clear understanding of the manner in which water flows into the workings, and of the conditions under which its influx is effected ; and second, to possess an intimate acquaintance with the mechanical means employed to remove the water which it has been impossible to avoid or to stop back. Thus the subject divides itself for the purpose of consideration into : Underground water, that is, water as it exists in the rock beds ; and Pumping machinery ; and under these two heads we propose to treat it; the latter, however, claims and will receive the larger amount of attention.

Underground Water. — The study of the conditions under which water exists in the rock beds is a wide one, and full of interest to the mining engineer. But it cannot be entered upon, except in a very general way, in a work like the present, which is required to deal, rather with the means of removing the water met with, than with the circumstances that bring it in the way of the miner. It is, however, desirable to take a general view of the subject before entering upon a consideration of the mechanical appliances employed to rid the workings of the water which finds its way into them.

The sedimentary rocks consist of permeable and impermeable beds, the latter being composed of clays. Now, as it is a well-known fact that the sandstones and the limestones may contain various proportions of argillaceous matter, and that the clays may be more or less largely composed of arenaceous and calcareous substances, it will at once appear that the degree of permeability may vary within very wide limits, and that, judged by this quality, no definite classification can be made, since the beds may pass, through insensible gradations, from the very open and permeable to the extremely dense and absolutely impervious. Sedimentary rock consists, as pointed out in the first chapter, of an aggregation of small, but of various size, particles of pre-existent rock, compacted by pressure, and often cemented together by the infiltration of some mineral substances. The interstices between these component particles are, when removed from the influences operating at and near the surface, always filled with water, and hence the quantity of water held by auy given rock will be proportional to the space afforded by these interstices. This fact is well illustrated by the case of a

4:26 Mining Engineeeing.

sponge : while its pores are distended, it will hold a certain and a large quantity of water ; but when, by compression, the pores are closed, nearly the whole of the water is expelled The interstices in the rock may be regarded as analogous in character to the pores in the sponge. It is evident that a rock compacted by pressure will possess a greater water space than a rock of the same kind whose particles have been cemented together, because the cement partially fills up the interstices. Thus a compact bed of sand will hold per unit of volume a larger quantity of water than a cemented sandstone. The particles of argillaceous matter exist in a state of extreme division, so that the interstices are insufficient to allow the presence of water; therefore it is that clay is impervious. As this substance becomes mingled with others, the interstices are filled up ; and the argillaceous sandstone, for example, contains a much smaller water space than the purely arenaceous rock.

So far we have considered the interstices between the component particles of a rock as reservoirs of water ; but in practice, we have to deal with them solely as passages for water. It has already been stated that, when the rock is removed from the influences which promote evaporation, these interstices are always full of water. When an accession of water takes place from above in consequence of the rains, the whole is set in motion, the escape being at points situate at a lower level than that upon which the rain falls. The quantity of water passing through a given section in a given time will again obviously be proportional to the water space existing in the rock, so that the same observations hold whether we regard the space as a reservoir or as a passage.

Thus it appears that there are strata which are water-bearing, and strata which are not waterbearing, and that these may alternate with each other. It must not be assumed, however, that because the nature and the texture of the rock are such as will give it a large water-bearing capacity, that, therefore, it is necessarily full of water ; and it may be remarked that, as a matter of fact, rock beds of a porous character are frequently passed through without any water being met with. For a stratum to contain water, the conditions must be favourable to its receiving water.

The source of underground water is rain, and hence it is obvious that the quantity received will, in a great degree, be dependent upon conditions prevailing at the surface. These, which may be described as conditions of reception, are deserving of careful attention. Suppose, for the sake of clearness of understanding, that a patch of impervious rock is underlaid by a permeable stratum, the latter being horizontal. As the patch of overlying rock has no water-bearing capacity, of the rain which falls upon it, one portion will remain upon the surface, being there retained in hollows, by the adhesion between the water and the rock, and by the obstruction offered by vegetation, and the rest will flow off by the streams, and be absorbed by the underljnng stratum. The former portion will be absorbed by the vegetation and removed by evaporation, and the quantity will clearly vary with the amount and nature of the vegetation, and with the physical features of the surface. A much larger proportion of the water descending as rain will flow off a sharply inclined than off a level surface. This fact is an important one to be taken into account in hilly districts. The portion which flows off will be added to that which falls upon the permeable stratum. Suppose, again, the conditions reversed, and that we have to consider the case of rain falling upon a patch of permeable rock underlaid by an impervious stratum. In this case, only the excess will flow off by the streams ; the remainder, over and above that absorbed by the plants and removed by evaporation, will pass down till it meets the underlying impervious stratum, and then flow out in all directions around the edges of the permeable bed. Now it is to be observed that if the lower and impervioiis bed were inclined, the water would flow out of the upper and permeable bed towards the dip and the strike only, and

Deainage. 427

not towards the rise, and that the flow will be greatest towards the dip. These are important facts to be considered in estimating the quantity of underground water likely to be met with.

But the land surface is usually formed by the upturned ends of inclined strata, and this is the case which we shall always have to consider in dealing with the water in underground workings. As an illustration of this case, suppose a permeable stratum cropping out to surface between two impermeable strata. It is evident that in such a case the permeable stratum can receive water only along the line of its outcrop, and that the quantity of water which it can receive will depend upon the extent of that surface and upon the conditions there prevailing, as already described. Thus the extent of the absorbing surface is, as we have shown, to be estimated, not merely by the area of the stratum exposed, but also by that of the impervious strata which drains itself upon the former. And the physical conditions which modify the results must also be taken into account.

It has already been stated that a notable proportion of the water which falls upon the surface as rain is absorbed by the plants and removed by evaporation. In consequence of this absorption and evaporation, the water spaces within the influence of these actions may be partially empty ; near the surface they may be completely empty, and the degree of vacuity will diminish in depth. When rain falls upon this surface, the empty water spaces must be filled up before any accession can be made to the whole body of water in the stratum, that is, before any excess can begin to flow off. This is the reason why the effects of heavy rains are not felt in the workings of a mine till some time after they have fallen, and sometimes not at all.

The foregoing may be regarded as the normal conditions under which water exists in the rock beds ; but it may also be met with by the miner under what may be described as accidental conditions. It was shown in the chapter devoted to geological considerations that rock beds are divided by joints, and fractured by faults of dislocation. The joint spaces may be filled with water, and the fissures along the line of the fault may serve as passages through which water may flow in large quantities, or in which it may stand as in a reservoir. Existing under these conditions, water may be met with in the impervious beds, and in the igneous rocks ; and in mining, the tapping of one of these reservoirs or water passages occasions the influx into the workings of a stream of water called a feeder.

It will be perceived on reflection that the foregoing considerations are of great and direct practical importance, since they enable us, by means of a survey, to determine the quantity of water likely to be met with in sinking at any given point, and to make provision against its entrance into the permeable strata, to some extent, by means of surface drainage. Of course, an estimate founded upon such data can be only roughly approximate, but it has its value. It is important to be able to ascertain whether water will or will not be found at a given point, and whether it is to be expected in large or in small quantities. It must, however, be borne in mind that the results arrived at by a consideration of the facts described are rather positive than negative ; that is, we may be certain of meeting with the water whose presence we have foreseen, but we cannot be equally certain of not meeting with water whose presence we have, after an examination of the ground, not foreseen, and this on account of the accidental circumstances to which attention has already been directed. A consideration of the same facts will also enable us to judge whether a feeder is likely to be temporary or permanent, and also of the quantity of water it is likely to yield. A clear understanding of the conditions under which water exists in a permeable stratum will moreover, enable us to perceive how the breaking down of the roof, and the consequent fracture

428 Mining Engineeeing.

of the overlying beds, may let down water into the workings. A knowledge, indeed, of such facts as we have briefly described is of daily application, and should be possessed by every mining engineer.

In judging of the effects of letting down the roof above which a water-bearing stratum is situate, the nature of the intervening rock must be taken into account. Beds of plastic clay sink without fracture, and shaly and marly beds may be broken down with a like result ; for though fractures may, to some extent, occur in these, the fissures will close during the descent, in consequence of the yielding character of the material. Thus the water will not be let down in such a case. But if the rock be strong sandstone, and especially if it be of coarse texture, it will be greatly fractured in its descent, and the fissures thus produced will be left open. In this case, if only a very thin impervious bed intervene between the water-bearing bed and the sandstone, or if the intervening bed be somewhat permeable, the water will flow down copiously into the workings, and in a manner very difficult to deal with. In judging of the quantity of water to be encountered in a fault, its extent and width must be taken into account, and also the degree to which it is filled up, and the nature of the contained material. Of no less importance is the configuration of the surface where it comes up to day. If the throw is visible at surface, the valley or hollow occasioned thereby will cause large quantities of water to enter; and the same result will occur if the fault, at any part, underlies a stream. The near presence of a fault is frequently indicated by an increasing degree of moisture in the rock. In the limestone, it is a common occurrence to meet with caverns and wide passages through which large quantities of water are circulating. These are called " pounds " and "swallows"; they are, doubtless, fissures which have been enlarged by the action of acid water. It is rarely possible to foresee the existence of such sources of water.

Means for Preventing the Influx of Water into Underground Workings. — Various means are adopted to prevent the influx of water into underground workings. Of these, some are applicable at the surface only, and they have for their object the lessening of the quantity entering the permeable bed. It is clear, from what has been said, that a system of drainage at that portion of the surface at which the beds or the faults crop out will greatly reduce the quantity entering. Obviously any such system must include, to some extent, the contiguous impervious beds, from off which, as we have shown, the water flows to the permeable bed. Hollows and streams upon the outcrop demand particular attention ; often it may be desirable to divert the course of a stream ; and in some cases, it may be well to puddle its bed at certain points. An example of such a system of drainage is to be found in the basin of the Rive-de-Gier, France, a large portion of which coal field could not have been worked had the surface drainage not been provided for.

In combination with the surface drainage, means will be employed underground to prevent the entrance of water into the workings. The method of stopping back the water in shafts by means of tubbing has already been fully described. That of shutting back, by means of dams, water entering certain portions of the workings, will be described in a subsequent chapter. Of the precautions to be taken against the entrance of water, the chief relate to the breaking down of the roof. This matter has already been remarked on. It may be hardly necessary" to add that great care should be observed not to let down, by the dropping of the roof, water from ponds, reservoirs, and streams at surface. It may be remarked that when the surface sinks over worked-out places, the principal fissures will exist along the perimeter of the sunken portion ; that is, between the portion which has subsided, and the firm ground.

Deainage. 429

Pumping Machinery. — The water which in greater or less quantities will always enter the workings of a mine, notwithstanding all the means employed to keep it out, must be removed to allow the operations of excavation to proceed. And as the influx will be continuous, the means employed must be capable of acting continuously. It is obvious that the only way of freeing underground workings of the water which has flowed into them is to convey it to surface. When the workings are in a hill, and thus above the general level of the country, or above the level of a neighbouring valley affording an outlet, they may be drained by means of tunnels called, in such cases, " adits," through which the water may be made to flow out. But when this favourable circumstance does not exist, the water must be lifted to surface. As the operation of lifting large quantities of water from great depths requires great power, and as, moreover, the removal of the water must go on continuously to prevent a flooding of the workings, the mechanical appliances used for that purpose possess very great importance and demand careful study. Such appliances we have now to consider, and in treating of them, it will conduce to clearness to determine the requirements and to examine the construction of each of the several parts separately.

It was pointed out in the chapter on Shaft-sinking that the shaft is continued down below the level of the workings to form a well into which the water from the workings is drained. This well is called the sump, and into it the pumps, or other mechanical appliances, dip. But besides the sump, another reservoir is provided somewhere along the water level, or water gate. It consists of an excavation made on the lower side of the level, of sufficient dimensions to contain the drainage of the mine for two or three days, and communicating with the sump by a passage or drain. The use of this reservoir, which is called the " standage," is to impound the water flowing from the workings during the time that the pumps are undergoing repair. The sump and the standage may therefore be regarded as adjuncts of the water-raising machinery.

Where the quantities of water to be dealt with are small, the drainage is frequently effected by means of a bucket or tank, similar to that described under the head of Shaft-sinking, which tank is raised and lowered by the winding engine during the time that the latter is not required to lift coals. This is a cheap method of raising the water. Commonly, however, it is necessary to have the water machinery distinct from the winding, so that both the water and the mineral may be raised simultaneously. In such cases, pumps are used, and it is this kind of machinery that now claims consideration. Many of the following remarks will be found in fuller detail in articles on "Pipes," and on "Pumps," contributed by the author of the present work, in 'Spons' Dictionary of Engineering,' to which the reader is referred for further information on these subjects.

The first requirement of a pump is due efficiency. This requirement is common to all classes of machines, and is of primary importance in all. In determining, however, what is due efficiency, regard must be had to the character of the work performed, and also to the conditions under which it is performed. A pump for draining a mine, for instance, may return in water raised 10 per cent, less than another pump applied to the draining of a surface, and yet the former may be a more satisfactory machine than the latter. Thus, due efficiency must be considered relatively not absolutely. This is more or less true of all machines ; but it is especially true of pumps, which are established under such various and unfavourable conditions.

A second requirement for a pump is that it shall be simple in construction, and not liable to get out of order. The nature of the work required of a pump demands almost absolute immunity from derangement. It is erected in positions where it is most difficult of access, and the cost of repairs is

4-30 Mining Engineering.

consequently excessive. Moreover, if required to work continuously, or at short intervals, a delay of a few hours may result in incalculable loss and inconvenience. And it must not be forgotten that pumps, more perhaps than any other kind of machinery, are entrusted to the management of unskilled hands. The rough and ignorant usage to which pumps of all kinds are constantly subjected, would be speedily fatal to their working, were they not constructed of few moving parts, of great strength and simplicity, easily replaced in case of accident, and capable of being repaired by the most inexperienced hands.

Force may be applied to a liquid through the medium of a pump in two ways. One way is to bring the liquid upon a piston working up aid down in a cylinder, to the upper end of which a pipe may be fixed ; the upward motion of the piston then raises the water at every successive stroke until it reaches the top of the cylinder or pipe. Pumps of this kind are called lift pumps, because the liquid is lifted by the piston to the required height. And it is obvious that this height is limited only by the strength of the materials and the force available. In such a case, atmospheric pressure is employed to raise the water a portion of the height. This part of the pump, which is below the piston, is called the " suction," and that above the piston the " lift." The suction should not exceed 25 feet in height, for though a column of water is not in equilibrium with the atmospheric pressure until it reaches a height of about 33 feet, the resistance occasioned by friction, as well as the rapid flow necessary to the satisfactory working of a pump, forbids the attaining of this limit. Even 25 feet is too high to ensure a perfect working, and when large quantities of water have to be raised, it is better to limit the suction to 20 feet. The height of the lift is theoretically limited only by the considerations mentioned above, but practically the limit is somewhat restricted. The piston rod is inside the ascension pipe, and consequently lessens the area or water space on that side of the piston, thereby largely increasing the friction. This circumstance necessitates the use of iron for the piston rods, in order to reduce their dimensions to a minimum. But even with this ma+erial, the dimensions requisite for a great height would considerably reduce the efficiency of the pump. Another reason for limiting the height of a lift is the necessity of counterbalancing the whole weight of the piston and rods. But a more serious objection to the use of a lift pump for a great height is the rapid wear and frequent derangement to which it is liable, with the consequent difficulty of repairs. This defect constitutes an objection to the use of lift-pumps, where a continuous working is an essential condition. The wear of the leather rings forming the packing of the bucket of a lift pump is often extremely rapid, particularly when it is aided by the action of water charged with particles of sand or gravel, or contaminated by mineral solutions that impart a corrosive quality. And there is no certainty as to the time a bucket will last ; for it may vary, according to circumstances, from two to three days to from two to three months. The labour of changing is in all cases expensive, but it becomes extremely so for a great height. Hence, it must be concluded that lift pumps are unsuitable for great heights and continuous working.

The other mode of applying force to a fluid by means of a pump is to bring the fluid beneath a piston working up and down inside a cylinder ; the downward stroke of the piston then forces the fluid up through a pipe provided for the purpose, or in any other direction that may be required. This kind of pump possesses many advantages over the preceding. The plunger variety, which is by far the best, was invented by Sir Samuel Morland in 1675. A remarkable feature of this invention is the stuffing box, without which the steam engine could hardly have come into existence. The hemp packing of this stuffing box is greatly preferable to the leathers of a piston, as giving less

Deainage.

friction, being much clieaper, more durable, more secure, and, what is of immense importance in all cases, more easily seen and repaired when defective. The packing may be tightened without even stopping the engine, and it requires only a few minutes' interruption of work to replace it when worn out. In no case is it necessary to remove the plunger itself, while, with the lifting pump, the bucket must always be withdrawn entirely from the working barrel, thus causing considerable delay 3very time the leathering requires to be repaired or renewed. Another advantage of the plunger pump, in the case of rods being employed, is that it requires less counterweight to be used. The height to which a liquid may be raised by a force pump is theoretically limited only by the strength of the materials and the force available, as in the case of the lifting pump ; but, unlike the latter, it is not restricted by other practical considerations. The force pump thus possesses great advantages over the lift in most cases where a pump can be applied ; but it is especially suitable in those where either of the conditions of a considerable height or a continuous working exists.

The essential parts of a reciprocating pump are, — the cylinder or barrel, the valves, the piston, and the piston rod ; and on the design and the construction of these the efficiency of the pump chiefly depends. In order to acquire a full understanding of the nature of these constituent parts, it will be necessary to investigate briefly the principles and the conditions to which their action is subject.

The Cylinder. — As the piston or bucket reciprocates in constant contact with the walls of the cylinder, the latter must be bored true in order that the piston may fit accurately and work with as little friction as possible. The tendency of the cylinder to become oxidized when iron is used as the material of construction often constitutes a serious difficulty, especially in cases where the water to be raised is charged with substances capable of determining rapid oxidation. In pumps for draining mines, the cylinders and pistons, when of iron, are frequently destroyed in a short time, and, of course, in such circumstances a satisfactory degree of efficiency is not to be looked for. To remedy this defect, the cylinders are sometimes lined with brass, and though the first cost is considerably enhanced thereby, the additional outlay is soon recovered in the higher efficiency of the pump, while the greater durability of the cylinder renders such outlay a real source of economy. The diameter of the cylinder is generally greater than that of the suction or the discharge pipes, and is calculated

in inches by the following formula; D V 034LN ' which Gr represents the quantity in

gallons to be delivered a minute, L the length of the stroke in feet, and N the number of single strokes a minute. To find the quantity in gallons that a given pump is capable of delivering a minute Gr= 034DLN; and to find the quantity in gallons delivered at each stroke, Gr S X -00283. For forcing pumps, D represents the diameter of the plunger.

The Valves. — The valves are a very important part of reciprocating pumps, and deserve the most careful attention. A large percentage of the power lost in a pump is often due to the influence of the valves, and it becomes, therefore, important to consider how this influence operates.

In the first place, it must be borne in mind that a valve has to fulfil two requirements of an opposite nature, and that therefore the complete fulfilment of one is incompatible with the complete fulfilment of the other. These requirements are : — to afford an unobstructed passage to the water in one direction, and to close the passage entirely in the contrary direction. The fulfilment of these requirements implies the satisfaction of antagonistic conditions. Those imposed by the former are, that the valve shall be of the same weight as the water it displaces, so that it may offer no resistance to the ascending column, that its presence shall not contract the area of the passage below that of

432 Mining Engineeeing.

the water way covered by the valve when closed, or otherwise obstruct the flow of the water, and that it shall move with the same velocity as the water. But even this set of conditions, apart from those implied in the second requirement, cannot be wholly complied with. Every variety of valve applicable to a pump belongs to one of two classes, known respectively as the hinged and the spindle valve. The former is hinged to its seat like a trap-door, and is so well known as to need no description ; this kind is usually called the clack valve. The latter rises perpendicularly from its seat, and the extent of its motion is limited by a spindle or rod fixed to its lower face, or by some similar arrangement. Now, it is evident that both these kinds may be made of any degree of lightness, and that therefore they fulfil equally the first condition. But the second condition can be satisfied only by the hinged valve; for this kind may open back out of the way of the passing current, while the spindle valve, rising perpendicularly — that is, keeping its axis always coincident with the axis of the water way — must necessarily obstruct the passage. The third condition is fulfilled only by the spindle valve ; for if this kind be equal in weight to the water it displaces, it will offer no resistance to the latter, and will consequently move with the same velocity, but the hinged valve being constrained to move in a circle, the velocity of any point in the valve varies as its distance from the centre. The consequences of this motion are, that the entering current is forced away from the side of the hinge, and a whirling motion is communicated to the water above the valve. The loss of efficiency due to this cause is probably considerable, fully equal certainly to that occasioned by the diversion of the current resulting from the obstruction offered by the spindle valve. Thus it will be seen that the first requirement, even when considered apart from the second, cannot be completely fulfilled. But when the second requirement is introduced into the question, an important modification of the former conditions ensues. For the latter demands that the tendency of the water to return shall close the valve, or at least be capable of 'ng it, that the valve shall be sufficiently strong to support the weight of the superincumbent water, and that it shall not allow any water to escape during the act of closing. The first of these conditions does not permit the clack to fulfil the second condition imposed by the first requirement by opening back out of the way of the passing current, for it is obvious that if this valve be open at an angle of 9 0°, a return current will not close it. The utmost limit that can be allowed is 70°. Hence the entei'ing water will be thrown off the face of the valve at an angle of 20°, and against the wall of the cylinder at the same angle with the forward line of direction, thus occasioning some resistance. The second and third of the above conditions require the valve to be heavier than the liquid, since the requisite strength can hardly be obtained without the employment of metal, and the valve must be capable of closing by its own weight. The excess of this weight above that of the liquid has of course to be supported by the entering current during the whole time of admission. Hence another source of resistance, due to the impossibility of fulfilling the first condition implied in the first requirement. The last of the above conditions is of the highest importance, and demands the greatest elucidation, since it refers to the chief source of loss, exerts the greatest modifying influence upon the first set of conditions, and seems to be the one least understood. The quantity of water lost through the valves, which quantity is usually termed the " slip" of the valve, is rarely equal in any two pumps of the same dimensions, and it varies from 5 to 20 per cent, of the stroke ; the former percentage, however, is of very rare occurrence, though the latter is common. "We believe that this serious loss, as well as the wide limits within which it is found to vary, arises from failing to appreciate the true nature of the slip. The fact that the loss is not reduced to some definite limits is a proof that nothing definite is known

Ekainage. 433

concerning the matter. The ignorance of makers is, in this case, excusable, since scientific authorities are not agreed upon this point. Thus we find it stated by one authority that the loss by slip is due rather to defects in construction than to faults in design, while another attributes it mainly to the form of the valve. Neither of these views is, however, borne out by experience. Yet the question cannot be of a nature to defy investigation, nor can it bs impossible to find a solution of a practical character. Indeed, it must be a simple and an easy matter to obtain approximate results sufficiently accurate to constitute a reliable and ready guide to practice. Such results we shall endeavour to obtain, leaving to mere theorists the labour of determining with rigid exactitude all the elements of the question. It may be well to state, however, that the conclusions to which our arguments lead have beon fully confirmed by experiment.

It is manifest that if the piston pause at the end of its stroke, the column of water which then fills the cylinder will remain at rest ; and if the pause be sufficiently long, the valves will close by their own weight. In this case, the water displaced by the falling valve rises above the latter, and consequently none escapes through the valve aperture. The slip is therefore reduced to zero. But if, on the contrary, no such pause be made, the valve will be closed by hydraulic pressure, that is, by the force of the returning current, provided the velocity of the piston be greater than that of the valve, due to its own weight. And it must be remembered that this velocity in a submerged valve is not great. Now it is evident, in this case, that the water occupying the space passed through by the valve in closing must be expelled, since it cannot, as in the former case, rise above the valve as the latter descends. This case, therefore, represents the maximum slip, and it is this that we have to determine. Let us first take the case of the spindle valve. This valve rises from its seating to a height limited by its spindle or rod. If the piston return instantly with a velocity equal to that of the falling valve, we shall have a case of the maximum slip. By equal velocities, it must be understood that we mean relatively equal velocities ; for if the area of the plunger be twice that of the valve, it is obvious that to possess a relatively equal velocity the former must descend with only half the absolute velocity of the latter, since they then displace equal volumes in equal times. It is manifest that in this case the quantity of water expelled by the forcing down of the valve is the column having the upper face of the valve as its base, and as its height the distance of this face from the seating. The amount of slip may therefore be expressed by s x h, s being the area of the valve face. The same reasoning applies to the hinged valve, the only difference being that the height of the column is, in this case, the length of the arc which is the path of the centre of the valve.

It follows from the foregoing that when no pause is made at the end of the stroke, the amount of slip increases as the lift of the valve. This conclusion is slightly modified in the case of the hinged valve by the speed of the piston, as we shall see later ; but, generally, it may be said that the slip the valve area x the mean lift. Here we see at once the cause of the serious loss of water that frequently takes place in pumps, as well as the absence of uniformity in the amount of the loss. Yalves are made to open as widely as possible, in order to afford an unobstructed passage to the water. To render this proceeding justifiable, the loss of efficiency occasioned by the obstruction offered by the valve must be greater than that due to the slip. For it must be remembered that the water which flows back through the valves represents so much power lost, the same water having been previously lifted ; but calculation will show that it is not so. Furthermore, it must be borne in mind that the greater travel of the valve causes a greater disturbance in the water,

3 K

434 Mining Engineeeing.

whereby the efficiency is again diminished, and a more violent concussion, resulting in a speedy destruction of the valve. Hence the practice of giving a high lift to the valve for the purpose of affording an unobstructed passage to the water is unjustifiable.

It now becomes necessary to determine what is the most advantageous degree of lift to be given to a pump valve. A consideration of the foregoing facts will show that the gain increases as the lift is diminished. What is the limit in this direction ? Evidently, if the valve be only slightly raised, the area of the passage afforded for the water between the lower edge of the valve and its seat will be less than that of its lower face, or the aperture which this face covers. Suppose, for example, a spindle valve 4 inches in diameter ; the area of the water way closed by this valve is 12 "56 square inches. If the lift of the valve be limited to inch, the passage afforded to the water will be 4 X 1416 X 25 3 141 square inches, or a diameter of 2 inches. When the water reaches this passage, the vein will be contracted, and will reduce the size of the opening still more. Through the opening thus reduced the water must pass without any diminution of volume in a given time ; hence its velocity must be increased. The excess of force necessary to produce this excess of velocity, the direction of the motion remaining the same, will evidently be the effect of the contraction, and will represent the resistance which the contraction occasions. To find the mathematical expression of this resistance, put D the diameter of the water way, D' the diameter of the contracted passage, and / the coefficient of contraction corresponding thereto. The expression of the velocity will then

Jjyi 5 the force requisite to produce this velocity, or the head of water in feet will consequently

be "0155 >2-p.,4 , the head due to the velocity of the water before reaching the contracted passage

being "0155 V; the excess of head, or the resistance due to the contraction, will thus be

Hence it follows that if a valve be not opened sufficiently to afford an uncontracted passage to the water, the resistances will be so increased as to outweigh the advantages resulting from the lowness of the lift ; and the limit may be fixed at that point where contraction begins. The best degree of lift for pump valves — in other words, the compromise between conflicting conditions that reduces the sum of their several disadvantages to a minimum — is thus expressed for both kinds of valves with sufficient accuracy for practical purposes by the simple formula, L '25 D, D being the diameter of the valve aperture, and L the height of that point in the valve which, when the latter rests upon its seat coincides with the axis of that aperture.

The kind of valve most frequently used, especially in large pumps, is the clack. Thei-e are numerous modifications of this as well as of the spindle variety, but as these forms are well known, it is unnecessary to describe them here.

When the water possesses corrosive qualities, metal valves are unsuitable, and as the water of mines is usually of this character, wood and leather are almost exclusively used in mine pumps. Whenever metal valves are so employed, they are made to beat or fall, not upon seats of iron, brass, or other hard metal, but upon faced rings of hard wood let into the part which would otherwise form the seat of the valve. By this means, the violent concussion to which they are subjected in closing- at the return stroke of the plunger is lessened. Sometimes a soft metallic alloy of lead or tin is used instead of the facing of wood.

Deainage. 435

The Piston. — The eflBciency of a pump depends in a great measure upon the state of the piston. If the latter is badly made or imperfectly leathered or packed, or if it has got out of order in consequence of wear and corrosion — and it is the part most subject to these influences — a large proportion of the motive force is absorbed by useless friction, or the pump partially fails to act by reason of the parts not being air-tight. We have already stated that the bucket, or lift-pump piston, is much more liable to derangement and wear than the plunger or forcing-pump piston. This is due to the different manner of packing them rather than to their different forms. The common form of lift-pump piston consists of a hollow cylindrical piece of wood, usually elm boiled in oil, to which an iron stirrup is attached, and having a valve on its upper end. In small pumps, iron or brass is used instead of elm wood. The advantage of employing metal for this purpose is that, a less thickness being sufficient, a larger water way may be obtained. To make the piston work air-tight in the cylinder, a piece of stout leather is applied to the outer surface, and held by a band or hoop. Around the lower end is a second hoop, and the hollow between these is filled up by winding on skeins of hemp dipped in melted tallow. As the hemp projects slightly beyond the hoops, it presses against the walls of the cylinder ; and a sufficient quantity must be wound on to make the pressure great enough to prevent the passage of air, and no more than enough, as any excess of friction is a waste of power and a cause of unnecessary wear. The weight of the water above the piston presses the leather outwards against the walls of the cylinder, and so prevents a leakage between the latter and the piston. Numerous modifications of these arrangements may be and are made, but they do not differ essentially from the system described. Some of these modifications have for their object the enlarging of the water way through the piston, and that this object is a desirable one will be acknowledged when it is borne in mind that considerable loss of power is occasioned by forcing a column of water through a contracted passage.

The plunger or solid piston of the forcing pump works through a stuffing box, and is therefore not subject to the wear and the liability to derangement which renders the bucket piston objectionable. It should be accurately turned, so that there may be no unnecessary friction or weai of the packing. When of small dimensions, the plunger may be wholly of brass, but when large it should be encased in brass, as iron is quite unsuitable in consequence of its liability to corrosion.

The weight upon the piston of a pump is always equal to that of a column of water whose base is the area of the piston, and whose height is the vertical distance from the surface of the pool to the point of discharge. Let H be this height in feet, and D the diameter of the piston, also in feet, and let us take the piston at any part of its stroke. Denoting the vertical distance from this point in the stroke to the point of discharge by h, and the height of this same point above the surface of the pool by h}, we have h + H. The piston will be pressed down by the weight of the atmosphere and by that of the column of water above it. Eepresenting the height of the column of

water requisite to hold the atmospheric pressure in equilibrium by t, and the ratio — - — by ir,

the expression of this weight is 62-4 7r' (f -t- A). The counter-pressure, or pressure beneath the piston, is equal to the atmospheric column, less the column of water below the piston ; that is, to 62'47r* — 'O- "The resultant of these two pressures, or the effective load upon the piston, is required to prove. This pressure upon the piston is independent of the diameter and inclination oi the pipes, and is evidently the same for the forcing as for the lift pump.

3 K 2

436 Engineering.

The stroke of a pump piston should be made as loug as practical considerations will admit. The quantity of water lost through the valves is the same for a long as for a short stroke, the diameter being the same. Hence the long possesses a considerable advantage over the short stroke in this respect. But a more important advantage consists in the less frequent change of direction. When it is considered that in large pumps the inertia of an enormous mass has to be overcome at every change of stroke, the reality of this advantage will be readily conceded. In mine pumps, the rods of which sometimes exceed 100 tons in weight, the stroke is usually from 8 to 10 feet.

Experiments have shown that when the valves are of the clack variety, the slip sometimes decreases with the increase of speed in the piston. In some cases, by doubling the velocity, the amount of slip has been reduced by one-half. This is due to the fact that the valve is closed by hydraulic pressure. When the valve is heavy and the velocity of the water low, a small quantity escapes before the inertia of the valve and the friction of its hinge has been overcome by the returning stream and its own gravity. But when the piston moves with a high velocity, the whole pressure of the piston is directly and instantaneously communicated to the valve, which is then closed wholly, as we have already seen, by hydraulic pressure. If this explanation is the true one, the slip will decrease with the increase of velocity only within certain limits, and no experiments of which we are cognizant have pj.ove'"' the contrary.

The speed of the piston is limited by the velocity of flow in the suction pipe. To find the extreme speed at which a piston may be driven, it will therefore be necessary to determine this velocity. Suppose the piston suddenly raised the whole length of its stroke, leaving a perfect vacuum below it ; the time T requisite to bring the water to the top of this space, provided it be already up to the foot valve, is

msV Ig

L being the height of the valve above the surface of the pool, I the length of the stroke, s the area

of the valve aperture, and m a suitable coefficient of contraction, the other letters having the same

signification as before. This formula does not take into account the friction of the water in the

suction pipe ; but in this case it would be very little. Representing the mean velocity with which

the water ascends in the cylinder by v, we have v . If the piston possessed a velocity Y greater than V, the water would be unable to follow it. V must therefore be less than ; and it should not

be greater than two- thirds of In practice, t may be taken as equal to 32 feet, and m to include

the friction of the water in the pipe, as equal to 0-60.

The expressions for v and T show that the velocity with which the water ascends in the cylinder, and consequently that which may be given to the piston, decreases as the length of the suction pipe increases, and increases with its diameter. In large pumps, the extreme limit is never attained on account of the great weight of the moving parts and the consequent strain which a high velocity would produce. Usually the speed of the piston in such cases varies from 6 inches to 15 inches a second.

Piston Rods. — When the pump and the motor are situate upon the same bed or near to each other, the piston is easily and efficiently worked through the medium of ordinary connecting rods.

Deatnage. 437

In such cases, the pump piston is connected with the steam piston, when steam is the motor, either directly, by means of a rod common to both, or indirectly, by means of a crank. With a water wheel the latter is the only method available. When, however, the pump is situate at a great distance from the motor, the transmission of the motive force to the piston is one of the most difficult problems relating to the subject of pumping. Numerous attempts have been made to solve this problem satisfactorily ; but the success which has attended the efforts of inventors has, until recently at least, not been commensurate with the ingenuity displayed.

The most obvious means of transmitting the force in these cases, as in those where the motor and the pump are near together, is, of course, the connecting rod adequately extended ; and this means has, for want of a better, been generally adopted ; for it will be seen that, though a connecting rod is a very suitable medium so long as it is of small dimensions, it becomes most unsuitable when the dimensions assume excessive proportions. When, for example, the pump is at the bottom of a mine and the motor at surface, the weiglit of the intermediate rods often greatly exceeds that of the column of water to be raised, and consequently a large proportion of the motive force is absorbed by the friction of these rods and in overcoming the inertia of their enormous mass. This defect, as well as others of considerable importance, will be made more apparent by a description of the system at present in use.

The operations in a mine may be carried on at several dififerent levels. In metalliferous mines, in which the ore is found in lodes, these levels are usually at a depth of ten fathoms below each other ; but in coal mines, in which the mineral exists in seams, the levels are in those seams. The water which collects in these several levels or stages is conveyed to a tank fixed in a recess cut in the side of the shaft. At the bottom level, it flows into a pool or well called the sump. A lift pump is fixed from the sump to the tank on the next level, and force pumps are placed from tank to tank. Thus the water is raised by stages. To actuate the plungers of the force pumps and the piston of the lift, a rod is carried down the shaft. As the depth of the shaft in a mine is great, and as the quantity to be raised is frequently very large, it is obvious that this rod must be very strong, and therefore must possess large dimensions. Usually it is composed of balks of Memel pine, perfectly sound and straight, and without knots or faults of any kind, such as are used for the masts of ships, and of as great a length as can be obtained. The lengths are put together by scarfed joints, and secured by stout wrought-iron plates bolted through the timber. To this main rod, the pistons of the pumps at the several levels are firmly attached by means of a set-off and strong iron straps. These piston rods work through guides to keep them in a straight line, and for the same purpose similar guides are placed at intervals down the shaft against the main rod. The rod where it passes through the guides is cased with hard wood, and kept well greased to lessen the friction. It will be seen from this description that the rods are of enormous weight. In deep mines, tho main rod alone frequently weighs upwards of 70 tons. The mode of working the pumps is to make the motor raise the rods, and then to leave the weight of the latter to force up the water. As, however, the weight of the rods is usually greatly in excess of that required to raise the water, this excess is taken off by means of a loaded lever, called a balance lever, or more commonly a balancebob. Fig. 638 shows one of th(.S3 balance-bobs. It consists of a stout balk of timber a, often from 20 to 30 feet in length, turning about an axis at b, and loaded at the end tZ by a box filled with stones or other heavy materials. The two ends are supported by iron ties passing over an upright support upon the axis. One of these bobs is placed at surface, and others may be set at intervals

Mining Engineeeing.

down tlie shaft, the unloaded end being fixed to the main rod c. When the shaft is inchned, the main rod is made to rest upon friction rollers ; in other respects the arrangements are unchanged by this circumstance. A vertical rod is made to communicate motion to an inclined rod, or vice versA, by means of a bent lever, called a V or angle-bob. As the motor may be situate at a considerable distance from the shaft, especially when the pumps in two shafts are worked by the same motor, the rods are carried along the surface of the ground, and connected with the main rod in the shaft by one of these V-bobs. Fig. 639 shows this arrangement. The horizontal, or, as they are usually termed, flat rods a, are attached by means of iron straps to the arm of the lever, and the main rod in the shaft b is attached in the same way to the other arm A. When in this position, the Y-bob is frequently double, as in the figure, the arms D and B serving as counterweights to A and C. Flat rods are carried upon friction rollers where the surface of the ground is level, and upon vibrating rods where the surface is depressed. One of these vibrating rods is shown in Fig. 640 ; they are arranged to stand vertically when the pump pistons are at the bottom of their stroke.

It is obvious that in the above system of rods a very large proportion of the motive force is absorbed by the friction of the various parts, and that consequently only a low efficiency can be obtained. The loss of power from this cause is immense, even when the pit work — that is, the whole system of pumps and rods — is kept in a perfect condition. But this is an extremely difficult thing to do. Some of the parts are continually getting out of order. Frequent repairs and alterations are needed, and these often necessitate a temporary stoppage of work, entailing much inconvenience and expense. This, added to a heavy first cost, makes the system a very expensive one. When considering the question of cost, it must also be borne in mind that this system requires a large shaft on account of the great space occupied by the pit work.

Such are the defects inherent in the system of transmitting the motive force by means of rods. As we have already stated, many attempts have been made to supersede this system. One of the most successful is to take the engine underground and to force the water up at one lift. This is, no doubt, in some respects a very great improvement, as the loss by friction is reduced to a minimum, and the first cost, as well as the cost of maintenance, is lessened in a very great degree. This system is, indeed, free from m'ost of the defects which we have pointed out in the Cornish pump. It has, however, defects of its own. The engine cannot be used for other purposes at the same time, and utter failure may result at a critical moment, namely, when a great and unexpected influx of water or an outbreak of gas has driven the men out of the workings. Besides this, it is of course open to the objection of being inapplicable in case of water power. To obviate these difficulties, another plan, a modification of the preceding, has been proposed, and in some instances successfully carried out. This consists in placing the boiler at surface, and conveying the steam down to the pumping engines through felted pipes. Where this system is applicable, it no doubt possesses some advantages over the preceding. But it is unsuitable for great depths in consequence of the condensation which must inevitably take place in the pipe ; and, like the preceding, it is applicable only in the case of steam power.

Pipes. — The pipes constitute an important part of a pump, and frequently represent a large proportion of the first cost. It is therefore essential to economy that they possess no excess of dimensions. The diameter of the pipes composing the rising main or pump tree, and the thickness of metal, are dependent upon the quantity of water to be raised a minute, and the height to which it has to be lifted, and these must be calculated accordingly. The friction of the water in the pipes.

Deainage. 439

whicli is one of the sources of a loss of power in a pump, is dependent upon the diameter of the pipes and the velocity of the water. This velocity should never exceed 4 feet a second. Hence, in determining the dimensions of a rising main, the question of friction must be taken into account. It may be remarked here, that in cases where no air vessel is used to equalize the flow, the diameter must be calculated for the greatest and not the mean dischar-ze. For example, suppose a 10-inch pump, worked by a crank, the path of which is 1 foot in diameter, and the velocity of which is twenty revolutions a minute. The quantity discharged a minute is 78-54 x 12 x 20 18849 cubic inches 67" 8 gallons. But during one-half of the stroke, the delivery is nothing, and it is a maximum at the centre of the other half, because the piston has then the velocity of the crank pin. The path of the crank being 3 '1416 feet in circumference, the discharge at this point is 78*54 x 37" 7 x 20 59219 cubic inches 213*2 gallons ; and it is for this discharge that the pipe must be calculated.

In calculating the requisite thickness of a cast-iron pipe under given conditions, it must be borne in mind that, whatever care be taken, it is impossible, during the process of casting, to keep the core always perfectly central, and that, consequently, a pipe may have an excess of metal on one side, and a corresponding defect on the other. And as the strength of a pipe is that of its weakest part, due allowance must be made for this defect. Besides this imperfection, others may exist, and hence it becomes necessary, in order to obtain security against accident, to take the factor of safety large, especially as the pipes of a pump are subjected to shocks. Some engineers take it at 6, but for heavy pump-work 10 is a better value. It is a common practice for engineers to calculate the weight of a pipe of the requisite thickness, and to specify the weight rather than the thickness, leaving the founder to fix that for himself, which long practice enables him to do with considerable precision. Absolute correctness, of course, cannot be obtained, and a margin of 1 lb. to the inch either way is usually allowed.

The resistance which a pipe offers to the internal pressure tending to burst it is equal to the cohesive strength of its two sides, and the effective area of that pressure is the internal diameter of the pipe. If the tensile strength of cast iron be taken at 15,000 lb. to the square inch, the thickness of a pipe to be subjected to water pressure will be given by the formula :

in which H represents the head of water in feet, and R the radius of the pipe in inches. Substituting the diameter for the radius, the formula becomes "0000144110. A pipe having this thickness is strained up to the bursting point. If 10 be taken as the factor of safety, we have, as the formula giving the requisite thickness in practice, 000144 HD. Thus, suppose a 10-inch pipe to be subjected to a pressure of 600 feet head. The required thickness of metal, as given by the formula, is 0*000144 x 600 x 10 0*864 inch. The thickness of the pipes of a pump tree may be made to vary at every 100 feet. Thus, in the case assumed, we shall have, for the first 100 feet from the bottom, 0*864; for the second 100 feet, i! 0*720 inch ; for the third 100 feet, t 0*576 inch; for the fourth 100 feet, 0*432 inch; for the fifth 100 feet, f 0*288 inch; and for the last 100 feet, 144 inch. But as it is imprudent to employ a pipe of a less thickness than inch, by reason of the imperfections of manufacture already pointed out, the reduction would, in the case assumed, cease at the third 100 feet.

The weight of a cast-iron pipe may be found by multiplying the cubical contents in inches by 0*26 lb., which is the weight of a cubic inch of cast iron ; or, more conveniently, the weight of a

440 Mining Engineeeing.

yard may be determined by the following formula: W 7 '35 (D' — (f), in which D represents the outside, and d the inside diameter in inches. The weight of two flanges is equal to about 1 foot of pipe. A common length of cast-iron pipe is 9 feet. Suppose now 10-inch pipes are required, capable of bearing a pressure of 400 feet head. The thickness for this pressure will be taken as I inch ; the external diameter will, therefore, be ll;j inches. Hence the weight of the whole pipe will be 3-33 x 7-35 (126-56 - 100) 650 lb., taking the weight of the flanges as equal to 1 foot of pipe. The weight specified to the founder will thus be 5 cwt. 3 qr. 10 lb. ; and allowing a margin of 1 lb. to the inch of diameter, the pipe delivered may weigh anything between 5 cwt. 3 qr. lb. and 5 cwt. 3 qr. 20 lb.

The joints of the pipes are always flange joints. To render the joint water-tight, a ring of lead or wrought iron, which has been previously wrapped round with a piece of common woollen cloth, and afterwards dipped in tar, is inserted between the flanges. The joint thus formed is very sound and durable, and it admits of being taken apart with the greatest facility. To preserve the pipes from the corroding action of the mineral water, they are sometimes lined with a thin casing of wood. The mode of putting in the wood is to place it in the form of staves, like those of a cask, round the interior of the pipe, leaving a small space between the last and the first inserted. Two wedges are then driven into this space from the two ends of the pipe by simultaneous blows of a hammer. This simple operation is sufiScient to keep the lining firmly in its position.

To Calculate the Efficiency of a Reciprocating Pump. — We have shown that the load upon the piston of a pump is equal to the weight of a column of water whose base is the area of the piston, and whose height is the vertical distance from the surface of the pool to the point of discharge. The lifting of this weight constitutes the effective work of the pump. To ascertain what proportion this work bears to the total work transmitted from the motor, it is necessary to determine the other resistances which the pump has to overcome, and which may be called passive resistances, since they merely absorb force without producing any useful effect. These are : — 1, the friction of the piston against the walls of the cylinder or the packing of the stuffing box ; 2, the friction of the water in the cylinder and pipes ; 3, the contraction of the fluid vein at its entrance into the suction pipe, and during its passage through the water way of the valve ; 4, the weight of the valve ; and 5, the inertia of the mass of water to be set in motion.

Besides the above, there is the resistance due to the friction of the rods, when the latter are employed, and this resistance is frequently greater than the whole of the other passive resistances together. But as it is very variable, depending as it does very much upon the state in which the rods are kept ; and as, moreover, it is not common to all reciprocating pumps, we shall leave it out of the question. In determining the passive resistances, it is not intended to give rigorously accurate results; an approximation is all that can be attained to, but the approximation is sufficiently near for practical purposes.

The friction of the piston depends upon the nature of the materials and the pressure of the water. When the leathering consists of a simple cup leather, its upper edge being pressed against the walls of the cylinder by the column of water resting upon it, the pressure is proportional to the height H, Also in other cases, and in general, the packing has to be tightened as the pressure increases, so that the friction still remains proportional to H. This proportion has been found by careful experiment to be about 06 of the weight of the superincumbent water when the piston is in a good condition.

Drainage, 441

The friction of the water in the rising main of a pump is very nearly the same as that of the water in an ordinary water-pipe, and may therefore be found with suiEcient accuracy from the

formula h -jj- , in which h is the head of water in feet due to friction, G the discharge

during the effective part of the stroke in gallons a minute, L the length of the pipe in feet, and d the diameter of the pipe in inches.

The head due to the velocity of flow through a contracted passage is given by the formula

((72~7To) which the letters have the same signification as above. Hence the resistance

due to the contracted passages will be represented by Qi 3)' + F Q,, -g j - J being the diameter of the second contraction.

At the beginning of the up stroke of the piston, when the water presses against the lower face of the foot valve, it meets with a resistance due to the weight of the valve. To overcome this resistance, a force at least equal to this weight must be exerted against the lower face of the valve. To determine the height of the column of water representing this force, let us take, for greater generality, the case of a clack. Let W be the weight of the valve in pounds, I the distance of its centre of gravity from the axis of rotation, s the area of the waterway, the distance of its centre from the same axis, and as the height sought, the measurements being in feet. W I will be the moment of the resistance due to the weight of the valve, and 62*4 s a; Z" will be that of the opposing force. And since the two forces must be equal, we shall have Wl= 62-4: s x I'-. Deducing from this equation the value of x and multiplying it by 62 "4 it' to find the force to be exerted by the

piston, we get ji . If the valve when closed, instead of being horizontal, makes an angle

with the horizon, this expression must be multiplied by cos. 6. With a spindle valve covering a

D' circular orifice of diameter d, we shall have simply W — ; and this value will be suflSciently exact

for all practical purposes for both kinds of valves. As the valve has to be held open during the whole of the stroke, this force may be considered to be exerted during the whole of the time the piston is ascending.

The inertia of the water, which we have given as one of .the resistances to be overcome, seldom occasions a loss of power, because usually the motion of the piston is regulated in this respect by the machinery to which it is connected. For instance, if it is driven from the crank of a wheel possessing a uniform motion, it starts from a state of rest with the water which it drags after it ; it rises at first with an accelerated motion, and the acceleration gradually decreases until at the middle of the stroke it becomes nothing. The velocity is then retarded until it becomes nothing at the top of the stroke. During the first half of the stroke, the motion has acquired an accelerating force diminishing progressively, and during the second half a retarding force increasing according to the same progression, and suflScient to entirely destroy the effect of the former. Thus, what it has been necessary to take from the motive force employed to overcome the inertia of the mass raised during the first portion of the stroke, will be given back by the inertia of this mass to the same force during the second half; and therefore the inertia will not have occasioned any loss of force.

We will now show the application of the above principles and formulae by means of an example.

442 Mining Engineeeing.

Let it be required to determine tlie sum of the resistances in a single-acting sucking pump, making twenty effective strokes a minute, and having the following dimensions : Diameter of barrel, D 75 feet ; length of barrel, L 5 feet ; length of suction pipe, 20 feet, whence L + L' H 25 feet ; diameter of suction pipe, d 'b feet ; length of stroke, Z 4 feet ; weight of foot valve, W 2 lb.

In this case, the discharge is 220 gallons a minute. But as the pump is discharging during onehalf of the time only, namely, during the up stroke, this quantity must be double in calculating the resistances.

Weight of the column of water to be lifted 62 4 tt H 686 25 lb.

Friction of the piston 686-25 X -06 41-17 „

G2 X L Friction of the water in the pipes (neglecting the barrel) h 24-46 „

(a a)

Eesistance due to contraction and velocity in suction pipe ft ( — J 11-17 „

Eesistance due to weight of valve W -jj 4 45 „

Total resistance 767-50 lb.

The loss of power is thus about 11| per cent. In the above case, the diameter of the valve orifice is the same as that of the suction pipe ; consequently there is but one contracted passage.

The Cornish system of pumps is the one generally applied to mining purposes. It consists, as we have already said, in having a pump at each level, and in working the whole of them simultaneously from one main rod. Figs. 641 to 643 show the details of this system. Pig. 641 is the first or lowest lift, and is always of the lifting or common bucket kind. The reasons for the adoption of this kind for the bottom lift are — the facility with which it may be lowered as the shaft is sunk deeper, and the liability of the bottom lift to be drowned by a rise of water, consequent on a stoppage of the pump for alterations or repairs. If a plunger pump were used in this case, a rise of a few feet would cover the whole of its valves and working parts, and so render them inaccessible for repairs before the water was got under. But the bucket of a lifting pump can always be drawn up to the top of its rising main A, Pig. 642, above which the water is not likely to rise before it is mastered. And as there is a contrivance for remedying, from the same level, any defect in the foot valve beneath the piston, the perfect working of the pump is secured until the water is lowered to its accustomed level. To enable the bucket to be drawn up readily, the rising main is about an inch larger in diameter than the working barrel, and the latter is made trumpet-mouthed at the top to facilitate the entrance of the bucket when lowered from above". The clack valve a is accessible, when the level of the water permits, by a door b. When, however, the water rises above this door, and the valve a gets out of order, the contrivance alluded to above must be resorted to.

In the clack piece below the barrel at A, the bore of the pipe is contracted at c to a size a little smaller than that of the working barrel, and thus made slightly conical. A drop valve made to fit this bore may then be dropped down through the pipe and barrel to its seat, as shown in the figure in dotted lines. The action of the pump may be continued by means of this temporary valve until the water has been sufficiently lowered to render the fixed valve a accessible. The drop valve is provided with a loop or handle, to allow it to be easily drawn up.

The bucket rod passes up the rising pipe A, Fig. 642, and is fixed to the main rod C by means

Deainage. 443

of a set-off and iron straps D. In this lift, the water is raised by the up stroke of the rods through the pipe A, whence it is discharged by the trough or collar-launder a into the cistern d.

The second lift is a plunger pump, and it takes its water from the cistern b. As this cistern may receive the water which drains into it from the level on which it is placed, the second pump may have to be of larger capacity than the first ; and this may be the case with each lift in succession. Pig, 642 is a section of one of the plunger pumps, Tbe plunger c is driven upon the wooden rod d, or, as it is technically termed, pole, and made tight by wedging into the bottom end. This pole is fixed to the main rod C by means of a set-off e, and iron straps and nuts, A guide / keeps the pole in a true line with the axis of the barrel, or, as it is called in Cornwall, pole-case.

When the plunger ascends, the water is sucked in through the wind-bore h and valve I into the double pipe or H-piece B, whence it is expelled by the descent of the plunger through the delivery valve k, and rising main B', which conducts it up to the cistern on the next level above. As all the other lifts are precisely similar to this one, they need no description. The height of each lift is usually from 30 to 40 fathoms. The main rod, as already described, works through guides fixed at intervals down the shaft, and that the friction of the rod against these guides may not be excessive, the former must be well made, firmly put together, and truly hung. At the top it is hung to the gudgeon of the outer end of the engine beam, or to the arm of a double V-bob, as shown in Fig. 639. The excess of weight above what is required to raise the water is taken off by means of balance-bobs. At intervals down the shaft, side pieces are strapped to the main rod, as S, S', Fig. 643 ; these serve a double purpose. Their primary use is to prevent the rods from descending too far, and so causing injury to the pumps and to the engine. When the rods have descended sufficiently low, the side pieces come to rest upon the blocks r, r', which are supported by the timbers t, t', let into the sides of the shaft. But another important use is to prevent the rods from falling down the shaft in case of fracture ; for should the main rod break at any point, the portion below the rupture would be supported upon the blocks, and thus incalculable mischief would be averted.

The system of pump which we have described is in many respects very suitable, for the purpose to which it has been almost exclusively applied, namely the draining of mines. It possesses no delicate parts, and it is of so simple a nature that any alterations or repairs may be effected by the most inexperienced hands. This is an important advantage in a mining pump. Another advantage claimed for it is the ability to take the water from each of the levels or stages in a mine. This advantage, however, has its compensating defect in the additional number of pumps required, and the greatly increased friction resulting therefrom. The defects of the system are numerous ; its first cost is great, and the cost of its maintenance is also great. The ponderous rods require constant attention and frequent repairs ; they occupy a large portion of the space in the shaft ; they must be counterweighted by balance-bobs, sometimes placed in cavities excavated horizontally in the sides of the shaft — a very expensive situation — and they are the source of great loss of power from friction. Also the mode of working the pumps by raising the rods and using their weight to force up the water is false in principle. It is lifting a heavy weight in order that by its fall it may bring up a less one. This may be the best mode of working this system of pumps ; but it is working at a loss nevertheless. That there may be no hitch in the working in consequence of obstructions, the excess of weight to be lifted must be considerable. Thus the total amount of loss from friction, and other causes, constitutes a very large percentage of the motive force.

444 Mining Engineeeing.

The drawings, numbered 644 to 648, show an example of an existing Cornish pumping engine, the general design of which is seen in the side elevation, Fig. 644, The cylinder A is 70 inches internal diameter, with a piston stroke of 10 feet; it is enclosed in a cast-iron steam jacket, communicating with the boilers by means of the pipe a, which also serves to return the water of condensation to the boilers, which are placed at a lower level, thus avoiding the waste of heat, which is often met with in other engines, by allowing the steam to escape from the jacket at nearly the boiling point. This jacket is surrounded by another casing of wood, the space between the two being filled with some bad conductor of heat, such as sawdust or ashes ; and the whole is enclosed by a casing of brickwork, or by an air-tight cavity formed by building a thickness of brickwork at a few inches distance, which is plastered on the outside and covered with wood panelling. The cjdinder cover and bottom are also protected from the cooling influence of the air, the former being fitted with a false lid or cap c, enclosing a thick layer of sawdust, or other bad-conducting substance, and the space d under the bottom kept constantly filled with steam by a branch from the pipe a.

B is the main beam, cast in two plates and bolted together, with distance blocks between to keep them parallel with each other. To the upper part of the beam is fixed transversely, by means of brackets, a strong bar of iron, g, called the catchpiece, which, when the piston arrives at the bottom of its stroke, touches the blocks h, fixed on the spring beams ; the descent of the piston being thus arrested, no damage can be done to the cylinder by the engine making too long a stroke in-doors. C is the plug rod for working the valves and cataract, and D, the top nozzle, shown in section in Fig. 645 ; it contains three valves. First, Vj , the governor or regulating valve, for regulating the admission of steam into the chamber kk oi the nozzle, whence it afterwards passes through the steamvalve Va into the cylinder. The opening of the governor valve is constant during the working of the engine, that is, it is not moved by the engine, but only occasionally by hand, for the purpose of regulation. In proportion as the governor valve is more or less raised, the steam is less or more wiredrawn, or reduced in pressure, as it passes from the steam pipe into the cylinder. By this means therefore, although the pressure in the boilers may occasionally vary, the mean effective pressure in the cylinder may be maintained constant with great ease and precision. The motion of the governor valve is commanded by a handle placed within reach of the engineman, and connected by a rod and lever with the stalk of the valve. Second, Yj , the steam valve, for admitting the steam into the cylinder. When this valve is raised, the governor valve being supposed open also, the steam finds a passage through it, from the nozzle chamber k k into the space I, and thence by the steam port m into the upper part of the cylinder. The chamber k k, would appear to be divided by the cover Os , belonging to the equilibrium valve ; but this appearance only arises from the position in which the line of section is taken, the steam being free to pass round, in the direction of the arrows, from the governor valve to the steam valve. Third, V3 , situate in the middle of the nozzle, is the equilibrium valve, for opening the communication between the spaces above and below the piston. When therefore this valve is opened, the steam above the piston will, by its excess of elasticity, find its way along the equihbrium pipe E, and by the lower port n, into the lower part of the cylinder, until the equilibrium is restored between the pressures above and beneath the piston ; which is then at liberty to be drawn upwards by the preponderating weight of the rods hung at the outer end of the beam.

It will be observed that the three covers, a, 0,0, which are bolted to the nozzle over the governor, steam, and equilibriimi valves respectively, are of sufficient size to allow the valves to be

Deainage. 445

lifted from their seats and taken out of the nozzle when the covers are removed, thus giving the opportunity for convenient examination or repair. The top nozzle is, like the cylinder jacket, enveloped in an external ctising of thin iron, leaving a space all round, which is filled with ashes or sawdust to prevent loss of heat,

F is the bottom nozzle, a section of which is shown in Fig. 646 ; it contains the exhaust valve V4, for opening or closing the communication between the lower part of the cylinder and the condenser. The nozzle chamber above the valve communicates with the cylinder by the lower port n, while to the bottom of the nozzle, under the valve, is attached the eduction pipe H ; so that when this valve is lifted, the steam in the lower part of the cylinder is exhausted into the condenser.

Gr is the cataract, shown in section in Figs. 647 and 648. The use of this ingenious apparatus is to regulate the period of opening the steam and exhaust valves, and thus to determine the interval between the successive strokes of the engine, that its rapidity of action may correspond with the quantity of water to be drawn from the mine, a! is a barrel in which works the plunger V, and is simply a small plunger forcing pump. The inlet is by a valve c', opening freely upwards, but the outlet is contracted at pleasure by a movable plug dl. The pump is placed in a cistern of water Gr, and the plunger is attached by the joint to the arm e' of the lever e'/'. When the plug rod C has descended nearly to the bottom of its stroke, a tappet upon the lower part of it strikes the end /' of the lever and thus raises the plunger 6', the water at the same time entering freely under the plunger through the valve c'. "When the stroke is finished and the plug rod begins to ascend, the tappet quits the lever, and the weight h' which is fixed upon the arm e', and which has been raised by the preceding motion, becomes in its turn the motive power, tending to expel the water from the pump by forcing the plunger down. But the inlet valve c' having closed, the only exit for the water is by the aperture left round the regulating plug 6!. It is plain, therefore, that by augmenting or diminishing the size of this aperture, the exit of the water, and thereby the descent of the plunger, may be accelerated or retarded at pleasure. To the end /' of the cataract lever is attached a rod m, which ascends vertically, opening first, the exhaust, and a short time after, the steam valve, thereby causing the commencement of the next stroke of the engine. It should be remarked that the rod m acts upon a catch that releases the weights w ; these, by their fall, open the valves and occasion a suddenness of action wLich is considered a great advantage, particularly as regards the admission of the steam into the cylinder by the steam valve. It is evident, then, that the interval between the time the tappet leaves the cataract lever and the commencement of the next stroke, which in fact determines the interval between two consecutive strokes or the number made in a given time, depends upon the time occupied by the descent of the cataract plunger, and therefore, ultimately, upon the degree of opening given to the regulating plug d'. This plug is capable of every degree of adjustment by means of a micrometer screw and handle connected with the regulating plug by a rod and the lever V. By turning the handle, the plug can be raised or lowered, and the aperture consequently increased or diminished as the quantity of water to be raised from the mine is greater or less, and the engine required to make a greater or less number of strokes in a given time accordingly.

H is the eduction pipe leading from the bottom of the exhaust valve nozzle F to the condenser K. L is the air pump, 2 feet 9 inches in diameter, the bucket of which has a stroke of 5 feet, half that of the piston. N is the feed pump of the ordinary plunger description.

The advantages possessed by the horizontal type of engine have led to its adoption for pumping

446 Mining Engineeeing.

purposes, and recently some very efficient designs have been introduced. Of these, some are intended to run at a high speed, and to drive the pumps through the medium of gearing, while others are designed to act directly, and to run consequently at a low speed. The latter are very suitable where the quantity of water to be raised is not great nor the lift very high. The pumping engines of the Messrs. Tangye and those of Hay ward Tyler and Co., are good examples of these for underground pumping. For large quantities of water and high lifts, the most suitable engine yet introduced is that known as the Differential Pumping Engine of the Messrs. Hathorn, Davis Campbell, and Davey, of Leeds, a distinctive feature of which engine is its differential valve gear. The following description of one of these pumping engines, which are working satisfactorily at a great number of collieries in this country, is given by Mr. Davey in a paper read by him before the Institution of Mechanical Engineers, in October, 1874.

" In Figs. 649 to 658 is shown the Direct-acting Differential Pumping Engine, in which a differential arrangement of valve gear is employed for effecting the distribution of the steam. The simplest form of this engine has a double-acting cylinder, with the power applied direct to the pumps. The Compound Engine, shown in Fig. 649, has a pair of horizontal cylinders, the back end of the high-pressure cylinder forming the front cover of the low-pressure cylinder, as shown in the plan, Fig. 650. There are two piston rods to the low-pressure piston, which pass through tubes cast on the sides of the jacket of the high-pressure cylinder ; these two rods and that of the highpressure cylinder between them are all fixed to one cross-head, to which is attached the connecting rod for working the pumps. The cylinders are bolted down upon a strong girder bed ; and the condenser is carried on a separate bed behind the low-pressure cylinder, the air pump being worked by a tail rod from the low-pressure piston.

" The differential valve gear, which is the particular feature of the engine, is shown in Figs. 651 to 654, and its action is illustrated in the diagrams Figs. 655 to 658. These diagrams are not drawn to scale, but are intended to show clearly the action of the gear, whilst Figs. 651 to 654 show a practical example of its application to a compound engine. The main slide valve G, Fig. 655 is actuated by the piston rod through a lever H working on a fixed centre, which reduces the motion to the required extent and reverses its direction. The valve spindle is not coupled direct to this lever, but to an intermediate lever L, which is jointed to the first lever H at one end ; the other end M is jointed to the piston rod of a small subsidiary steam cylinder J, which has a motion independent of the engine cylinder, its slide valve I being actuated by a third lever N, coupled at one end to the intermediate lever L and moving on a fixed centre P at the other end. The motion of the piston in the subsidiary cylinder J is controlled by a cataract cylinder K on the same piston rod, by which the motion of this piston is made uniform throughout the stroke ; and the regulating plug Q can be adjusted to give any desired time for the stroke.

" The intermediate lever L has not any fixed centre of motion, its outer end M being jointed to the piston rod of the subsidiary cylinder J ; and the main valve Gr consequently receives a differential motion compounded of the separate motions given to the two ends of the lever L. If this lever had a fixed centre of motion at the outer end M, the steam would be cut off in the engine cylinder at a constant point in each stroke, on the closing of the slide valve by the motion derived from the engine piston rod ; but inasmuch as the centre of motion at the outer end M of the lever shifts in the opposite direction with the movement of the subsidiary piston J, the position of the cutoff point is shifted, and depends upon the position of the subsidiary piston at the moment when the

Deainage, 447

slide valve closes. At the beginniug of the engine stroke, tlie subsidiary piston is moving in the same direction as the engine piston, as shown by the arrows ; and in the instance of a light load, as illustrated in Fig. 656, the engine piston, having less resistance to encounter, moves off at a higher speed, and sooner overtakes the subsidiary piston moving at a constant speed under the control of the cataract ; the closing of the main valve Gr is consequently accelerated, causing an earlier cut off. But with a heavy load, as in Fig. 657, the engine piston encountering greater resistance moves off more slowly, and the subsidiary piston has time consequently to advance farther m its stroke before it is overtaken, thus retarding the closing of the main valve Gr and causing it to cut off later. At the end of the engine stroke, Fig. 658, the relative positions become reversed from Fig. 655, in readiness for the commencement of the return stroke. The subsidiary piston. Fig. 653, being made to move at a uniform velocity by means of the cataract, the cut off consequently takes place at the same point in each stroke, so long as the engine continues to work at a uniform speed ; but if the speed of the engine becomes changed in consequence of a variation in the load, — if, for instance, the load be reduced, causing the engine to make its stroke quicker, the subsidiary piston has not time to advance so far in its stroke before the cut off takes place, and the cut off is therefore effected sooner, as in Fig. 656. On the contrary, if the load be increased, causing the engine stroke to be slower, the additional time allows the subsidiary piston to advance farther before the cut off takes place, and the cut off is consequently later, as in Fig. 657. This adjustment of the cut-off point in accordance with each variation in the load is entirely selfacting, and takes place instantly, however sudden or extensive the variation in the load on the engine may be ; consequently the engine is rendered safe in working against variable loads, as it automatically and instantly varies the distribution of steam with every increase or decrease of the resistance. The action of the differential valve gear is so sensitive and perfect that the load on the engine may be greatly varied whilst in full work, without requiring hand control by the stop valve ; engines on this plan may accordingly be employed to pump direct into town mains without the use of stand pipes or balance valves.

" The force acting on the subsidiary piston is much greater than that required for moving the slide valve, the excess being absorbed in driving the fluid in the cataract cylinder through the small adjustable aperture ; and as the resistance of the fluid increases as the square of the velocity, a very small variation only in the speed of the subsidiary piston can be effected by a considerable variation in the force upon it ; so that the speed is maintained practically constant for a given adjustment of the cataract plug, although the boiler pressure of steam may vary. The main slide valve is opened at the beginning of each stroke by the motion of the subsidiary piston, which is controlled by the cataract ; and a pause is consequently given at the completion of each single stroke of the engine, which allows time for the pump valves to fall to their seats. Slip in the water is by this means prevented, as well as the shock which occurs when pump valves close under the pressure from a moving plunger. This freedom from shocks in the pumps is an important point, giving safety from accidents, such as the bursting of pipes ; and at the same time the durability of the valves and their seats is materially increased.

" In Figs. 649 and 650, are shown the details of the arrangement for communicating the motion of the engine piston to the intermediate lever of the valve gear by means of the long lever and the connecting rod, the lever itself being actuated by a connecting rod from the engine cross-head, as shown in the drawing. An independent steam-starting or pausing cylinder is provided, the piston

4.48 Mining Engineeeing.

rod of whicli carries a rack gearing into a pinion on one end of a tubular shaft ; tlie other end of the shaft being made with a screw thread, its rotation traverses the outer end of the lever of the valve gear, and thereby opens the small slide valve of the subsidiary cylinder. The slide valve of the pausing cylinder is moved by tappets by means of a lever actuated by the same lever that works the inner end of the intermediate lever of the valve gear. The pausing cylinder is itself also controlled by a cataract cylinder on the same piston rod, and the length of pause after each stroke of the engine is consequently determined jointly by the two cataracts ; the first regulates the time of opening the small slide valve for starting the subsidiary piston ; after which this piston, under the control of the other cataract, has to travel a sufficient distance for opening the main slide valve of the engine. The adjustment of the latter cataract also determines the mean piston speed of the engine under the normal conditions of load and steam pressure.

" In Fig. 651 is shown a longitudinal section through the steam chests and slide valves of the two cylinders ; and Figs. 652 and 654 are transverse sections of the valves. The slide valve of the high-pressure cylinder has a couple of narrow ports through the thickness of the metal from end to end, as shown in the drawings, the effect of which is that while the engine is pausing at the end of its stroke for the valve to be moved from mid position through the extent of the lap, a communication is established from one side of the piston to the other ; so that, whatever the amount of clearance space left in front of the piston at the end of the stroke, it becomes all filled with steam that has just done its work behind the piston. This prevents the slight loss that would occur in having to fill the whole clearance with full boiler steam at the commencement of the return stroke ; the initial steam has now only to raise the pressure in the clearance from the terminal pressure in the high-pressure cylinder, instead of from the terminal pressure in the low-pressure cylinder. A double-beat valve is provided in the steam pipe, and is worked off the main valve spindle by means of a bell- crank lever and a pair of slotted connecting rods; these are fitted with right-and-left-handed screws, so as to afford a ready means of adjusting the degree of expansion in the high-pressure cylinder under the normal conditions of the engine, without the use of a back cut-off slide ; the main slide valve is also relieved from working under the full boiler pressure after the steam has been cut off by the doable-beat valve. The slide valve of the low-pressure cylinder is balanced by means of a steel ring inserted in an annular groove on the back of the valve; this ring is pressed outwards against the steam-chest cover by an indiarubber packing ring compressed beneath it in the groove; and there are also a series of small holes in the bottom of the groove for the admission of the steam pressure behind the packing."

To avoid the heavy cost of the rods and the incumbrance which they occasion in the shaft, the system of placing the engine underground is sometimes adopted. Of course, with such an arrangement, the engine must be of the horizontal type. The differential engine is very suitable for this system of pumping, and it has been adopted for raising water in this way in numerous instances. The pumps used are of the forcing class ; they draw the water from the sump, immediately above which they are placed, and force it to surface at one lift, thus removing the necessity for tanks in the shaft. It is obvious that this system possesses great advantages ; but it also possesses some defects. The great height of the lift necessitates the adoption of pipes of great thickness to withstand the pressure ; any disarrangement of these pipes, or of the pumps, is difficult to remedy ; and the engine is liable to be drowned while standing. If steam has to be conveyed to the engine from boilers at surface a great loss from condensation will occur ; but in some instances, this objection has been removed by

Drainage. 449

placing the boilers underground. This arrangement, however, does not remove the danger of drowning. Notwithstanding these somewhat serious defects, the advantages offered by the system are so great that it is probably destined to supersede, in very many cases where the conditions are favourable, the Cornish system with its cumbrous pit work. In Fig. 659, we have shown this arrangement of the Differential Pump. The engine is erected at a convenient level in the shaft, and the water is forced up from this level to surface in one lift. To pump from the bottom level, a hydraulic engine is used, as shown in the drawing. This engine is worked by the head of water in the rising main from the steam engine situate above.

Erection of the Pumps. — The manner of fixing the pumps in the shaft is shown in sufficient detail in the drawings to render a description of it unnecessary. A few remarks, however, concerning the operations of fixing are required in this place. Each forcing set rests upon a support usually consisting of stout oak buntons placed one upon another, or of balks of large scantling, securely set into the sides of the shaft. If the length of those timbers is considerable, they are often further supported by struts abutting against the sides of the shaft. It is obvious that these supports should be of great strength and very firmly fixed, since they have to bear, not only the weight of the pumps and the pump trees with the contained water, but also, during the down stroke of the plunger, that of a column of water having the sectional area of the plunger as its base and the distance from set to set as its height. In addition to this, they partly carry the tank from which the next set takes its water. In some instances, iron has been substituted for wood in these supports.

To lower the pit- work, crabs are fixed at surface, and by means of these, the several parts are let down on a strong hempen rope 6 or 7 inches in circumference. The lower or lifting set having been fixed in position, the forcing sets are built up in succession one above the other to the surface, care being taken to have the main rod directly under the end of the engine beam. The crab is also used in case of subsequent alterations and repairs, and it is often left permanently in position for this purpose. The compartment of the shaft in which the pumps are fixed should in general be sufficiently large to allow ladders to be set whereby easy access may be had to the various parts for the purposes of inspection and repairs. When the pumps are ready to be started, they should be filled with water from above in order to avoid the irregular motion which would result from working empty on steam being admitted into the cylinder of the engine.

The pumping arrangements required during the operations of sinking differ somewhat In character from the foregoing by reason of the special conditions under which the pumping has to take place. As the sinking proceeds, the pumps have to be lowered ; the gritty nature of the water to be raised causes a very rapid wear of the parts, and thus renders frequent repairs necessary ; and a cessation of the pumping for a few hours may. cause the pumps to be drowned. For these reasons, when, the water is not very abundant, it is a common practice to use pumps of a more suitable design and construction than those erected for the permanent work of the mine. To diminish the weight, the pipes are of wrought iron, which, like the cast pipes, are jointed with flanged joints. Pumps used for sinking should be of a somewhat large diameter, so as to be able to cope with an unexpectedly copious influx of water : it is a great disadvantage to be obliged to have recourse to

a second pump.

Lift pumps are invariably used in sinking. Two rods, called ground rods, or ground spears, are fixed, one on each side of the set, to the lift by means of iron coUarings or hoops ; these are lengthened as the sinking proceeds, and a lowering of the pumps becomes necessary. By these rods,

3 M

450 Mining Engineeeing.

the pump is suspended, througli the medium of ropes and five-fold blocks, called ground blocks, to buntons, or to shear legs, at surface, the other end of the rope being led to a crab, as already described. This crab is called a ground crab, and the ropes are known as ground ropes. The pumps are steadied in their positions by means of temporary buntons and collarings. The top of the pump column is furnished with a delivery or " hogger " pump, provided with flexible hose for the purpose of accommodating it to the constantly varying height of the column. As the sinking proceeds, the pumps are lowered, until the height of the lift has become inconveniently great. The lowering is effected by means of the ground ropes and the crab. The hogger pump having been removed, a fresh length of pipe is attached, and the hogger replaced ; this done, the pumps are again ready for action. The limit beyond which it is not prudent to extend the height of the lift is from 60 to 70 yards, and when this limit has been reached, a forcing set, called a standing set, is put in : this set must be firmly erected in the manner described for the permanent pumps. Below the standing set, the lift is again suspended, and lowered, as the sinking proceeds, in the same manner as before. When another 60 or 70 yards have been sunk through, a second standing set is put in, and the lift is suspended beneath the lower set. As tanks are required at these several levels, it may be inconvenient to make the sets equal in 'height. Thus tanks can hardly be placed in those portions of a shaft that are tubbed. For this reason, it may be necessary to limit the height of a set to 40 or 50 yards, or to extend it to 80 or even 90 yards. It may be remarked relatively to the working of mine pumps, that the engine should not be driven above the speed necessary to just keep down the water, for otherwise it will be " working on air," as it is called, and the irregular motion thereby occasioned must result in injury to the moving parts. Care should also be taken to prevent chips and other small pieces of wood from getting to the windbore of the pump, for if they be sucked through the snore-holes, they may become wedged between the clack and its seat, and so prevent the valve from working. The snore-holes which may be above the surface of the water must be plugged ; soft wood will be found to be the most suitable material for the plugs.

Cost. — As in the case of winding machinery, it is not possible to give indications of the cost of pumping machinery that shall be other than roughly approximate. The total cost is made up of that of the engine, which will be in relation to its power, and of that of the pumps and their fittings, which will increase with their diameter and especially with the depth of the shaft. The augmentation in the cost of the pumps as their diameter and the depth of the shaft increases will be greater than that in the cost of the engine required to work them. The following is the cost incurred in a certain case when the depth of the shaft was 200 yards :

Engine. £

Engine house, with cHmney .. .. .. .. .. .. .. ., .. 520

Cornish engine and two boilers, including cost of erection .. .. .. ,. .. 1920

Total £2440

Pit Work. £

Two plunger bottoms and one suction .. .. .. ., ., .. 250

Pipes for rising main, 12 in. and 13 in. .. .. .. .. .. .. 550

Main rod, with all attachments, wrought-iron straps, cast-iron sockets, &c., complete to

engine beam . . . . . . . . . . . . . . . . . . . 920

Fixing in shaft, and incidental expenses .. .. .. .. .. .. 690

Total £2410

Deainage. 451

Thus tlie grand total is 4850/., or 24/. a yard of depth. The foUowiDg is the specification of the engine and boilers, and the pumps, with the rising main.

SPECIFICATION OE A C0ENI8H PUMPING ENGINE AND TWO BOILEES, PIT WOEK, ETC.

The cylinder to be 40 inclies diameter, and long enough for a clear stroke of 9 feet ; to have a steam case, bottom and false bottom, metallic piston, and piston rod of fagoted iron ; cover to have brass bushings and lantern brass, bright false cover, and grease cups, cast-iron piston-rod cap ; beam to be bored for the pins, and pins to be of best fagoted iron, turned to fit ; stroke in shaft, 8 feet ; motion, main hoops, catch eyes, and main caps all of fagoted iron ; nozzles fitted with double-beat gunmetal valves and seats, and the top nozzle to have a neat cast-iron clothing ; the nozzle gear and working gear to have casehardened joints, and to be fitted bright and mounted on cast-iron Y-posts ; the condensing and feed work to be complete ; the bucket to have a brass face and indiarubber valve, and a cast-iron cistern to be provided for containing the condensing work ; the whole of the engine to be complete, with all the necessary bolts for the joints.

Boilebs.

The boilers to be two in number, each about 23 feet long, 6 feet diameter, with a flue about 3 feet 6 inches diameter, and to be provided with complete outfits, fire doors and frames, fire bars and sleepers, dampers and weights, tap pipes, manholes, double safety valves, steam and feed nozzles, and all the necessary pipes for connecting with the engine ; also water gauges and cocks complete, with all necessary bolts for joints.

Pit Woek.

The pumps to be divided into two plunger and one suction lift, each plunger lift to consist of a ram 12 inches diameter for 8-feet stroke, with stuffing box and gland, brass bushed case for ditto 9 feet long, 18 inches diameter; 1-| -piece and top clackpiece with valves and doors, and a 5 feet 12 inches flat-bottom strainer, with the necessary bolts and rings for joints. The suction lift to consist of a 9 feet 12 inches pointed strainer IJ inch thick, one 6 feet 12 inches clack piece with valve and door, one 10 feet 12 inches working barrel, bored and fitted with buckets, prongs, valves, and hanging joints, and the necessary bolts and rings for joints. The pipes to be sixty-three in number, viz. fifty-two 9 feet 12 inches for the plunger lifts, and eleven 9 feet 13 inches for the suction lift, with bolts and rings for joints. All the work to be of good material and workmanship.

Memoranda. — The following rules, formulae, and tables, are added as supplementary to the calculations relative to pumps and pumping already discussed and illustrated in the foregoing sections.

To find the contents of a pipe. — The quantity of water contained in a pipe of a given diameter and length may be accurately determined by the formula Q 0"00283 DL, in which Q represents the quantity in gallons, D the diameter of the pipe in inches, and L the length of the same also in inches. The area of a circle in square inches is 0*7854 and hence 0'7854 L the cubical contents in inches. But as a gallon contains 277 cubic inches, the quantity in gallons will be

0" 00283 W L. Example. — "What quantity of water is contained in a pipe 4 inches

in diameter and 24 feet in length? Here 0-00283 x 16 x 288 13'04 gallons, the quantity sought. To convert L into feet, multiply the coeflScient by 12; the formula thus becomes Q 0-03396 W L. Taking the same example, we have 0-03396 x 16 x 24 13-04 gallons, as before. When a rough approximation is sirfScient, the quantity may be found by assuming that the weight in pounds of the water contained in a yard of pipe is equal to the square of the diameter in inches. Thus, taking the foregoing example 16 x 8 128 lb. 12-8 ;gallons, the weight of a gallon of water being 10 lb.

3 M 2

452 Mining Engineering.

To find the pressure of water in a pipe. — The pressure of water in pounds to the square inch is given accurately by the formula P 0"433 H, in which P is the pressure sought, and H the head of water in feet. The weight of a cubic foot of water being 62 "4 lb., the pressure upon each

square inch of surface upon which the cube rests is 0*433 lb. This pressure will obviously

increase as the "head," that is, the height of the mass of water, increases. Example. — What is the pressure tending to burst the pipe when the height of the column of water is 100 feet ? Here P 0*433 X 100 43 "3 lb., the pressure sought. When roughly approximate results are sufficient, half the head in feet may be assumed to represent the pressure in pounds to the square inch. Thus, taking the preceding example, the head being 100 feet, the pressure will be 50 lb. The error, it will be observed, is on the side of excess.

Quantity of water delivered per stroke of pump. — The quantity in gallons of water delivered at each stroke of the plunger may be obtained from the formula already given for the contents of a pipe, namely, Q 0*03396 L, D in this case being the diameter of the plunger, and L the length of the stroke in feet. Example. — It is required to find the quantity of water delivered at each stroke when the diameter of the plunger is 8 inches, and the length of the stroke 4 feet. Here 0*03396 X 64 x 8*7 gallons, the quantity sought. This formula does not take into account leakage and slip, the value of which, as already pointed out, will depend upon the state of the pumps, and the system of driving them.

Quantity of water raised per minute. — When the quantity of water raised at each stroke is accurately known, the quantity raised per minute may obviously be determined by multiplying the delivery per stroke by the number of strokes a minute. But it is often convenient to measure the water actually raised, by means of a weir. To do this, a small reservoir must be formed into which the water delivered by the pump is to be led. This reservoir must possess sufficient dimensions to reduce the velocity of the stream practically to zero. The outlet from the reservoir must be by a weir having a perfectly level sill and vertical sides. The sill should have a thin edge, and is best constructed of wood. Over such a weir, the water will flow with a velocity due to the head, that is, to the height of the level of the water above the sill. This head is called the depth of water on the sill ; the expression is, however, inaccurate, for the head is always greater than the depth or thickness of the fluid sheet passing over the weir, and the difference becomes greater as the head increases. The water being in rapid motion when on the sill, the surface will slope back from this point to that at which the water is practically at rest. Hence to ascertain the head, a stake, divided into inches and' tenths of an inch, should be driven in vertically at some point in the reservoir where the water is undisturbed. The zero of the stake should correspond with the level of the sill, and the divisions should be clearly marked. If the weir be made one foot in length, the quantity of water passing over it a minute will be given by the formula Q 5*15 v /i, in which Q is the quantity in cubic feet, and h the head in inches. As a cubic foot contains 6 24 gallons, the formula may be made to give the quantity in gallons, by multiplying the constant 5*15 by 6*24; thus 32*14\/A. Example. — It is required to find the quantity in gallons passing over a foot weir a minute, when the head is 2 inches. Here Q 32*14 x a/s 32*14 x 2*828 90*9 gallons. By means of the following table, the quantity may be found by inspection.

Deainage.

Head of Water in

Cubic Feet a

Gallons a

Head of

Water in

Inches.

Cubic Feet a

Grallons a

Head of Water in Inches.

Cubic Feet a

Gallons a

Inches.

Minute.

Minute.

Minute.

Minute.

Minute.

454 Mining Engineeeing.

Chaptek Xl

Ventilation.

The ventilation of underground workings is one of the most important subjects claiming the attention of the mining engineer. Upon a suitable distribution and regulation of the ventilative currents depend, not only the prosecution of the excavations, but also the health and the lives of those engaged. The appalling accidents which so frequently happen from explosions of firedamp show the necessity for providing adequate and suitable ventilation through the workings of coal mines, and the necessity has been recently forced upon the attention of those in charge by legislative enactments. The question, however, is one that is by no means free from difficulty. The atmosphere of a mine, and especially of a coal mine is liable to vitiation from numerous and uncertain causes, and is subject to conditions of renewal altogether different from those prevailing at surface. It is, therefore, not surprising that no definite principles have been established whereby a sufficient ventilation might be determined for any given case, and that empirical rules are still followed, though the question has received long and careful consideration. The object of the present chapter is to make known the facts concerning ventilation, and to deduce from them some consequences that may serve as a basis upon which to found certain practical calculations.

Constitution of the Atmosphekb of Coal Mines. — The atmosphere at the surface of the earth in its normal state is made up of certain gases in definite proportions. The alteration of these proportions by any cause is described as vitiation, because the compound becomes unsuitable to the support of animal life from the moment that any one of the constituent gases exists in excess. It is obvious that the amount of the vitiation may vary from the smallest perceptible degree, the influence of which upon the health becomes apparent only after the lapse of a considerable period of time, through insensible gradations up to that in which animal life cannot exist for a moment. But it must be constantly borne in mind that any variation in the normal proportions of the constituent gases of the atmosphere constitutes vitiation. It may not be possible to determine with rigorous accuracy what the normal proportions are, but they have been ascertained with suflScient approximation for all practical purposes. When constituted according to these proportions, the atmosphere is called pure, and hereafter we shall speak of air as pure when it exists in this state.

But vitiation may be caused in another manner. Instead of merely changing the proportions of the constituent gases of the atmosphere, other gases may be added to them. The degree of vitiation in such a case must obviously be estimated according to the quantity of the added gases and their nature. Thus the air may be vitiated to a degree fatal to animal life by the addition of a given quantity of a certain gas, while its wholesomeness would be but slightly affected by the

Ventilation. 455

addition of the same quantity of another gas. Vitiation in this manner takes place chiefly in consequence of the decomposition of animal and vegetable matters which is constantly going on. Gases, however, are not alone added to the atmosphere to pollute it. Whenever a beam of sunlight is allowed to fall into a darkened space, the air will be seen to be laden with solid matters floating in it. Of these matters, some are mineral substances in a state of extreme division, and some are animal organisms or animal exuvi. The latter are extremely injurious to health, constituting as they do the germs of disease, and the former, as we shall see later, may become, under some conditions, a source of great danger.

Pure air is to be found only at surface, and there only in places which are removed from sources of contamination, as the tops of hills, and the heights of some table-lands. In other localities, a greater or a less degree of vitiation always exists. But when we descend into the mine, not only do we encounter the conditions existing at those localities at surface where the polluting agents are most abundant and active, but these conditions are greatly intensified. Hence we shall find the atmosphere of a mine laden with impurities, and otherwise vitiated to a degree hardly to be met with at surface, and requiring, consequently, to be frequently renewed to render it even tolerable. But besides the unwholesome nature of such an atmosphere, other and great dangers may arise from its altered constitution. These effects, as well as those due to the pernicious influence of impure air upon the animal system, will become more readily intelligible when the nature of each of the gases of which the atmosphere of a mine is composed, and that of the solid impurities which it contains, is fully understood.

Oxygen. — Oxygen is one of the elementary substances, and the most abundant in nature. The name of oxy-gen, or acid-maker, has been applied to it because by entering into chemical combination with numerous other substances it produces acids. Oxygen may exist both in the combined and in the free state; in the former state, it serves to form many substances very abundant in nature. In combination with silicon, it forms the solid acid silica, which mineral constitutes onehalf of the earth ; with calcium and carbon, it constitutes the limestones ; and with the gas hydrogen, water. Substances which are capable of combining with oxygen are said to have an affinity for that gas, and the process of combination is described as oxiaanon. Thus, when a piece of iron, for example, is exposed to the influence of a moist atmosphere, the affinity of the iron for oxygen causes the latter to enter into combination with the metal, and there is produced a new substance, known scientifically as oxide of iron, and familiarly as iron rust. In the process of oxidation, the oxygen is, in most cases, obtained from the atmosphere, in which that gas exists in the free or uncombined state. But under some conditions, oxygen may be liberated from one substance to be taken up by another. This happens when the gas is feebly held by the substance with which it has combined, and when it is brought in that state, under certain conditions, into the immediate presence of another substance for which it has great affinity. Chlorate of potash is a substance in which a large proportion of oxygen is held in feeble combination. If a carbonaceous substance be mixed with it, and the mixture exposed to heat or subjected to a heavy blow, the oxygen is liberated from the one substance and taken up by the other. But the oxidation of the carbon produces the gas known as carbonic acid, and as the volume of this gas is enormously greater than that of the solids from which it was formed, a sudden expansion takes place, an action which is described as an explosion. The same processes of liberation of oxygen from one substance and a combination of the same gas with another substance, take place when gunpowder, or any other explosive, is fired. In all such cases,

456 Mining Engineeeing.

the explosion is due to an extremely rapid oxidation of a substance, the oxygen required for the process being obtained by a decomposition of some other substance containing it. But generally, as before remarked, in all processes of oxidation, the oxygen is obtained directly from the atmosphere.

Oxygen is often described as the supporter of combustion, and the supporter of life. The description is accurate in so far as it regards animal life, but it is misleading in so far as combustion is concerned. Combustion is simply rapid oxidation, and, therefore, it is manifestly improper to describe as merely a supporter of combustion one of the agents which take an active part in the process. The substance with which the oxygen combines in the ordinary process of combustion is most frequently carbon. The proportions which enter into the combination are two atoms of oxygen to one atom of carbon; that is, two atoms of oxygen combine with one atom of carbon, and the product of this combination is, as already remarked, the gas known as carbonic acid. Let us take, as an illustration, the case of a lighted candle. Here the carbon of the substance of which the candle is composed is undergoing combustion, in other words, it is being subjected to the process of rapid oxidation. The oxygen which takes part in the process is derived from the surrounding atmosphere, and hence it is obvious that a constant renewal of the atmosphere is a necessary condition of the continuance of the process. Place the candle in a glass vessel, and close the latter so as to prevent any further access of air. Under such conditions, the candle will be seen to burn less and less brightly, until, when the atmosphere has been deprived of all its oxygen, it will be completely extinguished. An examination of the atmosphere within the vessel will then show that the oxygen has been removed, and its place occupied by carbonic acid. The action which has taken place is simply this, the oxygen which existed in the atmosphere in a free state has entered into combination with the carbon of the candle, the product being carbonic acid. We are now able to see why the candle will not continue to burn in an atmosphere deprived of its oxygen, and also, knowing the proportion of oxygen in the atmosphere, to calculate the quantity of air required to oxidize, that is, to consume, the whole candle. Precisely the same action takes place in the lungs of an animal as in the wick of the candle. Pure air is inhaled from the atmosphere, the carbon of the body is oxidized, and the product carbonic acid is exhaled into the atmosphere. The supply of carbon is obtained from the food taken into the stomach, the other substances being either assimilated for some other purpose than combustion or expelled in the excreta. The heat due to the process of combustion satisfies a necessary condition of life, and hence oxygen may be described as a supporter of life. It should be borne in mind that heat is always generated in the process of oxidation, and that the oxidation of a given quantity of carbon will always produce the same quantity of heat. Thus it is evident that the quantity of heat generated in a given time will vary with the rapidity of the oxidizing process. When the process takes place with sufficient rapidity to generate a sensible degree of heat, it is described as combustion. The combustion of the carbon of the animal body produces a very sensible degree of heat; the combustion of the carbon of the candle, proceeding more rapidly, produces a much higher degree of heat ; and the combustion of the carbon of the gunpowder, proceeding with extreme rapidity, produces an extreme degree of heat. The quantity of heat, however, as before remarked, is in all cases the same for equal quantities of carbon consumed.

We may now compute the quantity of air required for the combustion of a given quantity of fuel, and the effects of that combustion upon the atmosphere. It has already been stated that in the oxidation of carbon one atom of that substance combines with two atoms of oxygen. Now the

Ventilation. 457

atomic weight of carbon being 12 and that of oxygen 16, the two atoms of oxygen will weigh two and two-third times as much as the atom of carbon ; whence it follows that each pound of carbon will require for its complete combustion 2f lb. of oxygen, and the product will be 2f lb. of carbonic acid. In the oxidation or combustion of hydrogen gas, two atoms of the latter combine with one atom of oxygen, the product being watery vapour. As the atomic weight of hydrogen is 1 and that of oxygen 16, the atom of the latter will weigh eight times as much as the two atoms of the former, and 1 lb. of hydrogen will require for its combustion 8 lb, of oxygen. The proportion of oxygen in the atmosphere, when in its noimal state, is 23 per cent, by weight.

Suppose now the weight of a tallow candle to be oz., and an analysis of the tallow to show 8 3 per cent, of carbon. The other substances present will be mainly hydrogen and oxygen ; but as the excess of hydrogen is small, it need hardly be taken into account in the calculation. The weight of carbon in this case will be 1 24 oz., and if we assume it to be 1 25 oz., the neglect of the excess of hydrogen will be of no practical importance. We have seen that the quantity of oxygen required to fully oxidize a given quantity of carbon is two and two-third times the weight of the latter. Hence to consume the whole candle there will be required x oz. =0-2083 lb. A cubic foot of pure atmospheric air, at a temperature of 60° Fahr., weighs 0*0764 lb., and, as the proportion is

23 per cent., the weight of the oxygen contained in that quantity of air is 0*0176 lb.

The quantity of oxygen required to consume the candle being 0"2083 lb., the volume of atmospheric

air needed to effect the combustion will be 11*84 cubic feet. That is, if the candle

be placed within a covering provided with inlet and outlet apertures, 11*84 cubic feet of pure air must be admitted to effect the combustion of the whole of the candle. If the candle be consumed in

1 1 . Of

one hour the rate of supply will be — — -- 0*197 cubic foot a minute. If the matter be regarded

from the point of view of ventilation, it will be observed that the combustion of a candle deprives

approximately 12 cubic feet of air of the whole of its oxygen, and that the vitiation goes on at the

rate of 0*20 cubic foot, or a little less than a quarter of a cubic foot a minute. An ordinary

miner's oil lamp may be assumed to be equal in this respect to a candle.

Nitrogen. — Besides oxygen, the atmosphere contains nitrogen, and in much larger proportions.

It may be said indeed that the atmosphere is composed of these two gases, the use of the nitrogen

being mainly to serve as a diluent to the oxygen. Like this latter gas, nitrogen is colourless,

tasteless, and odourless, but, unlike oxygen, it has but little chemical affinity for other substances.

The proportion by weight of oxygen being 23 per cent., that of nitrogen is 77 per cent. They differ,

however, somewhat in specific gravity, the atomic weight of nitrogen being 14 while that of oxygen

is 16. Taking the mixture of 23 per cent, of oxygen and 77 per cent, of nitrogen as furnishing the

unit, the specific gravity of the former will thus be 1*10 and that of the latter 0*97. The proportion

of the two gases by volume may be taken approximately as 21 parts of oxygen and 79 parts

of nitrogen. Analyses of atmospheric air taken on the tops of hills far removed from contaminating

soui'ces have shown the composition by volume of pure air to be the following :

Nitrogen .. 79-100

Oxygen .. 20-867

Carbonic Acid .. „ .. .. .. 0-033

3 It

458 Mining Engineeeing.

It will be seen that carbonic acid enters into tbe composition, but only in a very small quantity. This gas will be described in the next section. In addition to the foregoing constituents, there is always present a small and variable quantity of watery vapour. Thus constitiited, the atmosphere must be considered pure ; we have now to consider it in a polluted state as it exists in a coal mine.

Carbonic Acid. — Carbonic acid, as we have seen, exists as a trace in pure air. When, however, the proportion indicated in the foregoing section is more than very slightly exceeded, the air must be regarded as vitiated, and this kind of vitiation is that which we have most commonly to deal with. The constitution of carbonic acid has already been described as one atom of carbon in combination with two atoms of oxygen. Thus in an atmosphere of pure carbonic acid, there will be a much larger proportion of oxygen than in pure air ; but it will become evident on reflection that this oxygen is not available for oxidation, since it is in combination with the carbon. The oxygen has, indeed, been already used to oxidize the carbon, and it is in virtue of its combination with the latter that the carbonic acid exists. In pure air, the oxygen is simply mixed with the nitrogen, and not in chemical combination with it. It will hence be seen how it is that combustion, which, as we have said is merely oxidation, cannot go on in an atmosphere of carbonic acid. It is a well-known fact that a candle is instantly extinguished on being placed in carbonic acid ; this furnishes indeed the common test for the presence of that gas. It will now be readily understood how the inhalation of carbonic acid becomes fatal to animal life. The combustion of the carbon of the body, the constancy of which action is a necessary condition of life, is arrested, and death inevitably ensues. It does not appear that carbonic acid is poisonous, but that its fatal effects are wholly due to the cessation of combustion occasioned by its presence in the lungs. Thus carbonic acid may be said to drown, in the same way as water drowns. It has been objected that the gas does not operate in this way alone because a single full inhalation of the pure compound is sufficient to cause death, whereas a person recovers from a few seconds' immersion in water. An explanation of this fact may be found in the high specific gravity of carbonic acid, which, having penetrated into all the small cells of the lungs becomes consequently difficult to expel.

As carbonic acid is composed of one atom of carbon and two atoms of oxygen, and as the atomic weights of carbon and oxygen are 12 and 16 respectively, the proportions by weight are 27*27 and 72 '73. If the specific gravity of the compound be calculated from these proportions relatively to pure air taken as unity, it will be found to be 1 524.

It has already been stated that carbonic acid exists in pure air in the proportion of from 3 to 0"4 per cent., and that when the proportion rises much above this, the atmosphere becomes unwholesome. When the proportion is as great as 3 or 4 per cent., the air is wholly unfit to be breathed ; at 5 or 6 per cent., it is dangerous to breathe even for a short time, and at from 8 to 10 per cent., it becomes certainly fatal to life. When the latter proportions are reached, a candle ceases to burn. Therefore, where a candle will not burn an animal cannot breathe. This is the test which the miner applies to an unknown atmosphere. But it will be observed that long before this point is reached, the atmosphere becomes dangerous to breathe for more than a few moments at a time, and that consequently the candle test indicates only the extreme limit. In providing for the requirements of ventilation, the constitution of pure air should, of course, be approximated to as nearly as possible.

Water, in common with some other liquids, possesses the property of being capable of absorbing gases. The quantity of gas absorbed varies with its nature and with its temperature, the quantity increasing as the temperature, and consequently as the elastic force increases. At the mean tempe-

Ventilation. 459

rature of 60° Fahr., and ordinary atmospheric pressure, water absorbs 025 of its own volume of nitrogen, 046 of its own volume of oxygen, and a volume equal to its own of carbonic acid. That is, a cubic foot of water will absorb 0-025 cubic foot of nitrogen, 046 cubic foot of oxygen, and 1 cubic foot of carbonic acid. This large absorption of carbonic acid by water is an important fact in ventilation, inasmuch as large quantities of the gas will be taken up by the water percolating the strata into the workings. In ridding workings of carbonic acid, and in protecting human life frojn its effects, this property of water may often be utilized.

The oxygen and the nitrogen are introduced into the mine by the ventilative current from surface. But the carbonic acid, and the other vitiating gases which we have yet to consider, are generated within the mine. It now remains to consider and to estimate the importance of the several sources of carbonic acid. The most obvious of these sources is the breath of the men and the horses employed in the mine. In the act of breathing, a larger supply of air is inhaled into the lungs than is needed for the purpose of combustion. The air which enters the lungs consists, as we have seen, when pure, of 79 parts of nitrogen and 21 parts of oxygen by volume, and experiments have shown that the air which is expelled from the lungs consists of 79 parts of nitrogen and from 17 to 18 parts of oxygen. Thus from 3 to 4 parts of oxygen have been taken up by the carbon in the process of combustion. It will be hence observed that a notable change has taken place in the composition of the air during its passage through the lungs. In the first place, the proportion of oxygen has been greatly reduced, and in the second place, for the free oxygen removed, there has been substituted the same proportion of carbonic acid. The composition of the air exhaled is thus :

Nitrogen .. .. .. .. .. .. 79 "0 parts

Oxygen .. .. .. .. .. .. 17-6 „

Carbonic Acid .. „ .. ,. ,. .. 3'5 ,,

The proportion of carbonic acid is here seen to be one hundred times larger than in pure air, and consequently wholly unfit to be again breathed. Knowing the degree of vitiation caused in the air by combustion within the lungs, it becomes necessary to determine the quantity of air respired in a given time. The solution of this problem, however, is involved in difficulty, inasmuch as the quantity varies with certain not easily determinable conditions. Different writers on this subject have assigned widely different values to this quantity; but it is clearly apparent that no general value can be given. A fairly close approximation, however, may be obtained for any given conditions, and to obtain this for those which prevail in a mine is the problem as it presents itself to the student of mine ventilation. It has been stated by eminent medical authorities that the mean of several hundred experiments conducted with great care and the aid of very accurate instruments showed the quantity breathed by a full-grown person when asleep to be 502 cubic inches a minute, and that this quantity was increased to 1500 cubic inches when the person was undergoing the exertion of walking at the rate of four miles an hour. It is a well-known fact that violent exercise quickens the breathing. Now it may be safely assumed that the exertion undergone by a miner while engaged in any of the operations of extracting coal is not inferior to that of walking four miles an hour, and we shall, therefore, approximate very nearly to the truth if we take the quantity of air breathed as one cubic foot a minute. We have seen that this quantity of air will be vitiated in the degree of 0-035 of carbonic acid, that is, this cubic foot of air will contain 0-035 cubic foot, or per cent., of carbonic acid.

3 N 2

460 Mining Engineeeing.

Hence the quantity of carbonic acid discharged into the atmosphere of a mine by each person there present will be 0'035 x 60 2'10 cubic feet an hour. In the absence of trustworthy experiments, it is generally assumed that a horse breathes six times the quantity of air required by a man ; this will give 0-035 x 6 0*210 cubic foot a minute, or 0-210 x 60 12-60 cubic feet an hour of carbonic acid for each horse employed in the mine.

A second obvious source of carbonic acid is the combustion of the candles and lamps used to give light in the workings. We have shown that the combustion of a candle deprives 0-20 cubic foot of air a minute of the whole of its oxygen, and that this oxygen is replaced by the product of combustion, carbonic acid. As the proportion of oxygen in pure air is 21 per cent, the quantity of carbonic acid produced will be 0-20 x 0*21 0-042 cubic foot a minute, or 0-042 x 60 2*52 cubic feet an hour, by each candle. It may be assumed, as previously remarked, that an oil lamp is equal in this respect to a candle.

Besides the foregoing, there are other sources of production of carbonic acid, the values of which are not so subject to calculation. Of one of these, however, namely, the combustion of gunpowder, the value may be ascertained with sufficient precision for all practical purposes. The combustion of 1 lb. of ordinary blasting powder produces about - 30 lb. of carbonic acid. As 1 cubic

foot of this gas weighs 0-1164 lb., for every pound of gunpowder consumed, ; =2-58 cubic

feet of carbonic acid will be discharged into the atmosphere. The explosion of carburetted hydrogen also produces large quantities of carbonic acid ; this must, however, be regarded as an accidental source, and will, therefore, be considered later. The chemical changes of decomposition which are continually going on in the timber and the other vegetable substances which are taken into a mine also produce carbonic acid. The quantities derived from these sources do not admit of being estimated, even approximately : they are comparatively unimportant. The foregoing are sources of production of carbonic acid. But large quantities of that gas already in existence may find entrance into the workings of a mine. It may exist in the strata, generally diffused throughout their mass, or imprisoned in cavities, or in partially open faults. In the former case, the gas will be given off slowly and regularly ; in the latter case, large volumes may be suddenly thrown into the atmosphere of the mine. When carbonic acid is discharged slowly into the atmosphere, as happens from the breathing of animals and the combustion of candles and lamps, it is at once diffused, in virtue of a property to be hereafter described. But when it enters in large quantities from fissures in the rocks, or is suddenly produced by an explosion, its high specific gravity causes it to sink in the atmosphere, and to lie upon the floor of the workings as a stratum of pure gas. If the source of discharge ceases, this stratum will be removed in a short time by diffusion upward into the atmosphere, and absorption downward into the moist earth. But if the discharge continue, the stratum will obviously remain permanently, and will increase in thickness within the limits allowed by the current of air passing through the workings. The presence of such a stratum of carbonic acid gas may be readily ascertained by means of a lighted candle.

To miners, carbonic acid is known under the several names of choke-damp, hlack-damp, and stytlie.

Carbonic Oxide. — We have seen that one atom of carbon combines with two atoms of oxygen to form carbonic acid. But, under certain not well-ascertained conditions, one atom of carbon combines with one atom of oxygen, the product being carbonic oxide. It will be observed that in the

Ventilation.

formation of ttis gas, only half the quantity of oxygen required to form carbonic acid is abstracted from the atmosphere. But the effect in vitiating the air is far greater. As carbonic oxide is formed of one atom of carbon and one of oxygen, the atomic weights of which are 12 and 16 respectively, calculation will show the specific gravity, as compared with that of pure atmospheric air, to be 0-975, or about equal to that of nitrogen, which is 0-971. Thus carbonic oxide will have a tendency to ascend towards the roof of underground workings, while carbonic acid, on account of its far higher specific gravity, has a much stronger tendency towards the floor. This gas is known to miners as the white-damp.

As carbonic oxide consists of carbon and oxygen in combination, it is obviously incapable of supporting combustion, and consequently of animal life. It is equally obvious that since the carbon is not completely oxidized, it is itself combustible, that is, it may be burned or oxidized into carbonic acid. But carbonic oxide is not a mere inactive substance like the acid which destroys animal life by choking the lungs ; it is a deadly poison, causing instant death, even when breathed in very small quantities. Experiments have shown that an atmosphere containing only 1 per cent, of this gas is speedily fatal to warm-blooded animals. Hence it will be seen that the lighted-candle test is inapplicable to the case of vitiation by carbonic oxide, since the degree of vitiation becomes fatal to life long before the combustion of the candle is visibly affected. This gas, like the acid, is tasteless, but it has a peculiar odour, by which, if not overpowered by other smells, its presence may be detected. The effects of inhaling air vitiated with a trace of carbonic oxide show themselves in a sensation of giddiness and in fits of fainting.

Carbonic oxide is the product of incomplete combustion. It is never produced in the lungs of an animal, nor probably in the flame of a candle ; but it not unfrequently results from the imperfect combustion of coal and wood. As a vitiating agent in the atmosphere of a mine, however, this gas is the product of an explosion, either of some useful agent, as gunpowder, or of a mixture of common air and carburetted hydrogen, or fire-damp. In the latter case, the formation of carbonic oxide, as we shall see later, is of very serious consequence. The formation of carbonic oxide by an explosion is a question that has not yet been sufficiently investigated to enable us to speak decidedly concerning the causes which determine the action. Indeed, by many, it is hardly suspected that this noxious gas is produced in an explosion in anything like appreciable quantities, and hence its fatal effects upon animal life are either attributed to some other cause, or left wholly unaccounted for. We are, however, able to distinguish the conditions under which this oxide is formed. If, for example, a charge of dynamite or of guncotton be fired by the usual means in a rock the resistance of which is not greatly inferior to the force developed, the product of the combustion will be carbonic acid with hardly a trace of the oxide, a result that indicates complete combustion. If the resistance opposed by the rock be greatly inferior to the force developed, in other words, if the hole be greatly overcharged, a considerable proportion of oxide will be formed by the explosion. The noxious character of the fumes due to an overcharge is well known to miners. If we reduce the resistance still more, and fire the charge in an unconfined space, the proportion of oxide produced will be still further increased, until it reaches its maximum when the charge is slowly burned in the open air. It would appear from these facts that the formation of oxide is, in some degree, dependent upon the tension of the gases generated. When the resistance and the force are nearly equally balanced, almost the whole of the charge is burned before rupture of the rock, and a consequent expansion of the gases, take place. Under such conditions, the tension approaches its maximum degree. When the resist-

462 Mining Engineering.

ance is greatly inferior to the force whicli the charge is capable of developing, rupture occurs long before all the charge is burned, and it is obvious that under these conditions, the gases are allowed to expand long before they have attained their maximum degree of tension. And when a cartridge is burned in the hand, the gases escape as fast as they are generated, a condition that gives the minimum degree of tension.

A consideration of the foregoing facts leads to two important practical conclusions : first, that an overcharge of a shot hole seriously vitiates the surrounding atmosphere ; and, second, that an explosion of fire-damp necessarily produces large quantities of carbonic oxide, large, that is, having regard to its deadly nature. This second consequence will be further considered in a subsequent section.

Hydrogen. — Hydrogen, like oxygen and nitrogen, is one of the elementary substances. In combination with oxygen, it forms water, whence its name, and in that state it exists in nature in great abundance. It also enters largely into the composition of vegetable matters, and hence is found, in considerable proportions, as a constituent of coal. Being commonly used for illuminating purposes, this gas is well known, as ordinary coal gas. In this state, however, the hydrogen is not pure. Hydrogen is the lightest known substance in nature, and for this reason, its weight has been adopted as the unit by which that of other substances is estimated. Thus the atomic weight of hydrogen being 1, that of carbon is 12, that of nitrogen 14, and that of oxygen 16 ; that is, the three latter substances are respectively 12 times, 14 times, and 16 times heavier than hydrogen. We have already stated that in the oxidation of hydrogen, two atoms of this gas combine with one atom of oxygen, the product being water. Hence the combustion of 1 lb. of hydrogen will require 8 lb. of oxygen, and the product will be 9 lb, of water. Taking the specific gravity of pure atmospheric air as 1, that of hydrogen will be seen by calculation to be about 0'07. This gas, therefore, has a strong tendency to ascend in the atmosphere, a property that is utilized in balloons. As a vitiating agent in the atmosphere of a coal mine, however, we have not to deal with hydrogen in a free state, but as it exists in combination with some other substances.

Sulphuretted Hydrogen. — Hydrogen combines with sulphur, in the proportions of one atom of the former to one atom of the latter substance, to form sulphuretted hydrogen. The combination takes place whenever hydrogen and sulphur are brought together, and either the former is in a nascent state or the latter is in a finely divided state. Hence it appears in the mine as a result of the decomposition of pyrites, or of some animal substance containing sulphur. It may also be formed in very small quantities by an explosion of gunpowder. As the atomic weights of hydrogen and of sulphur are respectively 1 and 32, 1 lb. of the former will require 32 lb. of the latter to sulphurize it into 33 lb. of sulphuretted hydrogen. The specific gravity of this compound is, relatively to air, about 1-17. Sulphuretted hydrogen is colourless, but it has an extremely offensive smell, that of rotten eggs, by means of which its presence may be detected. It is combustible, the hydrogen being oxidized into water, and the sulphur into sulphurous acid ; it burns with a blue flame. Its effects upon the animal system are extremely noxious, but authorities are not agreed as to the proportion which becomes fatal to life. It is certain, however, that this proportion is small. Like carbonic oxide, its presence cannot be detected by means of the lighted candle. It has been suggested to employ as a test moist carbonate of lead spread upon white paper, because the action of this gas blackens the preparation. But it is hard to see the need of a test to beings possessing olfactory nerves. As a vitiating agent, sulphuretted hydrogen is not of great importance in the ventilation of coal mines, since it is not liable to be generated in considerable quantities.

Ventilation. 463

Proto-Carburetted Hydrogen. — Carburetted hydrogen, known to miners under the name of firedamp, or simply gas, must be regarded as the chief vitiating agent in the atmosphere of a coal mine. The terrible consequences that may result from an accumulation of this gas render it necessary to provide a large excess of ventilative current to dilute it and to sweep it away as fast as it is given off. The volume of air admitted to a mine is thus chiefly dependent upon the quantity of carburetted hydrogen which the coal seam is liable to give off in a given time. In order fully to understand the necessity for making ample provision for this gas, its nature, and its effects upon the atmosphere under certain conditions, must be clearly placed before the mind. These subjects now present themselves for consideration.

Proto-carburetted hydrogen is a compound of carbon and hydrogen, in the proportions of one atom of the former substance to two of the latter. Hence it is obvious, since the atomic weights of carbon and hydrogen are known to be 1 2 and 1 respectively, that 1 lb. of hydrogen will combine with 6 lb. of carbon to form 7 lb. of proto-carburetted hydrogen gas ; in other words, in 7 lb. of the gas under consideration, there are 6 lb. of carbon and 1 lb. of hydrogen. Sometimes two atoms of carbon combine with two atoms of hydrogen to form bi-carburetted hydrogen, or olefiant gas, and this compound may become mingled with the proto-carburet in the atmosphere of a coal mine. The proportion of the bi-carburet is, however, always small. Relatively to pure air, it will be seen by a calculation that the specific gravity of proto-carburetted hydrogen is very low, namely, about 0*562 ; that of the bi-carburet will likewise be seen to be 0'985. Hence it will be observed that the former has a strong tendency to ascend in the atmosphere. The same tendency to liquation, that is, to separate itself from the atmosphere in consequence of a difference in density, exists in proto-carburetted hydrogen as in carbonic acid ; but while the latter collects upon the floor of workings, the former collects against the roof.

Carburetted hydrogen is not a very poisonous gas. Of course, if breathed pure, it will cause speedy death by reason of its inability to support combustion. But when mixed with twice it volume of air, it may be breathed for a short time without serious effects being felt. It will be observed, from the constitution of this gas, that though it is incapable of supporting combustion, it is itself combustible, its carbon and its hydrogen combining v/ith the free oxygen of the atmosphere, the former to produce carbonic acid, and the latter to produce water.

The great danger to be feared from proto-carburetted hydrogen is due to its comparatively unstable character. Oxygen unites strongly with carbon, so that the compound carbonic acid, consisting of one atom of carbon and two of oxygen, is y&cj stable. But the two atoms of hydrogen in carburetted hydrogen are more feebly held than the oxygen in oxidized carbon. Hence, under certain conditions of heat, the gas is liable to become decomposed, and its constituents to be taken up, as remarked in the foregoing paragraph, by the oxygen of the atmosphere. It has already been pointed out, relatively to chlorate of potash mixed with a carbonaceous substance, that decomposition and reconstitution under such conditions produce the effects known as an explosion. Such an explosion taking place in the workings of a mine is necessarily followed by the most disastrous consequences, some of which result directly from the enormous force developed, and others, often far more serious, indirectly from the fouling of the air by the products of combustion.

When the fire-damp contains a notable proportion of bi-carburetted hydrogen, it would seem that the conditions of combustion are fulfilled when the gas comes into contact with iron at a low red heat, that is, the compound may be fired by a red-hot wire. But in the absence of the bi-carburet, the

464 Mining Engineeeing.

conditions are fulfilled only by contact with ilame, a well-known fact that allows the firing of a blast to be effected by means of a red-hot wire. It is not improbable that some explosions of fire-damp that have been attributed to the firing of a shot have been occasioned by the heated wire in the presence of the bi-carburet. This, however, is a question yet enveloped in obscurity. It is obvious that no explosion can be produced in pure carburetted hydrogen, since there is no oxygen to oxidize its constituents. It is equally obvious that as oxygen is added, the explosion will become more violent, until it reaches its maximum, when the oxygen is in sufficient quantity to oxidize the whole of the carbon and the hydrogen ; above this point, the force of the explosion will become less as oxygen is added, especially when mixed with its diluent nitrogen, by reason of the dilution which takes place. Thus the explosive character of carburetted hydrogen is dependent upon an admixture of common air, and the force of the explosion is dependent upon the proportions of the mixture. It is also easy to see that the presence of carbonic acid in the mixture will tend to prevent combustion ; and that, consequently, the liability of the mixture to explode and the force of the explosion which may occur will be greatly dependent, when carbonic acid is present, upon the proportions of that gas. As, however, the proportion of carbonic acid in a breathable atmosphere is too small to influence combustion in an important degree, its power of modifying an explosion is practically unworthy of consideration. It has been found by experiment that when the proportion of atmospheric air is about five and a half times that of the carburetted hydrogen, that is, when 1 cubic foot of the latter is added to cubic feet of the former, the mixture becomes explosive. But with these proportions, the explosion is very feeble, the gases being merely " flashed." As the proportion of air is augmented, the force of the explosion increases, until it reaches its maximum, when the proportions are about 1 of carburetted hydrogen to of common air. Above this point, the force of the explosion diminishes until the proportions become 1 of carburetted hydrogen to 13| of common air, when the gases are again merely Washed.

It is important to observe the effect of the flame of a candle upon a mixture of carburetted hydrogen and common air, when the proportions are not those required to produce an explosion. When the proportion of air is near the limit of lo| parts to 1 of the gas, the flame of the candle is surmounted by a very distinct halo of blue flame, which is the carburetted hydrogen in combustion. The presen'' of carbonic acid gives a tinge of brown to this blue flame. As the proportion of common air increases, the halo becomes less distinct, until it vanishes altogether when the carburetted hydrogen has become so diluted that the combustion of the particles is too feeble to be visible. The same phenomenon occurs, in a less degree, when the proportion of common air is too small for the requirements of explosion ; but in this direction, it cannot be observed through so wide a range, inasmuch as the flame is soon extinguished by reducing the proportion of air. To illustrate the effects of flame upon a mixture of carburetted hydrogen and common air, let us consider an imaginary case, which, though it could not occur in practice, may serve to render our notions concerning this subject more clear. Suppose a heading to contain pure air, but to be without a ventilative current, and suppose a large volume of carburetted hydrogen to be suddenly given off, as from a blower. This gas will, by reason of its low specific gravity, ascend to the roof, where it will remain as a layer of the pure gas. As diffusion goes on, it will work its way down towards the floor and become mixed with the atmospheric air. We shall thus have a layer of the pure gas close against the roof, and beneath this, a mixture of the gas and air, the proportion of the latter increasing gradually as we descend. With the atmosphere in this state, let a lighted candle be placed upon the floor. Here it will burn brightly

Ventilation. 465

because it is in pure air. Eaise the candle until it enters the mixture of the pure air with the carburetted hydrogen. The first indication of the presence of the latter gas will be a lengthening of the flame. Eaise the candle slowly higher in the mixture and the blue halo will appear, at first very faint, but gradually increasing in distinctness as the proportion of gas met with is greater. When the proportion of 1 to about 13J of air is reached the gas will flash. Assume that only a layer of a definite thickness is fired at one time, and continue to raise the candle. A succession of explosions will now occur, each more forcible than the preceding, until the point is reached where the proportions are about 1 to 9 J. Above this point, the explosions will occur with a constantly diminishing force until they cease at the point where the proportions are about 1 to 5. Above this, the halo will again appear, though less distinct than before ; but it will rapidly vanish, and the flame of the candle diminish and become extinguished as the roof is more nearly approached. These phenomena afford a test for the presence of carburetted hydrogen in the workings, and the application of the test is called " trying the candle," or " trying the lamp," the lamp being commonly used for safety. Among miners, the halo is known as the " top," or " cap." This cap may be several inches in height ; to observe it clearly, the miner holds his hand before the flame of the candle to shield his eyes from the direct rays of light.

The source of carburetted hydrogen in a coal mine is the seam of coal itself. In the formation of coal by the decomposition of woody tissue, a gradual elimination of the oxygen and the hydrogen has taken place, in which process the hydrogen has entered into combination, either with the oxygen to form water, or with the carbon to form carburetted hydrogen. So long as these chemical changes went on at surface, or near the surface, the gaseous products escaped into the atmosphere ; but when in course of time, the seam became overlain by thick beds of almost impervious rock, the way of escape was more or less completely closed. As the gas continued to form under these conditions, its tension increased, and every pore and interstice in the coal became filled with gas under considerable pressure. When the seam was overlain immediately by a porous rock, as sandstone, the latter was permeated by the gas, a circumstance that renders a sinking liable to be invaded by gas before the coal seam is reached. As the gas exists, both in the rock and in the coal, in a state of considerable tension, it tends to escape into the workings as soon as the retaining cover of shale is removed or the seam broken into, a tendency which is increased by the low specific gravity of the gas. The tension of the gas in the pores or cells in the coal is often very great. A small lump of coal newly broken from the seam, if placed under a test glass, will give off in two or three days a volume of gas three or four times larger than its own volume. When we bear in mind that this gas was retained within the interstices between the molecules of which the coal is made up, we shall see that the tension must have been very high. As the coal is broken down, the gas is liberated, and hence, it will be observed, the quantity given ofi", other things being the same, will be proportional to the quantity of coal extracted. When the gas is abundant, it issues from the pores of the coal with a singing noise, similar to the simmering of a kettle. If the face be left standing for some time, the escape of gas continues to diminish as the pores near the surface are emptied ; but though it soon becomes imperceptible, it does not cease altogether. Hence abandoned workings, and workings that have been left to stand, are liable to become filled with explosive gas. This slow escape of the gas through the mass of the coal explains its absence in seams lying near the surface, and also in the portions near the outcrop of seams penetrating to a great depth. In the former case, the gas has permeated the overlying rocks and escaped into the atmosphere, and in the latter case, it has

3 o

466 Mining Engineering.

passed out through the coal itself. It will be obvious, on reflection, that all open fissures in the coal seam, or in communication with the seam, whether directly or through the medium of a porous rock, will be filled with gas if they do not communicate with the surface in either of the ways just mentioned. When a communication with the surface exists, such fissures will serve as channels to draw off the gas, and the coal in the neighbourhood of these will be comparatively free of it. But when the workings reach one of these fissures filled with the gas in a state of high tension, the latter rushes out in large volumes, sometimes with a sound resembling that caused by the blowing off of high-pressure steam from the safety valve of a boiler. Such an irruption of gas is described by miners as a " blower," and it is easy to see that an explosive degree of vitiation can hardly be prevented by ventilative means when the cause is one of these blowers. Here lies one of the greatest dangers to which coal miners are exposed. "When the workings are known to be approaching a fault, some precautions may be taken, but often the danger is only discovered when it is too late to avert it.

The quantity of gas given off by a blower will depend, first, upon the capacity of the fissure, and, next, upon the extent of coal surface with which it is in communication. When one of these reservoirs of gas is first tapped, it escapes through the orifice into the workings with a force commensurate with its degree of tension. As the discharge continues, the tension becomes less until, when the atmospheric pressure is reached, the gas issues in virtue of its low specific gravity and the property of diffusion alone. But it will be observed that this point will not be reached when the excess over atmospheric pressure of the original contents of the fissure has been discharged. The tension of the gas in the coal is equal to that of the gas in the fissure, and it is evident that as the tension of the latter is reduced by the discharge, the former will be given off to preserve equilibrium. Thus a very much larger quantity than the original contents of the fissure must be given off before equilibrium is restored with the atmosphere. The value of this quantity will obviously depend, for a given initial tension, upon the extent of coal surface in communication with the fissure. Whether or not, however, the communication is direct is a modifying circumstance to be taken into account, for if the coal surfaces communicate with the fissure only through the medium of intervening permeable rock, the escape of the gas from the coal, in consequence of the reduced pressure, must necessarily be very slow. In such a case, the fissure may discharge itself down to atmospheric pressure in a short time. Hence it will be seen that a blower may exhaust itself in a few hours, or continue with, of course, a constantly diminishing force for several years. The most favourable condition for the production of a large blower is the existence of an extensive fault, closed in its upper portion by impermeable material and open below, and intersecting several gaseous seams of coal. A blower may occur, however, without such a fissure as we have been considering. When the workings in operation are situate above a lower seam of coal, and at no great distance from it, the gas in this lower seam may burst up the floor in some weak place, and so enter the workings. Such an occurrence is by no means rare. In the same way, a blower may occur from an upper seam by breaking down the roof, or in consequence of the fracture of the intervening rock caused by the descent of the roof in v/orking out the coal.

Of a nature in some respects similar to that of a blower, are those irruptions of gas which take place from the goaf or worked-out portions of the mine. It has already been pointed out that faces of coal which are left to stand continue to give off gas slowly. Those portions of the unwrought seam, which may enclose the goaf on one or more sides, will therefore be understood to

Ventilation. 467

discharge themselves into the goaf. Also the waste coal that may be left will give off gas. But besides these, other sources of gas may exist, and be constantly Hable to furnish gas to the goaves. The fractures in the roof rocks may let down gas from a higher seam, or it may permeate the floor from a lower seam. Also the gas which is given off the faces of work may find its way into the goaves ; thus a goaf may be regarded as a reservoir from which the gas may issue in large quantities at any moment. Many of the disastrous explosions which have occurred have been occasioned by the fouling of the travelling ways by gas issuing from the goaf The conditions which determine a discharge of gas from the goaf are in the main barometric ; that is, the circumstance is due to variations in the pressure of the atmosphere. It will be observed that an extensive goaf will contain many thousand cubic feet of gas, and that the capacity of an air- way is such that it can contain only a very small fraction of that quantity ; consequently a discharge of only an exceedingly small proportion of the contents of the goaf must have a very notable effect upon the atmosphere of the air-ways. Now a barometric variation of only half an inch will produce a variation of about in the volume of the gas contained in the goaf. That is, assuming the goaf to be completely filled with gas, a fall of half an inch will cause about part of its contents to be discharged into the air-ways in immediate proximity thereto. If, for example, the contents of the goaf be 100,000 cubic yards, the discharge for a fall of half an inch of the barometer will be about 1640 cubic yards. It is easy to see that if the fall take place rapidly, the air- ways may become fouled to a dangerous degree. With respect to the escape of gas from the coal itself, there appears to be some confusion of ideas in the minds of certain mining authorities. It has been objected that because the tension of the gas is far greater than that of the atmosphere, the pressure of the latter cannot influence the discharge in an appreciable degree. It may be true that the discharge will be the same whatever the atmospheric pressure may be so long as this pressure remains constant ; but, as one writer has pointed out, the immediate effect of any variation must be an increase in, or a diminution of, the discharge, according as the pressure diminishes or increases.

Coal Dust. — We have already directed attention to solid matter as constituting a vitiating agent in the atmosphere of a coal mine. The most important of these solid floating matters is the dust caused by breaking up the coal. Some seams are wet, and in such a case the quantity of dust made is comparatively unimportant ; but when a seam is dry — and sometimes a seam is very dry — the air becomes laden with dust. So vitiated in this respect is the atmosphere of the working places and of the travelling roads in some mines, that it becomes necessary to water the floor frequently. It is obvious that this dust, consisting of minute particles of carbon, must exert a deleterious effect upon the health of the miners, and that, therefore, it will have to be taken into account when estimating the requirements of the ventilation. But there is danger to be feared from another direction. As the dust consists of particles of carbon intimately mixed with the air of the workings, it is evidently liable to combustion, and in a state of combustion it will necessarily be a source of extreme danger to those persons who are occupied in the workings. Nothing definite appears to be yet known concerning the combustion of the carbon in this state and under these conditions, though it has long been a subject of discussion. It is asserted by some that when mingled with pure air it may be fired by the flash of a blast of gunpowder, and that many of the minor fatal explosions that have occurred were due to this cause rather than to the presence of fire-damp. Though this is somewhat doubtful, it does not appear, with our present knowledge of detonation, to be beyond the limits of possibility ; but it is certain that when mixed with carburetted hydrogen the dust may greatly intensify and

468 Mining Engineeeing.

widely extend the effects of an explosion. Thus the consequences of an explosion of fire-damp in the presence of coal dust will be far more serious than when the latter is absent ; and hence it will be necessary on this account also to take the dust into account in estimating the quantity of air to be passed through the workings. It may be remarked here that when the atmosphere is laden with coal dust, the after-damp of an explosion is likely to contain a larger proportion of carbonic oxide than when it is free from that impurity.

After-damp. — Having pointed out and described the constituents of the atmosphere of a mine, in what may be called its normal state, it remains to consider how they will be affected by an explosion, and what the constitution of the atmosphere will be after an explosion has occurred. These are questions of the gravest importance, inasmuch as they affect the safety of all employed in a mine. The noxious gases resulting from an explosion are often, probably in most cases, more deadly in their effects than is the violence of the explosion itself. Generally only a very few are killed by the latter, while scores and even hundreds may fall victims to the insidious influence of the former. The gases due to an explosion of fire-damp are described by miners as the after-damp, or, more correctly, this term is applied to the atmosphere of the mine, or portion of the mine, as it exists immediately after an explosion.

To ascertain the nature of the after-damp, we must trace to their final results the effects of combustion in the explosive mixture of gases. Carburetted hydrogen, as we have seen, is composed of one atom of carbon in combination with two atoms of hydrogen; in the processes of combustion, these atoms are dissociated and recombined with the oxygen of the atmosphere, and it is evident that each molecule of the gas will require three atoms of oxygen to oxidize it into carbonic acid and water. It will be seen from the constitution of carburetted hydrogen, and it has already been pointed out, that in the formation of that compound, 1 lb. of hydrogen unites with 6 lb. of carbon. It will be found by calculation that the product, 7 lb. of carburetted hydrogen, will occupy, at the ordinary mean temperature, a space of 154*185 cubic feet. To oxidize this quantity, there will be required 24 lb. of oxygen, thus made up, namely, 16 lb. to oxidize the 6 lb. of carbon, and 8 lb. to oxidize the 1 lb. of hydrogen. As the whole of this oxygen is to be abstracted from the atmosphere, the volume of air needed to furnish this quantity will be 1365*964 cubic feet; and hence 1 cubic foot of

1365*964 carburetted hydrogen will require for its oxidation -ikj.iqk " 8*86 cubic feet of air. In other

words, the combustion of 1 cubic foot of fire-damp will deprive 8*86 cubic feet of pure air of

the whole of its oxygen. It will thus appear from these considerations alone that an explosion

of fire-damp will greatly vitiate the atmosphere. But the oxidation of 7 lb. of carburetted

hydrogen produces 22 lb. of carbonic acid and 9 lb. of water in the form of steam. Therefore the

oxidation of 1 cubic foot of that compound will produce i ka-iq; — 0*1427 lb. of carbonic acid, and

- - 0*0583 lb, of steam. The latter, however, having no serious vitiating effect upon the

atmosphere, may be neglected. We have already seen that a proportion of about 8 per cent, of carbonic acid in the atmosphere becomes fatal to animal life. Now a simple calculation will show that 0*1427 lb. of carbonic acid will vitiate in this degree 1*641 lb. of pure air, and it will be observed that this weight of air will, at the ordinary temperature, occupy a space of 21*48, or say, 21f cubic feet. Thus the combustion of 1 cubic foot of carburetted hydrogen will vitiate to a fatal degree, by its product -carbonic acid, 21| cubic feet of air. But, as we have already seen, to form

Ventilation. 469

this carbonic acid, a quantity of atmospheric air, equal to 8 "86 cubic feet, has been deprived of the whole of its oxygen ; or, regarded from another point of view, 7 cubic feet of pure nitrogen have been produced by separating it from its oxygen. This nitrogen must be taken into account as a vitiating agent. Unfortunately, in the absence of trustworthy experiments, we do not know at what point a reduction in the proportion of oxygen becomes speedily fatal to life ; but we may assume that that point has been reached when the air contains only half its normal proportion of oxygen. The 7 cubic feet of nitrogen due to the explosion will vitiate to this degree 17f cubic feet of pure air, which quantity must be added to that vitiated by the carbonic acid, giving a total of 21i + 17| 39 cubic feet. Thus an explosion of fire-damp will vitiate, to a degree that must be almost instantly fatal to life, as many times 39;j cubic feet of air as there are cubic feet of the fire-damp exploded. For example, if an explosion occur in a mixture containing 100 cubic feet of carburetted hydrogen, 3925 cubic feet of the ventilative current will be rendered unfit to breathe. This must be regarded as the minimum degree of vitiation due to an explosion of fire-damp. But if the air be laden with coal dust the effects of the explosion will be greatly intensified, the quantity of oxygen abstracted from the atmosphere, and, consequently, the quantity of carbonic acid formed being notably increased. Hence it will be observed that the consequences of an explosion of fire-damp are likely to be more serious in a dry place than in a wet place, a fact that should be taken due account of in estimating the requirements of the ventilation.

In the foregoing estimate of the degree of vitiation caused in the atmosphere of a mine by an explosion of fire-damp, we have assumed combustion to be complete, and the product, consequently, to be carbonic acid. But it was shown in a former section that the combustion of fire-damp in the air-ways of a mine is almost necessarily incomplete, and that the product of incomplete combustion is carbonic oxide. It was, moreover, stated that a proportion of one per cent, of this gas in the atmosphere is speedily fatal to life. Thus it will be seen that the estimate based upon the production of carbonic acid gives the minimum degree of vitiation, and that this degree may be very largely exceeded. As we are unable to determine the quantity of oxide formed in an explosion, since all the conditions of its formation are not known, we cannot estimate the degree of vitiation due to this source. But it is probably in all cases considerable, and in some cases, especially in those where the atmosphere is laden with coal dust, very great. "We have already pointed out one of the conditions under which carbonic oxide is formed, and it will be perceived that this condition must prevail in a greater or less degree whenever carburetted hydrogen is exploded in the working places or in the air-ways of a mine. The fatal effects of after-damp have often puzzled those who are practically acquainted with the nature of the foul gases generated or given off in a mine. Numerous instances have occurred of miners having been found dead with their lamps burning brightly by their side, and as it was known that carbonic acid could not, in such circumstances, have been the cause of their death, some other explanation of the event was sought; but our experience leaves us no room for doubt that in these cases the fatal effects must be attributed to carbonic oxide, and it is abundantly clear that in all cases of explosion the deadly nature of the after-damp is greatly intensified by the presence of that gas. "Were the acid only produced, escape would be far more easily effected, and the fearfully long lists of the dead which we now have to scan with such lamentable frequency would be much shortened.

Diffusion. — When two fluids, which have no chemical action upon each other, are brought together they spontaneously mix, and the mixing action goes on until the two fluids are equally

170 Mining Engineering.

diffused. This tendency to mingle is known as the property of diffusion, and it is a property of great importance to ventilation. The rapidity with which diffusion takes place varies with different fluids and according to certain conditions. It is slow in the liquids, and slower in some liquids than in others. To observe the action in a liquid, fill a vessel with distilled water and place in it, with the neck closed by a stopper, a small phial containing, say a saline solution. Remove the stopper slowly to avoid troubling the liquid, and leave it to stand for some time. If the contents of the phial and of the outer vessel be now analysed, they will be found to contain the same proportion of the saline matter, thus showing that the solution in the phial has diffused itself throughout the liquid mass. In gases, by reason of their expansive force, diffusion takes place far more rapidly than in liquids. To observe the action in a gas, fill a vessel with carbonic acid, and let another vessel be filled with atmospheric air. Place the latter above the former and make a communication between them by means of a tube. If the vessels be left to stand for a short time, and their contents then examined, both will be found to contain the same proportions of air and carbonic acid. If, instead of atmospheric air, the upper vessel had contained hydrogen, the same action would have taken place, and, on examination, in each there would have been found equal proportions of carbonic acid and of hydrogen. The action of diffusion, it will be observed, takes place independently of gravity, for though the carbonic acid is about twenty-two times heavier than the hydrogen, the former has ascended into the upper vessel and displaced the latter. It will hence be seen that when the gases have once become mixed, they will persist indefinitely in that state. But a difference in the specific gravity occasions a difference in the rapidity with which the gases become diffused, the heavier gas being the less diffusible. Thus, in the example quoted, the hydrogen will diffuse itself in the downward direction about five times more quickly than the carbonic acid in the upward direction. Hence we have the following two laws of diffusion : — 1, Gases that have no chemical action one upon another become rapidly mixed when brought into contact, and their mixture is uniform and persistent ; and 2, the rapidity with which the mixture of the two gases takes place increases with the difference of their specific gravities. It has been observed that the molecules of hydrogen disperse themselves in the atmosphere, when the latter is not in motion, at the rate of about 12 inches a minute.

The importance of this property of diffusion in the ventilation of a mine will become manifest on reflection. The carbonic acid given off in the breath of those employed, and from the candles or lamps used, is instantly diffused throughout the large volume of air constituting the ventilative current. Also accumulations of that gas out of the force of the current are dispersed, in course of time, in this way. So carburetted hydrogen, as it is given off by the coal, becomes instantly diffused in the atmosphere instead of forming, as it would otherwise do, an explosive mixture in certain parts. And even when that gas is given off in large quantities by a blower, this property of diffusion acts to bring down the proportions below the explosive point the moment the quantity of air becomes sufficient. So, again, diffusion acts to dissipate accumulations of gas in hollows in the roof out of the influence of the force of the passing current. It would appear, however, that diffusion from a stagnant mass of gas into a moving mass of another gas is very slow, and that the rate diminishes as the velocity of the latter increases. Hence it often becomes necessary to remove accumulations of gas against the roof by partially closing up, by means of brattice cloth, the lower part of the air-way, so as to direct the current against the roof for the purpose of sweeping out the gas. It is the slow diffusion under such conditions that prevents the air in the ways from being often fouled to the explosive point by gas from the goaves. Indeed, were it otherwise, there could hardly be an

Ventilation. 471

accumulation of gas in the goaves. It is true that explosions are sometimes attributed to this cause, but where the air fouled is in fairly rapid motion the possibility of fouling by such means may fairly be doubted. Of course, diffusion may act in conjunction with a decrease in the pressure of the atmosphere to bring about such a result. The question, however, has not yet been fully investigated. Chemical Notation. — As the gases which we have described in the foregoing sections are usually denoted by symbols, for the purpose of conveniently representing them in chemical formulae, it is desirable to indicate in this place these symbols, and to point out the mode of employing them. The substances under consideration are represented by their initial letters ; thus the symbol of oxygen is O, of nitrogen N, of hydrogen H, of carbon C, and of sulphur S. The combination of any two of these is represented by writing their initials together, and the proportions in which they have combined are denoted by figures placed against and beneath them. Thus the symbol of carbonic oxide, in which one atom of carbon has combined with one atom of oxygen, is C ; that of carbonic acid, in which combination two atoms of oxygen are united with one of carbon is C O2 ; that of proto-carburetted hydrogen, in which two atoms of hydrogen are joined to one of carbon, is C H2 ; that of bi-carburetted hydrogen, in which combination there are two atoms of carbon, C2 Ha ; and that of sulphuretted hydrogen, in which there is one atom of hydrogen to one of carbon, is S H. The symbol for water is H2 0, the compound being composed of two atoms of hydrogen and one of oxygen. The chemical reactions of substances one upon another are shown in the form of an algebraic equation, thus :

CHa + 03 CO2 + HaO.

That is, three atoms of oxygen added to one molecule of carburetted hydrogen, under conditions in which they can combine, or, which amounts to the same thing, taking the example already given, 24 lb. of oxygen added to 7 lb. of carburetted hydrogen produce carbonic acid and water, the oxygen combining with the carbon and the hydrogen in the proportions of two parts with the former and one with the latter. Taking the above weights, the product will obviously be 22 lb. of carbonic acid and 9 lb. of water, as pointed out in a former section.

Volume op the Yentilativb Current. — As the atmosphere of a mine becomes rapidly and seriously vitiated, it is necessary to provide means for constantly renewing it. This is the object of ventilation, which consists in expelling the vitiated air and in supplying its place with an equal volume of pure air. The first question that here presents itself for consideration is, What quantity of air shall be admitted in a given time ? or more correctly, what quantity of air shall be expelled in a given time ? since it is the vitiated air that we have to deal with. Obviously this quantity will be dependent upon the degree of vitiation caused, or liable to be caused, in that time. Here then we have to fall back upon the ascertained facts treated of in a former part of this chapter. In estimating the value of these facts, it will be observed that some of the sources of pollution are constant, or nearly constant, in their action, and therefore subject to calculation ; and that others are exceedingly variable, and therefore capable of being treated only by approximate evaluation. These two classes of vitiating sources must hence be considered separately. Moreover, such an estimate must be based upon the facts already proved, that air containing more than 0-35 per cent, of carbonic acid is very unwholesome to breathe, and that an atmosphere containing 7 per cent, of carburetted hydrogen has reached the farthest limit of safety.

It was shown in a former section that a man when working in a mine discharges into the

472 Mining Engineering.

atmosphere, by the act of breathing, 2 '10 cubic feet of carbonic acid gas an hour. To dilute this quantity of gas down to the highest allowable degree of 0'35 per cent., there must be added to it 600 cubic feet of pure air. Thus each man present in a mine will vitiate by his breath 600 cubic feet of air an hour, or 10 cubic feet a minute. It was also shown that a candle or a lamp produces about 2*52 cubic feet of carbonic acid an hour, to dilute which down to the requisite degree there will be needed 720 cubic feet of pure air. So that a candle may be said to vitiate the atmosphere at the rate of 720 cubic feet an hour, or 12 cubic feet a minute. Assuming the number of candles or lamps to be equal to that of the persons employed, and referring the former to the latter, we thus have 10 + 12 22 cubic feet of pure air required for each person per minute.

But besides this vitiation by carbonic acid, there is that due to the effluvia proceeding from the human body, a source of vitiation not to be neglected. These effluvia, which are derived from the various secretions of the body, and which are being constantly given off at every pore, are immensely increased in quantity by violent exertion, such as is undergone in a mine. And as they contain the germs of disease, it becomes necessary to provide for their speedy removal into the outer atmosphere. Though the quantity of effluvia is not calculable, it will be convenient to include it among the sources of vitiation which we are now considering. The surface of the human body is, in a person of mean stature, about 16 square feet, and if we allow a film of air, inch in thickness, uniformly spread over this surface, and changed at intervals of 30 seconds, we shall have made adequate provision for the effluvia. Such a provision will require 2 cubic feet of pure air a minute, and this quantity must be added to that already determined, giving thus a total quantity of 24 cubic feet of air a minute for each person present in the mine.

It has been ascertained, as already stated, that a horse, of the mean size of those usually employed in mines, produces, in the act of breathing, approximately six times as much carbonic acid as a man ; consequently, it will vitiate the atmosphere to the extent of 10 x 6 60 cubic feet a minute. Also the surface of the body of a horse is approximately six times that of a man, so that the total quantity of air vitiated will be 10x6 + 2x6 72 cubic feet, the quantity vitiated by six men irrespective of their lamps. Including the effects of the latter, the quantity of air required for a horse is equal to that required for three men.

"We have now to take account of the effect of the explosion of gunpowder. Here, at the outset, we are met by the difficulty of determining, under any given conditions, the quantity of explosive consumed in a given time, since shots are fired at irregular intervals, and with varying charges. But it is possible to ascertain the quantity of powder burned during a shift; and if we take the maximum observed, and distribute it in equal quantities and at regular intervals over the time of the shift, we shall obtain a degree of approximation sufficiently near for practical purposes. It has already been shown that the combustion of 1 lb. of gunpowder produces 2*58 cubic feet of carbonic acid, which, it will be observed, is about the same quantity produced in an hour by the combustion of a candle. But carbonic acid is only one of several products of the explosion. There is a notable quantity of nitrogen liberated from the saltpetre, and discharged into the atmosphere as free nitrogen. There may also be formed small quantities of sulphuretted and of carburetted hydrogen. In addition to these, there is always a large proportion of solid matter, consisting mainly of sulphate and carbonate of potassium, discharged into the atmosphere as smoke. These products will vitiate at least twice as much air as the carbonic acid. The force of the explosion will also produce a large quantity of dust, which will be thrown upon the atmosphere with the products of combustion. The

Ventilation. 473

quantity of the duSt will vary with the physical condition of the coal and the degree of moisture in the seam ; but it will always be suflSciently large to render a considerable volume of air unfit to breathe. Hence it will be und.erstood that the combustion of 1 lb. of gunpowder will vitiate about tour times as much air as a candle in an hour, or as much as two men in the same time. If an hour of time were consumed in burning the gunpowder, obviously the pound of the explosive would require the same quantity of air to be supplied in that time as the two men, namely, 1440 cubic feet. But in the one case the production of gas is gradual, whilst in the other case it is practically instantaneous. After an explosion, however, a certain time is allowed for the ga es to disperse themselves before the men return to the working place. The results, therefore, are nearly the same as if that time were consumed in the production of the gases, the latter being carried along by the ventilative current, becoming mixed up with it and diffused throughout it to the extent allowed by the length of the time. If the time be a quarter of an hour, the atmosphere affected by the products of the combustion of 1 lb. of powder will obviously be vitiated to a degree four times greater than that due to the presence of two men with their lamps, since in four times the time the latter would vitiate it to an equal degree. Assuming, therefore, the time allowed to elapse between the explosion and the return of the men to be a quarter of an hour, for each pound of gunpowder consumed an hour, the quantity of air required by eight men must be added to the ventilative current ; this quantity will be 24 X 8 192 cubic feet a minute.

It now remains to consider the variable sources of vitiating agents, which, as previously pointed put, can be treated only in an approximative way. Such agents are the carbonic acid existing in the strata, and the proto-carburetted hydrogen given off by the coal seam. The carbonic acid due to the decomposition of vegetable and animal substances in the mine may be neglected, as the quantity of gas so produced is small, and of this a large proportion is taken up by the water present. Also the large blowers described in a former section must be neglected, since it is impossible to provide a ventilative current of sufficient volume to meet the requirements of such abundant sources. The most that can be done is to make ample provision for the ordinary exhalations of gas, and the small blowers which frequently occur. The rest must be left to watchful car, and a prudent use of the safety lamp.

We have seen that carburetted hydrogen may exist in the coal in a state of high tension, and that consequently when the mass is broken up, the gas may be given off rapidly. As the tension is reduced, the quantity given off in a certain time becomes less, and as the gas has to force its way through the pores of the coal to reach the exposed surface, the process of discharge may continue for a long time. Moreover, the low specific gravity of carburetted hydrogen gives it a tendency to escape even after its tension has become equal to that of the atmosphere. Thus the discharge of gas from the coal, though variable in quantity, may be considered as continuous, a circumstance that was pointed out in a former section. From these facts, it will appear that the quantity of gas discharged into the atmosphere of a mine will bear some relation — 1, to the extent of surface exposed in the coal seam ; and, 2, to the cube of coal broken in a given time ; that is, to the coal surface swept by the ventilative current, and to the amount of the output. By taking account of this relation, we may approximate to the quantity of air required to dilute the gas.

If a cubic inch of coal be taken from a seam that gives off but little gas, and immediately placed under a testing glass, or other receptacle from which the air may be withdrawn by means of an air pump, it will be found to give off, within a short time, a volume of gas about equal its own.

3 p

474 Mining Engineeeing.

Hence, when sucli coal Is newly broken from the seam, it may be assumed that the quantity of gas given off by it will not exceed this ; that is, a cubic foot of the coal may be expected to give off a quantity of gas not exceeding 1 cubic foot before it reaches surface. This quantity may therefore be taken as a basis whereon to calculate the requirements of the ventilation in so far as the output is affected. We have seen that to keep the mixture above the explosive point, there must be not less than fifteen parts of pure air to one part of the carburetted hydrogen. Hence for every cubic foot of coal broken from the seam, 15 cubic feet of air must be passed through the working places. This quantity is, however, only just sufficient to keep the atmosphere above the firing point, and it may .be insufficient to do that in cases where the gas is given off very rapidly, for the inability of such a mixture to explode depends upon the completeness of the diffusion. The quantity of 15 cubic feet must, therefore, be increased. But as it is desirable, not only that explosion should be avoided, but also that the atmosphere should be maintained in a wholesome state, the increase should be great. Furthermore, we must take into account some other agents of vitiation in like manner dependent upon the quantity of coal broken. In workings in pyritous coal, small quantities of sulphuretted hydrogen may be given off ; in any case, carbonic acid may be liberated ; and in all cases a quantity of dust will be made. It is evident that the quantity of dust thrown into the atmosphere will increase with that of the coal broken and conveyed along the travelling roads. To keep the atmosphere, into which all these vitiating agents are discharged, in the requisite state of purity, the 15 cubic feet of air should be increased to 100 feet; that is, for every cubic foot of coal broken from the seam and conveyed to surface, 100 cubic feet of pure air should be passed into the workings.

It now only remains to determine an adequate quantity of air to dilute the gas which is constantly being given off from the standing surfaces. In this case we have no basis whereon to found a calculation, and the most suitable mode of treating the question seems to be that adopted for the effluvia given off from the human body. Still assuming the mine to make but little gas, it would appear that if we could cover all the exposed coal surfaces with a film of pure air of a uniform thickness of 1 inch, and change this film every minute, we should have made ample provision for the gas exuding from those surfaces. Such a provision would require 75 cubic foot of gas a minute for each square yard of surface. But as it is impracticable to distribute the air in this equal manner, the quantity should be increased to 1 cubic foot a minute. The additional quantity will also be a provision for the gas which may escape by permeating the rock. In workings according to the system of long wall, the exposed coal surfaces will be chiefly the working faces. But in post-and-stall workings, there will be, besides the working faces, the exposed surface of the pillars left in the broken mine. Hence it will be obvious that the latter system will require a more abundant ventilative current than the former ; and it will, on reflection, become equally obvious that the conditions prevailing under the post-and-stall system are such as to render a more powerful ventilation necessary.

It must be borne in mind that the quantities which we have determined are those required in a mine in which but little gas is given off from the seams, and, therefore, they must be taken as the minimum allowable under the most favourable circumstances. To provide for the requirements of gassy seams, these quantities must be multiplied by a suitable factor of safety, in the same way that the breaking strain in materials is multiplied, to which they are analogous in character. The value of this factor in any particular case must be left for the engineer to determine in accordance with the circumstances with which he has to deal. It may be 2, 3, 4, or 5 ; or even greater in very gassy seams particularly liable to give off blowers, or where the dangers of extensive goaves have to be provided for.

Ventilation. 475

Example. — To show tbe practical application of the results arrived at in the foregoing considerations, we will take an example of a mine for which the ventilation has to be determined. To simplify the calculations, we will assume that the number of men employed underground is one hundred and fifty, and the number of horses five ; that the average consumption of gunpowder is 5 lb. an hour ; that the daily output is 300 tons in twelve hours ; and that the extent of coal surface exposed, the workings being by long wall, is 500 square yards.

Here we have, for the men, 24 x 150 3600 cubic feet ; for the horses, 72 x 5 360 cubic

feet; for the powder, 192 x 5 960 cubic feet; total for these sources of vitiation, 4920 cubic feet

a minute. The output being 300 tons, and the exposed surface 500 square yards, the former will

300 X 27 X 100

require — 1125 cubic feet and the latter 500 cubic feet a minute, the ton being

12 X 60 Jo

taken as a cubic yard. The sum of these two quantities is 1625, and as we are supposing the seam

to be fairly free of gas, we may take the factor of safety as 2. This will give us 1625 x 2 3250

cubic feet, which, being added to the quantity already found, gives us the total quantity required,

namely, 4920 + 3250 8170 cubic feet a minute. Had the workings been on the post-and-stall

system, the vastly larger exposed surface would have required a considerably larger volume of air.

Also, if there were much goaf it would be prudent to make the factor of safety greater than 2. Shortly

put, the quantities which go to make up the total volume of the ventilative current are as follows :

V m24 + A72 +jpl92 + ylOO s,

where Y is the ventilative current in cubic feet a minute, m the number of persons employed, h the number of horses in the mine, p the weight in pounds of the gunpowder consumed an hour as a maximum, q the output or average quantity of coal raised a minute, and s the exposed surface of the coal in yards. For the preceding example the expression becomes :

y 150 X 24 + 5 X 72 + 5 X 192 + 2 (11-25 x 100 + 500) 8170.

In the example, we have considered one district only ; when, as is commonly the case, the mine consists of several districts, the volume required for each district must be found separately ; and the total of these quantities will be the total volume to be admitted into the mine. The factor of safety adopted may vary from district to district as well as from mine to mine. The particular conditions of any given case may always be taken account of in the factor of safety. As before remarked, the value of this quantity must be determined according to the circumstances by the person whose duty it is to provide an adequate ventilation, or to test the adequacy of an existing current.

Measurement. — Thermometries Barometric, and Dynamic. — Having described the means and the methods whereby the quantity of air necessary to adeqiiately ventilate the workings of a mine may be determined, it now remains to show how the quantity actually circulating is measured, and how the volume of air is affected by variations of temperature and atmospheric pressure. These questions involve a consideration of the principles and the mode of action of the several instruments known respectively as the " thermometer," the " barometer," the " water gauge/' and the " anemometer."

The Thermometer. — The use of the thermometer is to indicate the temperature of the body with which it is placed in contact ; for purposes of ventilation, this body is always the atmosphere. The action of the thermometer depends upon the well-known fact that all bodies expand when heat is applied to them, and contract when heat is abstracted from them. Of the three classes of bodies, the

3 p 2

476 Mining Engineering.

degree of expansion is least in solids and greatest in gases, the mean being found in liquids. For this reason, the gases furnish the most delicate means of measurement, and they are often used for that purpose. But as in practice superior advantages of convenience are offered by the liquids, these are commonly adopted. Moreover, as the liquids differ among themselves in the matter of these advantages, mercury is generally chosen, because it is the one that expands most regularly, because it does not boil until a very high temperature is reached, and because, being a much better conductor of heat than the other liquids, it most quickly takes the temperature of the body with which it is in contact. It is, therefore, with the mercury thermometer that we have chiefly to deal. For measuring very low temperatures, alcohol is preferred on account of its not being subject to congelation at the lowest yet known.

The action of a thermometer is easily understood. Suppose a bulb, or globe, A, Fig. 660, into which enters a small glass tube B, the globe and tube being filled with mercury up to the point m. If heat be applied to the globe, the mercury within it will expand, and, the walls of the globe being unyielding, will ascend the tube. It will be observed that as the capacity of the globe is much greater than that of the tube, a very slight degree of expansion in the former will become plainly perceptible in the latter. If the source of heat be removed, the contents of the globe will contract, and the column in the tube will sink to the point at which it originally stood. Thus we have a plainly visible effect of heat, and we now require to know, in order to be able to measure the temperature, the magnitude of this effect for a given quantity of heat. Suppose the capacity of the tube above the point m to be of that of the globe and of the portion of the tube below that point, and suppose that an increase of 1 degree in the temperature of the mercury causes the column to ascend from the point m to the point m'. It is obvious that we have only to measure the distance between m and m' to know the degree of expansion which has taken place in the mercury as a consequence of the increase of 1 degree in its temperature. Suppose this distance to be part of the length of the tube above m, which we will call the zero point. As the capacity of the whole length is of that of the globe and the portion of the tube below the zero point, the capacity of the portion m m', which has become filled will be of or That is, an increase of 1 degree in the temperature of the mercury has caused it to expand of its bulk. This ratio, yirj) or 0-0001, would then be called the coefficient of expansion for mercury, this expression being used to signify the degree of expansion due to an increase of 1 degree in the temperature. It has been found by experiment that the true coefficient of expansion for mercury is j, or 0*00018, for the Centigrade thermometer. Knowing the capacity of the reservoir and that of the tube, we may thus calculate the divisions to be marked on the tube. The zero point m is found by placing the mercury reservoir in a vessel containing melting ice. We may convert the instrument into an air thermometer by placing a short column of mercury in the tube and filling the reservoir beneath with air having such a degree of tension that the column shall stand at m when the temperature is that of melting ice. The coefficient of expansion for air has been found to be 0*00367, whence it will be perceived that such a thermometer will show a smaller variation of pressure than the mercury instrument.

The Barometer. — The use of the barometer is to indicate the weight or pressure of the atmosphere, which is constantly varying within narrow limits. This change of atmospheric pressure experts, as we have already seen, an influence upon the discharge of gas from the coal, and also may determine an irruption of gas from the goaf. Hence these variations of pressure constitute an important question in ventilation, and attention to the proper placing of the barometer, the use of which, as remarked above, is to indicate these variations, has recently been rendered obligatory by Act

Ventilation. 477

of Parliament. The principle of the barometer, like that of the thermometer, is easily understood. If a tube 35 feet long, closed at one end, and filled with water, be placed in a vessel of water, with the open end downward, care being had to keep the end covered to prevent escape of the water till it is immersed. Fig. 661, the column of water in the tube will sink until it reaches a height of about 33 "9 feet, at which point it will stand. The descent of the column has left a vacuum above the water at the closed end of the tube, and at the height of 33 '9 feet, the descent is arrested by the opposing pressure of the atmosphere. This shows the weight of the atmosphere to be equal to that of a column of water 33 9 feet in height ; that is, the pressure of the atmosphere upon a square inch of surface is equal to that of a column of water 33*9 feet high resting upon that surface. But, while the pressure of the water is constant, that of the atmosphere, as we have already observed, is variable. Now, as the column of water in the tube is in equilibrium with the pressure of the atmosphere, the height of the former will vary with the latter ; that is, when the atmospheric pressure increases, the column will rise, or become longer, to balance it, and when this pressure diminishes, the column will, for the same reasons, sink, or become shorter, the excess of water being taken up from, or discharged into, the vessel which acts as a reservoir. It is obvious that any other liquid may be used instead of water, and it is clear that a liquid having a much higher specific gravity than water would be far more convenient, since the length of the tube would be proportionally reduced. The liquid which best fulfils the required condition is mercury, the specific gravity of

which is 13" 6. As mercury is 13 6 times heavier than water, the length of the tube will be reduced

from 33*9 feet to 2*49, say 2 feet 6 inches. Chiefly for this reason the mercuric column

has been adopted for barometers, though it should be remarked that another serious defect of the water column lies in its liability to become frozen at low temperatures. This difficulty has, however, been removed by substituting wine for water. The mercury barometer is constructed upon this principle of a column balanced by the pressure of the atmosphere, and it is clear that any variation in this pressure will be followed by a corresponding variation in the length of the column. In ordinary language, an increase or a decrease in the length is described as a rise or a I'all of the mercury, and to ascertain the amount of the variation, the glass tube containing the column is graduated, according to the metrical system, in fractions of a metre, according to the English system of measures, in fractions of an inch. The amplitude of the variation in pressure, that is, the mean difference between the greatest and the least height of the column, increases from the equator towards the poles ; in England if we except extraordinary disturbances, the greatest variation is 1*6 inch, and is included between 28-7 and 30 '3 inches. The weight of a cubic inch of mercury being 0-49 lb., the pressure of the atmosphere at the mean barometric height of 29 inches is 0-49 X 29 14-2 lb., and the extreme variation 0*49 x I'B 0-78 lb., or 112-3 lb. to the square foot. The diurnal mean height of the barometer is found by adding together the heights observed at the end of each of twenty-four consecutive hours, and dividing the sum by the number of hours. The annual mean height is found by adding together the mean diurnal heights for the year, and dividing the sum by 365, the number of days in the year. The mean annual height varies in different parts of the world ; but the m-ean general annual height at the level of the sea" is 30 inches. In order to be able to compare the heights of the barometric column, or, as they are usually expressed, the "barometric readings," observed in different places, correction must be made for differences of level, since it is obvious that the higher we ascend, the less the pressure of the atmosphere becomes. The correction is made by reducing the readings to that of the general sea level.

478 Mining Engineeeing.

A A . . .

The amount of the correction is given by the formula C orTu which A is the altitude, or height

above sea level, in feet, h the height of the mercury column in inches, and H the height of a column of air capable of balancing a column of mercury 1 inch in height. The value of H may be determined by comparing the densities of mercury and air, the former of which is 10,466 times greater than the latter. Hence a column of mercury 1 inch in height will require to balance it 10,466 inches, 872*16 feet, which height is the value of H. With this value, the formula

A A becomes C da.q Example : Let it be required to compare the readings of two barometers

in different localities, one situate 250 feet, the other 160 feet above sea level, the readings being 29 50

inches in both. The question is. What is to be added to each reading to make them both correspond

250 X 29*5 to the mean sea level? The quantity to be added to the former is — -„.,„, „ 0'28 inch, and

the quantity to be added to the latter is noif-A.o inch. Thus the reading of the former,

reduced to the sea level, will be 29*50 + 0*28 29*78 inches; and that of the latter, reduced to the same level, 29*50 + 0*23 29*73 inches; whence we see that the difference in pressure is 29*78 — 29*73 0*05 inch. This method of reduction is sufficiently accurate for moderate elevations ; but it will be evident that it is not applicable to great heights, since, as the air becomes rarefied as we ascend, the value of H is variable.

Correction must also be made, in all observations, for the effects of temperature. It has already been shown that the mass of mercury expands and contracts with the application and the withdrawal of heat, and it is obvious that the length of the column will consequently vary with the temperature. To ascertain the height due to atmospheric pressure, therefore, it is necessary to take account of this effect of the temperature. For this reason, barometers are always fitted with a thermometer. The correction is made by reducing the reading to zero of the Centigrade thermometer, to which the 32nd degree of Fahrenheit's instrument corresponds; that is, the height of the column is that which would appear if the temperature were at the freezing point of water. The height of the barometer being H at degrees, let h be its height at zero. If we represent the density of the mercury at zero by d and its density at t degrees by d', we know that the heights

. h d' H and h are in the inverse ratio of their densities d and d', that is, -5 -7. But if we represent the

volume of the mercury at zero by 1, its volume at t degrees will be 1 D D being the coefficient of expansion for mercury. Now the ratio of the volumes 1 and 1 +'Dt is equal to the inverse

ratio of the densities, that is, . From these equalities, we have =:r- ; whence

cL i + u t a. i + D t

H . 1

h :j . Substituting for D its value rrrK , we get

H H X 5550

h

-. 5550 4- t

Example. — Let it be required to find the true height of the barometer which marks 30 inches when

the temperature is 25 C. Here we have A 29 -86 mches, the height sought.

Ventilation.

The following table gives the correction, that is, the quantity to be subtracted, for each degree of Fahrenheit's thermometer :

Temperature.

Correction.

Temperature.

Correction.

Temperature.

Correction.

Temperature.

Correction.

o

o

To illustrate the foregoing methods of correcting for level and for temperature, let it be required to compare the readings of two barometers in two distant localities, the height in one place, 300 feet above the level of the sea, being 29 "50 inches, and the height in the other place, 120 feet above the level of the sea, being 30" 20 inches, the temperature being in the former place 60°, and, in the latter

place, 75°. Here we have

300 X 29-50

0-34, and

120 X 30-2

0*14, the corrections for

26164-8 ' 26164-8

altitude; whence we have 29*84 and 30-34 as the reduced readings. But the temperature being 60° in the former case, and 75° in the latter, these readings, corrected from the table, become 29-76 and 30-22 respectively. Hence we see that the difference in the atmospheric pressure is 30-22 - 29-76 0-46 inch.

When tbe tube enclosing the column of mercury is of small diameter, correction will also be required for the capillary attraction. But if the diameter be not less than half an inch, this influence may be neglected. For this reason, the tube should never be made less than half an inch in diameter.

It has been objected that the barometer is useless as a monitor to the furnace-man, warning him when to increase his fire, because its indications are given several hours after the event has occurred. This objection, however, only applies to small tubes in which the friction and the capillary attraction are great, or to that production of folly, the wheel barometer in which the friction to be overcome by the column is enormous.

As an application of the foregoing to practice, let it be required to find the quantity of air, mingled with vitiating gas, that may be expected to be given off from the goaves in consequence of a fall of the barometer from 30 - inches to 29 - 5 inches. Here the difference of pressure is - 5 inch, and putting x for the quantity sought, we have, for each 1000 cubic feet of gas in the goaves :

30-0 : 0-5 :: 1000 -.a;,

section. Thus if the goaves contain 100,000 cubic feet, the quantity given off will be 1666 cubic feet. Of course, we may find the value of x by taking the pressures instead of the heights of tbe

Mining Engineering.

mercuric column represetiting them. Thus 30 inches of mercury represent- a pressure of 2116 ''8 lb. to the square foot, and 29 5 inches a pressure of 2081 5 lb., showing a. difference of 35*3 lb. to the square foot. Honce

2116-8 : 35-3 :: 1000 : x.

whence w

16' 66 cubic feet as before.

TTie Water Gauge. — The water gauge is an instrument for measuring the dynamic force of a current of air, that is, the pressure which a current of air exerts against a fixed surface upon which it impinges perpendicularly. It is of common use in mines to indicate the force of the current, whence the volume passing in a given time, and the loss occasioned by friction may be calculated. The water gauge is a very simple instrument ; it consists, as shown in Fig. 662, of a bent glass tube, containing in the bend a small quantity of water. One end of the tube is open to the current, the other end is open to the atmosphere away from the force of the current. It is evident that as the current enters the tube and presses upon the water therein contained, the latter will ascend in the other arm of the tube, till the column balances the force exerted. Thus, the weight of the water being known, we have a measure of the force due to the velocity. The weight of a cubic inch of water is 0*036 lb., so that when the column stands 1 inch high, the pressure is 0-036 lb. to the square inch, or 5 '2 lb. to the square foot. By graduating in fractions of an inch the ascending arm of the tube, the indications may be easily read and the pressures calculated. Thus if the height of the column be 3 inch, the pressure will beO-036xO'3 0- 0108 lb. to the inch, or - 0108 x 144 1 555 lb. to the foot. The water gauge is used to show the force of the current generated by a ventilating fan, or by a furnace, and is therefore constantly referred to by the mining engineer. The following table shows at a glance the pressure corresponding to a given height of the water column :

Pkessuee

OF AlE AS SHOWN BY THE WaTEK GauGE.

Height

Pressure in lb. to

Height

Pressure in lb. to

Height .

Pressure in lb. to

Height

Pressure in lb. to

in Inches.

the Square Foot.

in Inches.

the Square Foot.

in Inches.

the Square Foot.

in laches.

the Square Foot.

Ventilation. 481

The Anemometer. — The anemometer, like the water gauge, is an instrument for measuring the dynamic force and the velocity of a current of air. But in the former, the force is made to act upon vanes, in the same way as it acts upon the sails of a windmill, a mode of action which gives to the vanes a velocity proportional to that of the current. An important point to be gained in the construction of anemometers is to reduce the friction to the lowest possible limit, since the friction not only diminishes the velocity of the vanes, but, in a very light current, it may prevent them from revolving altogether. Herein lies the chief defect of all self-registering apparatus of this kind, for by multiplying the parts of the mechanism for the purpose of rendering the instrument more complete, we necessarily increase the friction. The anemometer in common use in mines is that known as Biram's, and this is probably the most perfect instrument of its kind yet invented. Though self-registering, its action is very delicate ; some of them will revolve in a current moving with a velocity as low as 30 feet a minute, but in general a somewhat higher velocity than this is required to k( ep it in motion. It consists of a number of vanes upon which the air impinges, the number of the revolutions being registered by a pointer upon the face of a dial forming a part of the instrument. It is made in three sizes, 4, 6, and 12 inches in diameter, the mechanism being contained in a cylindrical box or case. The registering apparatus is in front of the wheel or set of vanes ; it consists of six small circles, marked respectively X, C, M, X M, C M, and M, the divisions on which denote the units of the denomination of the respective circles ; that is, the X index in one revolution passes over its ten divisions and registers 10 x 10 100 feet; the index, in the same way, registers 1000 feet, and so on up to 10 million feet. Thus the observer has only to record the position of the several indices at the time of his first observation, by writing, in their proper order, the lower of the two figures on the respective circles between which the index points, and to deduct the amount from their position at the second observation, in order to ascertain the velocity of the air which has passed during the interval. Example : If 100 revolutions 200 feet a minute, we have

2 27 miles an hour, a veloc'ty of 88 feet a minute being equivalent to 1 mile an hour.

When the velocity of the air is known, the quantity passing in a given time can be easily calculated if the sectional area of the air-way is also known. For example, let it be required to determine the volume of air passing in a minute along an air passage, the dimensions of which are 7 feet by 6 feet, when the velocity of the current is 4 feet a second. The sectional area of the passage being 7 x 6 42 square feet, and the velocity of the current 240 feet a minute, the volume passing will evidently be 42 x 240 10,080 cubic feet. If the passage were circular in section, and 7 feet in diameter, we should have : the area 7' x 7854 38 48, which multiplied by the velocity gives 9235 cubic feet a minute.

EETARDATioisr OF THE Flow OF AiR. — It is obvious that to pass a given quantity of air through the air-ways of a mine, a certain force must be expended, and for the purposes of ventilation it becomes necessary to know what this force is. This question involves a consideration of the resistances to be overcome ; these resistances are, chiefly, that due to the friction of the air against the sides of the ways, that occasioned by a contraction of the way, and that offered by obstructions in the line of flow. The first and the second of these sources of resistance are subject to calculation, the last can be determined only approximatively.

Friction. — The column of air in a circular pipe of a determinate length may be regarded as a solid piston or rod which has to be driven through by the application of external force. As in the

3 Q

482 Mining Engineering.

case of the solid, this column will be subjected to the resistance due to friction between its surfaces and those of the pipe in which it moves. But the air being a highly elastic body, will press equally upon every part of the rubbing surfaces, which the inelastic -solid will not do. This is the only essential difference to be observed in the two cases. Now two things become evident on reflection ; first, that this friction between the surfaces of the air column and those of the containing walls must be considerable ; and, second, that, the pressure being constant, the friction must vary as the surfaces in contact. The pressure indicated by a column of 30 inches of mercury being 14*7 lb. to the square inch, or 2116 8 lb. to the square foot, it will be seen that every square foot of rubbing surface is pressed with a force of 2116 "8 lb. ; such a degree of pressure must occasion considerable friction. Also, the pressure being everywhere the same, it follows that the total value of the friction will increase as the extent of the rubbing surfaces increases.

From the latter fact, follow three important practical consequences. First, for a given section of air- way the resistance due to friction will increase as the length of the way. If, for example, we have an air-way, the sectional area of which is 6 x 6 feet, the perimeter, that is the bounding lines, will be 6 X 4 24 feet ; then, if the air-way be 1 foot in length, the extent of the rubbing surface will also be 24 feet, 6 on the roof, 6 on the floor, and 6 on each of the two sides. If we double the length of the air-way, we shall evidently double the extent of the rubbing surface, and consequently double the resistance due to friction. If the length of the way be made 100 feet, or 1000 feet, the surface, and, cc'isequently, the resistance will be increased a hundred, or a thousandfold. Thus it appears that one of the requirements of ventilation is that the " runs," that is, the distance which the air current has to travel, should be made as short as possible. Second, the value of the resistance due to friction will be different for different forms of section. Evidently the form which has the least perimeter will offer the least extent of rubbing surface. The perimeter of a circle is its circumference, which is equal to 3*1416 times its diameter, and as the circumference is equal to

3 545 v/ area, a circle whose area is 1, has a perimeter equal to 3 "545. But the perimeter of a square whose area is 1, is 4. That is, if the area of a circular air-way be 1 square yard, its perimeter will be 3 '545, or a little more than 3-j yards, and if the area of a square air-way be 1 square yard, its perimeter will be 4 yards. Again, if the section be rectangular, and the dimensions be 2 yards by yard, the area being still 1 square yard, the perimeter will be2x2 + yards. Thus it appears that the best form of section is the circular ; but, in practice, this is rarely convenient: The best convenient form is the square, which should, therefore, be approximated to as nearly as the circumstances will permit. In practice, the form of the section is usually determined by other considerations, which have already been described. But it may be desirable, in some cases, to accommodate the form of the section to the requirements of the air current. Third, the resistance due to friction in a single air-way of a given area is less than that due to the friction in several airways having collectively the same area. For example, in an air-way 10 feet square in section, the area is 100 square feet, and the perimeter 10 x 4 40 feet. Also, in an air-way 5 feet square in section, the area is 25 feet, and the perimeter 5 x 4 20 feet. As the area in the smaller way is only one-fourth that in the larger, four of the former will be required to make up the area of the latter. But four times the perimeter of the smaller way will be 80 feet, or double that of the larger. Hence the friction in the four small ways will be twice that in the single large way. From this it appears that one large air-way is to be preferred to several smaller ways having collectively the saffie area. This question, like that of the form of the section, is often determined by other

Ventilation. 483

conditions ; but the principle should be borne in mind in laying out the workings of a colliery, so that it may be complied with as far as circumstances will permit.

To illustrate the foregoing, let it be required to compare the resistances due to friction in two air-ways, one of which is 6 feet x 7 feet, and the other 5 feet x 9 feet in section, the velocity of the air being the same in both, when they are equal in length, and also when the former is one-fifth longer than the latter. Representing the former by A, and the latter by B, we find that the perimeter of A is 6x2-f7x2=26 feet, and that ofBis5x2-f9x2=28 feet. Thus the rubbing surface is greater by 2 feet in the latter than in the former, and as the whole rubbing surface in A is 26 feet, the whole rubbing surface in B is greater. But if A be i longer than B, the additional length will go to compensate the difference. If the rubbing surface in A be 1, that in B will be 1 , when the lengths are equal ; if A be j longer than B, the rubbing surface in the former will be of 1- or nearly 1% of B; that is, the rubbing surface, and consequently the friction, in A will be about greater than in B.

To overcome the friction of the air in the ways, a certain amount of pressure must be applied to the column ; this pressure is usually estimated in pounds to the square foot. We have seen that the same sectional area may possess different perimeters, that is, two air-ways equal in area may vary in the extent of their rubbing surfaces. Now, the velocity of the air being the same, it is obvious that the pressure per square foot requisite to overcome the friction will vary with the area, since the resistance is dependent upon the perimeter, and the pressure per unit of surface is dependent upon the number of units in the surface for a given resistance to be overcome. The case is precisely analogous to that of a steam piston ; for a given load against the piston, the steam pressure per square inch upon its face will vary with the area of the face. For example, if the resistance against the piston be 1000 lb., and the area of the piston 10 square inches, the pressure must be 100 lb. to the inch; but if the area be 50 inches, the pressure required will be five times less, or 20 lb. Suppose again, as an example, the case of two air-ways, one of which is 8 feet x 4 feet, and the other 6 feet X 6 feet in section. Here the area of the former is 32 feet, and that of the latter 36 feet ; but their perimeters are equal, that of each being 24 feet. If the air columns in these ways be moving with the same velocities, evidently the resistance due to friction will be equal in each, since the rubbing surfaces are equal ; but as the sectional areas of the columns, or the surfaces over which the pressure is distributed, are to each other as 32 to 36 8 to 9, the pressure required in the square way will be only of that required in the other ; that is, for every 1 lb. of pressure to the foot required in the latter, f lb. will be sufScient in the former. The total pressure is of course equal in both cases. These facts, which are almost self-evident, show the necessity of taking into account the area over which the pressure, as indicated by the water gauge, is distributed, as well as the extent of rubbing surface which determines the resistance.

Hitherto we have assumed the columns of air to be moving with uniform and equal velocities ; it remains now to consider the effects of a change of velocity upon the friction. It is evident that if we double the velocity of the column of air, we practically double the extent of the rubbing surface, since, in a given time, we pass twice the quantity of air through the way ; in other words, we double the length of the column to be propelled through the way in the given time. Naturally, this will double the resistance to be overcome in the time. Such a result is sufficiently obvious. But it will appear on reflection that a further increase of the resistance will take place. It will be obser ed that this doubled moving surface, that is, the surface of the column of air, passes over the fixed

3 Q 2

484 Mining Engineeeing.

surfaces, that is, the sides, roof, and floor of the way, with a double velocity; and this double velocity, as might have been expected, is found to double the friction. So that the double velocity will double the friction of double the quantity, the result thus being a fourfold increase of the original resistance, or the resistance before the velocity was doubled. That is, the original velocity being 1, and the resistance 1, the new velocity will be 2, and the resistance 4. So also it will be seen that if the new velocity be 3, the resistance will be 9 ; or if 4, the resistance will be 16 ; and so on. This is expressed by saying that the resistance due to friction increases as the square of the velocity. This rapid increase of the resistance shows that air-ways of large sectional area are to be preferred to ways of small sectional area, on account of the higher velocity necessary in the latter to pass a given quantity of air in a given time.

To illustrate the application of this law, let it be required to compare the resistances due to friction in two air-ways, A and B, equal in length, and having the same perimeters when the velocity in the former is 3 feet, and the velocity in the latter 7 5 feet a second. Here the velocities are as 1 to 2 5, that is, the velocity in B is times greater than in A. As the resistance increases as the square of the velocity, its value in A will be 1, and in B (2 '5) 6*25. Thus the resistance in

the air-way A is of that in the air-way B.

We have now to ascertain the value of the friction of the air against the sides of the ways, that is, the force necessary to overcome the resistance due to the friction. The value of the resistance, or what is the same thing, the amount of force requisite to overcome it, is always expressed in what is called " head of air," that is, the height of a column of air, of the same density as the flowing air, sufficient to exert the force. This " head " may be readily converted into inches of water as indicated on the water gauge. The head is always expressed in feet, and as the weight of a foot of air at 60° Fahr. is 0*765 lb., and that of an inch of water is 0°036 lb., which would give a pressure of 5"2 lb. to the square foot, we have only to multiply the head found by 0'0765 lb., the pressure of a foot of air, and to divide the product by 5 2 lb., the pressure of an inch of water, to find the

indication of the water gauge. As — 68, we may divide the head at once by that number.

o '

Thus if the value of the friction found be 30 feet, the indication of the water gauge for that pressure

will be 44 inch. A reference to the table will show that this reading represents a pressure

of 2-28 lb. to the foot.

It will be understood from the foregoing considerations that the head will be some fraction of the product of the rubbing surface by the square of the velocity, divided by the sectional area of the air-way. Thus if h represent the head, s the rubbing surface, v the velocity in feet a second, k the fraction alluded to, and a the sectional area of the air-way, we have

h

a

The fraction k is called the coeflScient of friction, and its value must be determined by experiment. The results of careful investigations undertaken by numerous scientific authorities have shown the value of k for iron and earthenware pipes, tunnels, and other bricked channels of uniform section and a fairly smooth surface, to be, for a velocity of 1 foot a second, 0' 00011. The value of the

Tentilation. 485

friction varies with the nature of the material, and with the smoothness of the surface ; the above value is a mean for the channels mentioned. Though the results arrived at by different authorities are accordant for these cases, we find an utter absence of agreement when the experiments have been conducted in the air- ways of mines. In all cases, the resistance due to friction has appeared to be much greater in those ways than in those regular channels of which mention has already been made ; but as the results are discordant among themselves, it has not been possible to ascertain what the value of the friction really is under such conditions. Now as these results differ widely from one another, it is clear that errors of observation have been committed ; it is equally clear that the conditions prevailing in a mine are identical in nature with those which influence the friction in bricked tunnels. It is true that the air becomes heated in its passage through the ways, but the variation in the density due to this cause is not great, hardly appreciable indeed in the resistance from friction.

As the roughness of a rubbing surface increases the resistance due to friction, it is evident that the value of the coefficient k will be greater for the air-ways of a mine than for earthenware pipes and bricked tunnels ; but its value should be practically constant for all air-ways. As far as our observations have extended, this value is twice that already given ; that is, the friction in an air-way of a mine is about double that in an earthenware pipe or a bricked railway tunnel. This will give us 0*00022, and such a value will be found to represent the resistance very accurately. But the values usually given co k are from four to nine times greater than this. These larger values, as well as the discrepancies existing between them, are easily accounted for. Resistances due to other and variable causes have been included in that attributed to friction, and, in some cases, errors of observation may have been committed. Such errors may have occurred in measuring the sectional area of an air-way. The ways of a mine are generally timbered, and, in taking the dimensions, we may measure from rock to rock, or from timber to timber ; the former method will give us the actual, the latter method, the effective area. The timbering, as described in a former chapter, consists of two uprights, surmounted by a headpiece, or cap, and, in some cases, resting upon a sole, or base, similar in form to the headpiece. Thus we have a series of frames projecting from the rock, and forming between them a series of panels. In these panels, the air has but little forward motion, a fact which may be easily proved by holding a lighted candle in one of these recesses. The disturbance of the flame will show that the air, which is in slight whirling motion, forms no part of the advancing current. The same thing may be observed in small hollows by the side of a stream of water. Thus, in calculations relative to currents of air, the effective sectional area only of the way is to be taken into account. It will be observed that this mode of measuring makes the rubbing surface wood, and diminishes its extent in so far as the fixed surface is concerned. But as the air impinges upon each of the timbered frames, a portion of its momentum is destroyed, and the resistance to the flow is thus rendered about equal to that which would be caused if the whole rubbing surface were of wood ; that is, if all the sets were in contact.

But there are other resistances to be considered in underground air-ways, due mainly to obstructions. The ways themselves are rarely quite uniform in section, and the expansion and contraction of the air column in passing through them causes a resistance to the flow. Besides this, pieces of rock may be often seen at frequent intervals projecting beyond the line of the timbering, and offering an obstruction to the current. Also at the working faces, the coal which has been broken down may partially block up the way. But the principal obstructions are the bodies of the

4:86 Mining Engineeeing.

men and horses employed and the tubs present in the ways. These obstructions not only destroy the momentum of the current, but greatly increase the friction. Suppose, for example, a train of tubs in an air- way ; when the current meets this obstruction, its motion will first be checked, and then it will be constrained to pass round it on all sides. But it will be observed that since the obstruction has greatly reduced the effective area of the way, the velocity of the air must be proportionally increased; and this increase of the velocity, as we have seen, will greatly increase the friction in that portion of the way. As a train of tubs may occupy nearly the whole area of the way, it is easy to see that the resistance to the flow of the current may be great. The same effects are produced, in a less degree, by the bodies of the men and the horses present. Obviously the smaller the sectional area of the way, the greater will be the effect of these obstructions. Since these causes of resistance are very variable, it is clearly impossible to estimate their value otherwise than approximately. Our observation has shown this value to be equal to that of the friction in the empty ways, under the most favourable conditions. Thus, if we include the value in the coeflScient k, and it will be convenient to do so, it will become h 0*00044. Grenerally, however, it will be higher than this, and we shall obtain something like a general mean value for coal mines if we assume yb 0-00066.

To show the application of this coefficient, let it be required to find the resistance due to friction in an air-way 7 feet x 8 feet in section, and 2000 feet in length, the velocity of the current being 4 feet a second. In this case, the rubbing surface is 30 x 2000 60,000 square feet, and the sectional area 8 x 7 56 square feet. Putting these values for their representative letters in the

„ , , , 0-0 0066 X 60000 x 16 ,, pi + -d 4- ,i.- ,x.

formula, we have h li-di leet. Keierrmg this to the water gauge,

we have — 5— =0-17 inch pressure. Again, suppose the intake to have the foregoing dimensions, bo

and the return to be 8 feet square in section, the two ways being each 1000 feet in length, and

the velocity in the intake 4 feet a second, as before. Here the resistance in the intake is

, 0-00066 X 30000 x 16 , ,

h 37; 5-65 leet. But m the return way, we have a different sectional

56 ''

area, and therefore shall have a different velocity. Putting x for the new velocity, we have

56 : 64 : 4; whence w — wr — 3-5 feet a second. The rubbing surface in the return is

32 X 1000 32000, and the square of the velocity is 12-25. Thus the value of the resistance in

this way is A 4-04. Adding this to the resistance already found,

we have 5-65 -]- 4-04 9 -69 feet as the total resistance, or a reduction of 1-62 foot of head due to the enlarged section of the return way. Eeferring this to the water gauge, the pressure is

-gg- 0-14 inch.

The pressure which we have been considering is that required to overcome the resistance due to friction and obstruction ; it remains to take account of that required to put the air in motion. Expressing, as before, the pressure in terms of the head of air, the velocity due to the pressure will be equal to that which a body would possess when it had fallen through a height equal to the head. Thus a column of air 1 square foot in section and 13-09 feet high weighs 1 lb., and such a column

Ventilation. 487

will consequently exert a pressure of 1 lb. to the square foot. This pressure will produce a velocity in the air current equal to that acquired by a heavy body in falling through a height of 13-09 feet. This is expressed by the well-known formula for gravity, h2g, whence V y/ h x 2g, m which V is the velocity in feet a second, h the height, or space fallen through in feet, and g the velocity in feet acquired by a falling body at the end of one second of time, the value of which is 32-2.

Thus V \/7i X 64' 4 8"02\//t. And from this we deduce h -nT—, Now suppose the air

current has a velocity of 5 feet a second ; the head required to produce this velocity, irrespective of

friction, is h — — - 0*38 foot. This value must be added to that found for friction and other d4"4

resistances. It will be observed, however, that the pressure required to produce velocity is not

great, and as the resistances already treated of are estimated only approximately, in practice it may

be neglected, for the purpose of simplifying the calculations.

As another example illustrative of the foregoing, let it be required to find the pressure necessary

to produce the ventilative current under the following conditions : The air- way through which the

current flows is, for the first 300 yards, 6x6 feet in section ; for the next 250 yards, 6x7 feet in

section ; and for the remaining 400 yards, 6x5 feet in section, the velocity in the first portion being

. r X J -P XI, C X X- A 0-00066x21600x16 no r . t xi. -jji

4 teet a second, ror the portion, n — 6-33 leet. In the middle por-

tion, the area is greater, and, consequently, the velocity will be reduced ; the reduction will be from

S x

4 feet to 3-4 feet, since 36 : 42 : : ic : 4; whence x — " =3-4. The resistance in this portion

M, 1 .. 17 0-00066 X 19500 x 11-6 o rr r x t xi i x x- xi will therefore be A jz 3-55 teet. In the last portion, the area of the

way is less, and, consequently, the velocity will be increased ; the increase will be from 3-4 to 4 - 7

42 X 3 '4 feet, since 42 : 30 : : a; : 3-4 ; whence x 4-7. The resistance in this portion will

xt, r I, 2. 0-00066x26400x22-1 oo r , t. ,. . . therefore be A 12-83 leet. Ihus the total resistance is

6-33 + 3-55 + 12-83 22-71 feet;

which, referred to the water gauge, is =0-34 inch. The pressure indicated by this reading

Do

will be seen from the table to be 1-76 lb. to the square foot.

It should be borne in mind that a sudden contraction of the air-way, such as indicated in the foregoing example, occasions a resistance which we have not there taken into account, namely, that known as due to the contracted vein. If, for example, we have an air-way closed by a door having an opening through it to allow a passage for the air, the quantity which passes through the opening will be only 65 of that which should pass according to the head of pressure and the area of the aperture. This loss is occasioned by the particles of air being directed towards the centre of the opening, which prevents the discharge from taking place over the whole area. Thus, suppose the opening in the door to be 1 foot square and the velocity of the air in the way leading to it 4 feet a second, in such a case, 4 cubic feet a second ought to pass through ; but the actual quantity passing will be found to be only 0-65x4=2-60. If there be no other escape for the air, obviously its velocity of

488 Mining Engineeeing.

4 feet a second, which would otherwise be due to the pressure, will be reduced in a proportionate degree. Thus the interposition of the door will occasion a serious loss of pressure. The same effects in varying degrees, according to the form and dimensions of the passage, are caused wherever a sudden contraction takes place ; and hence it will be seen to be highly desirable that the air- ways of a mine should, as far as other conditions will allow, be uniform in section.

As friction is dependent upon pressure, it has been stated that a given height of water gauge will pass a larger quantity of air in a given time when the barometric pressure is low than when that pressure is high, and that, consequently, the greater tendency of the coal to give off gas is counteracted by the increased ventilation. But though it is probably true that a slightly increased volume of air passes at those times, it is none the less true that the air is less dense ; that is, a cubic foot of air consists of fewer atoms when the barometer is low than when it is high, and, consequently, the diluent power of the foot of air is less. The statement must, therefore, be regarded as erroneous and dangerous.

Ventilative Arrangements. — We have now to consider how the ventilative current is to be conducted through the workings of a mine, that is, how its course is to be directed so as most completely to attain the end in view. This is a very important question, since it is possible, by a faulty distribution of the air, to render wholly insufficient a volume which otherwise would be adequate to all the requirements of the mine, and to create the very dangers which it is desired to avoid.

The distribution of the air current should be commenced as near the bottom of the downcast shaft as possible. It was pointed out in a former chapter that the workings of a mine are laid out in districts separated from each other by barriers of coal. This division is made chiefly for purposes of ventilation, as pointed out in the chapter referred to. Each of these districts is ventilated by its own air current, which should be conveyed to it as directly from the downcast shaft as possible. This system of breaking up the column of air descending the downcast into several currents for the purpose of keeping the ventilation of the several districts, distinct is known as that of splitting the air, and it constitutes the most important improvement of recent times. The separate currents obtained in this way are called splits, and it will appear obvious, from a consideration of the facts treated of in the foregoing sections, that the quantity in each of such splits must be determined according to the requirements of the district it is intended to ventilate, each district being regarded, from this point of view, as a separate mine. "Where there are workings to the rise and to the dip, the splits are distinguished as " rise splits " and " dip splits," and the circumstance of inclination in the ways will influence in some degree the quantity of air to be distributed. In dip workings, the gas disengaged from the coal at the faces readily passes away into the ventilative current by reason of its low specific gravity, which, as already pointed out, gives it a strong tendency to ascend. But in rise workings, this same tendency prevents the gas from readily dispersing itself, and causes it to collect in the working places, whence it must be swept by the force of the ventilative current. Hence it is necessary in some cases to increase the quantity of air circulating in these rise workings, which may be effected by increasing the factor of safety described in a former section. But the inclination of the ways exerts also an influence upon the ventilative current, which must be taken into account in making the modification. It will be understood from the principles already discussed that if the ways have no inclination, each split will get a certain proportion of the air for a given total pressure, and that this proportion will remain unaltered by a variation of that pressure, whatever the relative lengths of the air- ways may be. But when an inclination exists, a variation of the total pressure will

Ventilation. 489

affect the rise more than the dip splits, so that an accumulation of gas might he expected in the rise rather than in the dip workings in consequence of a reduction of the pressure, irrespective of the tendency in the gas to collect there.

The area of a shaft 14 feet in diameter is 153'9 square feet, sufficient for five separate air-ways each of 30 square feet area, or of any dimensions giving an aggregate area not exceeding that of the shaft. It is important to the free flow of the current that the air-ways leading from the downcast shaft and to the upcast shaft, in those parts where the current is undivided, should he of large sectional area.

The ventilative current naturally tends to take the easiest course from the downcast to the upcast shafts ; this course may be either the shortest, or the way of largest sectional area. No two districts of a mine are identical in every respect ; they must necessarily differ from each other, either in the length of the ways to be traversed by the air, or in the direction of the workings ; and in no cases are they similar in the sectional area of the roads, the obstructions existing in the roads, the number of persons employed, the quantity of coal broken in a given time, the gaseous character of the seam worked upon, the extent of goaf adjoining the ways, or the degree of moisture met with. Hence the air has a tendency to distribute itself unequally among the several districts, and it is necessary that an unequal distribution should be made. But as the currents tend to take the easiest course to the outlet, the largest volume may traverse the district in which the least is required ; in order, therefore, to distribute the air in the required proportion, means must be provided for regulating the quantities passing into each split. "We have already seen that the resistance to the flow of a current of air increases rapidly with the velocity of the current, and that a sudden contraction of the way occasions a notable diminution of theoretical discharge. These facts are utilized to regulate the resistance according to the requirements of the district to be ventilated, for it is evident that the quantity of air passing into each split will be determined by the resistance which it encounters in its course to the outlet. The means employed for controlling the relative resistances consist of doors, called regulators, placed in the air-ways for the purpose of diminishing the area in any required degree. These regulators may be constructed in various ways, the object being merely to obtain the power of enlarging or diminishing, at pleasure, the aperture through which the air is to pass. Commonly a wooden frame is built into the air-way, and one-half of the way boarded up ; over the other half a sliding door is placed, which may be drawn back in a groove in the framing to give the desired opening. The degree of opening required is found by experiment. It is of the utmost importance to the safety of those employed that the sliding door be secured in its proper position by means of a padlock. This precaution is needed in all forms of regulators. Sometimes the door is made to slide vertically instead of horizontally, the aperture then being in the upper part of the way. This arrangement is favourable to the passage of the current, but it wholly obstructs the way for travelling use. frequently the door covers the whole area of the way, and is provided with a sliding shutter for regulating the passage of the current. Obviously each of these modes of constructing the regulator offers advantages under certain conditions. It will be observed that any form of regulator must seriously obstruct the traffic in the travelling ways. To avoid the very grave economical consequences of placing such obstructions in the ways along which the mineral is conveyed, the regulators are usually placed in the return ways, which are comparatively little used as travelling roads. The effect of contracting the passage near the outlet is evidently the same as that caused by contracting the passage near the inlet, since the resistance occasioned thereby must clearly be the same in both cases.

3 R

490 Mining Engineeeing.

In an air-way of a given sectional area, the quantity of air passing in a given time is dependent upon the velocity of the current. It has been pointed out that the resistance opposed to the flow of the current increases rapidly with the velocity, and that, consequently, it is desirable to keep the velocity low. But when dealing with existing air-ways, the quantity to be passed in a given time can be varied only by increasing or diminishing the velocity. It becomes, therefore, desirable to point out the limiting conditions of these variations other than those imposed by the rapidly increasing resistance. . It has been found by experiment that a velocity less than 2 feet a second is insufficient to effectively remove the vitiating gases generated in a mine ; 2 feet a second must, therefore, be accepted as the lowest limit. On the other hand, it has been found that a velocity greater than 5 feet a second will force the inilammable gas through the wire gauze of a Davy safety lamp, so that the limit in this direction must be fixed at 5 feet a second. Thus the conditions of safety require that the ventilative current should pass through the workings with a velocity nowhere less than 2 feet and nowhere greater than 5 feet a second. Comfort and convenience, however, require that the lower limit should be approximated to rather than the higher. A current of air having a velocity of 3 feet a second is quite perceptible, and any increase of this velocity becomes unpleasant, and operates injuriously upon the health of the miners and inconveniently upon the flame of the candles. A velocity of 3 feet a second is probably the best under ordinary conditions. To determine the velocity of the current with accuracy it is necessary to have recourse to the anemometer, and this instrument should be made frequent use of in coal mines, especially those of a fiery character ; but it may be approximately found, after a little experience, either by observing the inclination of the flame of a candle, or from the sensation felt in the face when it is turned to the current. To ascertain the velocity by the latter method, the observer stands with his back to the current for a few seconds, and then turns himself quickly round in the opposite direction. If greater accuracy is required and the anemometer is not at hand, a small quantity of gunpowder may be exploded at a fixed point, and the time during which the smoke is travelling to another fixed point, over a measured distance, observed. Formerly this method was very generally employed.

When the requisite quantity of air has been allotted to a given split, it has to be directed in a convenient manner through the workings. Inasmuch as the air, if allowed to follow its own course, would take the easiest way to the upcast shaft, it is evident that in a network of galleries, such as exist in a mine, many parts, and especially the distant parts where probably the greater number of men aie employed, would be utterly without ventilation. In order to convey the air up to the working faces and to ventilate efficiently every portion of the workings, it is necessary to determine a circuit or course for the ventilative current, and to force it to follow that course by blocking up all the sideways that open into it. The means adopted for blocking up these side-ways are of two kinds, according to the character of the ways. If the way is not to be used as a travelling road, the barrier may be a permanent one. Such a barrier is called a " stopping," and it may be constructed, according to its importance, of bricks laid dry and backed up with rubbish ; of bricks laid in cement, carefully plastered on the face and backed up with several yards of stowage ; of a double wall so constructed of bricks, and having the interval between them filled with stowage ; or simply of stowage closely packed. In all cases, care should be taken to make these stoppings air-tight, for otherwise the leakage will seriously reduce the volume of air travelling towards the working places. It has been found by experiment in numerous instances that the loss from this cause has amounted to one-third

Ventilation. 49 1

and even to one-half; so that a split may receive a proper proportion of air, while the district to which it passes may be insufficiently ventilated at the working faces. All stoppings along the principal air-ways should be well and substantially built. In erecting a stopping, especially along by the principal ways, the effect of an explosion of gas must be kept in view. It is obvious that if a stopping be blown out, the ventilative current will take the shortest way to the upcast through the passage made by the destruction of the stopping, and the whole of the workings beyond will be deprived of air at a time when it is most required. Important stoppings should, therefore, be strongly backed with stowage. To increase the resistance of a stopping, the brick wall is often curved so as to enable it to resist after the manner of an arch. Two walls so curved, having, of course, their convex sides outward, and filled in with several yards of stowage, constitute the strongest possible stopping. When leakage occurs, it takes place chiefly between the stopping and the sides of the way.

If the way is to be used as a travelling road, obviously a permanent stopping cannot be erected. In such a case, doors are used. It is manifestly impossible to construct a door capable of resisting the force of an explosion. For this reason, doors should be avoided as much as possible ; it is particularly to be desired that they should not be placed in positions where their destruction would cause the ventilative current to be taken off the working places. It is also impossible to make a door airtight, so that their employment occasions a serious loss. The loss may be very great if the doors are not well constructed and carefully hung. Usually they are made of oak, and the joints in them are made air-tight by tongueing. The framing should be set in brickwork, so as to allow no escape of air between it and the sides of the way. In hanging the door, care should be taken to make it rest closely against the framing to reduce the leakage as much as possible. To the same end, the parts of the framing and of the door which are in contact, should be covered with felt. The framing should be inclined for the purpose of causing the door to close by its own weight, and the latter should be hung to open in the direction in which the loaded tubs are moving. At important doors, a boy is stationed to open the door when required, and to close it immediately the tubs have passed. In unimportant situations, a single door may be sufficient; but in other cases double doors will be required. The distance of the doors apart should be such that the longest train of tubs may stand between them. The use of the double doors is primarily to keep the way constantly closed, for the second door is never opened until the first has been shut. But it will be seen that another advantage lies in the reduction of the loss of air by leakage consequent on the increased resistance offered by the two doors. In some very important situations, treble doors are used, in which cases there are always two closed. When doors are placed in important situations, it is a common and laudable practice in some localities to provide hanging or safety doors for the purpose of quickly restoring the ventilation in the event of the ordinary doors being blown away by an explosion. These safety doors are made to turn about a horizontal axis fixed in the roof into which they are recessed. If an explosion occur to carry away the ordinary doors, the safety doors will be left uninjured, being out of the way of the blast ; as soon, therefore, as they can be approached they may be let down, and the ventilation restored. It is easy to so arrange the fastening of the safety door that it will be blown away by the force of the explosion, and allow the door to drop of its own weight. In such a case the ventilation is instantly restored. As a precaution against the fatal effects of after-damp, the device is worthy of general adoption.

It is not sufficient that the air be made to pass through all the ways of a mine ; as the headings

3 R 2

492 Mining Engineering.

advance, they get beyond the reach of the current, and it then becomes necessary to provide means for causing it to pass up to the working faces. The means employed for this purpose consist either of cloth or wood bratticing, or, in certain cases, of iron or wooden pipes. A description of these methods of ventilating headings was given in a former chapter.

It frequently happens that the outgoing current has to be conducted across the course of the ingoing current. To do this, the course of the outgoing, or, as it is commonly called, the " return," current must be raised above or depressed below the plane of the " intake " or ingoing current. The more common practice is to take the return over the intake. This is effected by raising the roof of the intake at the point of junction, and restoring the way to its original height by means of a brick or stone arch. The hollow above the arch then affords a passage for the return current. In very important positions, the return is taken over the intake by means of a stone drift in the roof rock. These points of junction of the courses of the ingoing and the outgoing currents are called " crossings."

Sometimes, to shorten the run of the air, or for some other purpose, it becomes desirable to conduct the current through the goaf, or worked out portions of a mine. In such a case, a way is kept through these excavated districts by means of strong pack- walls. On account of the difficulty of maintaining such air-ways, there is danger lest they become of too small sectional area to allow an easy passage to the current. If the " drag " of the air, as it is called, that is, the loss of head due to friction, be borne in mind, the importance of guarding against this danger, both in goaf-ways and in crossings, will become plainly manifest.

The main air-ways through which the ventilative current passes from the downcast shaft are called the "intakes," and those through which it is conveyed to the upcast shaft are called the "returns." These ways should, for reasons already given, have a large sectional area. It is obviously desirable that the returns should be at least equal in sectional area to the intakes; properly they should be somewhat larger, because the current of air becomes heated in its passage through the workings, and consequently augmented in volume.

It is easy to see that by employing the means, and adopting the arrangements described in the foregoing paragraphs, a current of air may be conducted through the workings along any course desired. That is, a certain course from the downcast to the upcast shaft may be determined for the air, and the current made to follow that course. Thus the problem of ventilation is theoretically and generally solved. But, in practice, the course cannot be arbitrarily chosen. In this, as in all other matters relating to the laying out of the workings of a mine, numerous conditions have to be satisfied, and hence it happens that the best course is rarely that which theory requires.

The first and most important condition in determining the course of an air-current is that the air shall pass as directly as practicable from the downcast shaft to the working places. Formerly the pernicious custom was prevalent, and it has not yet been wholly abandoned, of airing all the excavations in succession, from the point of ingress to the point of exit, taking in the working places on the way. By this method, the ventilative current often had to pass through much of what is known as the " broken " mine before it arrived at those parts where most of the miners were at work. In such a case, the men have constantly to breathe vitiated air, a consequence of very grave importance. But the arrangement is peculiarly conducive to danger from explosion. If a discharge of fire-damp should take place in the ways, the explosive mixture will pass directly and certainly to the lights used by the miners in the working places. The opposite of this arrangement, and the only

Ventilation. 493

proper one, is to convey the air first, and as directly as possible, to the working places, and then to direct it back through the broken workings and goaf. A primary principle of ventilation is that air shall never pass from broken workings to the men engaged at the working faces. This principle should be borne in mind when providing against the effects of an explosion, for the destruction of doors and stoppings may, when these are improperly placed, entirely change the distribution.

In taking the air through the broken mine in post-and-stall workings, a system of splitting the current is adopted. That is, instead of directing the whole current down one bord and up the next, the stoppings are so placed in the headways of every second or third bord that the current may divide itself among two or three bords. With such an arrangement, the divided current passes down two or three adjoining bords, and up the two or three next adjoining bords. This is called " coursing " the air, and the coursing is said to be in twos or in threes, according as the current is divided between two or among three bords. It will be observed that this system, by practically increasing the area of the ways, diminishes the resistance from friction.

The arrangements for delivering the vitiated ventilative current into the upcast shaft will vary according to the means employed to create the current, and the degree of vitiation produced in it. When a fan is used, the air from the returns may be conveyed directly to the bottom of the upcast shaft. But when the ventilation is effected by means of a furnace, such an arrangement may be highly conducive to danger from explosion. If little or no gas is given off by a mine, the air from the returns may be safely discharged into the upcast through and over the furnace. But if the air be laden with fire-damp, or if it be liable at any time to arrive laden with fire-damp, it must be discharged into the shaft at a point sufficiently above the furnace to avoid all danger from the flames coming into contact with it. To do this, an inclined drift, called a " dumb-drift," is driven from a point in the return way, sufficiently remote from the furnace, to the shaft through the roof rock. In such a case, the furnace must be supplied with pure air directly from the downcast shaft.

Means of Producing the Ventilative Current. — Having shown what quantity of air is required under given conditions, and described the means employed for conveying that quantity through the workings, it remains only to consider the means of producing the current. In treating of the question of resistance, the value of the force employed to overcome it and to produce motion was estimated in " head," or height of the column of air the weight of which was the force required. The immediate cause of the current is such a column of air, which is described as the " motive column," and the means we have now to consider are those employed to produce that column.

It is a well-known fact that as we descend into the earth we find, at a short distance from the surface, a temperature which is the mean temperature of the year at that place, and that beyond this depth, the temperature increases constantly at the rate of about 1° Fahr. for every 60 feet in depth. Thus, while the temperature at surface is continually varying, that of the rocks in the workings of a mine remains constant. This condition of things will give existence to a motive column, and evidently the height of the column will increase directly with the difference between the surface and the underground temperatures.

As an example, take the case of a mine having an upcast and a downcast shaft, each 1000 feet in depth, and suppose the temperature of the rocks at that depth to be 78° Fahr. The problem then is what will be the height of the motive column for any given temperature at surface? It was shown in a former chapter that the volume of air varies directly as the temperature, when the pressure remains constant, and that the amount of the variation was of the volume at zero for each degree

494 Mining Engineeeing.

of temperature, measured on Fahrenheit's scale. Hence the density of air at a given temperature and under a given pressure may be readily calculated. If the facts discoursed of in the section of this work relating to the thermo-dynamic properties of air have been fully understood, no difficulty will be experienced in applying these calculations to the case in question. Let it be assumed that the surface temperature is 40°. The air entering the workings through the downcast shaft will tend to put itself in equilibrium with the temperature of the rocks, and as the course to be followed is usually long, and the velocity of the current low, equilibrium will be produced by the time the air has reached the upcast shaft. It must also be borne in mind that the presence of men, horses, and lamps in the workings contributes notably to raise the temperature of the air. Thus the temperature of the air in the upcast shaft is that of the underground workings, while the temperature of the air in the downcast shaft is that of the surface, or at most its mean temperature can be only slightly in excess of that of the outer atmosphere. Now, as the two columns of air, namely, that in the downcast and that in the upcast, are different in temperature, they must also be different in density ; in other words, being equal in height, one must be heavier than the other. The problem then is, how much heavier is one column than the other ? or to express it in the usual manner, how much of the heavier column must be taken away to make it equal in weight to the lighter column ? This quantity is what has been described as the head, and as the motive column, because it is the quantity which represents the force acting to produce a current. If we represent this head, in feet, by H, the depth, also in feet, of the downcast shaft by D, the temperature of the downcast by t, and the temperature of the upcast by T, we have :

or representing the difference of the two temperatures by d,

Bd

H

T + 459

In the example under consideration, the temperature of the air in the downcast is 40°, and that of the air in the upcast 78°; the depth is 1000 feet. In this case the difference of temperature is 38°, and hence we have :

H 70-8 feet.

78 + 459

Thus the pressure due to the difference in density of the air in the two shafts is that which would be caused by a column of air of the density of that in the downcast shaft, and 70 8 feet in height. Referred to the water-gauge, this pressure is 1 '04 inch.

It thus appears that when the outer temperature is low, a powerful ventilative current will be caused by natural means, and that it will increase with the depth of the workings from surface. The direction of the current will be determined by particular conditions of the case. One shaft may be wetter than the other, and a shaft in which there is falling water becomes necessarily a downcast, where no greater disturbing cause exists. For this reason, the pumping shaft will generally become the downcast. Other conditions are : — the relative depth of the two shafts, the direction of the prevailing winds, and the configuration of the surface. When the current has once been produced, it will continue in the same direction so long as the difference between the underground and surface

Ventilation. 495

temperatures remains in the same direction, but it will diminish in velocity as the difference decreases, until it becomes nil when the difference is nil. When such conditions exist, there will be no ventilation ; but as the surface temperature rises above that underground, a current of air will again set in, and increase in velocity as the difference increases. As, however, the difference is now in the other direction, that is, is now in favour of the atmosphere at surface, the direction of the current will be reversed, if there be any difference in the depth of the shafts or in the level of their orifices at surface, and may be reversed if these circumstances do not exist. Hence it will be observed that in winter the current will flow continuously in one direction, but will vary in force with the temperature at surface ; and that in summer the current may flow sometimes in one direction and sometimes in the other, that it will be generally weaker than in winter by reason of the nearer approach to equality between the underground and the surface temperatures, and that stagnation may frequently exist for a longer or shorter time. It thus appears that, in a mine, a ventilative current will be created by natural means, but that it is very uncertain, both in power and in direction. In winter, it may be abundant; iu summer, it may be altogether insufficient. For this reason, natural ventilation cannot be relied upon, and it becomes necessary to have recourse to artificial means of producing a current. These means are : ]., the furnace ; and, 2, the fan.

The Furnace. — The means which naturally suggests itself for remedying the defects of natui al ventilation is heat artificially applied to the rising column of air in the upcast shaft, so as to keep the difference of temperature in the two shafts uniform and in the same direction at all seasons of the year. This means, which must obviously be effectual, has, therefore, been generally adopted. The mode of applying heat to the air in the upcast is that afforded by the furnace in which coal is consumed ; this mode is known as " furnace ventilation."

The furnace consists essentially of an iron grating upon which coal is burned, so placed and constructed that the air from the returns, when not laden with gas, may pass through it and over it. The heat which is generated in the furnace is in this way communicated to the air, and the temperature of the ascending column in the shaft is thus artificially raised. The ventilative effect of the furnace, that is, the pressure caused in the downcast by the augmentation of temperature in the upcast due to the furnace, is measured by the difference in temperature between the descending and the ascending columns of air, in the way already described. It will plainly appear, from what has been said respecting natural ventilation, that, to produce a given ventilative current, the higher the temperature of the outside atmosphere, the greater will be the consumption of coal. Hence the average daily consumption will be greater in summer than in winter ; and it will be seen that the fires must be regulated according to the surface temperature. But besides this temperature, there are other modifying circumstances, already pointed out, to be taken into account. One of these is the variation which occurs in the atmospheric pressure, which may occasion an outburst of gas in the workings. Thus the furnace fires must be regulated according to the indications of the thermometer and the barometer ; and it will hence be seen that the duties of the furnace-men require care.

To obtain the greatest effect from a furnace, it should be placed as near as possible to the bottom of the upcast shaft. When the latter is used solely as an air shaft, and the return air is not liable to be laden with explosive gas, the furnace may be placed in the return way, and the whole of the air passed through and over it. In such a case, the way is enlarged at that point and bricked. If the way be in rock, the brickwork will consist of a single arch in contact with the rock ; but if the way be in coal, a double arch, that is, two concentric arches, having several feet of space between

496 MINING ENGINEEEmG.

them, will be needed to avoid all danger of firing the coal. The upper arch supports the rock, the lower encloses the furnace. Through the space thus left, the air is allowed to circulate. When the upcast is used as a drawing shaft, some other situation for the furnace must be selected. The best arrangement in such a case is to place the furnace in an excavation made for the purpose by the side of the return way, and to put it into communication with the latter by a narrow drift, and with the shaft by an inclined drift. In this case, only a portion of the return air passes over the furnace. When the return air is liable to be laden with explosive gas, it must, as already pointed out, be conducted into the upcast without passing over the furnace ; in such a case, the latter must be supplied with a special current of air. The construction of a ventilating furnace is very simple, and needs, therefore, no detailed description. Its general design will be at once understood from the drawings. Figs. 662 and 664. It is important that the dimensions should be such as will give the requisite ventilative current in unfavourable weather without forcing, so that there may be a margin of power for extraordinary occasions. In proportioning the dimensions, perfect combustion of the coal should be provided for in order to obtain the maximum of effect for the coal consumed. The space over the top of the fire, through which the air passes to the shaft, should also be provided with arrangements whereby it may be reduced or increased, within certain limits, at pleasure, for the purpose of regulating the combustion of the coal. It may be remarked here that perfect combustion cannot be obtained unless the fires upon the grates are kept thin.

If the air-ways of the mine are of fairly large sectional area, it will be generally sufficient if the furnace heats the return air to the extent of frotc 1 5 to 30 degrees of temperature, according to the circumstances of the case. It must be borne in mind that as the friction increases as the square of the velocity of the air current, the consumption of coal will increase in the same ratio. If there were no loss of heat in the upcast shaft, the furnace would be the most economical means of- producing the ventilative current available. But aa the ascending column of air becomes cooled by conduction through the sides of the shaft, there is always a loss of effect, greater or less according to the nature of the rock, the presence or absence of water, the diameter of the shaft, and the velocity of the current. To partly compensate this loss, the height of the column is sometimes increased by building a chimney over the shaft.

The Fan. — Another means of rarefying the air in the upcast shaft is afforded by the fan. This machine, the general construction of which is too well known to need description, is placed in suitable communication with the upcast, from which it tends, when set in motion, to draw the air by a mode of action that is universally understood. The rarefaction which is by this means caused in the upcast occasions a difference of density between the two columns of air, a circumstance which, as we have already shown, gives rise to a current.

It will be at once perceived that mechanical ventilation possesses some advantages over furnace ventilation, and also that it has some defects. Concerning these advantages and defects there has been much controversy, and in this controversy both have been exaggerated. One advantage offered by the fan is that it may be erected at surface, and is therefore independent of conditions existing underground, a circumstance of some importance in the case of an explosion or a flooding of the workings. It is also claimed for it that it cannot be the cause of an explosion. But the same merit may be claimed for the furnace when properly placed and constructed. An undoubted merit of the fan lies in the fact of its rarefying the air without increasing its temperature. But the principal advantage claimed for the fan is its economy, estimated on the relative consumption of

Ventilation. 497

fuel. This claim, however, does not appear to be fully justified by the results of experience. When the upcast is very wet, the advantage may, and probably will, be on the side of the fan. But with a properly constructed furnace and a fairly dry shaft, it is hard to see, when we consider how the heat IS applied in the two cases, how the advantage can be on the side of the machine. Grenerally the furnace is carelessly and the engine carefully fired, and in this fact the explanation may be found of some of the discordant results observed. In respect of this matter of economy too, it must be borne in mind that the first cost of the fan is greatly in excess of that of the furnace. A defect of the fan is its liability to break down suddenly. It will be observed that the ventilative action of a fan ceases with its motion ; but in the case of a sudden extinguishing of the furnace fires, the heat of the shaft would keep up the ventilation for a considerable time. It is true that the chance of a breakdown of the fan is somewhat remote ; but it exists. Notwithstanding, however, the acknowledged defects of mechanical ventilation, the fan is rapidly coming into common use, the advantages of the system outweighing, in the opinion of practical men, its disadvantages. For shallow working especially when they are extensive, the system is particularly suitable.

Ventilating fans have from time to time undergone great modifications, both in their general design and in the details of their construction. The first important improvement is due to M. Letoret, who enclosed the fan within a circular casing. By this means, the air which is being acted upon is isolated from the mass of air outside, and consequently the whirling and eddying motion of the air, which at first occasioned so great a loss of the motive force, is avoided. Various other improvements have been made by other persons, and these have led the way to the very perfect design known as that of M. Guibal. In the Gruibal fan, which is now commonly adopted, Letoret's circular casing is improved in construction, and provided with a sliding shutter whereby the outlet may be enlarged or diminished. The degree of opening which gives the best effect for a given case is determined by experiment. The casing enclosing the upper portion of the fan for about f of its circumference allows a clearance to the vanes of about 2 inches; from this point the casing slopes away below the fan till it ends in the side of the chimney. This gradually enlarging outlet passage constitutes an important improvement. In consequence of the increasing sectional area of the passage, the velocity of the air is reduced, by the time it reaches the atmosphere into which it is discharged, to one-fourth or one-fifth, and the vis viva to one-sixteenth or one-twenty-fifth of their original values. These conditions are obviously favourable to the utilization of the force applied. The vanes of the Gruibal fan have also been improved in some of the details of their construction. By a system of interlacing of the arms, a very strong structure is obtained. The general design, and some of the details of construction, of the Gruibal fan are shown in the drawings Fig. 103 and 104.

Very few reliable experiments have been recorded to show the comparative cost of working the furnace and the fan. The following results have been ascertained and tabulated by Mr. D. P. Morison. But in comparing these results, it must be borne in mind that the furnace examples given are upwards of twenty years old.

3 s

Mining Engineeeing.

o

Eh

H-l

!z!

n iz;

o

P

o

P

Co

O

M

H

O

o

Is

power per taken at ier boilers foot).

to

Os

(M

Co

C3 Oi 00 CO

Co

cq

00 to o o

O

O

o

o

00 to

Co Co

Cm

Co

Cm

Cm

Co

to lo cq cq

I— (

rH rH

rH

7—i

rH

rH

T-i ,-1

Oq

g o3

O O

O

o

t-

rH cq o o

to to

to

Co

to

l-s's

M

&=3

o

Cq rH

o

Co

rH

O O

dS

,

to

o cq

<rq

o

iO

CO Tjl . .

O O

S&

to

lO to

in

lO

tX

to

xo in

g 8

iO

to to

to

to

to

to

CD to

t- t-

S3 S

.s

t-

Oj

tH

U3

o o cq 5o

en

to

(M

rH

g

O

in

t-

Os

Co

to tH Oi

o

►g

iH

i-H

i-H CO CN

Cm

i-H

Co

to

tr-

Co

rH Oi

O

o

O

i-H

Co

o 00

t-

io

Co

t- iO

in

iO

02 ; : :

o

Co

Co

tH

Co

; ;

o

Cc

i-H

cq

lO

tJH

r-l

lO

t§

Cd

a

S (M

o

o

o

O

o cq o o

S

Ot

o

iO

tH en (M o

:

:

:

:

:

; ;

ca

.1

o

iH

tH

o

i-( O I-H tH

w

tt

t*-t

o

£ Co

in

o

1H

o o

lO

iO

o

o

lo in

iM

cx>

1

to

to : : :

Co

to 05

Co

00 o cn lo

o t-

o

i-H

cq

o

i-H

cq cq

cq

(fq

T-<

cq iO rH CO

rH rH

11

Co

o

t-

o

CO Cs lO t-

o 00

(N

rH

in t-

fe-S P

Co

o

to

o

t- cq

o

00 cq to cq

t- rH

S=3S

o

tH

cq

CO o o to

o o

o

o

lO

to

cq 00 rH rH

CO in

I— t

t— 1

1-1 Cq r-i

t-l t-l

T-t

J-l

rH rH rH cq

o

h

ated tlve powe gine.

to

to 05

Co

1—t

lO

Co

en

b-

Indie

effec

Horse-

t- o

cq

to t-

cq

f-i

00 —1

cq

f— N

a

a

a a

a

a

.s

o3

o3

§

%

'

.

"

"S

o

Co

to t-

Co

o

J

Co

cq

Co Co

T-H

ee

o

rQ

fe

S i;

Pn

. Pj

o '

a

'

d

.g

a

"d M I'd -4J I'd

P„0 O O Cd

g35 Mo g2

M QQ 'd : ;

£u3 S 3 .,

ll! ft

S wjg '3'S

03 Ph 02

Co Co

o

1

gl

rH CO Cq CO

cn

o

t-

o o o o

.3

to lo lO lo

o to

to

t-

Co

Co

t- t- t-

Zo Zo

00 00 00 00

00 00 00 00

Oo 00

rH 1-t tH i-H

T-H

rH

T-{

1—i

rH

rH rH rH rH

I-H rH

a 1

Ventilation,

Comparative Cost Undee Similar Conditions.

Quantity of Aie pee Minute, 50,000 Cubic Feet ; Watbe Gauge, 1 Inch 7 875 Hoesb-powbe ; Coals at 2s. &d. A. Ton.

Name of Mine (see preceding Table).

System of Ventilation.

Coal per Horsepower in Air per Hour.

Cost per Horsepower in Air per Hour.

Coal required per

24 hours

to perform the

above duty.

Cost of Coal per Annum.

Average of first six experiments

Tyne Main

Hetton

Sacre Madame

Pelton

Staveley

Swindon

Whitehaven

Elswiok

Homer HiU

Furnace

Fan, Guibal

lb.

pence.

tons.

£ s. d.

3 s 2

500 Mining Engineeeing.

Chapter Xii.

Incidental Opeeations.

LiaHTiNG THE WORKINGS. — The means employed to give light in the working places and in the ways of a mine bear, as we have seen, an important relation to those employed to give ventilation. In so far as vitiation of the air is concerned, the question of lighting has already been fully discussed , but it remains to treat it briefly from other points of view.

As an item of cost, the means of lighting the underground workings deserve the careful consideration of the mining engineer, Undei' an economical management, the cost of lighting can hardly amount to less than 5 per cent, of the total working cost, and it may be much more. It behoves, therefore, those whose duty it is to control the expenditure to look well after this account, which, more than any other perhaps, is liable to be swollen by extravagant waste. But it is in relation to the safety of the men employed in the underground workings that the question assumes its highest degree of importance, and it is under this aspect that it presents itself for consideration in this place.

In the primitive times of mining, oil lamps were universally used ; and this same means of giving light in the workings is still generally employed upon the Continent where naked lights are admissible. In many collieries, the lamp retains its well-known classical form ; but more commonly, its form is globular, cylindrical, or conical Often it is provided with a hook or a spike for the purpose of attaching it to the timbering, or to the rock. Lamps of this character are still used in some of the Scotch collieries ; but they have been entirely abandoned in England. In English collieries, the tallow candle is now always used when ihe atmosphere is sufficiently pure to render protection unnecessary. The reason of its adoption is probably the superior light which it affords ; but it constitutes a much more expensive means than the oil lamp. The frequent removal of the candle from one point to another, and the influence of the ventilative current, aided by the high temperature of the surrounding atmosphere, causes the tallow to " swear " or " gutter " away, as it is termed, at a very rapid rate, and this waste is still further favoured by the carelessness of the collier, who rarely allows his candle to assume the vertical position. The miner's candle is small ; for ordinary conditions, they number about twenty to the pound, but in fiery mines they are not uufrequently made as small as fifty to the pound. Sometimes the candle is set in a holder provided with a spike for the purpose of fixing it to the timbering, or to the rock ; but oftener, it is merely stuck into a lump of soft clay. To carry the candle from place to place, a common practice is to hold it by a piece of tow passed round it for that purpose.

Were it not for the presence of fire-damp in a mine, the lighting of the workings would present

Incidental 0Peeati0N8. 501

no grave diflSculties. It was shown in the preceding chapter that the ventilation should be so provided for that under ordinary conditions an explosive mixture could never be formed. But it was also shown that circumstances may occur in which it becomes impossible to prevent an accumulation of gas. In such cases, the naked light cannot be used. The first attempt to overcome the difficulty of lighting the workings in an atmosphere laden, or liable to be laden, with fire-damp was the steel mill, in which a disc of steel was made to rotate rapidly in contact with the edge of a flint. The stream of sparks thus produced emitted a feeble light without having its heat sufficiently concentrated to fire the gas. It was not, however, till the introduction of the Davy lamp that fiery mines could be worked with anything approaching to comfort or to security. The principle of this lamp is founded upon the fact, observed by Sir Humphry Davy, to whom the invention is due, that flame will not pass through fine wire gauze. The explanation of this fact is this : in order to pass through the gauze, the gases in combustion must be divided into a great number of little jets, each distinct from the rest. These lose their heat by being brought into contact with the metal, and are consequently extinguished. In accordance with this fact, Davy constructed a lamp in which the wick was surrounded by a cylinder of wire gauze, and it was found that when an explosive mixture was fired inside this lamp, the flame did not reach the gas outside. The gauze used was composed of 28 wires to the linear inch, giving 784 apertures to the square inch. Davy's lamp is still in common use almost in its original form, and the same principle has been adopted in all other safety-lamps of more recent introduction. Indeed it is but fair to state that all the safety-lamps now in use are but modifications of the Davy.

If the principle upon which the Davy lamp is founded be clearly understood, the degree of safety it afibrds will be readily perceived. As the wire gauze prevents the passage of flame by acting as a refrigerator, it must necessarily itself become heated, and it is evident that its action as a refrigerator must diminish as its temperature increases, until it becomes nil when its temperature is equal to that of the burning gases. For this reason, if a lamp be kept for a short time in an explosive mixture, the gauze will become red hot, and, in that state, it will allow the flame to pass, and the gas outside will be fired. Thus a safety-lamp aff'ords no security to a miner remaining in an explosive atmosphere, but only protects him for a few moments when he is brought into accidental contact with it. The use of the lamp under such conditions is to warn him of the presence of the gas, and to protect him for a time sufficiently long to enable him to withdraw from the place. When the gas fires in the lamp near the roof of the workings, the miner immediately lowers it to the floor out of the way of the gas ; or, if the whole atmosphere be charged with it, he quickly draws down the wick to extinguish the flame, and retires from the place. The lamp must be lowered gently towards the floor of the workings, and the miner must withdraw slowly from the place so long as his lamp remains alight. The reason for this will be understood from what has already been said. If a lamp be placed in a strong current of air, the flame will be deflected so that its point will be directed towards the gauze, and this point, acting hke the flame of a blow-pipe, will quickly heat the wires against which it is directed and allow the heated gases to pass through. For this reason, the safety-lamp affords no security in a strong current of air, and it is obvious that the efiBct of a current is obtained by moving the lamp rapidly through a still atmosphere. Hence arises the necessity for avoiding a sudden, jerky, or rapid motion. Experiments have shown that a current of air having a velocity exceeding 7 feet a second is sufficient to produce the effects described. This fact must be constantly borne in mind, and it is particularly necessary to remember

50'2 Mining Engineeeing.

it when moving against tlie current. Suppose, for example, the current to be moving with a velocity of 4 feet a second ; if the lamp be carried against this current with a velocity of 4 feet a second, we have the conditions for passing the ilame.

There is yet another source of danger to be guarded against in the safety-lamp, namely, the presence of inflammable material upon the gauze. The atmosphere of dry mines is laden with coal dust, and this dust is deposited upon the wires of the gauze, especially if the latter has become smeared with oil. Should gas fire in the lamp, this dust may inflame and fire the explosive mixture outside. But even without the coal dust, the oil itself may, under similar conditions, become inflamed. It has been found by experiment that when a gauze which has been smeared with oil is heated quickly to a red heat, it gives off fumes which inflame at that temperature. As the gauze of safety-lamps is very liable to get into this state, means must be provided for removing the oil. These means are of two kinds. Sometimes the lamps are placed in a kind of mufSe, and heated to a temperature sufficient to carbonize the fatty matters, and afterwards brushed with a hard brush. This process is very effectual in cleaning the gauze, but it rapidly destroys it by oxidation. The other method of removing the oil consists in dipping the lamps into a heated alkaline solution, and afterwards brushing them and rinsing them in water slightly charged with lime. Apparatus have been devised by means of which these operations are automatically and rapidly performed. The necessity for abridging the time required for these operations will be acknowledged when it is borne in mind that they have to be performed and the lamps replenished and trimmed in the interval between two shifts.

Safety-lamps are given out to the miners, on entering the mine, clean, supplied with oil, trimmed, lighted, and securely closed. On leaving the mine, they give them up at the lamp room, where they are opened, examined, and prepared for the next shift. The examination of the lamps is important, for the gauze may have been damaged in the workings, and an imperfect safety-lamp must be regarded as more dangerous than a naked candle, inasmuch as it gives unfounded confidence. To examine the gauze, the lamp is held up to the light and turned slowly round. It is also necessary to see that the lamp has not been opened, for, unfortunately, a miner, notwithstanding the danger to himself and to those about him, will sometimes open his lamp to obtain more light, or even for the purpose of lighting his pipe. To provide against this danger, various means have been devised for locking the lamps. The security afforded by a lock turned by a key is, however, not great, since the miner who opens his lamp may relock it. To overcome this difficulty, lamps have been so constructed that the act of opening them extinguishes the light ; but inasmuch as the lamp may be easily relit with a match, these arrangements are of little use. Another means of securing the lamps, which has been adopted in many collieries with satisfactory results, consists in riveting the gauze with a lead alloy rivet. As the collier who opens one of these riveted lamps finds it impossible to reclose it, he is certainly discovered on delivering up his lamp. The rivet, or leaden pin, is put through the adjoining rims of the upper and the lower portions of the lamp, and is stamped with some device. Eecently a magnetic lock has been introduced, and the results obtained are said to be very satisfactory. The lock closes itself with a spring, and as this spring is entirely out of reach, it cannot be drawn back by ordinary means. To open it in the lamp room, the lamp is placed over the poles of a powerful electro-magnet, by which the bolt is withdrawn. This lock, which was exhibited in the Paris Exhibition of 1867, has been patented in England by the Messrs. Craig and Bidder.

Incidental Opeeations. 503

As before observed, tbe ordinary Davy lamp as at present used is almost identical in form with that constructed by the inventor. It consists of an iron wire-gauze cylinder fixed to a brass ring, and screwed on to the oil vessel. The upper portion of the gauze is double for greater protection. Extomally it is guarded by three iron rods placed equidistant from one another, and attached at the top to a metal roof, above which is the loop for suspending the lamp. For the purpose of trimming the wick and extinguishing the light, a wire passes up a close-fitting tube from the bottom of the oil vessel. The average weight of one of these lamps is 1 J lb., and the average cost 7s.

A grave defect of the Davy lamp is its small lighting power. A moment's reflection will show that a very large proportion of the rays of light emitted by the flame are intercepted by the wire gauze. Tbe proportion of opening to solid in the gauze adopted is about 1 to 4 ; that is, of the total surface of the gauze, about is solid metal. We cannot infer from this that only j of the light is utilized, because some of the rays falling upon the wires are reflected ; but the proportion utilized certainly does not exceed -5. Hence the light emitted in the horizontal direction is very small. But it is evident that the proportion of light emitted through the gauze in other directions must be still less, by reason of the obliquity of the rays and the gauze, and that the proportion utilized diminishes as the point to be illuminated is situate nearer the roof of the workings. The light thrown in the upward direction is still further diminished by the double gauze and solid metal roof, so that the roof of the workings is only very feebly illuminated. This constitutes a very serious defect, inasmuch as it prevents a dangerous state of the roof from being observed, and furnishes a plausible excuse to the miner for opening his lamp.

Numerous modifications of the Davy lamp have been made for the purpose of remedying these defects. The attempts have in all cases been more or less successful ; but also in all, success has been obtained by incurring defects of another kind. It is for this reason that the Davy in its original form still holds its ground. The chief means adopted in these modifications for utilizing a larger proportion of the light consists in employing glass in the place of a portion of the gauze. The defect of this means lies in the fragility of the material, which necessitates the adoption of a great thickness. It can hardly be dispute, however, tnat oy employing a short cylinder of thick glass of a suitable quality, properly protected on the outside by vertical iron rods, a light greatly superior to that of the Davy is obtained without incurring serious danger from the fragility of the material. It should be remarked here, that when gas fires in a lamp so constructed, there is some danger of the glass cracking if rapidly cooled.

Some modifications of the Davy lamp have been made to lessen the danger due to strong currents of air, and to the heating of the gauze. It will be observed that the employment of a cylinder of glass partially accomplishes the former object; but the end in view is more or less completely attained by providing certain points of influx and efflux for the air, by means of which distinct currents are formed that are not readily affected by the agitation of the external air. To effect the second object, the air is introduced as near to the flame, and passed as directly to it, as possible, in order that an explosive mixture may burn as it reaches the flame, while the chief portion of the space inside the lamp is filled with gases that have been already burned.

Dr. Clanny's invention consisted in the substitution of a short cylinder of thick glass for the lower portion of Davy's wire gauze. The feed air enters, and the products of combustion escape, through the gauze above the cylinder. This arrangement is unfavourable to combustion, and hence the gain due to the substitution of the glass for the gauze is partially lost. Indeed, the light given

504 Mining Engineeeing.

Ly a Clanny lamp is but little superior to that furnished by a Davy, -while it possesses the disadvantage of being much heavier and of being constructed of a fragile material. The glass cylinder, however, in the Clanny is thick and well protected by vertical iron bars. This lamp, which was the first modification of the Davy, is still in use in some collieries of the north of England.

George Stephenson slightly increased the diameter of the Davy, and added a glass cylinder throughout the whole length of the lamp. This cylinder is placed inside the gauze, and is covered by a cap of perforated copper. The glass serves as a protection to the gauze against the heated gases inside, while the gauze serves as a protection to the glass against blows, and also keeps the lamp safe should the glass be accidentally broken. Air is admitted to the lamp through small holes in the rim below the cylinder. This method of admitting the feed air is a very good one, inasmuch as it tends greatly to prevent overheating, and also, in a considerable degree, to preserve the lamp from the injurious influence of currents of air. When the air inside becomes highly heated, the flame is extinguished. The feed-air holes must be kept free from oil and dust, and the lamp be held vertically to enable it to burn well. It will be observed that the improvements in this lamp are not directed towards the removal of the defect of insufficient light. The Stephenson lamp, familiarly known as the " Greordie," is in common use in England.

Mueseler's lamp is the most satisfactory modification of the Davy yet introduced. Like the Clanny, it has a short cylinder of thick glass around the flame, and draws its feed air in through the gauze above the glass. But it is provided with a central conical metal chimney, placed immediately above the flame and covered on the top with wire gauze. The products of combustion pass directly up this chimney, and cause a strong upward draught. By this means, the air is drawn briskly down on the inside of the glass cylinder, thus keeping the latter cool, and promoting combustion on the wick. The glass cylinder is protected in the usual manner by vertical iron rods. These lamps give an excellent light, and for that reason are pre'erred by the miners to those already described. They have long been in general use in Belgium, where their adoption in fiery mines has been rendered obligatory. The fact of their being but little affected by a strong draught, constitutes an important advantage over the Davy.

All the lamps described in the foregoing paragraphs have received modification at the hands of later inventors ; but none of them have proved to be of much value in practice. The most important additions that have been made consist in the means of locking the lamps, to which attention has already been directed. In adopting safety-lamps, there is some danger of a diminished vigilance being exercised in the matter of the ventilation. This danger should be kept constantly in view by those to whom such highly important duties are entrusted. Safety-lamps should be supplemental to good ventilation ; not a substitute for it.

BoRiNa FOR Water. — Not unfrequently in prosecuting the workings of a mine, it becomes necessary to take precautions against inundation. This happens when the workings approach an old waste, that is, former workings that have been abandoned. Unfortunately, no accurate record of the positions of such old workings exists in the majority of cases, and the miner is consequently exposed to the danger of breaking unexpectedly into them. As these old wastes are usually filled with water under the enormous pressure of several hundred yards of head, an irruption from such a source must be attended with disastrous consequences. In numerous instances, these inundations have caused a great loss of life, and in all, serious injury to, or a total destruction of, the workings. Hence it becomes the duty of the mining engineer, whenever the near presence of old wastes is

Incidental Opeeations. 505

suspected, to see that sufficient precautions are taken to prevent the occurrence of a disaster of that character.

The means employed to guard against an inundation from old wastes, are bore-holes kept in advance of the workings. When the workings have reached the neighbourhood of the waste, a heading, or more frequently, for reasons already given, a pair of headings, is driven, in the direction in which the waste is supposed to lie. In the face of these headings, a horizontal bore-hole is kept in advance of the excavation. The end of this bore-hole should never be less than 6 yards in from the face. The necessity for keeping a strong barrier between the mass of water and the men at the forebreast will be seen when the great pressure is borne in mind. The hole is bored to a distance of about 8 yards from the face, and the excavation then carried forward for a distance of about 2 yards ; the boring is carried forward 2 yards farther, and followed through the same distance by the excavation ; these operations are continued in this manner until the water is met with. If the seam be a thick one, it may be desirable to have two bore-holes, one near the floor and the other near the roof.

But the boring in the forebreast or face of the heading is not sufficient. Neither the situation of the waste relatively to the workings, nor the form of its boundary is accurately known, consequently the heading may not be approaching the waste directly, or if approaching directly, it may be passing alongside an advanced portion of the waste. It is easy to see that in such a case an inflow of water might take place behind the men at the face, and that the bore-hole parallel to the axis of the heading would afford no protection. For this reason, holes are bored laterally at intervals of a few yards. These holes, which are called " flank-holes," are bored obliquely to the axis of the excavation, that is, they are bored in the line of junction of the face with one side of the heading, at an angle of about 45° with the leading bore-hole. These flank-holes are repeated at intervals of 5 or 6 yards. It is almost needless to remark that flank-holes should be bored from both sides of the drift, when driven single, and from the outer sides of both drifts, when driven double. In some cases, however, as the consort drift is kept a few yards behind the leading drift, some of the holes may be safely dispensed with. All of these operations, upon which the safety of a great number of men may depend, require to be intelligently directed and carefully performed.

As the end of the bore-hole approaches the waste, the near presence of the latter will be indicated by water oozing through the rock into the bore-hole. The distance at which the indications will appear will depend upon the character of the rock and the pressure of the water. When the borehole has pierced the intervening barrier of rock and thus " tapped " the waste, the water will rush through the hole with great force ; to arrest this discharge speedily, suitable means must be at hand. It is obviously necessary that these means should be ready for immediate application when the waste is tapped. Usually a long wooden plug is employed. This plug, which should be of soft wood, as fir, is made to taper slowly, the smaller end being of such a size as to fit the hole loosely. It is driven into the hole with sledges and tightly wedged to secure it in position. The plug and the wedges should be quite dry when applied that the swelhng due to the moisture may tend to tighten them in the hole. To be prepared for all contingencies, there should be at least two of the plugs ready at hand. The insertion of the plug offers some difficulty, by reason of the force with which the water issues from the hole. Sometimes the force is too great for the strength of one man ; in such a case, the plug is tied to the middle of a bar, and at right angles to the latter, one end of which is then held by one man, the united strength of the two thus apphed to the bar being sufficient to force in

3 T

506 Mining Engineeeing.

the plug. Sometimes it is intended to unwater a drowned waste. When this purpose has to be eiFected, the wooden plug is bored out when everything is in readiness to convey the water away, and the waste is slowly drained. Instead of the wooden plug, an iron tube provided with a tap is sometimes used in such a case.

As soon as the exploring drifts have reached the waste, and the hole has been securely plugged, other similar drifts should be set off 20 or 30 yards back and at right angles to the first, for the purpose of ascertaining with precision the position of the waste. These, like the first, will be preceded by bore-holes, and flank-holes will be required on the side next the waste. By proceeding in this way, the limits of the drowned waste are clearly ascertained, and a sufficiently strong barrier of coal is left to protect the new workings. It will be seen from the nature of the operations described that it is necessary to proceed in these explorations with the utmost caution.

While treating of the subject of inundations, it may be well to direct attention to a phenomenon sometimes caused by them, and known as the " water-blast." If the water should accumulate to a considerable height at the botton of the shaft, the air in the rise workings will be pent up, and as the water ascends these workings, this pent-up air will become more and more compressed. The tension of the air is also increased by the addition of the gases, which, even under such conditions, may be given off from the whole coal. In consequence of this, the equilibrium of the forces may be destroyed, and the air may escape through the water with a violence similar to that of an explosion. If lights be in the way, the gases will probably be fired. Grreat caution is therefore needed in drawing down the water of an inundated mine. Mathias Dunn relates an instance which occurred at the " Percy Main " Colliery many years ago. This colliery had taken fire and it had become necessary to flood it. When, after the extinction of the fii e, the engine was started to unwater the mine, the water stood in the shaft to a height of 25 fathoms. The engine worked for several weeks without lowering the water in the shaft, the level of which, however, rose and fell several times. At length, " an immense eruption of inflammable air issued suddenly from the mouth of the pit, and continued from eight to ten minutes to cast up a prodigious quantity of gas, when it suddenly ceased and became tranquil ; in half an hour a similar eruption took place, and for twenty-six hours, these eruptions were repeated at regular intervals of half an hour, when they ceased, and the gas continued to discharge itself in gluts and beatings like a 'water-hammer,' with a loud noise, through the column of water, which, in the meantime, had fallen suddenly to within a fathom or two of the bottom of the shaft."

Dams. — It sometimes becomes desirable to shut back by means of a dam the water which enters abandoned workings. The dam is constructed in the way leading to the abandoned district, and is intended to serve the same purpose as the solid barriers of coal left around a drowned waste. These structures have to be erected under conditions which are not met with at surface. Hence they have a special character, and, for this reason, demand a special study on the part of the mining engineer. They do not, however, in general offer very great difficulties ; all that is required to ensure their efficiency over and above what is needed for works of a similar nature, is to obtain a full understanding of the conditions under which they will have to exist. With this knowledge, the inventive engineer will readily adapt the means at his disposal to accomplish, in the best manner, the object he has in view.

The two principal requirements of a dam are : first, that it shall be perfectly water-tio-ht ; and second, that it shall be capable of resisting the pressure that may be brought to bear upon it. That

Incidental Operations. 507

a dam may be perfectly water-tight, it must be constructed of impervious materials, and the pressure must tend to close rather than to open the joints in the structure ; these joints must, moreover, be well caulked to prevent the passage of water. It is also especially necessary to make the junction between the dam and the sides, roof, and floor of the way in such a manner that the water cannot force its way along it. To render the dam capable of resisting the pressure that may subsequently be brought to bear upon it, it must be constructed of strong materials, and these must be disposed so as to offer sufficient resistance without becoming deformed. From this point of view also, the junction of the dam with the walls of the way requires special attention. It must be borne in mind, in designing and executing such works, that the pressure to be resisted is enormously great. Take, for example, the case of workings 1000 feet from surface. Here the pressure of the water against the dam may be as great as 430 lb. to the square inch, which will amount to a total pressure, upon a dam erected in a way 40 square feet in sectional area, of 1100 tons. To resist such a force as this, the dam must be securely placed and very strongly built. It should not be forgotten that the yielding of a dam would entail the most disastrous consequences, and that, therefore, it should possess a great excess of strength.

The material used in the construction of dams is most frequently wood, sound well-seasoned oak being preferred. It is used in pieces from 4 to 5 feet in length, squared and tapered according to the radius of the arch to be formed by the dam. These pieces are laid down side by side in rows, one upon another, with their larger ends towards the water. They thus act as the voussoirs of an arch ; indeed a dam so constructed is an arch composed of wooden voussoirs. The depth, or length, of these voussoirs must be proportioned to the pressure to be resisted ; a common length is 5 feet. It is of the utmost importance that these pieces should be accurately cut, so that they may bear evenly one upon another throughout their whole length. They are prepared at surface ; and it is well to build up the dam there as the pieces are prepared, in order that the structure may be examined by the light of day, and any defect observe J. Each piece, as it is placed in position, should be numbered to ensure its occupying the same position underground, and care should be observed to send it down in a thoroughly dry state. When the dam has been built up in its position underground, the joints are wedged in the same way as the wedging curbs for shaft tubbing. A detailed description of this operation will be found in the chapter devoted to shaft-sinking.

The preparation of the site of a dam of this character demands special attention. The rock against which the dam rests acts as the abutments of a bridge, and to enable it to bear the enormous thrust of the arch upon which the pressure of the water is exerted, it must receive the strain in a suitable manner. Also in laying out these " foundations," the tendency of the water to creep between them and the dam must be borne in mind, and measures taken to prevent any leakage along these lines of junction. The site for the dam must be chosen at a point in the way where the rock is strong and sound ; this is a matter of primary importance. To prepare the abutments for the dam at this point, the four walls of the way, that is, the roof, the floor, and the two sides, are carefully cut to form the faces of a pyramid having its summit at a determinate point, situate a certain distance beyond the site of the dam. The length of the faces or walls thus prepared is usually about 6 feet. The position of the apex of the pyramid must be determined according to the pressure to be provided for. This point will be the centre of a sphere towards which the four faces of the frustum of a pyramid, formed by the prepared sides of the way, equally converge. The pieces of wood which are to form the dam are cut according to the inclination of these faces. It is obviously

3 T 2

508 Mining Engineeeing.

necessary that these faces should be true and smooth. If the rock is of a suitable texture, it is chiselled to a smooth face ; but if it is of a coarse texture, it is chiselled rough and cemented. Upon the bed thus prepared, the wooden voussoirs are carefully laid, and the dam built up to the roof.

In the execution of the work, however, certain difficulties have to be overcome. To render the dam sufficiently water-tight, it is desirable, if not indeed, absolutely necessary, that the wedging and caulking of the joints should be performed on the side whence the pressure comes, that is, on the face of the dam which is presented to the water. It will be observed that when the operations of edging and caulking are performed from that side, the pressure tends to close the joints. The difficulty lies in leaving a way of egress for the men employed. In the case of a dam of the kind we are considering, an iron pipe is used. This pipe, which is of cast iron, is conical, and sufficiently large in diameter to allow a man to crawl through it. It is built into the dam near the bottom, the pieces with which it is in contact being shaped to fit it accurately. When the dam is completed, a conical wooden plug, made to fit the pipe, is prepared and attached to a rope by means of a staple driven into its smaller end. This plug, which, of course, must be passed in before the dam is built, is covered near its larger end with vulcanized indiarubber, to make a water-tight joint with the pipe. "When the dam is completed, and the men have retired through the pipe, the plug is drawn in by means of the rope, and further tightened by attaching the latter to a lever. The subsequent pressure of the water forces in the plug still more firmly.

The water which the dam is designed to keeji back must be allowed to flow away freely during the progress of the operations. Generally, the most convenient arrangement consists in providing a small bay a little above the dam, and leading the water from this through the iron pipe, left to afford a means of retreat for the men, by means of flexible tubing. It is sometimes thought desirable to let out the air before the pressure of the water comes upon the dam. This is effected by boring an auger-hole through one of the pieces, and connecting a small iron tube with it on the inside, which tube is carried up into a little hollow made in the roof. When the water begins to issue from the auger-hole, it is certain that all the air has escaped, and the hole may then be plugged with wood.

The following description of a dam constructed some years ago at the Creusot mines in France is given as affording a good typical example from actual practice :

This dam, which was constructed under the direction of M. Petitjean, the chief engineer, was designed to resist a pressure of 707 feet head. The radius of the sphere chosen was 16 feet 6 inches for the extrados, and 10 feet 10 inches for the intrados of the arch; the length of the wooden voussoirs used was 5 feet 6 inches. In works of the same character previously executed, the radius chosen had been 23 feet; but in this case, it was reduced to 16 feet 6 inches for the purpose of throwing the pressure chiefly upon the rock. As the pressure which the wood was capable ot supporting without crushing had been estimated at 970 lb. to the square inch, a length of 3 feet 4 inches would have been sufficient for the voussoirs. The length of 5 feet 6 inches offered, therefore, a wide margin of safety.

The utmost care was observed in preparing the rock. To mark the centre, that is, the apex of the pyramid described in a foregoing paragraph, a bar was fixed vertically, in the middle of the way, at a distance of 16 feet 6 inches from the extrados, and firmly wedged to the roof and the floor to prevent it from shifting. In the middle of the length of this bar, that is, at the point of intersection of the two axes of the way, a steel point was fixed. The sides of the way were then cut accordinoto the radii from this centre, the faces dressed and the joints in the rock run with cement. It

Incidental Operations. 509

was not attempted to make these faces form a regular sector, as any undulation might be easily followed by the voussoirs. To ensure this, an exact model was taken of the way at that point after the rock had been prepared, and the wood was shaped thereto at surface.

The dam was constructed of thirteen horizontal rows of voussoirs, each row being tightened up by a " key -piece," shaped to be driven in between two voussoirs. The pieces having been sent down numbered, and in a perfectly dry state, they were laid upon the rock, which had previously received a Coating of red-lead, and if the impression showed imperfect contact at any point, they were planed till the defect was removed. Before they were finally laid, a bed of moss was spread of an inch thick over the rock, to which it was made to adhere by means of a coating of tar. The dam was then built up, each row of pieces being keyed, and the joints between the outer rows and the rock caulked with moss. In placing the last row, particular care was taken to obtain a perfect contact between the wood and the rock. The upper faces of the pieces having been covered with moss, made to adhere by means of tar, they were placed in position and wedged up from below by means of flat pieces of wood, of the same width and length as the voussoirs, tapered at the edge to allow of their insertion. The wedging was then proceeded with. This operation was commenced by driving in fir wedges at a distance of about inch from the line of the joints, and not in the joints themselves. This is worthy of note as a peculiarity of the case. These fir wedges were 14 inches square and elliptical in section, their thickness being only an inch, or a little less. They were thoroughly dry and well greased with tallow. The first entered to their full length ; then they began to crush and to break off at about two-thirds of their length ; and later, when they had penetrated to about one-half their length. The same thing occurred with all the fir wedges subsequently used, and in general it may be stated that, as a mean, the whole number of fir wedges penetrated to about two-thirds of- their length ; the oak wedges were all driven in to their full length. Of the fir wedges, 1689 of all dimensions were driven in before recourse was had to oak wedges. The latter were 8 inches long, and of the same thickness as the fir. Those first used were flat, and 1|- inch broad ; those used later were square in section, and inch on the side. Of the oak wedges, 2558 were driven in. When no more wooden wedges could be made to penetrate, 552 steel wedges were got in, the greater number between the wood and the rock. The dam was thus composed of thirteen rows or courses, containing 142 pieces, the smallest of which were 6 inches square at their smaller end ; and 4799 wedges, cubing together, 58 feet. The depth of the thickest course was 13 inches; that of the thinnest, which was the top course, was 6-| inches. The convex surface of the extrados was 112 square feet, and the concave surface 49j square feet.

When the dam was completed, the air was allowed to escape through a small pipe placed in the upper part. Four hours after the water had risen to the top of the dam, the pressure indicated 50 feet, and little capillary jets of water began to escape through the wood. In the twenty-four hours which followed, it was estimated that from 30,000 to 40,000 gallons of water escaped in this way in the form of spray. As the compression of the wood proceeded, this action diminished, until it ceased altogether after the one hundred and thirty-second day, the pressure then indicating 570 feet.

In this case, means of egress was furnished by an old pit, so that it was not required to build an iron pipe into the dam. For the purpose, however, of discharging the water if desired, two conical castiron pipes provided with taps were built in. These taps, or valves, afi'orded each a water-way 5 inches in diameter. While the dam was in course of construction, they afibrded an outlet for the water, the

510 Mining Engineeeing.

quantity of which exceeded 6200 gallons an hour. The two courses of voussoirs between which the pipes were placed were made somewhat thicker than the rest to allow for the cutting away necessary. The cost of this dam amounted to 480Z.

It is frequently required to construct a dam underground to resist a moderate pressure of water. In such cases, some simpler structure will be adopted than that we have described. The conditions of the case will determine the kind of structure most suitable. Sometimes masonry is used ; such dams consist of two or more concentric arches placed several feet apart, the interval, or intervals, between them being filled up with clay well rammed. Masonry is, however, generally unsuitable, inasmuch as the least yielding of the abutments causes fraction and breakage.

UiSTDERGROUND FiRES. — Underground fires constitute one of the disasters which may happen to endanger the existence of a colliery. When, by any accident, a seam of coal is set on fire, it becomes exceedingly difficult to extinguish it. The progress of the fire is very slow, but its advance is continuous and sure. The difficulty of extinguishing an underground fire lies chiefly in the impossibility of approaching it. The heat generated is, under the conditions present, alone sufficient to prevent immediate access to the burning mass ; but the accessibility of the region in which the fire is raging is rendered still more remote by the vitiation of the air by the combustion of the coal . Besides this, there is the ever present danger of an explosion of fire-damp. For these reasons, the fire must be dealt with from a distance, and hence the difficulty of extinguishing it.

An underground fire may occur as the result of an accident, such as might occasion a conflagration at surface. A miner's candle may come, by careless handling, into contact with some highly combustible substance, as straw, or dry chips of wood, and from this, the timbering may become ignited. Or the coal may be ignited directly by sparks from an underground engine, or from the ventilative furnace, when due precautions have not been taken to prevent such an occurrence. Another cause of fires is the ignition of the hydrogen gas as it issues from the coal ; or it may be, and frequently is, occasioned by an explosion of fire-damp. A third and fruitful cause of fire in underground workings is spontaneous combustion. In order to be able to guard against the efi'ects of those chemical reactions which are denoted by the term " spontaneous combustion," it is necessary to ascertain clearly what the conditions are under which it can take place. When the seam is what the miners describe as " brassy," that is, when it contains a large proportion of iron pyrites, one of the conditions of spontaneous combustion is present. Iron pyrites, on being exposed to the influence of a moist atmosphere, become decomposed, and, when much moisture is present, the decomposition proceeds rapidly. Decomposition is necessarily attended by a liberation of heat, and if the action take place under conditions which prevent the escape of heat, combustion of the sulphur must speedily ensue. All the conditions of spontaneous combustion are present, when we have a loose heap of small pyritous coal exposed to a moist atmosphere. The air penetrates the heap and decomposes the pyrites ; the heat generated can escape but slowly, and as a consequence the free sulphur becomes ignited. Until recently, it was believed that spontaneous combustion can take place only under these conditions. But it has of late been discovered that the presence of pyrites is not necessary. Pure coal may fire more readily than sulphurous coal. The only essential conditions appear to be : first, that the coal shall be broken up into small pieces so as to expose a large surface to the air ; and second, that there shall be a sufficient mass of coal to prevent the heat from escaping as fast as it is generated. When such a mass of coal is exposed to a moist atmosphere, oxidation takes place, heat is generated and accumulated, and combustion, that is, very rapid oxidation, ensues. The coals which appear to be

Incidental Operations. 511

the most subject to this action are those kinds which contain a large proportion of oxygen ; whence it IS to be inferred that the oxygen has a tendency, under the conditions pointed out, to combine with the carbon.

It will be observed that the conditions necessary to combustion are the same whether iron pyrites be present or not, that is, in either case, there must be a mass of small coal exposed to a moist atmosphere. Hence the means to prevent the occurrence of spontaneous combustion will be the same in all cases. The application of these means demand a brief notice in this place, as constituting some of the operations incidental to mining.

One of the means used to prevent the occurrence of conditions favourable to spontaneous combustion, consists in removing all the small coal to the pit-hill at surface. This is, however, a somewhat costly proceeding, and is, moreover, not always practicable. It may be well to adopt it to some extent when the seam is very pyritous. Another means consists in excluding the air from the accumulations of small coal in the workings. This is effected by shutting off the worked-out portions by barriers erected in the ways. These barriers may be constructed simply of rock stowage, or of two parallel brick walls, the space between which is filled with clay. These barriers require continual inspection, however, on account of the injury caused by the descent of the roof. The injury may not be confined to the barriers, but may extend to the solid ribs of coal left to enclose the district ; and it will be readily perceived that if a district is not hermetically enclosed, the means employed must be inefficacious. This method of excluding the air from old workings is often adopted with success ; but in many cases, it is utterly inapplicable. It is easy to see that many systems of working are wholly unfavourable to its adoption.

Another method, which may often be successfully applied, is the reverse of the preceding, and consists in admitting a strong current of air to the dangerous masses of coal. By this means, the heat generated by the chemical reactions is abstracted from the mass, which is thereby prevented from attaining the temperature of combustion. This method may be more easily applied to thin seams than to thick seams. When used in conjunction with the method of packing the worked-out portions, it is generally the most convenient and effective.

It will be understood from the manner in which spontaneous combustion takes place that the nature of the roof will influence it in no inconsiderable degree. Thus, where the accumulations of small coal are not large, spontaneous combustion can hardly occur beneath a sandstone roof. The reason of this is that the heat escapes as fast as it is generated. But if the roof be composed of a soft shale, and in most cases the roof is composed of that material, the heat is confined, the shale being impervious to the gases formed. If, however, the roof become much broken up during its descent, the fissures formed may allow the heat to escape. For similar reasons, workings near the outcrop are less liable to accidents from spontaneous combustion than deeper workings.

When a fire has broken out in underground workings, and it has not been possible to extinguish it by the application of water before it had gained a firm hold on the coal, measures must be speedily taken to isolate the portion of the workings in which the fire is raging. This is effected by erecting stoppings, or barriers, in the air-ways leading to and from the fire. The labour of constructing these stoppings is difficult and dangerous, on account of the heated and vitiated air which the workmen compelled to breathe. The difficulties and dangers increase as time is allowed to elapse, so that it is of the utmost importance to proceed quickly. As the barriers are intended to prevent the access of air to the burning mass, it is obviously necessary to make these structures air-tight. The cutting off

512 Mining Engineeeing.

of the air current quickly reduces the intensity of the fire, and it would appear at first sight that when the oxygen of the air which had been enclosed has all been taken up, the fire will be extinguished. But it will be perceived on reflection, first that it is impossible to exclude the air altogether by reason of the porosity of the rocks and of the coal itself ; and second, that the coal contains a greater or a less proportion of oxygen, which allows combustion to proceed slowly without the access of atmospheric air. For these reasons the fire will continue to smoulder, and will be, therefore, ready to break out afresh the moment air is readmitted to that portion of the mine. In numerous instances, these isolated fires have been known to smoulder for years, and there is no reason in any case to hope that it may be extinguished in this way. Hence when the inflamed district has been isolated, and the intensity of the fire reduced, means must be taken to extinguish its remains. The means employed are water, and carbonic acid gas.

The flooding of the burning portion of the mine may offer serious difficulties. If the fire occur in the dip workings, the situation may be favourable ; but in some cases it becomes necessary to flood the whole mine. That necessity may happen irrespectively of the situation of the burning portion. When the fire has been caused by an explosion of fire-damp, it may not be possible even to enter the mine, in which case, the shafts themselves must be sealed up. The sealing is effected by means of a strong wooden platform or scaffolding suspended in the shaft. The scaffold is made to fill the shaft, and is hung by means of stout chains to baulks of timber laid across the mouth. A quantity of plastic clay is thrown down upon the platform to hermetically close up the shaft. The operation of flooding a mine is very simple, and needs no description. The pumps having been stopped, the water in the mine is allowed to rise ; this water is supplemented by other water from surface. When a stream is near, a portion of it may be conducted to the shaft. The unwatering of the mine, however, after the fire has been extinguished is a slow and costly work, and the damage done to the workino-s may be very great. Flooding is, therefore, to be had recourse to only as a last resource.

Kecently, carbonic acid gas has been successfully applied to the extinction of underground fires, and it is probable that in the future, it will be generally used in the place of water. Though, in some respects, its application is more difficult than that of water, yet its effects are more potent, and, what is very important, it has no damaging action upon the workings. The gas may be cheaply produced in large quantities from limestone by means of hydrochloric acid. An important fact to be borne in mind is that carbonic acid gas may often be applied in a portion of the mine which could not be reached by water, except by flooding the whole workings. When the burning district can be isolated by means of stoppings and barriers, this gas offers a convenient and effective means of extingushing the smouldering fire. Assuming that the gas is generated from limestone and hydrochloric acid, it is obvious that it may be applied in various ways. The arrangements for distributing the gas must be made -in accordance with the particular circumstances of the case ; this will be a question for the engineer to determine. In general, a system of pipes and tubing will constitute the most suitable means. The following interesting description of the manner of applying carbonic acid gas to the extinction of an underground fire at the Wynnstay Colliery, Ruabon, devised and successfully carried out by Mr. George Thomson, was given in a paper read by that gentleman before the members of the Iron and Steel Institute.

" The colliery at which the fire occurred is of considerable extent, being capable of producing an ' output ' of a thousand tons of coal a day. It comprises a ' winning ' of between five and six hundred acres, under which five separate seams of coal are wrought in conjunction, to the same shafts.

Incidental Opeeations. 513

There are two downcast shafts, which we will denote as A and B respectively, from which coals are drawn by separate engines, A being 14 feet, and B 12 feet in diameter. The 'upcast' shaft C in the ' crop,' is 15 feet in diameter, and is at present used only for ventilation. The extent of the workings may be gathered from the calculation that it would take about a million cubic yards of water to fill them. The coal is worked somewhat after the Lancashire method, levels and crossings at right angles being driven, of 3 to 5 yards in width, to the extent of the boundary of the district of work, thus cutting the coal into a series of parallelograms about 50 by 30 yards, and is then worked back ' homewards ' in the direction of the shafts.

" At the time of the catastrophe to which I am about to refer, there was an underground highpressure steam engine, which drew the coal out of the ' deep ' workings, the steam for which was brought from the surface by cast-iron pipes, and the ' exhaust ' steam was conveyed thence by similar pipes into a return air-course, where the fire occurred, and which will hereafter be referred to as ' the region of the fire.' The ventilation is produced by a powerful double furnace, close to the ' upcast,' and the quantity of air passed through the workings, when the colliery was in ordinary work, was over 200,000 cubic feet per minute. The coals gave off a large quantity of carburetted hydrogen gas, especially the two upper seams, and consequently, the workings, being of a dangerous character, have to be conducted with great care and caution. The quantity of gas given off is generally from 600 to 800 cubic feet per minute.

"One day at the end of January, 1874, a fire was discovered about mid-day in the return aircourse, near to where the exhaust steam was delivered, and it is supposed to have originated spontaneously, for the place had been examined on the morning of the same day, and reported in order. Every effort was made to suppress the fire, but it nevertheless continued to increase rapidly, and at length became unmanageable, so that in view of the great extent and complicated character of the ventilation, together with a large quantity of carburetted hydrogen to be dealt with, there was no alternative but to withdraw the men and horses from the workings as quickly as possible, and to seal up the shafts. A scaffold was accordingly placed in each shaft as low down as practicable, and all were covered over with sand and clay to make them as air-tight as possible ; but a cast-iron pipe, of 6 inches diameter, furnished with light valves opening outwards for the purpose of relieving the outflow of gas from the mine, was left through those of shafts B and 0. Shaft A was first closed, and then B and C were stopped simultaneously, so as to avoid unnecessary draught or pressure, as the case might be. Before leaving the workings, several stoppings were put in, and the ventilating furnace was damped out ; but in consequence of the intensity and rapid increase of the fire, so long as it continued to be supplied with air, the whole of the mine remained well ventilated.

" It is scarcely necessary here to explain that 5 volumes of air must be added to the carburetted hydrogen gas before it becomes explosive; that it so remains until the air exceeds 14 volumes to 1 ; and that the most explosive mixture is about 9 volumes to 1. As soon, therefore, as the shafts were all sealed, it was clear that the gas given off from the mine might form an explosive mixture with the air that remained unconsumed by the combustion of the fire, so that at some point an explosion might, and indeed was very likely to, occur. All remained quiet for 72 hours, but at the end of that time a sharp explosion occurred, considerably disturbing the scaffold on shaft A, sucking down that on B, and blowing off, with considerable violence, that on 0. We were now in great diflSculty, because from the fact of fresh air being admitted, it was not improbable that at any moment another explosion might occur, and the expediency of flooding the workings with water was fully discussed, and was

3 u

514 Mining Engineering.

thought by some to be the only means by which the colliery could be recovered. But preparations were at once made to repair and strengthen the scaffold on shaft A, and to put ' hanging scaffolds ' on B and C, suspended by chains from strong baulks of timber laid across the top of each shaft. Several yards thick of clay were ' puddled ' on each scaffold, with a stratum of water on top to make all air-tight, taking the precaution of leaving, as before, cast-iron pipes of 6 inches diameter through the scaffolds to the tops of the shafts B and C, furnished with light valves opening outwards only, and also with supplementary pipes of ' gas tube,' 1 inch diameter, having stop cocks, by which to ascertain, from time to time, the outward or inward pressure by water gauge. These scaffolds were put in and made tight, and all the shafts effectually sealed at the end of the sixth day after the explosion — the two ' downcasts ' having been secured by the end of the second day.

" For some little time at first we loaded the valves on the outflow pipes equal to about 7 inches of water gauge, so as to prevent, by the pressure of gas, the possibility of any current of air getting through the fissures of the strata or otherwise, and then at that pressure allowed the gas to blow through them. On the evening of the second day, after the re-sealing had been completed, the welcome fact disclosed itself, that the gas escaping from the valves would put out the safety lamp when held close to it, but would fire in the lamp when held at sufficient distance to allow of the necessary mixture of air for the purpose, clearly showing that the mine was now filled with carburetted hydrogen, that the point of explosion had been safely passed, and that now no fire could live in such an atmosphere ; and by analysis we found roughly it consisted principally of carburetted hydrogen, 10 per cent, carbonic acid, with traces of carbonic oxide, nitrogen, and oxygen.

" We had now only patiently to await events, watching, by means of the appliances adopted every change in the mine, which was carefully recorded. A register was kept twice daily of the atmospheric pressure indicated by the barometer, the pressure outwards from, or inwards to, the mine, indicated by the water gauge, the temperature of the ' downcast ' and upcast shafts, together with occasional analyses of the escaping gases. A registering thermometer was let down by copper wire through the ' outflow ' pipe, which was temporarily covered during the operation by a board with a slit in it for the wire, the temperature being taken at different depths, but in the upcast, chiefly at a depth of 245 yards, opposite to the return air-course from ' the region of the fire,' and in the ' downcast ' at a depth of 200 yards. Early in March, an accident happened to the sealing scaffold in the upcast shaft, which fell down the pit, and this caused some disturbance of the observations at that period ; but as the shaft was re-sealed without delay, the effect passed off in the course of a week. It is worthy of remark how sensible the outflow of gas is to the changes of the barometer, the water gauge of course rising as the barometer fell ; and when a sudden rise occurred in the barometer, for a time the water gauge would indicate an inward pressure until the gas given off by the mine gradually increased the pressure again ; a forcible illustration of the extreme importance of minute and constant barometrical observations to the managers of ' fiery ' mines, more especially when the workings are extensive.

" In the month of May, after many consultations, when the temperature in the upcast shaft bad remained nearly stationary for several weeks, and had, in fact, approached what might be considered the normal temperature at the depth of 250 yards, it was thought probable that the fire was extinguished, and it was deemed not imprudent to attempt a re-entry of the mine.

" This, however, was a formidable undertaking in view of the fact that some million cubic yards of carburetted hydrogen gas was pent up in the workings, and that, although the fire might virtually

Incidental Operations. 515

be extinguished, yet in the immediate region of it, probably a high temperature existed, and there might be smouldering fire in some of the fissures, which, on the admission of fresh air, might re-kindle. The first idea was to open one of the downcast shafts (B) only, taking air down it temporarily by canvas tubing, and thus feeling our way, as it were, to the region of the fire ; but the difficulty here was the large quantity of gas to be dealt with, and the complicated character of the ventilating currents in the five seams of coal, all of which were more or less connected, and they had. doubtless been totally disorganized by the explosion shortly after the first sealing of the pits ; so that even if we were able to reach the fire, although there could be no direct current through the upcast, yet by the law of diffusion of gases sufficient air would be obtained for combustion if any fire remained. But ultimately the colliery manager suggested the plan of first descending the upcast shaft by means of a loose scaffold, somewhat in the manner of a piston in a cylinder, and by that means stopping up the return air course from ' the region of the fire,' and when that was accomplished to open the upcast (0) and one downcast (B), and so restore the ordinary ventilation as far as the explosion had left the currents undisturbed, except through the ' region of the fire.' This idea seemed to me the most feasible, and after I had added to it the outflow pipes to carry off the noxious gas without its coming in contact with the men on the scaffold (without which, as the sequel proved, we should not have succeeded) the plan was adopted, which I will briefly describe in detail, and which ultimately proved successful.

" A loose scaffold was constructed, fitting as closely to the sides as practicable, and consistent with its moving down the shaft, and suspended by a strong wire rope passing over the pulley to a powerful double-purchase windlass, for the purpose of raising or lowering the scaffold at pleasure. A strong wooden box was placed across one side of the shaft, and connected with an air tunnel into a chimney or cupola 12 feet in diameter. Cast-iron pipes 14 inches in diameter were also provided, each running through the scaffold and furnished with throttle valves, having handles to open and close them as required. Tubing of canvas on iron hoops 2 feet in diameter was joined on to the box from each pipe, and a length of 20 yards at a time was placed on the pipe, and gradually drawn off as the scaffold descended, and by taking care that the joinings of the tubing on the respective pipes were at different depths, and made alternately, both pipes were never closed at the same time, unless it was found necessary to do so for special reasons.

"Another tube of canvas and iron rings of 3 feet 6 inches diameter was also fastened to the box, and connected with a wooden frame on the movable scaffold : this tube was also in lengths of 20 yards, which were coiled on the frame and opened out as the scaffold descended. Brattice cloth was nailed round the edge of the scaffold, which prevented any inflow of air. A separate rope passing over the pulley was taken to the drum barrel of a winding-engine close by, the steam boilers of which having been removed to a distance of 200 yards, so as to avoid any danger of the gas from the mine being ignited by the boiler fires, and by this rope the men passed up and down, and the necessary materials were lowered for the operations. A steam jet was introduced into the air cupola, so as to increase the draft, and the exhaust steam from the engine was also passed through it. In order also to avoid as far as possible the necessity of taking even safety lamps into the shafts, we arranged a series of reflectors, consisting of bright tin plates, fastened to frames of wood held at the top and on the scaffold, and by that means the whole of the operations were performed without any artificial light whatever.

" By this apparatus thus arranged, the men gradually descended the shaft, and by means of the

3 u 2

516 Mining Engineeeing.

valves on the outflow pipes and the brattice cloth, around the edge of the scaffold, were able to regulate the outflow of the gas from the mine, and the purity of the air on the scaffold. If the valves on the outflow pipes were not sufficiently open, gas came through the brattice cloth, round the edge of the scaffold, through which, on the contrary, if the valves were too open an inward draft immediately set in. The operations to be accomplished were first to put up temporary stoppings; next to put a permanent and effectual stopping, coming from the region of the fire, and then to return and take out the temporary stoppings, and withdraw the movable scaffold from the upcast.

" The whole of this work was successfully completed in about three weeks from its commencement, and we then proceeded cautiously to unseal the downcast shaft, and, having removed the scaffold, descended the shaft, the ventilation being in a measure restored through such of the air-courses and roads as still remained partially or wholly open. "We also placed a water tank on surface connected with a waterworks main, and carried water pipes from it down the shaft, 2 inches diameter the first 100 yards, inch diameter the second 100 yards, and 1 inch diameter the remaining 110 yards to the lower ' mouthing,' and thence along the roadway ; the pipes being proved to a pressure of 1000 lb. to the square inch, and having taps and hose pipe by which to play water when necessary upon the debris in the roads or elsewhere.

" Proceeding now with our explorations, we found that the fire had raged with extreme violence all round the engine, the ironwork of which had, at one time, evidently been nearly at a white heat, for the screw-pins of the pipes, &c., had been drawn out of the bolts at a welding heat, the threads of the screws being obliterated. All appearance of fire, however, had now disappeared, and the temperature at that place was only 85° Fahrenheit. Having put in a stopping, we continued our explorations and the clearing up of the roads as quickly as practicable, playing water where necessary on the fallen roof and rubbish, the temperature of which varied considerably in different places.

" Proceeding onward, a fall of roof occurred some distance forward, which, on reaching the floor, burst into flames. The men played water upon it, but were immediately surrounded with so noxious a gas that they were unable to hold the hose pipe, being struck down insensible as fast as they essayed the work, and consequently they were compelled to retreat. Stoppings were then put in, during the construction of which one or more slight explosions occurred. The temperature then began to increase rapidly all round the ' region of the fire,' and we determined, without further delay, to put in a series of permanent and effectual stoppings in such positions as to thoroughly wall out the fire from any connection with the other workings. The engine was removed, and the ' down brow ' abandoned, thus temporarily abandoning the deep workings.

" Through some of the stoppings we left the water pipes, and through others observation pipes, all furnished with taps made quite air-tight ; and having shut off the water, we connected the water pipes with an apparatus which we constructed for the production of carbonic acid gas, by the decomposition of limestone with hydrochloric acid, and which, by these means, we forced at pleasure within the stoppings.

" The apparatus for the production of carbonic acid gas wasconstructed in the following manner : Two strong wooden boxes, 6 feet square by 2 feet deep, were provided, and lined with sheet lead to resist the action of the acid. Pipes with taps were fixed into the upper side of the box, and manlids were provided, the latter for charging the box with limestone, the former for introducing the acid. Pipes with plugs were also fixed into the bottom of the box for the purpose of discharo-ing the

Incidental Opeeations. 517

residuum, chloride of calcium, after the decomposition of each charge. Two cast-iron pipes with separate valves, and also a valve common to hoth, were connected to the box to convey away the gas as it was produced. Small pipes provided with taps were also inserted for allowing the air to escape, and also for attaching a mercury gauge during the operation to indicate the pressure of the gas. Whilst one box was giving off gas, the other was being charged, so that a continuous flow was kept.

" The charge used was about cwt. of limestone, broken very small, and the ' mand ' being fastened down the hydrochloric acid was poured in, and the mercury gauge was watched so as to keep the pressure tolerably equable, usually about 3 inches of mercury. We found generally that 120 gallons of the acid, of 1*12 strength, decomposed the charge of limestone, which, by calculation, gave us about 12*0 cubic yards of gaa. The gauge indicated when the charge was exhausted, and then the valves, &c., were shut and the residuum withdrawn, and thus the operation was repeated alternately as long as needful. Altogether we put down about 6000 cubic yards of carbonic acid gas, and we believe that it had a very important effect. The gas collected from all the pipes through the different stoppings from time to time would not support combustion, and the temperature within the stoppings continued very moderate. It may be interesting to state here that, in analyzing the gases within the stoppings, we found that a mixture of 5 per cent, of carbonic acid with 25 per cent, of atmospheric air, and 70 per cent, of carburetted hydrogen extinguished flame instantaneously. On adding more air to the mixture, and applying a match, it would not explode ; but when pure oxygen was added, and a match applied, the mixture exploded gently. Further, when this gas was deprived of the carbonic acid by means of caustic soda, and a match applied, it would burn when issuing into the open air.

" The pits were sealed up from February to the end of May, a period of four months. The downcast shaft was re-entered at the beginning of July, and we commenced to draw coal again about the end of August, while we have now reached nearly our usual 'output.' No change whatever has appeared at any of the stoppings, all of which are quite cool ; and the temperature within that in the main level is only about 70° Fahrenheit, so that there is every reason to believe that all is quiescent in and about ' the region of the fire.' "

518 Mining Engineeeing.

Chapter Xiii.

Suefaoe Wokks.

The surface works of a colliery are important both in character and in magnitude. Upon their suitability to the particular circumstances of the case depends in a great measure the successful prosecution of the underground workings. When the coal has been raised to bank, it must be quickly disposed of to make room for the next load waiting at the bottom of the shaft, and provision must be made whereby all the requirements below ground may be promptly supplied. The design and the disposition of the surface works will, therefore, demand the careful consideration of the engineer, who will plan them in accordance with the magnitude which it is intended the underground workings shall assume. In opening up a new colliery, the laying out of the pit bank and the erection of the surface buildings will be carried on simultaneously with the preliminary operations below ground, in order that the requirements of the workings may be met as soon as they are sufficiently developed to allow the output to be commenced.

The pit-head gear constitutes a portion of the surface erections, and is one that demands careful attention. This portion has, however, been fully treated of in a former chapter. But in connection with the pulley frames there are other erections, which either form a portion of the frames themselves, or are joined on to them. These erections are the floors and staging by which the pit mouth is reached, and upon which the coal, as it is landed, is run out, weighed, and tipped. This staging is at such a height from the general level of the ground that an ordinary railway truck can be run underneath to receive the coal tipped from the tubs in which it is brought to surface. It is not often however, that the coal is tipped directly into the trucks or waggons ; usually it is shot out upon a system of screens, by means of which the various sizes are separated. In such a case, a waggon is placed under each screen, and these waggons are run out and assorted as they are filled. But before the tubs are tipped, they have to be weighed. The operation of weighing is effected by running the tubs on to a weighing machine, which, for convenience, may be placed between the pit mouth and the points from which the tubs are tipped over the screens. It is of the utmost importance, where the output is large, to lay out the platform around the shaft mouth in such a way as to facilitate all of these operations. After being weighed, the tubs are run out to the tipping points, where they are made to pass on to the tipping or " teeming " cradles, which are wrought-iron cages mounted on trunnions ; these hold the tubs while their contents are being tipped over upon the screens. It is easy to see that all of these arrangements admit of endless modifications. In England, the pit-head gear usually stands out in the open air ; the staging around the pit mouth is sometimes left exposed, and sometimes covered in by a light wooden roofing to protect the men at work from the weather ;

Sueface Woeks. 519

but as the sides are left open the protection is only partial. Upon the continent, and especially in France and in Belgium, the whole of the head-gear and the staging is enclosed, so that the men may work in comfort during bad weather. Some of these erections possess considerable architectural merits, and constitute a pleasing feature of the colliery districts. They form a striking contrast to the bare structures to which we are accustomed in this country.

The engine house constitutes one of the most important of the surface buildings. On the Continent, it is included under the same roof as the head-gear, and the pit-mouth platform, the former of which is made to occupy a central tower or dome. But in England, the engine house forms a separate building. The position of this building must be selected with reference to convenience, having regard to the operations to be carried on at surface. Its distance from the shaft has already been incidentally treated of in the chapter devoted to winding. It should be sulEciently large to allow all the operations to be carried on there to be executed with facility ; it should be well lighted, that the engineman may see distinctly every part of his engine, and the signals from the shaft ; and it should extend sufficiently far to enclose the winding drums. Besides the winding engine house, there will be required an erection for the pumping engine, and several lesser buildings as workshops and offices. All of these must be designed in strict accordance with their use, and disposed, relatively to one another, in the most convenient manner.

In cases where coal washing is practised, suitable machinery, with the necessary erections, will be required. At many large collieries, the machinery for washing is of a very important character. These structures will constitute a portion of the surface works that will require careful attention in their design, their construction, and their position. When a colliery is so situate that its produce may be conveyed away by water carriage, the surface works will include a wharf, and the means of discharging the coal into the vessels lying alongside. At many of the north of England collieries, the means provided for discharging the coal into vessels form a very important portion of the surface works.

Other structures that may have to be provided are coke ovens. Where the coal is of a quality that renders it suitable for metallurgical operations, a large proportion of it will be converted into coke for use in the blast furnace. This is notably the case in the Durham district. But coking may be required in any locality, for steam and other purposes, and it affords a means of utilizing the small coal made in working. Some varieties of coal are of a very tender character, and it may become a commercial necessity to render it saleable by converting it into coke. In such a case, ovens will have to be erected, and these will require to be disposed in a convenient manner and in favourable positions relatively to the pit mouth, and the points from which the produce is conveyed away.

Besides the erections described, the surface works will in all cases include a system of tramways for conveying the produce from one point to another. In some cases, this system will be an extensive one, especially when coking is carried on largely. The surface tramways are laid with heavier rails than the underground ; but otherwise they are the same in character. The remarks given in the chapter on Haulage, apply therefore to these roads. They should be laid out, or rather the points which they serve should be selected, so as to utilize as much as possible the force of gravity. Frequently, at large collieries, small hauling engines are erected at surface to work these tramways.

Among the surface works of a mine, might with propriety be included the dwelling houses of the miners, which it is not unfrequently necessary for the mine owners to erect. There is a social question attached to this matter which colliery proprietors would do well to consider. Hitherto but

520 Mining Engineeeing.

little has been done in this country. The dwellings of the mining population are generally of a wretched character. In the Principality, and in some parts of Scotland, this is notably the case. The lead has, in this matter, been taken by Continental colliery proprietors, foremost amongst which ought to be mentioned the large companies owning the Blanzy and the Anzin mines in France. During the last thirty-five years, the former have founded a town and several populous villages. The system followed by them consists in purchasing an extensive tract of land adjoining their collieries, upon which they erect suitable miners' houses as they are required. The houses are each in two separate tenements, consisting of two rooms on the ground floor, with garrets above, and a cellar beneath. Attached to each, is a garden of 100 square yards, in which is a pigstye. These houses are let at a moderate rental. One part of the estate is laid out in building plots, and upon these, any miner in the employ of the company can build a dwelling house for himself ; the company advance the money for the building, and the miner pays it back as rent. No interest upon this money is claimed so long as the miner remains in the service of the company. A somewhat similar system has been adopted by the Anzin Company. Their miners' houses, of which they possess about 1500, are of two stories, the sleeping room being over the living room. Whatever may be said against such a system as that adopted by these great coal companies, it at least possesses the unquestionable merit of ensuring healthy and sightly dwellings for the mining population.

The surface works of a colliery, which we have merely mentioned, demand a full consideration from the mining engineer. A detailed description of them, however, would exceed the limits of a single chapter : such a description of these works, and of the machinery used in mining, it is proposed to give in a separate form as a sequel to the present work.

Management And Accounts. 521

Chapter Xiv.

Management And Accounts.

Though the duties of management and of accounts do not fall properly within the category of those incumbent upon the mining engineer, yet it is required of him that he should be familiar with them. It is therefore desirable to point out briefly those duties to which his attention will be chiefly directed.

The practice of underground surveying has passed almost completely out of the hands of the mining engineer, into those of the mining " surveyor," for whose use many valuable special treatises have been written. The subject does not, therefore, present itself for consideration in the present work. But though surveying forms no part of the " practice " of the engineer, he is required to be acquainted with its principles, and to be able to apply them when occasion demands it. For this reason, the first years of his pupillage are largely devoted to the study of the subject under the guidance of a surveyor. The practice of a mining engineer includes, however, a good deal of drawing office work, and a constant study of underground plans ; and it is obvious that though he may depute to another the surveying and plotting of existing workings, designs of workings not yet opened out must be drawn by his own hand. The proper carrying out of underground surveys is a matter of vital importance in coal mining. The " plan " should at all times show the actual state of the workings, for the safe and economical preservation of which it is an indispensable guide. The work of surveying may, indeed, be said to enter largely into the operations of mining, and to effect, in no small degree, the cost of those operations. It is, therefore, incumbent upon the engineer to see that this work be efficiently performed.

In the work of accounts, the mining engineer will have to take an important part. It devolves upon him to make the labour of the miners remunerative. Profit is the object aimed at, and he is required to make the profit as large as possible, consistently with the well-being of the men employed, and with the future extension of the workings. The success of methods and systems is measured by the economical results, and their retention or abandonment determined accordingly. These results, however, are to be learned only from the cost sheets, by comparing them with the receipts for the produce. The work of exploration, too, must be carried on simultaneously with that of extraction, but its extent will be limited by considerations of present profit and future prospects. Thus the balance-sheets will demand the careful and constant study of the engineer, who, while he exercises a strict supervision over the expenditure of labour and of materials, will do well to require that the records of such expenditure should be kept accurately and in minute detail. In this matter, he will be brought into immediate communication with the " office," with the duties of which he should be familiar.

522 Mining Engineeeing.

The duties of an engineer who has charge of a colliery are numerous, various in nature, and important in character. As the director of all the operations, he is held responsible for all results. Upon his skill and care depend, not merely the prosperity of the undertaking commercially considered, but also the health and the lives of those employed. He determines what work shall be proceeded with, the form and the dimensions an excavation shall possess, the method and means by which it shall be executed, and the number of men to be occupied on it. He has to control the use of material ; to see that everything be done to secure the safety of the ways and the working places ; to ascertain the state of the ventilation in every part ; to require that due precautions be taken against the occurrence of accidents ; to remedy an accident which has occurred ; to exercise a constant supervision over the winding and the pumping machinery ; and to regulate the conduct of the surface operations so that they may not impede the performance of those which are carried on below ground. These and numerous other duties constantly claim his presence and his attention, and render his position one of heavy responsibility. As, however, it is impossible for him to discharge all these duties directly, his authority has to be deputed to others, and transmitted through the several grades of manager, overman, and deputies. This state of things necessitates the establishment of clear regulations, and the maintenance of strict discipline. Upon these two points, the engineer, as the responsible head, must direct special attention. The duties of all under his direction should be clearly defined, and the proper performance of these duties rigidly exacted. Without discipline in a coal mine, disaster will, sooner or later, inevitably come, and hence he who feels the weight of his responsibility will not hesitate to deal severely in all cases of an infraction of the rules laid down. A recent Act of Parliament has made both the engineer and the manager amenable to the law for any breach by their subordinates, of the general rules which have received the sanction of the Legislature. The matters requiring attention are clearly indicated in the following General Rules and Regulations for the Management of Coal Mines, contained in the Act referred to :

Geneeal Eules.

1. An adequate amount of ventilation shall be constantly produced in every mine, to dilute and render harmless noxious gases to such an extent that the working places of the shafts, levels, stables, and workings of such mine, and the travelling roads to and from such working places, shall be in a fit state for working and passing therein.

2 and 3. During the twelve months following the discovery of inflammable gas in the mine, a competent person shall, before the time for commencing work in any part, inspect with a safety lamp that part of the mine and the roadways leading thereto ; the inspection shall be made once in every twenty-four hours, if one shift is employed, and once in every twelve hours, if two shifts are employed ; and a report of tlie state of the ventilation shall be recorded in a book kept at the mine for that purpose, and signed by the person making the same. In a mine in which inflammable gas has not been discovered during the preceding twelve months, the inspection shall be made once in every twenty-four hours.

4. All entrances to any place not in actual course of working and extension, shall be properly fenced across the whole width of such entrance, so as to prevent persons inadvertently entering the same.

5. A station or stations shall be appointed at the entrance to the mine, or to different parts of the mine, as the case may require, and a workman shall not pass beyond any such station until the mine or part of the mine beyond the same has been inspected and stated to be safe.

6. Whenever the mine or any part thereof is discovered to be dangerous by reason of gases prevailing therein, or of any other cause, every workman shall be withdrawn from the mine or part thereof, and they shall not be readmitted until the mine or part thereof has been inspected by a competent person, and reported by him to be safe.

7. In every working approaching any place where there is likely to bo an accumulation of explosive gas, no lamp or li"ht other than a locked safety lamp shall be used, and whenever safety lamps are required a competent person shall examine every safety lamp immediately before it is taken into the workings for use, and ascertain if it be secm'e and securely locked and in

Management And Accounts. 523

the said part of a mine a person shall not, unless he is appointed for the purpose, have in his possession any key or contrivance for opening the lock of any such safety lamp, or any lucifer match or apparatus of any kind for striking a light.

8. Gunpowder shall not he stored in the mine ; and it shall not be taken into the mine except in a case or canister containing not more than 4 lb. ; and a workman shall not have in use at any one time in any one place more than one of Buch cases. Iron or steel tools shall not be used for loading a charge of gunpowder, and a charge of powder which has missed fire shall not be unrammed. During three months after inflammable gas has been found in the mine, gunpowder shall be taken into the mine only in cartridges, and shall be used only after the places have been examined by a competent person, and found to be safe. If, however, inflammable gas be present, powder may be used in stone drifts, and in shafts where the return air does not pass through any place in actual course of working ; and also in the mine during the absence of those ordinarily employed therein.

9. Where a place is likely to contain a dangerous accumulation of water the working approaching such place shall not exceed 8 feet in width, and there shall be constantly kept at a sufficient distance, not being less than 5 yards in advance, at least one bore-hole near the centre of the working, and sufficient flank bore-holes on each side.

10. Every underground plane on which persons travel, which is self-acting or worked by an engine, windlass, or gin, shall be provided (if exceeding 30 yards in length) with some proper means of signalling between the stopping places and the ends of the plane, and shall be provided in every case, at intervals of not more than 20 yards, with sufficient man-holes for places of refuge.

11. Every road on which persons travel underground where the load is drawn by a horse or other animal shall be provided, at intervals of not more than 50 yards, with sufficient man-holes, or with a space for a place of refuge, which space shall be of sufficient length, and of at least 3 feet in width between the waggons running on the tramroad and the side of such road.

12. Every man-hole and space for a place of refuge shall be constantly kept clear, and no person shall place anything in a man-hole or such space so as to prevent access thereto.

13. The top of every shaft which for the time being is out of use, or used only as an air shaft, shall be securely fenced.

14. The top and all entrances between the top and bottom of every working or pumping shaft shall be properly fenced, but this shall not be taken to forbid the temporary removal of the fence for the purpose of repairs or other operations, if proper precautions are used..

15. Where the natural strata are not safe, every working or pumping shaft shall be securely cased, lined, or otherwise made secure.

16. The roof and sides of every travelling road and working place shall be made secure, and a person shall not, unless appointed for the purpose of exploring or repairing, travel or work in any such travelling road or working place which is not BO made secure.

19. Every working shaft used for the purpose of drawing minerals or for the lowering or raising of persons shall, if exceeding 50 yards in depth, be provided with guides and some proper means of communicating distinct and definite signals between the bottom of the shaft and the surface.

20. A sufficient cover overhead shall be used when lowering or raising persons in every working shaft, except where it is worked by a windlass, or where the person is employed about the pump or some work of repair in the shaft, or where a written exemption is given by the inspector of the district.

21. A single linked chain shall not be used for lowering or raising persons in any working shaft or plane except for the short coupling chain attached to the cage or load.

22. There shall be on the drum of every machine used for lowering or raising persons such flanges or horns, and also if the drum is conical, such other appliances, as may be sufficient to prevent the rope from slipping.

23. There shall be attached to every machine worked by steam, water, or mechanical power and used for lowering or raising persons, an adequate brake, and also a proper indicator (in addition to any mark on the rope) which shows to the person who works the machine the position of the cage or load in the shaft.

24. Every fly-wheel and all exposed and dangerous parts of the machinery used in or about the mine shall be and be kept securely fenced.

25. Every steam boiler shall be provided with a proper steam gauge and water gauge, to show respectively the pressure of steam and height of water in the boiler, and with a proper safety valve.

26. After dangerous gas has been found in any mine, a barometer and thermometer shall be placed above ground in a conspicuous position near the entrance to the mine.

29. A competent person appointed for the purpose shall, once at least in every twenty-four hours, examine the state of the external parts of the machinery, and the state of the head gear, working places, levels, planes, ropes, chains, and other works of the mine when in actual use, and once at least in every week shall examine the state of the shafts by which persons ascend or descend and the guides or conductors therein, and shall make a true report of the result of such examination, and such report shall be recorded in a book to be kept at the mine for the purpose, and shall be signed by the person who made the same.

Mining Engineeeino.

The following regulations are also provided : —

No boy under the age of ten years, and no woman or girl of any age may be employed in any mine below ground. Between the ages of ten and sixteen, boys may be employed only under certain restrictions, which provides for their attendance at school.

Steam-engines may not be placed in the charge of any person under eighteen years of age.

More than twenty persons may not be employed in a mine access, to which can be had through one shaft only.

Every mine must be under the control and daily supervision of a manager, who shall be the holder of a certificate as a guarantee of his fitness for the post.

The owner, agent, or manager is required every year to send to the inspector of the district a return specifying the quantity of coal raised during the year, and the number of persons employed. He is also required to give notice to the inspector of any accident that may have happened in the mine within twenty-four hours of its occurrence.

Notice is required to be given to the inspector of the commencement of a new working, and of the abandonmeTit of an old working.

The top of the shaft, or any other entrance to an abandoned mine, must be securely fenced.

A correct plan of an abandoned mine must be sent to the Secretary of State.

An accurate plan of the workings of a mine must be kept at the ofGce of the mine ; and this plan must show the workings up to at least six months previously. The plan must be produced to an inspector who may require the progress of the workings, up to the time of such production, to be marked upon it.

Special rules for the conduct and guidance of the persons employed must be established in every mine. These rules must be approved by the Secretary of State, and signed by the inspector of the district. An exact copy of these special rules, and an abstract of those given above, are required to be kept posted in some conspicuous place at or near the mine, and a printed copy of each is required to be supplied gratis by the owners to each person employed in or about the mine.

Any person defacing posted notices is liable to be fined forty shillings.

The following form of Annual Eeturn is furnished to mine owners :

Annual Eetuen Feom Ownee Oe Agent.

Name of Colliery

Name of Pit Name of Seam

Year ending the_

Average Number of Persons employed

Mode of Ventilation.

Furnace or Pan, with Description.

Diameter and Depth of downcast and upcast Shaft.

Number of Splits and Quantity.

Average Length of

Sectional

Area of

Air-ways.

Average

Total

Quantity of

daily.

Downcast.

Upcast.

Air-ways.

fresh air m cubic feet per minute.

Above Ground.

Under Ground.

Diameter in feet.

Depth in feet.

Diameter in feet.

Depth in feet.

Quantity in cubic feet per minute.

The matters claiming the attention of the manager and of the engineer in charge, are clearly set forth in the following Special Rules, drawn up to suit the requirement of the coal workings in Lanarkshire and adopted in that district. These are given as an example of a set of the Special Rules required to be made ; but they are besides worthy of attentive study as constituting a succinct and clear statement of the duties of the mine manager.

Management And Accounts. 525

Special Eules.

For the conduct and guidance of the persons acting in the management of this mine, or employed in or about the same to prevent dangerous accidents, and to provide for the safety and proper discipline of the persons employed in or about the mine, in terms of section 52 of the Statute 35 & 36 Vict. cap. 76.

In these Special Rules, the word " agent " means a person having, on behalf of the owner, care and direction of any mine, or of any part thereof, and superior to the manager ; the word " manager '' means the certificated manager under the Act, and includes the plural as well as singular ; the word " overman " means a person employed and acting under the manager, and includes plural as well as singular ; the word " miners " means every person employed in the mine, in the cutting or excavation or removal of coal, ironstone, shale, fireclay, or other minerals, metals, or materials.

Agent.

1. The agent, where one is appointed separate from the owner, shall have, as representing the owner, the care and direction of the mines committed to his charge ; and it shall be his duty to take a general supervision thereof ; to see that the manager attends to and performs his duties ; and generally to act as the owner's representative, and see that the mines are conducted in conformity with the requirements of the Act.

N.B. — The agent is furnished, for Ms guidance, with printed copies (1) of (lie Act -itself, (2) of the Statutory Abstract thereof, and (8) of the Special Rules.

Manager.

2. Generally, the mine (or division of the same, when divided in terms of the statute) to which the manager has been appointed, shall be under the control and daily supervision of the manager, whose duty it shall be to carry out, and see carried out, the various provisions of the Act, so far as incumbent on him, or on those acting under his control and directions, and to see that sufficient materials and appliances are always provided for the proper carrying out of all necessary operations. — Copies of the Statute itself, of the Abstract thereof, and of these Special Rules, are supplied to each manager.

Ovbbman.

3. Subject to the control and supervision of the manager, the whole operative details shall be imder the care and charge of the overman. The overman shall see that the workman of every class, in their several departments, discharge their duties ; and shall receive and attend to all reports made to him, as to the state of repair of the air-courses, machinery, mid-wall trapdoors, roads, cubes, and working places. He shall cause remedies to be provided where needed ; and shall see the General and Special Eules faithfully and vigorously enforced ; and he shall have power to hire and discharge workmen.

4. He shall have under his immediate and special charge, the shaft, slides, pumps, and relative fittings, all of which he shall keep safe and efficient.

5. He shall attend to the ventilation, in terms of General Eule, No. 1 ; and to the observance of the other General Eules, so far as these, from their nature, can be observed by himself, or fail to be observed by others under his charge.

6. He shall perform the special duties, as to the examination of machinery and others, set forth in General Eule, No. 29.

7. He shall see that a plentiful supply of timber, for props and other purposes, required by the workmen to carry on their operations with safety to themselves, is always ready ; and shall cause the same to be cut in proper lengths, and laid down in the working places as provided for in Eule 28.

8. He shall, without delay, report to the manager, or agent, or owner, any matter or thing coming under his notice, necessary to be observed or carried out, with a view to compliance with the General or Special Eules, which he cannot perform.

N.B. Copies of the Statute itself, of the Abstract thereof, and of these Special Rules, are supplied to each overman.

Pit-headman (ok Banksman).

9. The pit-headman, during the several shifts, if more than one, shall, subject to the control and supervision of the manager, have charge of the workmen employed about the pit-head, and each workman shall act under his directions. He shall observe, that, at all times, there is sent down the pit, a stock of timber for props and other necessary purposes, for the use of the miners and other workmen, and report to the manager, if at any time he observes, or has it reported to him, that there is a deficiency of such timber or other articles. He shall superintend and direct the safe removal from the cage of all loaded hutches arriving at the pit-head, and see to the safe replacing of the return hutches on the cage. He shall be in attendance in the morning, or at such other time of the day as the miners' shift commences, and shall see that no person is allowed to go upon the cage until the engineman has ascertained and reported the safety of so doing, in terms of Special Eule 16. He shall regulate the number of men descending at a time, taking care that not more than four to a single cage, or eight to a double cage, shall ride on such cages respectively, and no one along with a hutch.

526 Mining Engineeeing.

10. The pit-lieadman (in absence of some other person specially appointed for the purpose, and independently of the manager or overman) shall, once at least in every twenty-four hours, carefully inspect the ropes, chains, slides, pit-head frame, and other apparatus used for the lowering and raising of the cages, so far as exposed to his observation ; and if he discover, or be informed of any defect or weakness likely to jDroduce danger, he shall stop the raising or lowering of men or materials until puch defect or weakness be remedied. He shall also be careful to prevent the fall of any stone, coal, or other substance into the shaft from the surface, and shall communicate to the manager or overman any necessity for a skilled person being employed to rectify any defect in the shaft, ropes, chains, pit-head frame, and other apparatus.

11. It shall be his duty to see that the shaft is securely fenced in at the close of the shift.

12. In the absence of a " weigher," specially appointed for the purpose, it shall be the duty of the pit-headman to act as weigher, and to see that all tubs or hutches are properly filled with the " mineral contracted to be gotten," and that the proper deductions are made, in respect of stones or materials, other than the minerals contracted to be gotten, or in respect of tubs, baskets, or hutches improperly filled — in terms of section 17 of the Act.

Weigher.

13. Where a person is specially appointed as weigher, it shall be his duty to attend to the matters embraced in the immediately preceding rule.

Enginbman.

14. The engineman at the pit-head shall, during the hours of his shift, remain continually in charge of, and so near his engine, as at all times to have it completely and entirely under his control. He shall be careful that the engines and boilers are always in good working condition, and that the pumps and whole machinery and gearing connected with his engine are ia a safe and effective state, and any fly-wheel, or exposed and dangerous parts of the machinery, securely fenced. He shall have charge of the furnacemen, where these are employed, and be responsible for the regularity with which steam is kept up, and for the proper state of the boilers. He shall have steam raised, and the engine and machinery in working order, in time to allow the firemen, roadsmen, overman, or manager to descend the pit to examine the condition of the mine, before the miners' or other workmen's shift shall commence.

15. He shall thoroughly acquaint himself with, and shall watch and attend to the various signals made for raising or lowering the cage, whether laden with men or materials, or when empty — shall carefully and exactly set down the cage at the landing places — shall observe the indicator attached to the machinery, showing the position of the load in the shaft, and manage the brake connected with the engine. The engineman shall further attend to and see that any steam and water gauges, and safety valve attached to the steam-boiler are kept in good order.

16. Before allowing the descent of workmen into the mine on any morning, the engineman shall be bound to run each cage, at least once, from the pit-head to the pit-bottom, to ascertain whether everything is right, and if any defect shall be discovered, he shall stop the engine, and shall not, on any pretext, allow the descent of workmen until the matter has been reported to the manager, overman, or person in charge, who shall direct what remedy shall be necessary. The engineman shall not allow any workman to descend the pit until the fireman shall have reported the safety of doing so.

17. He is prohibited from allowing any person whatever to interfere with the engine, in any way, while being wrought, *tid from allowing or permitting any person other than those authorized by the owner, agent, manager, or overman, to enter or remain in the engine-house.

18. He shall attend to all signals, and make the necessary return signals, which shall be as follows :

19. The bottomer, or person acting in his absence, shall make the following signals from the bottom, being those appointed in this mine for guiding the ascent of the cage, and

20. He shall strike or ring the signal bell once, for the ascent of the cage, whether loaded or empty.

21. The engineman shall make a counter-signal, if there be any reason why the cage should not ascend, and in case the signal mentioned in Special Eule 20 be given at any time when the cage is in motion, the engineman shall immediately stop the engine.

22. The bottomer shall strike or ring the signal bell thrice, in rapid succession, intimating that men are about to ascend when the engineman shall signal that all is ready ; thereupon the bottomer shall make the usual ascent signal of one stroke of the bell, whereupon the cage shall be raised.

23. The bottomer shall strike or ring the bell twice, when he desires the engine to be reversed, and the ascending cage returned to the pit-bottom, and to remain there.

N.B. — Copies of the Abstract of the Act, and of the Sjjecial Bules, are furnished to the engineman.

Fornaoemen.

24. Subject to the control of the manager or overman, the furnaceman shall act under, and obey the directions of the engineman.

Management And Accounts. 527

Eoadsmen.

25. The roadsmen, in their different divisions and shifts, if more than one, shall, at least daily, make careful inspection of the whole roadways and working places, from the pit-bottom throughout the mine, and shall keep the same free from all obstructions, and of the fixed height and width, necessary for proper passage, and for ventilation. They shall repair and remedy all damages and defects in the roads of the mine, and shall examine and put, and keep in proper condition, all trapdoors, and see the regulations enforced that the same are kept closed ; and wherever practicable, shall endeavour to make and keep such trap-doors self-acting. They shall make and place sufficient trap-doors wherever the progress of the operations of the mine shall render these necessary.

26. The roadsmen shall also lay rails in the roads where requisite, and in the absence of the manager or overman, they shall receive all reports or communications from the miners and other workmen, as to falls and defects in the roads, roofs, and buildings, and shall proceed to, and repair or remedy, the falls and defects.

27. They shall stop the passage of men and materials, through or under defective roads, roofs, or places, until the necessary repairs shall have been executed. They shall receive information concerning any interruption in the ventilation, or of any other cause of danger, and communicate with the manager or overman immediately, and shall aid and assist in the rectification and remedy of the same, and shall, when so employed, be permitted to use only safety lamps, in mines where inflammable gas has been found within the preceding twelve months. All lighted or combustible substances are forbidden to bo used in the course of such operations.

28. It shall be the special duty of the roadsmen, in their different divisions, if more than one, to observe that an adequate supply of timber for props and other necessary purposes, is always ready at the place where the miners are at work, for the use of the miners, in supporting the roofs and sides of their working places, and to report to the manager or overman if they shall observe any want of such timber. For the purpose of carrying out this rule, roadsmen are empowered to call upon drawers, putters, and drivers, whether employed by the owner or miner, to convey such necessary timber from the pit-bottom, or other place of general delivery, to the working places in connection with which they are employed.

29. The roadsman shall report to the manager or overman any instances of neglect on the part of miners, in not carrying forward their faces or walls, in accordance with the plan pursued in working the mine. They shall also examine and report to the manager or overman instances of neglect, and acts of carelessness on the part of the miners or brushers, in failing to remove, or in not removing with proper caution, the strata necessary to be removed to form roads, or in not carrying forward the brushing with sufficient regularity, and of the proper dimensions, or in leaving the brushing with loose or hanging stones in and about the strata " brushed."

30. As removing falls from the roofs of roads and air-courses, and repairing defects therein, are within the roadsmen's duties, and as they are charged with the maintenance of all roads and passages in the mine, they are enjoined to proceed with the greatest caution — both for their own safety and the successful execution of their duties. In these operations they must therefore be careful, and are required to prevent all other workmen coming near any di iective places, or interfering with them when at work. They are required to undertake no repairs of unusual magnitude or danger, without sufficient assistance, and until provided with every necessary material, which will be supplied on application to the manager or overman.

31. Without prejudice to the foregoing directions, it will be the special duty of the roadsmen to observe the matters embraced in the following General Eules :

(1.) Upon discovering that any part of the mine is dangerous, in terms of General Eule, No. 6, to withdraw therefrom any

workmen therein employed (which workmen shall be subject to the roadsman's orders, to that effect), and report the

state of matters to the manager, overman, or fireman. (2.) To report to the manager or overman, where they observe any violation of General Eule, No. 8, as to use of

gunpowder. (3.) To see that every man-hole, or place of refuge, is kept clear, in terms of General Eule, No. 12. (4.) To examine the roof and sides of every travelling road at least daily, and see that the roofs and sides are safe, in

terms of General Eule, No. 16. (5.) To report any damage to any fence, casing, lining, means of signalling, or otherwise, that may be observed, in terms

of General Eule, No. 27. (32.) Generally, the roadsmen shall observe and fulfil the whole duties falling within their departments, under the Statute. They are furnisJied with copies of the Statutory Abstract, and of these Special Bules.

Firemen.

33. If inflammable gas has been found in the mine, within the preceding twelve months— which it shall be the duty of the manager to ascertain and intimate to the fireman — then it shall be the duty of such fireman, or firemen, if more than one, in their respective divisions or shifts, to perform the duties of examining and inspecting, with a safety lamp, the mine and roadways, and making the report thereon, all in terms of General Eule, No. 2,

528 Mining Engineeeing.

34. If inflammable gas has not been found in the mine within the preceding twelve months — which it shall be the duty of the manager to ascertain and intimate to the fireman — then it shall be the duty of the fireman, or firemen, if more than one, in their respective departments, to inspect the mine and roadways, and make a report in terms of General Eule, No. 3.

35. In making the examinations provided for by the foregoing rules, the fireman shall mark with chalk the day of the month upon the face of each working place — as 1, 5, 10, 25, or other numbers, as the case may be. He shall be careful to ascertain that every part of the mine and roadways so to be examined, are free from fire-damp, choke-damp, and other impurities, and are safe for workmen to enter and work therein ; and in case fire-damp or other impure air shall be discovered in any working place, road, or level, the firemanshall, in the first instance, thoroughly clear the same of such impurity — if that can be done easily —and shall thereupon report to the miners and other workmen, that the same are safe ; but if the impurity cannot be readily or at once cleared out, the miners and workmen shall not be permitted to enter any such working places, roads, or levels, until the impure air shall have been, by further appliances, entirely dispelled. He shall prevent miners, or other workmen entering the roads or working places until a report shall have been made that they are safe. If no fire-damp, choke-damp, or other impurity shall be discovered, or suspected to remain after such inspection, the fireman shall make report to the miners and workmen, and allow them to proceed to work, and shall thereupon, without delay, enter such report in the book kept for the purpose.

36. If the fireman shall encounter falls from the roof, in any of the roads which he requires to traverse, or in working places imder the care of the miners, he shall not proceed farther in the direction of such falls, so as to pass under the broken roof, but shall endeavour cautiously, to ascertain if there be any accumulation of fire-damp or other impurity in, about, or beyond the falls, so that the safest way of clearing the same may be learned, and shall proceed elsewhere through the mine to examine the unobstructed parts thereof, and to complete his inspection ; whereupon the fireman shall report to the manager or overman the state of the falls, and whether free from impurity, to the end the necessary directions may be given for having the same cleared away, and the roof secured ; and until this shall be done, no miner or other workman shall be at liberty to proceed near, or be under the broken roof unless employed in remedying the same.

37. In case, from any cause, the operations of the mine shall have been discontinued for an unusual length of time, and thereafter resumed, no workman shall be allowed to descend the shaft until the manager, overman, or fireman shall have first descended and reported on the state of the workings ; and in discharging this duty the manager, overman, or fireman must proceed with great caution, and shall not go farther into the workings than he, from his own experience, shall deem safe ; and in case there are reasonable grounds for apprehending the presence of impure air, he shall return to the pit-head, and remain there until precautionary measures shall have been applied to restore the proper ventilation of the mine.

38. Without prejudice to the foregoing rules, it shall also be the duty of the fireman to fence or cause to be fenced all entrances, in terms of General Eule, No. 4 ; as also, in going his rounds, to observe and report to the manager or overman upon the following matters, embraced in the General Eules : —

(1.) Any deficiency in the amount of ventilation, as provided for in terms of General Eule, No. 1.

(2.) Any attempt on the part of workmen to violate General Eule, No. 5, as to going beyond the appointed station.

(3.) Any violation of terms of General Eule, No. 8, as to use of gunpowder.

(4.) Any failure to keep clear man-holes, in terms of General Eule, No. 12.

(5.) Any failure to make secure the roof and sides of travelling roads and working places and General Eule No. 15.

(6.) Any violation of General Eule, No. 27, as to the damaging of fences, signals, &c.

39. It shall be the duty of the fireman, when he discovers that any part of the mine is dangerous from the presence of noxious gases, to cause the workmen to withdraw from the mine, or the part thereof so found dangerous, in terms of General Eule, No. 6, and all workmen shall be subject to his orders in respect of this matter; and he shall thereupon, as the " competent person " appointed for the purpose, inspect the mine, or such parts thereof as are dangerous, in manner and to the effect provided for in the said General Eule, and make a report as therein provided for. Also, he shall fit up bratticing where required, of suitable height and length, so that air may be at all times conveyed from the principal air-courses for the use of the workmen, and see that all entrances are properly fenced, in terms of General Eule, No. 4.

40. It shall be his duty to see that the miners are attending to the security of the roofs and sides of the working places and for that purpose to visit each working place at least three times each day at proper intervals ; and in case of finding that any miner is failing so to secure his working place, by propping the same, or otherwise, to point out to such miner any such failureand should such miner refuse or fail to perform such repairs as may be necessary to render the place secure, to require him and his assistants to remove from such working place. Besides the periodical examinations already provided for it shall be the duty of the fireman, when applied to by any miner, stating that his working place is, in the matter of propping, in a dangerous condition, which requires the intervention of a skilled person, to proceed to such working place, examine the same and cause such remedies to be applied as shall appear to be necessary for the safety of the place, the miner himself assisting in any necessary operation.

41. It shall likewise be the duty of the fireman or firemen in their diflerent departments (unless some other person shall

Management And Accounts. 529

be specially appointed), where gunpowder is being used, to act as the "competent person," in terms of General Eule, No. 8 (/) and to ascertain the state of " inflammable gas," in terms of the said General Eule, and to prevent gunpowder being used otherwise than as there provided for.

N.B. — Copies of the Abstract of the Act, and of these Special Bules, are furnished to each fireman.

BOTTOMER AND SiGNALMAN.

42. The bottomer shall attend during the working shifts in the mine, to regulate the number of men who shall ascend on the cage at a time — to keep order among the drawers arriving with loaded hutches at the pit-bottom — to see that the loaded hutches are carefully placed on the cage, and to secure them — to make the appointed signals necessary for regulating the ascent of men and materials — to examine and report to the manager on the state of the signal apparatus, and of the hutches used in the pit, and of the cages wrought in the shaft ; and also on the state of the slides or guide rods in which the cage moves.

43. He shall, along with the fireman, attend to and keep in proper order, the cube or rarefying furnace in the pit.

44. The bottomer shall attend to and answer the signals made by the engineman from the surface.

45. He shall not allow any miner, drawer, or other worker in the pit, to make signals while he, the bottomer, is on duty.

46. He shall not suffer more than four men at a time to ascend the shaft in a single cage, nor more than eight in any double cage ; he shall not allow any person to ascend along with a hutch whether empty or loaded ; and he is forbidden to signal the ascent, if more than the appointed number shall go on the cage, or if any worker shall attempt to ascend with a hutch.

47. In the unavoidable temporary absence of the bottomer, the roadsman, or some other qualified person, shall make the necessary signals from the pit-bottom, and receive and attend to the signals sent from the surface.

48. The bottomer, or such person acting in his absence, shall make the following signals, being those appointed in this mine for guiding the ascent of the cage :

(1.) He shall strike or ring the signal bell at the surface once for the ascent of the cage, whether loaded with minerals or

empty, and shall observe any counter-signal, in case of any reason why the cage should not ascend. (2.) He shall strike or ring the signal bell thrice, in rapid succession, when men are about to ascend ; and after a panse,

during which a signal shall be made from the surface that all is ready, he shall make the usual ascent signal of one

stroke of the bell, whereupon the cage shall be raised. (3.) He shall strike or ring the signal bell once, if he observes anything wrong while the cage is in motion ; and twice

when he desires the engine to be reversed, and the ascending cage returned to the pit-bottom, and to remain

there.

49. No deviation from these signals shall be permitted on any account. The ascending signals shall not be made until the cage with its load, whether of men or materials, are securely placed and everything be ready for the ascent.

50. The bottomer shall not leave his post at the pit-bottom until the whole workers of his shift shall have first safely ascended the shaft.

51. He shall prevent, or report to the manager or overman upon any neglect or violation of the General Eules, or Special Rules, coming under his observation ; for which purpose copies of the Abstract of the Act, and Special Bules themselves, are furnished to him.

Miners and other Workmen.

52. Such miners and other workmen are, and shall be, generally subject to the control and orders of the agent, where one has been appointed, and of the manager and overman ; but they shall also be subject to any directions which the roadsman, engineman, fireman, or bottomer may give, in their respective departments, for the purpose of preventing the workmen from infringing, or of causing them to comply with, any of the provisions of the Act, or of the General or Special Eules.

53. Such miners and other workmen shall not proceed into travelling roads or working places until it shall have been reported to them by the fireman or other person appointed for the purpose, that the travelling roads and working places are safe to be entered.

54. Until such report, or intimation of safety, be so made, no such miner or other workman shall pass beyond the station appointed ; and, if no other place or station has been appointed, they shall always understand that the pit-head is the station at which they are required to wait the necessary examination and report.

55. If while at work, or at other time, any miner or workman shall discover, or be informed of the existence of any obstruction in the ventilation, or stagnation, or impurity in the air of the mine, or the existence of any defect in the walls, roofs or in any other parts thereof, he shall be bound to give instant information of the circumstances to the manager, overman, roadsman, or fireman, so that these defects may be remedied, and danger therefrom averted.

56. Miners are expressly forbidden to go into, or improperly near any place throughout the whole mine, where danger is known or suspected to exist. They are forbidden to continue at any part of a face where a sudden outburst of fire-damp shall

3 Y

530 Mining Engineering.

happen, or where danger, from any cause whatever, shall apparently threaten, until the same shall have been examined and reported safe, or the impurity or other cause of danger removed.

57. The common but highly dangerous practice among miners, of testing the quantity of fire-damp escaping from a " blower," by igniting it with their lamps, is peremptorily prohibited.

58. Whether the operations shall be conducted by the " long wall " or " stoop and room " system, a sufficient number of suitable props being supplied at their working places, the same shall be set up by the miners in their working places, where the roof and sides require to be secured by them, in terms of General Eule 16. These props and any necessary sprags or gibs shall be set up at such times, in such number, and at such points, within the working limits, as shall, from time to time, be necessary.

59. But, besides being bound to prop and secure according to their own skUl and experience, miners are required to place props within their working places in such manner as the fireman, or other person authorized to that effect, shall deem necessary and shall direct, for the safety of the workmen and the mine.

60. When employed to return upon and remove stoops left in any seam, miners shall be bound to prop and secure the roof and strata around each stoop before commencing to cut or remove the same, and such places shall be deemed "working places" under these rules.

61. If, from accident or any other cause, miners are at any time unable to find a sufficient supply of prop-wood, at the place appointed, they are expressly forbidden to remain in their working places.

Deawees, Puttees, and Deivers.

62. Drawers, putters, and drivers shall not be permitted to approach, or to enter the roads or working places, until the miners shall have been allowed to proceed thither to work. They shall carefully convey their loaded hutches to the pit-bottom, or siding, or wheel, as the case may be : and when the hutches are brought to the pit-bottom, they shall not be pushed forward till the bottomer shall have taken charge of them. All drawers, putters, and drivers shall be subject to the orders of the roadsmen in carrying out Rule 28 as to the conveyance of timber to working places.

Bbtjshees and Eeddsmbn.

63. Brushers and reddsmen shall, in the formation of roads, remove from the strata as much thereof as shall make them of the height and breadth required for the purposes of the mine, and shall carefully build up the side walls, and properly remove or stow away surplus material. In detaching strata, and in the use of gunpowder for blasting, great caution (and attention to the General Eule, No. 8) must be observed, and every fragment of stone shattered or unloosed shall be taken down. If, in the course of their operations, brushers and reddsmen shall expose a lipe,'' or joint, in any of the strata, indicating the probability of a fall at that place, or if a " blower " shall be opened, or an accumulation of gaseous substances be encountered among metals, or if they shall observe any other cause of danger, they shall report the circumstance instantly to the manager, overman, or roadsman, and means shall be taken by the brushers and reddsmen, in the meantime, to secure the " lipe " ; but if the accumulation of impure air shall be so considerable as to render it at all hazardous to continue brushing or building further, until means shall have been taken to overcome and disperse the same, the brushers and reddsmen shall cease work, and shall be careful not to approach, with unprotected lamps, the places where danger exists, nor at all, unless accomplished by the fireman or roadsman.

64. In brushing and building drawing roads towards faces, brushers and reddsmen are required to make their brushing and building regular and continuous, keeping pace with the progress of the miners, so that the side buildings may be carried in, and the road formed, at a convenient distance back, simultaneously with the excavation of coal or other minerals.

Clerks and Others.

65. Every clerk, or other person, employed and instructed to keep any register of boys and memorandum of certificates, in terms of the Statute, shall be bound to make the necessary entries, so far as materials are furnished to him for that purpose, for the use of the owner, agent, or manager.

DooE Keeper.

66. Every person employed in keeping a trap-door, for the production or promotion of ventilation in the mine, shall, during his shift, remain continually at the post assigned him, and carefully observe the directions he receives from the manager, overman, roadsman, or fireman, as to the opening and shutting of such doors, either on the occasion of other workmen passing through the same or at the beginning or end of the shift.

Miscellaneous Eegulations.

67. The manager, fireman, or roadsman are authorized to examine safety lamps in terms of General Eule, No. 7, without prejudice to the appointment of any other competent person for that purpose ; and in this mine the word " workings," into

Management And Accounts. 531

which safety lamps may not be taken in terms of said General Eules, shall include all parts of the mine (below ground), from the pit-bottom inwards.

68. If, in proceeding to their working places, or in travelling along any formed road, or other part of the works, the maintenance of which, under these regulations, devolves on the owner, agent, or manager, miners, drawers, or other workmen shall meet with or see any fall from the roofs, or shall observe any dangerous place in the roofs, walls, or elsewhere in their progress, they shall not pass the same, but shall instantly report the occurrence to the manager or roadsman, or other person known to have the maintenance of such places under his charge; and miners, drawers, and other workmen- shall not return past the fall or dangerous place, until the same shall have been made secure, which it shall be imperative on the manager, overman, or other person having the charge, forthwith to do.

69. As a matter of common safety, miners, drawers, and all other workers, who shall observe, or who shall come to the knowledge of any damage to, or deficiency in, any road, roof, or air-course, or in any roof, permanent or temporary brattice, or in the shaft, buildings, cube, oi other appliance or work, devised for making, maintaining, and promoting the effective ventilation of the mine, shall be bound instantly to communicate such damage or deficiency to the manager, overman, roadsman, fireman, or other person in charge, so that the same may be forthwith repaired or rectified.

70. In like manner, every miner, drawer, and other workman, who shall observe or come to know of any defect or flaw in the cage, ropes, or chains, or in any part of the engine, machinery, and gearing, used in or about the mine, whereby the BufSciency thereof may be impaired, shall be bound forthwith to communicate the same, as above.

71. No miner, or other workman, shall be permitted to introduce into the mine any stranger or person employed by them on any pretence, without the consent of the owner, agent, or manager.

72. Every miner, or other person, who shall be the immediate employer of any boy or male young person, shall be bound to see that such boy or young person leaves the mine when his period has expired.

73. Miners, drawers, and all others who shall have occasion to pass through any trap-door, shaU thereupon closely shut the same, and shall on no account leave it open. On discontinuing work at the end of a shift, and especially where no work is to be done in the mine on the following day, care must be taken by every workman closely to shut all trap-doors, and thereby prevent the proper current of air necessary for ventilation from being diverted.

74. All workmen are expressly forbidden to throw into, deposit, or leave coals or other minerals, wood, stones, or rubbish, or materials of any kind, in any air-course or road, so as to interfere with, or hinder, the air passing into and through the mine.

75. All workmen are prohibited from entering or remaining in any place throughout the whole mine, where not absolutely required by duty to be at the time.

76. Miners and all others are prohibited from knowingly or wilfully defacing or removing marks which may be made in any part of the workings, for the guidance of the workmen in their operations. AH workers are forbidden to displace, injure, or damage in any way the stoops, props, hutches, rails, or any part of the machinery, gearing, and apparatus.

77. Meetings of miners and other workmen, in a body, within the workings, or in any of the roads or air-courses, or at the pit-head, are strictly prohibited.

78. Workmen ascending or descending the shaft shall not be allowed to leave the cage while it is in motion, nor until it shall have rested at the landing place.

79. No workman shall be permitted to enter, or to continue in the mine, while in a state of intoxication.

80. Wherever explosive gas is known to exist, and safety lamps are used, no person shall be allowed to smoke tobacco in such part of the mine, or to have in his possession any lucifer match or other material intended for lighting tobacco.

81. Wherever safety lamps are required, or directed to be used, no person shall use any open lamp.

(Name of the Mine)

{Name of the Owner) {Name of Manager) {Name of Inspector)_ {Address)

UB, AH persons employed in the mine, in whatever capacity, are specially requested to peruse the whole of these rules,

under whatever head, so as to make themselves acquainted with the terms thereof, and nothing in these rules shall be construed to prevent any arrangement between miners and their employers, as to payment for work done in redding falls " in working places.

3 T 2

532 Mining Engineeeing.

Chapter Xy.

Chaeacteeistigs Of The Coal Fields Of Geeat Beitain And Ameeica.

The characteristic features of the coal fields of G-reat Britain and of America form an interesting subject for consideration by the mining engineer. It would, however, manifestly be beyond the scope of the present work to describe minutely these features, or even to point them out in the briefest possible way. The subject is one for consideration in a special treatise. But it appears desirable to indicate the chief distinguishing features of the various coal fields, in so far as they have an important bearing upon the labour of extraction and the marketable value of the produce. Such indications, therefore, are briefly given in the present chapter.

The Dueham Coal Field. — The great coal field of the north of England, known as the Durham and Newcastle field, extends from Staindrop, near the north bank of the Tees, on the south, to the mouth of the Coquet, on the north, a distance of about 50 miles. The structure of this field is that of an irregular basin or trough, the longer axis of which runs north and south. It may be described as bounded on the east, from the mouth of the Coquet to the mouth of the Tyne, by the North Sea, and from the mouth of the Tyne to its southern extremity, by the Permian formations; on the south by the Permians, which are overlaid farther south by the New Eed Sandstone, and on the west by the millstone grit and Yoredale rocks. These limits are not, however, those of the field, nor even of the accessible portion of it. On the north-east, the measures pass beneath the sea, under which the workings of some important collieries have been extended to considerable distances. To the southeast, the measures continue underneath the Magnesian Limestone, which has been pierced by shafts in numerous places. The loose and water-bearing character of these rocks renders the operations of sinking extremely difficult and costly. The number of seams of coal workable in any one section is said to be twelve, having an aggregate thickness of 50 feet. The Durham coal field possesses greater natural advantages than any other known field. The seams lie at a very moderate angle, about 1° 50' ; they are of a convenient thickness for working, being from 3 feet to 6 feet thick ; and they are usually overlaid by a good roof. Besides this, the coal is of excellent quality, being bituminous in nature and free from sulphur. The latter quality renders it particularly suitable for use in the blast furnace, for which purpose a large proportion is annually converted into coke. The best " household " qualities, with which the London markets are mainly supplied, are raised in the district extending from the Tyne to the Wear ; the districts north of the Tyne furnish the denser steam coal and from the outcrops on the west, are raised the tender coals which are converted into coke.

This coal field is but little disturbed by faults. Whin dykes traverse it in an east-south-east direction but they do not seriously derange the seams of coal. The most remarkable fault is the

Chaeacteeistics Of The Coal Fields Of Gee At Beitain And Ameeica. 533

90-fathom dyke, so called because it displaces the beds to that extent on the coast near Cullercoats, where it first appears.

The Cumberland Coal Field. — Upon the western coast, and upon a line passing due west from the southern extremity of the Durham coal field, is the district known as the Cumberland coal field. This field stretches from Maryport on the north, along the coast of the Irish Sea, to St. Bees on the south, and extends inland to a distance of about 5 miles, at which distance the beds crop out. From Maryport, the coal field extends eastward to Bolton. Its length is about 25 miles, and its greatest breadth about 6 miles. South of the town of Workington, the thick coals are thrown out by a large fault, which brings up the lower coal measures. Another great fault, having a downthrow on the south-west, brings the productive measures in again at Whitehaven. As the coal seams beyond this fault dip slightly to the east, they crop out beneath the sea, and as a large quantity of water finds its way along the bedding planes, they cannot be worked generally beyond the coast-line. In one instance, however, the workings have been extended nearly 2 miles under the sea. From Maryport to Bolton, the coal measures are overlaid by Permian strata.

The aggregate thickness of the coal seams in this district is notably less than that of the Durham district on the opposite coast. The quality of the coal is also much inferior for household use and for coking purposes. Some of the seams are, however, remarkable for thickness and regularity. The Main Band seam is from 9 feet to 12 feet thick.

The Yorkshire and Derbyshire Coal Field. — The Yorkshire and Derbyshire coal field is the largest in England, covering as it does an area of about 800 square miles. Its geological features are similar to those of the Durham coal field ; as in the latter, the measures pass eastward beneath the Permian and New Red Sandstone beds, and are bounded on the west and north by the millstone grit, against which they crop out. On the south, the field is bounded by the New Red Sandstone. This large coal field extends from the towns of Derby and Nottingham on the south, to those of Bradford and Leeds on the north, a distance of about 65 miles, the greatest breadth being about 20 miles. The seams dip gently to the east ; but near the middle of the coal field a slight undulation occurs, which for a time gives the seams a dip in the westerly direction. The measures are continued eastward beneath the newer formations, which in one notable instance, that of the Shireoaks colliery, have been pierced.

The chief seams of coal occur in the lower measures, the bottom beds of which are remarkable for the occurrence of seams with a ganister floor. Important beds of ironstone also occur in the lower measures. The average number of workable seams in this field is sixteen, having an aggregate thickness of about 45 feet of coal. These seams are only occasionally interrupted by faults. The most important coal seams are, the " Kilburn coal," a bed which is developed only in the south of Derbyshire, but which is remarkable as being the purest " household " coal known ; the " Top Hard," which in Derbyshire is from 5 to 6 feet thick, and which gradually thickens northward, until in Yorkshire, where it is known as the " Barnsley thick coal," it becomes fiilly 9 feet in thickness ; and the " Clod," or " Black Shale " of Derbyshire, the Silkstone of Yorkshire. The latter is the most valuable seam of South Yorkshire, and is undoubtedly identical with the famous " Arley mine " of Lancashire. The " Top Hard " and "Lower Hard" of Derbyshire furnish the valuable splint coal, while the "Upper Soft" and "Lower Soft " furnish varieties well known in the London markets.

The Lancashire and Cheshire Coal Fields. — The South Lancashire is one of the most important of the English coal fields. It is very irregular in form, but g.nerally, it may be described

534 Mining Engineeeing.

as being bounded on the south and the west by the New Red Sandstone, and on the north and the east by the millstone grit. The western boundary is a great fault, which throws down the New Red Sandstone. The whole field is traversed by faults of great magnitude ; some of these have dislocated the strata to the amount of hundreds of yards. The length of this coal field is 32 miles, and its average breadth 6 miles.

The measures have been divided into the upper, middle, and lower series. The upper series contain several thin beds of coal, the middle series contain all the more important seams, and the lower series contain the "ganister" coals. The total number of seams above 2 feet in thickness is from sixteen to twenty, having an aggregate thickness of coal of about 70 feet. The seams are generally from 3 to 6 feet thick. The lowest seam of the middle series is the " Arley mine," a seam of very great value. The most valuable seam is the cannel coal of Wigan, which, however, thins out in all directions from Wigan as a centre. Other important seams are the Pemberton 5 feet and 4 feet mines, and the " King coal."

The Cheshire coal field is formed of the middle and lower series of Lancashire in their extension beyond the Mersey. On the west it is bounded by a great fault, known as the " Red Rock fault," which brings in the Permian and the New Red Sandstone beds. Several thick seams of good quality are worked in this field, which is divided on the south-east by only a narrow interval from that of North Staffordshire. The Dukinfield mine, the shaft of which cuts the black mine seam at a depth of 686 yards, after passing through no fewer than twenty- two workable seams, is remarkable as being one of the deepest in England.

The North Staffordshire Coal Field. — The North Staffordshire coal field, though of comparatively small extent, is one of great resources. It is triangular in shape, the apex being to the north, and in close proximity to the Cheshire coal field. On the east, it is bounded by the millstone grit, against which the seams crop out ; on the west by the Permian and New Red Sandstone beds, beneath which the measures plunge, and through which the seams may yet be reached for some miles to the south-west ; the southern boundary is a very irregular line due to faults of dislocation, which have let down the Permian rocks in patches. In the central and northern portion of the coal field, the strata have been thrown into a double fold along synclinal and anticlinal axes, which appear to converge towards the north. Disturbing forces have, however, done but little to derange the strata. But though generally undisturbed, the field is marked by several important lines of fracture. On the north-west it is bounded by the prolongation of the " Red Rock fault " of Cheshire, which, towards the north, brings the Red Marl nearly into contact with the Mountain Limestone. Two other parallel faults running south-east and north-west, throw the beds down to the east to the amount of about 350 yards and 200 yards respectively.

The measures are very rich in coal ; in one portion of this field there are not fewer than forty seams of coal exceeding 2 feet in thickness, and having an aggregate thickness of 140 feet ; in another part, there is an aggregate thickness of about 110 feet, in twenty-four seams of coal. Some of these seams furnish coal of an excellent quality. One of the peculiar and most valuable features of this coal field is the occurrence of rich beds of carbonaceous ironstone as a roof to the coal seams, so that both can be worked together. Adjacent to the North Stafibrdshire coal field, is a small outlying field, containing six or seven seams, named after the town of Cheadle. The area of the North Stafibrdshire coal field, within the boundaries described above, is about 75 square miles.

The South Staffordshire Coal Field.— This remarkable coal field occupies a strip of country

Chaeacteei8Tics Of The Coal Fields Of Great Beitain And America. 535

running north and eoutb, about 21 miles in length, and an average of 7 miles in breadth. It is bounded on all sides by Permian and New Red Sandstone rocks, and appears to have been upheaved bodily along two great and approximately parallel lines of fracture. Beyond these boundary lines, however, the Permian rocks on the east have been pierced, and the main seams of coal reached within a moderate depth.

The number of workable seams of coal in this field is six, having an aggregate thickness of 65 feet. The most remarkable of these seams is that known as the " Thick Coal," or " Ten- Yard " seam, a magnificent deposit of coal varying from 25 to 35 feet in thickness. Towards the north, this great seam becomes split up into nine distinct seams, having an aggregate thickness of 30 feet. The measures of this coal field contain also several valuable seams of ironstone.

Two features are worthy of note in this coal field. The first is the absence of the millstone grit and Carboniferous Limestone, the coal measures resting immediately upon the Silurian shales. The second is the frequency with which igneous rocks have been intruded. The thick coal is often interrupted by rock-faults, or " horses-backs."

The Shropshire Coal Fields. — Around the town of Shrewsbury, there exists an unimportant coal field containing two or three seams of no great value. Two small outlying tracts of coal measures cap the Clee Hills at a height of 1780 feet above the level of the sea. These coal fields, which are each about a mile in diameter, are covered with a bed of basalt, to the presence of which their preservation is probably due. Several thin seams of coal are worked in these measures. The important coal field of Shropshire is that of Coalbrook Dale. This field is bounded to the west, partly by a great fault that brings in the New Red Sandstone, and partly by Silurian rocks ; to the east, it is bounded by Permian rocks, beneath which the measures pass. The strata are much broken by faults. On the northern portion of this field, the total thickness of coal is 55 feet ; but the seams diminish rapidly in thickness southward. The number of workable seams is six, giving an average thickness of 27 feet. The value of this coal field, the area of which is only 28 square miles, is greatly increased by the presence of rich beds of ironstone.

The Leicestershire Coal Field. — The Leicestershire coal field, though small, is a valuable one. It is an irregularly shaped district, covering an area of about 15 square miles. It is bounded on all sides by rocks of the New Red Sandstone age. This field may be divided into three districts, that of Moira, on the west, that of Ashby-de-la-Zoucb, in the centre, and that of Coleorton, on the east. The number of seams of a workable thickness is generally ten, having an aggregate thickness of 45 feet of coal. The "Main-Coal" of Moira is 12 feet thick, of which the lower 6 feet, being of inferior quality, is not worked. The "Main-Coal" of Coleorton is from 6 to 8 feet thick. The central district of Ashby-de-la-Zouch is bounded on two sides by downcast faults which bring in the coal seams of Moira and Coleorton. Recently, shafts have been sunk to the coal seams through the overlying New Red Rocks beyond the boundaries of the field.

The Warwickshire Coal Field. — The Warwickshire coal field covers a tract of country only 15 miles in length by 2 miles in breadth. It runs in a south-easterly direction from the town of Tamworth, and is surrounded by rocks of Permian and New Red Sandstone age. The lower portion of the measures are i;productive ; in the upper portion, there are five seams, having an aggregate thickness of about 26 feet of coal. At the northern end of the district, these seams are separated by about 120 feet of shales and sandstones, which decrease in thickness southward until the seams of coal all come together to form one bed 26 feet thick. A similar occurrence has been

536 Mimng Enginebking.

noted in the South Staffordshire coal field. The lower measures of the Warwickshire coal field are traversed by several intrusive sheets of igneous rock. Upon a mass of this rock, the millstone grit rests. It is probable that the productive area of both this and the last-described coal fields will be greatly extended by sinkings through the Triassic rocks.

The Somersetshire Coal Field. — The important coal field known as the Bristol and Somersetshire field extends from the Mendip Hills northward to a distance of about 26 miles, covering an area of about 150 square miles. It narrows towards the north, so as to form generally a nearly equilateral triangle. The measures of this coal field are exposed in patches a large portion being covered by newer formations. They rest on the south-west and north-east upon the Mountain Limestone ; on the east they are covered by the Bath oolites, so that their termination in this direction is uncertain.

The measures of this coal field are divided into three series : the upper consists of the Radstock group, containing six seams having an aggregate thickness of 12 feet of coal, and the Farringdon group, containing four seams, the aggregate thickness of which varies from 6 to 1 2 feet ; the middle series consists of a great thickness of sandstones called the Pennant Rock, containing a few thin seams ; the lower series is composed of the Bedminster and Yobster groups containing from twenty to thirtyfive seams of coal having an aggregate thickness of about 60 feet. The remarkable features of this district are the thinness of the seams, which by suitable methods of working are wrought profitably, and the generally highly disturbed character of the strata ; on the south, the seams as they approach the Mountain Limestone are thrown into the vertical position, so that a shaft may follow the seam for 200 or 300 feet. Much of the coal in this part of the district is so broken as to be commercially valueless.

The Forest of Dean Coal Field. — This important little coal field forms a perfect basin, the strata dipping on all sides to the centre. As the measures rest upon the Mountain Limestone, these rocks form an encircling belt rising above the tract of coal measures which they enclose. The area of this coal field is about 34 square miles. It contains eight seams of coal above 2 feet thick, having an aggregate thickness of 24 feet. The lowest thick coal, known as the Coleford High Delf seam, varies in thickness from 4 to 11 feet. This seam is interrupted by one of those faults of erosion called " horses," of which this is a very remarkable example. All the seams of this field are very variable in thickness. In the centre of the basin, the seams lie horizontally ; towards the eastern margin, they rise much more rapidly than they do towards the western edge. Small quantities of clay ironstone are found in the coal measures, and rich deposits of brown haematite occur in the Mountain Limestone.

The South Wales Coal Field.— The South Wales coal field is, in many respects, the finest in G-reat Britain. In extent, it covers an area of 906 square miles ; in mineral wealth, it possesses an aggregate thickness of 84 feet of workable coal, and abundant deposits of clay ironstone ; and in variety of produce, it offers all the kinds of coal from the highly bituminous to anthracite. The general form of this coal field is that of an oval basin or trough lying nearly east and west. It is separated by Caermarthen bay into two portions, that lying to the east of the bay being by much the larger. The measures rest upon the Carbouifcruus Limestone, which rises to form its southern eastern and northern boundary. As the breadth of basin or trough is from 12. to 16 miles and the strata dip rapidly, the seams would soon reach an unworkable depth, were the field not traversed throughout nearly the whole of its length by a remarkable anticlinal axis, which divides the basin

Chaeacteeistics Op The Coal Fields Of Gee At Beitain And Ameeica. 537

into two troughs ; it is also worthy of note that this axis of elevation is near the southern side of the basin where the dip is steepest. The field is traversed by numerous lines of dislocation, which run generally nearly north and south,

A very remarkable feature of this coal field is the change which the seams undergo in their extension towards the west. In the eastern portion, the seams are highly bituminous ; as the centre of the field is approached, the same seams become semi-bituminous; and in the western portion, they become anthracite. Sir H. De la Beche has pointed out that this change takes place along a plane dipping gently towards the south-south-east ; so that in the same spot, while the coals at the base of a hill may be anthracite, those which crop out above may be bituminous. The lower measures of this coal field form a distinct zone, rich in coal and in ironstone. Above these, comes a great thickness of sandstones, called the "Pennant," comparatively poor in coal. And above the Pennant, is an upper series, rich in coal. The western portion of the field, which yields only anthracite, has been greatly disturbed.

The North Wales Coal Field. — The North Wales coal field occupies a strip of country having an area of about 82 square miles in the counties of Denbighshire and Flintshire. It is bounded on the west by the Carboniferous Limestone resting upon Silurian rocks, and on the north, east, and south by the New Red Sandstone and the Permian formations. The seams of coal, though not numerous, are thick, one being 9 feet and another 15 feet in thickness. There is also a bed of canuel of excellent quality. The production of this coal field has greatly increased within the last few years. The general dip of the beds is north-east, and they pass under the New Red Sandstone, so that it is highly probable the field will be, at some future time, extended in that direction. The Flintshire district is sepr rated from the Denbighshire district by an upthrow of the Carboniferous Limestone and the millstone grit over a small tract of country. The former district covers an area of 35 square miles, and contains an aggregate thickness of 35 feet of workable coal ; the latter district is about 47 square miles in extent, and contains an aggregate thickness of 30 feet of coal. The " Lower Four-foot " seam of the Flintshire district is exceedingly rich in oil.

The Coal Fields op Scotland. — The carboniferous rocks of Scotland form a band stretching from sea to sea, from the Firth of Clyde on the west, to the Firth of Forth on the east. The whole of this band is not productive of coal, so that there exists a number of distinct fields or " basins," separated from one another by barren tracts of the lower strata, or vast masses of igneous rock. These fields are :— 1, The Ayrshire coal field ; 2, The Lesmahago coal field; 3, The coal field of the Clyde Basin; 4, The Clackmannan coal field; 5, The Mid-Lothian coal field; and 6, The Fifeshire coal field. The Ayrshire coal field on the west coast is separated from the field of the Clyde basin by hills of Devonian and Trappean rocks. The measures rest unconformably upon the older formation, and are overlaid unconformably by rocks of Permian age. They are frequently interrupted by extensive sheets and vertical dykes of dolerite and basalt. The district is a very rich one, and is remarkable for its splint coals, and blackband ironstone. The Lesmahago is a small field lying to the south of the Clyde basin. It is nearly surrounded by the Old Red Sandstone, upon which the measures rest unconformably. This coal field produces a famous gas coal. The coal field of the Clyde basin is traversed by the river Clyde, whence its name. At the base of the measures, are the calciferous sandstones, with which are associated great sheets of trap rock. The strata are much broken by intruded sheets of melaphyre and dolerite, which constitute great impediments to mining operations, and by vertical dykes of basalt and dolerite. The district is remarkable for its splint and

3 z

538 Mining Engineeeing,

gas coal, for the famous Boghead cannel, and for its blackband ironstone. The Clackmannan coal field is separated, that of Fife by an uprising of the lower carboniferous rocks, and from that of the Clyde basin by the river Forth. It is divided into three districts by large faults. This field contains some important seams of coal. The Mid-Lothian coal field consists of a double trough, the axis of which lies nearly north and south ; the two troughs are separated by the Eoman camp limestone. Northward the seams are overlaid by the sea of the Firth of Forth, till they reappear in the Fifeshire coal field, a rich district, but greatly disturbed in its eastern portion. Both of these fields contain some fine seams of coal of excellent quality. Like all the Scottish coal fields, they are remarkable for the presence of numerous intruded masses of igneous rocks. The production of the coal fields of Scotland is already very large, and it is rapidly increasing.

The Coal Fields op Ireland. — Denudation has removed from Ireland the rich series of coal measures which at some earlier period she evidently possessed. The Carboniferous Limestone remains over a large portion of the centre and the south-west, and upon this at intervals rest patches of coal measures forming small and isolated coal fields. Those of the south produce anthracite, while those ot the north contain bituminous coal. These coal fields are of little commercial importance:

The Coal Fields op the United States op America. — In closing this work on coal mining, it seems desirable to direct attention to the vast resources of the United States of America, which a few years hence will assume the position of the chief coal-producing country in the world. The great coal fields of the States are five in number, and they occupy collectively the immense area of 197,000 square miles. They are denominated as follows : 1. The Appalachian coalfield, consisting of a series of basins in the States of Pennsylvania, Ohio, Maryland, Virginia, Kentucky, and Tennessee, extending over a distance of about 875 miles in an unbroken length. The larger portion of this vast field produces anthracite. Some of the seams are of very great thickness. 2. The Illinois and Indiana coal field, a tract of country having an area of not less than 51,000 square miles, and containing generally eight workable seams of coal, having an aggregate thickness of 50 feet of coal. 3. Tlie Iowa, Missouri, and Arkansas coal field, which covers an immense extent of country, but which is poor in coal. 4. The Texas coal field, a large tract of country that may be regarded as an extension of the last-named field ; and 5. The Michigan coal field, covering an area of 15,000 square miles, of the mineral wealth of which little is yet known. Although the last three fields cover a very large extent of country, their importance is not great, since they contain but an insignificant thickness of coal. But the Appalachian and the Illinois and Indiana coal fields possess an importance which it would be difficult to over-estimate. The Pittsburg seam, which varies from 5 feet to 14 feet in thickness, covers an area of upwards of 14,000 square miles. Some of the anthracite seams attain locally a thickness of from 40 to 50 feet, while the average of the southernmost part of the anthracite field has been estimated as 70 feet of workable coal. The average aggregate thickness of workable coal throughout the whole of the vast Appalachian field is certainly not less than 25 feet. In the Illinois and Indiana field, the general average thickness is 45 feet. It thus appears that coal mining in the United States of America is destined to assume, at no distant date, a degree of importance to which it could never attain in the Old World.

Index

Page

Acicular rocks 4

Acid 7

„ carbonic 458

„ felspars 5

„ hydrochloric 6

Adularia 5

Aerial rocks 3

After-damp 468

Agent, duties of 525

Agglomerate, volcanic 14

Air-box for shaft ventilation 246

Air, calculation of pressure 480

„ coefficient of expansion 476

„ compressed, advantages of, in mining 169

„ „ as a motor fluid 169

„ „ conditions of equilibrium 171

„ „ conversion of heat into work .. .. 172

„ defects of 170

„ „ inconvenience of high pressures .. 175

„ „ loss occasioned by 154

„ „ pressure of 171

„ „ ratio of pressure to volume .. .. 172

„ „ temperature of 171

„ „ volume of 170

„ compressing, loss of work by clearance in cylinders 176

by teat 175

„ „ „ by leakage 176

„ „ „ in transmission .. .. 177

„ compressors, Blanzy collieries 184

„ „ capacity of reservoirs 188

„ CoUadon's .. 180

„ „ CoUadon's, table of dimensions of . . 183

„ „ conduits 188

„ „ construction of 178

„ „ joints for air conduits 188

J, „ reservoirs 188

,, „ Eonchamp collieries 184

J, „ Sarrebruck collieries 178

jj „ Sommeiller's, table of useful effect .. 177

„ „ Sturgeon's high-speed 186

„ „ table of useful effect of 177

Page

Air compressors, water column, defects of 178

„ drag of 492

„ friction of 481

„ friction of, coefficient of 484

„ heat expended in compression of 174

„ heat expended in expansion of 173

„ loss of head by friction 492

„ loss of work in compressing 175

„ pipe for ventilation 293

„ pressure shown by water gauge 480

„ retardation of flow 481

„ specific heat of 172

„ thermo-mechanical properties of 170

„ velocity of flow 481,490

Air- ways, area of 489, 490, 492

„ crossings 492

„ doors 491

„ intakes 492

„ regulators 490

„ returns 492

„ stoppings 490

Alabaster 5

„ calcareous 5

„ gypseous 5

Albite 5

Alpine granite 10

Altered clays , 25

„ limestones 25

„ sandstones 24

Alternation of rock-beds 29

Amazonite 5

America, coal fields of 538

Amorphous rocks 4

Amygdaloidal rocks

Analysis, comparative, of different varieties of fuel .. 67

„ of coal 63,69

„ „ proximative 69

„ of rocks 8

Anamesite 13

Andesin 5

Andesite 13

3 z 2

Index.

2,

Anemometer

Angle of dip

„ of equal resistance

„ of equilibrium

Anorthite

Anttraoite

Anthracitous coal

Anticlinal, axis of

„ curves

Anzin, coal tubs at

„ miners' houses at

Apbanite

Aqueous rocks

Arenaceous limestone

Argillaceous flagstone

„ limestone

„ sandstones

Ash of coal, estimation of

Asphalt

Atmosphere, measurement of forces of

„ variation in pressure

„ of coal mines, after-damp

J, „ carbonic acid

„ „ carbonic oxide

„ „ coal dust ..

„ „ constitution of

„ „ diffusion

,, hydrogen

„ nitrogen

,. oxygen

„ „ proto-carburetted hydrogen

„ „ sulphuretted hydrogen ..

Augers for boring in clay or sand

Augite

Axe handles or helves

Axis of anticlinal or synclinal

Aymestry limestone

Page

7,18

Back-oasinq a Shaft 256

„ advantages of 257

„ cost of 271

Backing deals 237

Bala beds 43

Balance-sheets 521

Band 3

Banksman, duties of 525

Barnstaple beds 44

Barometer 476

„ correction for level 477

„ correction for temperature 478

„ principle of 477

23,49

Basalt

„ tuff . Basic felspars . Bass Basset Bath stone Batt .. .

Page

Bearing curbs 252

Beche 140

Bed 3

Beds, interstratified 27

„ wealden 50

Bell-mouths 57

Bickford's safety fuse 142

„ „ cost of 143

„ „ rate of burning 142

Bind 21

Biram's anemometer 481

Bitumen, varieties of 63

Bituminous coal 64

„ „ analysis of 64, 65

„ „ specific gravity of 64,65

„ „ varieties of 64

„ limestone 23

shales 21,57

Black-damp 460

Black marble 45

Blaes 22

Blanzy, coal tubs at 357

„ air compressors at 184

„ dimensions of air compressors 184

„ miners' houses at 520

Blast furnace, coal for use in 74

Blasting, effects of overcharging 462

„ electric, advantages of 208

„ in coal 335

„ means of firing the charge 141

„ powder and sawdust mixed 224

„ sledges 131,132

„ stick 211

„ tools used in 134

„ apparatus, electrical 208

„ gear, beche 140

„ „ cartridges 141

„ „ claying-iron or bull 140

„ „ drills or borers 134

„ „ fuses 141

„ „ jumpers 135

„ „ rammers or tamping-irons 140

„ „ scrapers 139

„ „ sets of 139

„ „ sledges 139

„ „ swab-stick 140

„ operations, advantages of circular holes .. 229

„ „ boring 225

„ „ boring holes in shaft-sinking . . 248

„ „ charging the hole 227

„ „ clearing the hole 225

„ „ failure of shots 228

„ „ firing the shots 228

„ „ inserting detonator in charge . . 227

„ „ preparing hole for charging , . 226

„ „ shelter for blasters 228

„ „ triangular holes, Cleveland district 229

Index.

Page

Blasting powder, Brain's 200

„ E. S. M 194

„ Horsley's 199

„ principles of 214

jj „ action of explosives 216

,, „ advantages of cartridges . . .. 226 J, ,, advantages of simultaneous

firing 221,225

„ „ angling the holes 222

„ „ application of 222

„ „ conditions of disruption .. .. 221 „ „ damage by overcharges .. 217,462

„ „ disruptive force required .. 217

„ „ economical considerations .. 224 „ „ line of least resistance .. 214,216 „ „ position of holes .. .. 216,221

„ „ table of charges of powder .. 218

„ „ tamping 216, 218

„ „ waste of explosives 217

Blind coal 15

Blowers 466

Bluestone 22

Boards or bords 305

Boghead mineral 66

Boilers, dimensions of 417

„ power of 417

Boite a mousse, Kind-Chaudron's 267

Bombs 14

Bore-holes, evidence afforded by 88

„ determining position of 88

„ obtaining sections of strata from .. .. 93

„ removing debris from 91

Borer-bits for rock drills 167

„ sharpening 168

„ Z form, advantages of 168

Borers, hand 134

Boring, advantages of double-hand sets 139

„ auxiliary tools used in 139

„ diamond system 121

„ „ cost 123

„ „ rate of progress 122

„ example of journal of 114

„ for water 504

„ general considerations concerning 113

„ Mather and Piatt's system 117

„ special systems of 117

„ apparatus, cost of 117

„ appliances, advantages of iron rods .. .. 113

JJ „ box-bell and screw-bell .. .. 104

JJ „ brace-heads or tillers 102

„ causes of accidents to 108

„ clearing tools 91

„ counterweights to rods 101

crow's-foot 103

„ cutting tools 89

„ cutting tools, angle of cutting edge 91 „ cutting tools, care required in maintaining dimensions of ., .. 90

Page

Boring appliances, cutting tools, simplicity of form

necessary 90

„ determining the nature of accidents

to 103

„ „ extracting tools 103

„ „ great strength required in frames 97

„ „ guide-tubes 101

„ „ guides for rods 95

„ „ hand-dogs 108

„ „ headgear 96

„ „ height of shear-legs 96

„ „ hollow rods 92

„ „ importance of double - pulley arrangement 99

„ „ lengthening pieces for rods .. .. 102

„ „ lifting-dogs 102

„ „ nipping-fork or tiger 102

„ „ objections to the use of iron rods 94

„ „ parachute Ill

„ „ regulating tools 93

„ „ rocking levers 99

„ „ rods 98

„ „ rods, quality of iron for .. .. 93

„ „ shear-legs or frames 113

„ „ shutters for guide-tubes .. .. 102

„ „ sliding joints in rods 95

„ „ sludgers 92

„ „ special clearing tools 92

„ „ spring poles 101

„ „ stirrups 96

„ „ stroke counters 101

„ „ tube cutters 107

„ „ tube drivers 105

„ „ tube extractors 106

„ „ tubing 104

„ „ verifying tools 93

„ „ wad-hook 104

„ frames, examples of 98

„ operations and appliances 89

„ „ application of steam power .. .. 101

„ „ arrangements with contractors .. 115

„ „ causes of accidents .. .. 103,111

„ „ changing tools 109

„ „ choice of cutting tool 109

„ „ choice of site for hole 107

„ „ clay lining through sand .. .. 112

„ „ commencement of hole 108

cost 115, 116, 123

„ „ cutting tubes 107

„ „ determination of nature of rock

from debris 112

„ „ deviation of hole from vertical .. 112

JJ „ diameter of hole 113

J, „ driving tubes 105

J, „ employment of steam power .. 114

JJ J, erection of shear-legs or frame .. 108

JJ „ examination of debris 112

JJ „ extracting broken rods or tools .. 103

Index.

Boring operations, extracting tubes 106

„ fixing guide-tube 108

„ journal 113

„ length of stroke for rods .. 100, 109

„ lining hole with tubes 104

„ lowering rods 110

„ obtaining solid cores .. .. 121,122

„ precautions against accidents .. Ill

„ presence of water necessary .. .. 92

„ putting down tubes 110

„ raising rods 109

„ rapidity of execution essential .. 110 „ rate of progress .. .. 115,120,122

„ reduction of diameter by tubing .. 105

„ register of tubes put down .. .. Ill

„ samples of strata to be preserved 113

„ selection of workmen 108

„ sinking the staple 107

„ surface erections 108

„ the water jet Ill

„ through running sand .. .. 111,112

„ working lever or rocking bar 100, 109

Bornhardt's electrical machine 212

Bottomer, duties of 529

Boundaries of rock-beds, determination of 53

Brace-heads or tillers 102

Brain's blasting powder 200

„ powder, composition of 200

„ „ merits of 200

„ radial system of boring 249,294

Brakes 369

„ winding engines 421

Brasses in coal 59

Brassy coal 59

Bratticing 286

„ methods of constructing . 246

„ permanent, cost of 271

Breccias, limestone 23

„ trappean 12

„ volcanic 14

Brick drum for sinking in quicksand 260

Bricks for shaft walling 239

Bridgewater treatise 48

British coals, table of composition of various .. .. 68

Brown coal 66

Brushers, duties of 530

Bull 140

Bunter 48

Burleigh rock-drill 159

Burys and Co.'s interchangeable picks 128

Bytownite 5

Cages 398

„ cost of 399

„ safety 399

„ safety hooks 399

„ weight of 399

Oainozoic 38

Page

Caking coal .. 64

Calcareous alabaster 5

„ sandstones 19

„ spar 5

Calciferous sandstones 46

Calcite 5

Calc-spar 5

Calliard 20

Calorific power of carbon 71

„ „ of coal 69,71

„ „ „ formula for determining, Du-

long's 71

„ „ „ formula for determining,

Griiner's 72

„ „ „ formula for determining, objections to 72

„ „ „ methods of estimating .. .. 71

„ „ of hydrogen 71

Calp 47

Cambrian period 42

Cannel coal 63,66

„ „ uses of 66

Caoutchouc, mineral 63

Caradoc beds 43

Carbonaceous limestone 23

„ shale 21

Carbon, calorific power of 71

„ period 38,45

„ „ characteristic fossils of 51

Carbonic acid 458

„ „ absorbed by water 459

„ „ effects on animals 458

„ „ proportion in atmosphere 458

„ „ sources of 459

„ „ specific gravity 458

„ „ test for 458

„ „ gas, apparatus for production of .. .. 516 J, „ „ for extinguishing underground

fires 512

„ oxide 460

„ „ effects on animals 461

„ „ sources of 461

„ „ specific gravity 461

Carboniferous limestones 45,46

Carburetted hydrogen 463,473

„ „ effects on animals 463

„ „ effects on flame 464

„ „ sources of 465

Cartridges 141

„ for bore-holes, advantages of 226

Cast-steel picks 128,130

„ „ objections to 130

„ sledges 132

Cataract, Cornish engine 445

Catsbrain 20

Cellular rocks 4

Cement for shaft walling 240

Chains, winding 4,09

Index.

Chalk

Character of rock-beds, determination of

Check

Chemical geology, Bischoff's

„ notation

„ solution

„ rocks

Cheshire coal field

Chisels for boring

Chlorite schist

Chloritic limestone

Choke-damp

Chronological order of formation of rocks

Clanny lamp

Classification and origin of rocks Clay

fire

Kimmeridge

Oxford

pipe

porcelain

marl

spade

Claying-iron

Clays, altered

Clear-burning coal

„ „ analysis of

„ „ specific gravity of

Clearing tools for bore-holes

Cleat

„ cause of

„ importance of, in mining

Cleavage and foliation

„ effects of deposition on

„ of felspar

Clerks, duties of

Cleveland ironstone, position of

Clinkstone

Clod

Clymenia limestone

Coal, abortive sinking for

advantages of different systems of working

analysis of

anthracitous

„ analysis of

„ specific gravity of

„ uses of

back or end of

bituminous

„ analysis of

„ specific gravity of

„ varieties of

blind ..

brassy

caking

calorific power of

23,50

18,20

21,57

21,25

, 140

G4

11,13

29,50

63,69

64,65

64,65

69,71

Coal, calorific power of, formula for determining, Du-

long's 71

„ formula for determining,

Griincr's 72

„ formula for determining, objections to 72

„ methods of estimating ..

cannel .,

„ uses of

changes undergone by, during formation

chemical composition of

classification of

clear-burning

„ analysis of

„ specific gravity of

cleat of

composition of

conditions necessary in, for use at sea

cone-in-cone

constituents of

63,66

56,67

crystallized 63

difference in quality of beds in same seam ,. 59

effects of age on character of 62

estimating earthy impurities in 59

estimating value of seams 59

evaporative power of various classes 73

evidences of vegetable origin of 58,67

extent of market for 82

face of 60

flaming 64

„ analysis of 65

„ specific gravity of 65

for blast furnace 73

for domestic use 77

for forging purposes 74

for gas manufacture 66,67,76

for metallurgical purposes 73

for steam purposes 75

for use in kilns 77

free-burning 63

fuliginous 65

„ analysis of 65

„ specific gravity of 65

gaseous 65

„ analysis of 66

„ specific gravity of 66

„ varieties of 66

hoo-cannel 66

increase of bulk when broken 78,284

inferior quality of, at outcrop 87

influence of partings on quality of 59

injurious effects of iron in 69

imperfect - 49

importance of cleat in mining 61

impurities in 59

iron pyrites in 59

large and small, comparative value of .. .. 78 lignite or brown 66

Index.

Page

Coal, local names of 67

„ mingey or dicey 60

„ mode of occurrence of 56,58

„ modification of qualities of 62

„ number of tubs required per cubic yard .. .. 78

„ origin of 58

„ parrot 66

„ percentage of water in 69

„ picks 128

„ proximate analysis of, determination of specific

gravity 70

„ „ „ estimation of asb .. .. 70

„ „ „ estimation of moisture .. 69

„ 5, „ estimation of sulpbur . . 70

„ „ „ estimation of volatile

matters 69

„ rocks associated with 56

„ semi-bituminous 63

„ „ analysis of 63

„ „ specific gravity of 63

„ sledges 131,132

„ slyne of 60

„ specific gravity of 64,68

„ spontaneous ignition of 60

„ steam 63

„ systems of working 305

„ table of relative value of different sizes .. .. 79

„ torbanite or boghead mineral 66

„ uses of different qualities 73

„ varieties of 56

„ vegetable remains in 57

„ wedges 130

„ blasting gear 139

„ cutting machines 315,339

„ „ advantages of 339,341

„ „ Donisthorpe's 344

„ Fritz's 343

„ „ the Economic 342

„ „ Warsop and Hill's 342

„ „ Winstanley and Barker's .. 339

„ dust, effects on atmosphere 467

„ „ in air of mines, danger of 467

Coal fields, America 538

„ „ Cheshire 533

„ „ Cumberland 533

„ „ Derbyshire 533

„ „ Durham 532

„ „ Forest of Dean 536

„ „ Ireland 538

„ „ Lancashire 533

„ „ Leicestershire 535

„ „ North Wales 537

„ „ of Great Britain and America, characteristics of 532

„ „ Scotland 537

„ „ Shropshire 535

„ „ Somersetshire 536

„ South Wales 536

Page

Coal fields, Stafi'ordshire 534

„ „ Warwickshire 535

„ „ Yorkshire 533

„ getting 314

„ „ blasting 335

„ „ hewing 333

„ „ in fiery seams 338

„ „ influence of cleat 317

„ „ in thick seams, long pillar 324

„ „ „ long wall 326

„ „ „ post-and-stall .. .. 324

„ „ „ square work 323

„ „ in thin seams, dip workings 829

„ „ „ long wall 828

„ „ „ paper on 327

„ „ „ rise workings 328

„ „ loading 347

„ „ long-pillar work 324

„ „ long wall 814,333

„ „ material for stowage 329

„ „ packing the gob 335

„ „ post-and-stall 337

„ „ removing pillars 337

„ „ removing the coal 334

„ „ removing timbering 336,338

„ „ timbering 336

„ „ waste 316

„ measures 46

„ „ subdivisions of 46

„ „ nature of 56,84

„ mines, constitution of atmosphere 454

„ „ division of, into districts 310

duties of agent

S5 5)

5)

banksman ..

33

Js

bottomer

J3

brushers

))

clerks and others

S) 5)

3)

doorkeeper ,.

n ))

Sj

drawers

n

„

drivers

))

3)

engmeman ..

V S)

9)

firemen

J3 ))

furnacemeu..

5)

manager

U

miners and other

workmen

3)

overman

3)

pit-headman

?)

putters

reddsmen ..

roadsmen ..

"

signalmen ..

weigher

!) 33

general rules

miscellaneous regulations ..

3) 31

special rules

Coal mining, effects of occurrence of igneous rocks on

Index.

Coal mining, importance of faults in

„ seams, calculation of produce of

), „ composition of

„ „ determination of character of

,j „ continuity of

„ „ existence of

„ „ difference in quality in same

„ „ difBculty of determining continuity of .

!, „ distinctive characters of

1, „ estimating value of

„ „ evidence of continuity of

„ „ evidence of outcrop

„ „ faults

„ „ identification of

„ „ outcrop of

„ „ separation of, into beds

„ „ termination of

„ „ thick

„ „ thick, methods of working

„ „ thickness of

„ thin

„ „ thin, methods of working

„ „ thinness of, at outcrop

„ searching for, cost of labour

cost of materials

cost of production

determining continuity of seams

difficulties attending

evidence afforded by borings evidence afforded by streams evidence of local traditions general commercial questions general engineering questions general survey of district . . hasty conclusions to be avoided .

horizontal headings

in a new locality

in a partially known locality

market

means of conveyance

outcrop of seams

preliminary considerations ..

side drifts

special survey of district

trial headings

trial pits

tubs, bodies of

„ capacity of

„ cost of

„ dimensions of

„ height of

„ importance of lubrication

„ iron

„ qualities requisite in

„ resistance of, to traction

special forms of

„ wheels and axles

Page

Coal tubs, wooden 357

„ workings, commercial limit of depth 87

„ „ depth of 86

„ „ mechanical limit of depth 86

„ „ practicable limit of depth 86

Coals, British, table of composition of various .. .. 68

Coke 63, 66, 74, 76

„ for smelting purposes 74

„ ovens 519

„ percentage of, from various coals 68

Colladon's air compressor 180

„ „ table of dimensions .. .. 188

Collieries, Blanzy, air compressors at 184

„ Eonchamp, air compressors at 184

„ Sarrebruck, air compressors at 178

Collodion 203

Colour of rocks 8

Columnar rocks 4

Combustion, nature of .. .. 456

„ spontaneous, causes of 510

Compact limestone 22

Compact rocks 2,4,7

Comparative value of large and small coal 78

Compensating joints in air conduits 188

Composition of coal 67

Compound limestones 23

Compressed air, advantages of, in mining 169

„ „ as a motor fluid 169

„ „ conditions of equilibrium 171

„ „ conduits for 188

„ „ conversion of heat into work .. .. 172

„ „ defects of 170

„ „ fixing pipes 288

„ „ hauling engines 875

„ „ inconvenience of high pressure . . .. 175

„ „ loss occasioned by 154

„ „ pipes for 288

„ „ position of safety valve on pipes . . 289

„ „ pressure of 171

„ „ ratio of pressure to volume .. .. 172

„ „ receivers for 188

„ „ temperature of 171

„ „ volume of 170

„ „ construction of machines for .. .. 178

. J, „ loss of work by clearance in cylinder 176

,, „ by heat 175

„ ,, „ by leakage 176

„ „ „ in transmission .. .. 177

Concretionary rocks 3,4

Conduits for compressed air 188

Cone-in-cone coal 63

Conglomerate 12,19

„ dolomitic 48

„ limestone 23

„ trap 12

„ volcanic 14

Conical winding drums 415

4 A

Index.

Contracts for borings 115

„ for shaft-sinking 271

Cooking, coal for 77

Cornbrash 49

Cornish engines 4:44

„ „ cataract 445

„ pumping engine, specification ., .. .. 450

„ pumps 442

„ „ drop valves 442

„ „ merits and defects of 443

repairing

Cornstones 23,44

Correction for temperature, table of 479

Corves 235

Cost of shaft-sinking 271

Cotton gunpowder 204

Counterweights, determination of curves for . . . . 414

„ for boring rods 101

„ for loads in winding 418

Cradle for walling 240

„ rope for supporting 240

Creep, cause of 308

Crenoidal limestone 23

Cretaceous period 50

Cribs 237

Crossings in air-ways 492

Crystalline limestone 5,22

rocks 2,3,4,7

Crystallization of limestone, cause of 25

Crystallized coal 63

Cuboidal rocks 4

Cumberland coal fields 533

Curbing 236

„ backing deals 237

„ dimensions of 237

„ distance between cribs 237

„ fixing 237

„ joints for 237

„ stringing deals 237

„ timber for 237

„ wooden, cost of 271

Curbs, bearing 252

„ dimensions of 257

„ ring 242

„ walling , 242

„ wedging 238, 251, 252, 255, 256

Currents, effects of, on stratification 26

Curtis and Harvey's E.8.M. blasting powder .. .. 194

Curves, anticlinal 29

„ effect of slip 352

„ elevation of outer rail in 361

„ influence of, on traction 352,360

„ in tramways 352

„ synclinal 29

Cutting picks 127

„ tools for boring 89

„ „ angle of cutting edge .. .. 91

„ „ simplicity of form necessary 90

Page

Dams 506

„ construction of 507,508

„ cost of 510

„ example of 508

„ preparation of site 507

Danks 22

Darlington rock-drill 162

Davey's pumping engine 446

„ „ absence of slip and shocks 447

„ valve gear 446

Davy lamp 501

„ defects of 508

„ modifications of 503

Dawdon Winning, sinking at 274

Deals, backing 237

„ stringing 287

Definition of rooks 1

„ strata 26

Denbighshire grits 43

„ slabs 43

„ slates 43

Denudation 36

Deposition of beds, effects of, on cleavage 26

Depth of rock-beds, determination of 54

Derbyshire coal field 538

Determination of rocks 6

Detonation 204

„ advantages of 207

„ nature of 204

„ Eoux and Sarrau's experiments.. .. 204, 206

„ to produce 205

„ V. explosion 206, 207

Detonators for gunpowder 205

„ importance of nature of 205

„ insertion of, in charge 227

Devonian period 44

„ „ characteristic fossils of 51

Diabase 12

Diallage-rock 12

Diamond rock-drill 166

„ system of boring 121

„ „ cost 123

„ „ rate of progress 122

Diffusion of gases 469

Dingle beds 45

Di-nitroglycerine, formula for 196

Diorite 12

Dip 28

„ angle of 28

„ direction of 28

„ indication of direction of 53

joints 30

„ measurement of 28

., angle of 53

„ of rock-beds, determination of 53

„ true, Hopkinson's formula for determination

of 55

Direction and inclination of faults, relation between .. 36

Index.

Page

Direction of dip 28

Dirt-partings 69

„ influence on value of coal 347

Dislocations and faults 81

Displacement and fracture 32

Districts, advantages of division into 310

„ division of mine into 310

Divisions of time, geological 39

Doleritic-tuff 14

Dolomite 13,23,25,47

Dolomitic conglomerate 48

Domestic purposes, coal for 77

Doorkeeper, duties of 530

Doors in air-ways 491

„ safety 491

Downcast or downthrow 33

Drainage 425

„ cost of pumps and engines 450

„ Comish engines 444

„ Cornish pumps 442

„ differential pumping engine 446

„ erection of pumps 449

„ feeders 427

„ preventing influx of water 428

„ pumping machinery 429

„ sinking pumps 449

„ standage 429

„ sumps 429

„ underground water 425

„ of shafts 244

„ „ feeders 244

„ „ tuhs for 245

Drawers, duties of 530

Drawing shaft 230

Drifts, exploring 505

„ or trial headings 87

„ stone 287

DrUls, hand 134

Drivers, duties of 530

Driving levels 277

„ „ bratticing 286

„ „ stone drifts 287

„ „ thirlings 285

„ „ timbering 296

„ „ ventilation 285

Drums, winding 409

Dubois-Frangois rock-drill 156

Dulong's formula for estimating calorific power of

coal 71

Dumb-drift 493

Durham coal field 532

Dykes 15,32

Dynamite 197

„ charging holes with 227

„ composition of 197

„ merits of 197

„ V. gunpowder 208

Page

Economic Coal-outteb 342

Effects of thrust and creep 308

Electric blasting, advantages of 208

,1 „ causes of accidents 209,213

,) „ conducting wires 211

)) „ cost of insulated wires 212

,) „ fixing wires in headings 212

„ „ insulation of wires 212

„ „ insulators 212

,, „ joints in connecting wires .. .. 211

„ „ machines.. 212

„ „ precautions against accidents .. .. 214

„ fuses 208

„ Abel's 209

„ „ blasting stick 211

„ „ composition of 209,210

„ „ conditions necessary in 211

„ „ construction of 209

„ „ dangers of 209, 213

„ „ Mowbray's 210

„ „ varieties of 209

Electrical blasting apparatus 208

„ machines 212

„ „ Bomhardt's 212

„ „ Mowbray's 213

„ „ varieties of 212

Endless-chain system 376, 382

„ „ duration of chain 383

„ „ engine 383

„ „ engine plane 383

„ „ method of working 383

„ rope system, No. 1 378, 384

„ „ engine 384

„ ,j „ engine plane 384

„ „ „ method of working .. .. 385

No. 2 378, 386

„ „ „ arrangement of ropes . . 387

,, engine 386

„ ,, „ engine plane 386

)) „ method of working .. .. 387

Engineer, duties of 522

Engine house 519

Engineman, duties of 526

Engine shaft j 230

Engines, Fowler's 391

„ dimensions of cylinder 418

duty of 417

„ power of 417

„ winding 415

„ „ dimensions of 243

„ „ Eobey and Co.'s 248

Eocene period 50

Equilibrium, angle of 362

conditions of, in compressed air .. .. 171

Erosions 32

„ cause of 32

E.S.M. blasting powder 194

Evaporative power of various classes of coal .. .. 73

4 A 2 ;

Index.

Examination of rocks, instruments for 6

Excavating tools, blasting gear 139

„ borers or drills 134

„ for various kinds of rock 145

„ hammers 130

„ picks 125

„ rock drills 145

„ shovels 124

„ sledges 130

„ wedges 130

Excavation, classification of rocks for 143

Explorations 621

Explosion, different degrees of 204

„ V. detonation 206, 207

Explosive compounds for mining purposes 190

Explosives, action of 214

„ advantages of detonation 207

„ blasting stick 211

„ Brain's blasting powder 200

„ cartridges 141

„ choice of detonating substance 205

„ classification of 191

„ cotton gunpowder 204

„ detonation of 204

„ dynamite 197

effects of 190

„ electric blasting apparatus 208

„ electric fuses 208

„ fuses 141

„ guncotton 201

„ gunpowder 193

„ Horsley's powder 199

„ lithofracteur 198

„ means of firing 204

„ nature of 190

„ nitroglycerine 195

„ noxious effects of 192

„ relative value of 190

„ rending, advantages of 192

„ shattering, advantages of 191

„ simple explosion of 204

„ spontaneous action of 192

„ table of relative strength 207

„ waste of, in blasting 217

Face of Coal

Faikes

Fan and furnace ventilation, comparative cost . . „ „ „ comparative results

„ Guibal 497

Farewell rock 46

Faults and dislocations 31

„ determination of 54

„ importance of, in coal mining .. .. .. 31

„ Lanesfield 35

„ obtaining stowage from 331

„ relation between inclination and direction .. 36

Taok

Faults, step 35

„ strike 35

„ throw off 33

„ trough 35

„ trough, explanation of formation of 35

„ width of 33

Felspar 5

„ cleavage of 5

Felspars, acid 5

„ basic 5

„ lime 5

„ potash 5

„ soda 5

Felspathic rocks 9

„ sandstone 19

Felstone 10

„ porphyry 11

tuff 12

Fetid limestone 23

Fibrous rocks 3,4

Filling shovels 125

Fire-clay 21,57

Fire-damp 463

„ blowers 466

„ causes of explosion 241

„ effects of explosion 468

„ effects on flame 464

„ explosion of 464

„ sources of 464

Firemen, duties of 527

Fires, underground 510

„ „ causes of 510

„ „ extinguishing 512

Firing explosives, means of 204

„ „ Eoux and Sarrau's experiments .. 204

Fissile 3

Flaggy 3

Flags 3

„ Llandeilo 43

„ Lingula 43

Flagstones 3, 19

„ argillaceous 21

Flaming coals 64

„ „ analysis of 65

„ „ specific gravity of 65

Flinty slate 25

Foliation and cleavage 31

Force pumps, advantages of .. 431

Forest of Dean coal field 536

Forging, coal for 74

Formation of rock-beds 25

„ of rock-joints 30

„ of rocks, chronological order of 38

Formula for cast-iron tubbing 254

„ for discharge of pumps 431

„ for flow in suction pipes 436

„ for friction of water in pumps 441

„ for pressure on pump pistons 435

Index.

Formula for pump cylinders 431

„ for strains in pulley frames 402

„ for strains in ropes 408

„ for strength of ropes 407

„ for velocity of flow through valves .. .. 434

„ to determine friction 355,358

„ height of outer rail 361

„ value of gravity 359

FossUs, characteristic, Carbon period 51

„ Devonian period 51

„ importance of knowledge of .. 50

„ Lias 52

„ Old Eed Sandstone period .. 51

„ Permian period 52

„ Silurian period 51

„ Triassio period 52

in coal 57

variety and number of 51

Fowler's clip puUeys 369,370

„ engines 391

Fracture and displacement 32

„ ofrocks 8

Fragmental rocks 12

Free-burning coal 63

Freestone 19

Fresh- water limestones 24

Friction, influence of, on traction 358

„ in wheels, formula to determine 355

„ of air 481

„ „ coef&cient 484

„ „ effects of velocity on 483

„ „ force necessary to overcome .. .. 484

„ of ropes 370

„ of tubs, formula to determine 358

Frying-pan shovels 125

Fuel, comparative analysis of different varieties

of 67

Fuliginous coals 65

„ „ analysis of 65

„ „ specific gravity of 65

Fuller's earth 21

Furnace, construction of 495

„ position of 495

„ regulation of fires 495

„ ventilation 495

Furnacemen, duties of 526

Fuses 141

„ advantages of the use of 142

„ Bickford's safety 142

„ electric 208

„ safety, cost of 143

„ safety, rate of burning 142

Galliaed

Gannister beds

Gras, coal for manufacturing

quantity yielded by diflierent varieties of coal

Gas-making, coal for 66, 67, 76

Gaseous coal 65

„ „ analysis of 66

„ „ specific gravity of 66

„ „ varieties of 66

Gases, absorption of, by water 458

„ diffusion of 469

Gault 50

Geological evidence afforded by streams 84

„ knowledge, importance of, in mining .. 50

„ plans and sections, directions for making . . 52

„ sections 54

„ surveying 52

„ „ difficulties of 52

„ „ value of tables of sines and tangents 54

„ time, divisions of 39

Geology, chemical 8

„ influence of, on mining 1

„ Jukes and Geikie's Manual of 8

Getting the coal 314

Glassy rocks 4

Glonoin or nitroglycerine 195

Gneiss 24

Gob-roads 311

Gradient of roads 362

Grafting spade 125

Granite 9

„ Alpine 10

„ graphic 10

„ hypersthenic 10

„ porphyritic 10

„ syenitic 10

Granitic rocks 9,14

Granular rocks 4

Graphic granite 10

Gravity, effects of, on traction 359

„ formula to determine effect of 359

„ haulage by means of 366

„ specific, carbonic acid 458

„ „ carbonic oxide 461

„ „ determination of 9

„ „ hydrogen 462

„ „ nitrogen 457

„ „ of coal 62-68

„ „ of coal, determination of 70

„ „ ofrocks 8

,. oxygen 457

„ „ proto-carburetted hydrogen . . . . 463

„ „ sulphuretted hydrogen 462

Great limestone 45

Great oolite 49

Greensand, lower 50

Greenstones 6,11

Greenstone-tuff 12

Greywacke 25

Grit, millstone 19,46

Grit or gritstone 19

Grits, Denbighshire 43

Index.

Page

Gruner's formula for determining tie calorific power

of coal 72

Guibalfan 497

Guides and keeps 396

„ iron 397

„ wire rope 397

„ wooden 396

Guide-tubes for bore-holes 101

Guncotton 201

„ action of 203

„ and nitroglycerine, comparison of ., .. 201

„ compressed 202

„ composition of 201

defects of 203

„ merits of 203

„ necessity of purity 202

„ preparation of 202

„ Professor Abel's experiments 206

„ purifying 202

Gunpowder 193

„ advantages of cartridges 194

„ advantages of detonation 207

„ charging holes with 227

„ Curtis and Harvey's E.S.M 194

„ effects of explosion on ventilation .. .. 472

„ compressed 194

„ compressed, advantages of 206

„ cotton 204

defects of 194

„ detonators 205

„ merits of 194

„ safety of, in transport 194

„ V. dynamite 208

Gypseous alabaster 5

Gypsum 5, 7, 24

Half-on 319

Hall, Sir James, experiments on crystallization of

limestone 25

Hammers and sledges 130

„ and sledges, making , „ 132

„ various forms of 131

Hand-borers or drills 134

Hand-dogs 103

Handles or helves, cost of 133,134

„ „ choice of wood for 183

„ „ economy in cleaving wood for .. 133

„ fitting 184

„ for picks 126, 132

„ „ making 183

„ „ rate of making 134

Hardening rock drills 137

„ steel 137

Hardness of rocks 3,4

„ „ table of 4

Hastings sands 60

Haulage .. , 345

„ air engines 375

PAGlt

Haulage, comparative merits of systems 390

„ considerations affecting 345

„ endless-chain system 376,382

„ endless-rope system. No. 1 378,384

„ endless-rope system, No. 2 378, 386

„ men and horses .. .. 372

„ motors 366

„ self-acting planes 366

„ sledges 347

„ putting the coal along the face 346

„ steam engines 373

„ systems of 375

„ tail-rope system 376,379

„ tramways 349,351,860

„ tubs 348

„ engines 373

Hazel 20

Headgear, calculation of strains 402

„ construction of frames 404

„ dimensions of timber 403

„ direction of strains 401

„ for shaft-sinking 243

„ height of frames 243,400

„ iron frames 405

„ pulleys 404

„ ropes 405

Headings, driving 283

„ horizontal 88

„ trial 87

Headways 805

Heat, conversion of, into work 172

„ expended in compression of air 174

„ expended in expansion of air 173

„ specific 172

„ unit of 71,172

Hewing 333

Holing, labour and danger of 334

„ picks 127

Horizontal trial headings 88

Hornblende 6

Hornblendic limestone 23

„ rocks 9

„ schist 20

„ traps 11

Horse-power, effective 417

„ nominal 417

Horses'-backs 32

Horses, power of 372

Horsley's powder 199

„ „ composition of 200

„ „ merits of 200

House coal, qualities desirable in 77

Houses for miners 519

Huronian beds 42

Hydrochloric acid 6

Hydrogen 462

„ calorific power of 71

„ specific gravity 462

Index.

Hydrogen, carburetted

Page

„ effects of flame 464

„ effects on animals 463

„ sources of 465

proto-carburetted 463

„ danger of 463

„ specific gravity .. .. 463

sulphuretted 462

„ effects on animals 462

„ specific gravity 462

Hypersthene rock 12

Hypersthenic granite 10

Iceland Spab 5

Igneous rocks 2,7,9

„ „ effects of occurrence of, on coal mining 17

„ „ mode of occurrence of 14

Ignition, spontaneous, of lias shales 49

Ilfracombe beds 44

Incidental operations 500

Inclination and direction of faults, relation between .. 36

„ of rock-beds 27

Inertia of water 441

Inferior oolite 49

Influence of geology on mining 1

Ingersoll rock-drill 162

Interchangeable picks, Burys and Co. 128

Interstratified beds 27

Inundation of workings 504

Ireland, coal fields of 538

Iron for boring rods, testing quality of 94

in coal, injurious effects of 69

manufacture, coal for use in 73

pyrites in coal .. .. 59

red short 73

rods for boring, objections to the use of .. .. 94

Ironstone, bands of 57

„ black-band 58

„ Cleveland, position of 49

Iron tubs 357

Joints 30

„ compensating, in air conduits 188

„ dip .. .. .. 30

„ importance of, in mining 31

„ master 30

„ strike 30

Journal of boring, example of 114

„ of shaft-sinking 270

Junctions in tramways 851,364

Jurassic period 48

KaINOTOMON EOCK-DEILL 160

Kaolin 20

Keeps 397

Kelve 22

Kcrsantite 11

Page

Kersanton 11

Keuper 48

Kibbles 235

„ danger of collision of 235

Kiesulguhr 197

Kilns, coals for use ia 77

Kimmeridge clay 49

Kind-Chaudron system of shaft-sinking 266

„ „ boite a mousse 267

„ „ clearing tool 269

„ „ cutting tool or trepan .. .. 268

„ „ fixing tubbing 269

Kitchen coal 77

Labeadoeitb 5

Lacustrine limestone 24

Laminated 3

Lamination of rocks 26

Lamps 500

„ safety 501

Lancashire coal field 533

Landing stages 518

Lanesfield fault 35

Lateral shift, apparent 34

Laurentian period 42

Layer 3

Leicestershire coal field 535

Level-bearing 28

Levels, bratticing 286

„ dimensions of 280

„ direction of 279

„ driving 277

„ driving the heading 283

„ economy of walling 297

„ form of 280

„ importance of 277

„ inclination of 280

„ laying out 278

„ means for preserving direction of 281

„ „ „ inclination of 282

„ operations of driving 281

„ stone drifts 287

„ thirlingg 285

„ timbering 296

„ ventilation of working places 285

„ walling 303

Lias 48,49

„ characteristic fossils of 52

„ lower 49

„ upper 49

„ white 49

„ shales, spontaneous ignition of 49

Liecke's formulEB for nitroglycerine 196

Lifting dogs 102

Lighting the workings 500

„ candles 500

„ cost of 500

difficulties attending 501

Index.

Page

Lighting lamps 500

„ naked lights 500

„ safety lamps 501

Lignite 66

Lime felspars 5

Limestone .. .. 2, 7, 18, 22

„ altered 25

„ arenaceous 23

„ argillaceous 23

„ Aymestry 43

„ bituminous 23

„ breccias 23

„ carbonaceous 23

„ carboniferous or mountain 45

„ cause of crystallization of 25

„ chloritic 23

„ compact 22

„ compound 23

„ conglomerates 23

„ crystalline 5, 22

fetid 23

„ fresb-water 24

„ great 45

„ hornblendic . . -. 23

„ lacustrine 24

„ magnesian 7, 23, 47

„ micaceous 23

„ oolitic 22

„ saccbaroid 22

„ Scaur 45

„ serpentine 23

„ silicious 23

„ talcose 23

„ Wenlock 48

„ shale, lower 45

„ „ upper 45

Lingula flags 43

Lipey blames 22

Lithofracteur, composition of 199

„ merits of 199

Llandeilo flags 43

Llandovery beds, lower 43

„ „ upper 43

Loam 21

Local names of coal 67

Long-pillar work 324

Long-wall 314

„ details of workings 333

„ direction of face to cleat 316

„ dip 320

„ „ workings 312

„ gob roads 311

„ holing 333

„ importance of direction of stalls .. .. 316

„ inclined roads 321

„ influence of cleat on workings 317

„ influence of direction 322

„ in thick seams, French method 307

Page

Long-wall, length of stalls 315

„ packing the gob 335

„ pressure on face 3J.7

„ removing the coal 334

„ rise workings 320

„ the wall face 315

„ timbering 336

„ working home 311

„ „ out 310

Lower greensand 50

„ lias 49

„ red sandstones 47

Loxoclase 5

Lubrication of tub wheels, importance of 358

Ludlow beds, lower 43

„ upper 43

Lydian stone 25

Lynton beds 44

Machine Boeing, advantages of 290

„ „ Brain's system 294

„ „ charging 291

„ „ choice of drill 288

„ „ division of labour 292

„ firing 292

„ „ lighting 294

„ „ position of holes 289,295

„ „ preliminary conditions 287

„ „ provisions 288

„ „ removal of debris 290,292

„ „ systems of 289,294

„ „ tamping 291

„ „ ventilation 293

„ drilling, economy of 168

„ rock-drills 145

„ „ action of 147

„ „ advantages of 146

„ „ automatic v. hand feeding .. ,. 149

Burleigh 159

„ „ borer-bits for 167

„ „ comparative merits of .. ,. 167

„ „ comparative table of 169

„ „ conditions of work 147

„ „ conditions to be fulfilled by .. 148

„ „ Darlington 162

„ „ dimensions of 169

„ „ drill to rotate automatically .. 153

„ „ Dubois-Frangois 156

„ „ economy of 168

.. Ingersoll 162

high piston speed undesirable .. 151

„ „ Kainotomon 160

., „ provision against accidents ,. 189

), regulation of automatic feed .. 154

„ Sach's .. 157

J) „ strength required in 150

„ „ stretcher bar for 156,168

Index.

Page

Machine rock-drills, striking part to be heavy .. .. 151

n „ supports for 148

5) „ in mines 155

5) „ in tunnels .. .. 155 jj supports, conditions to be fulfilled by 148

1, „ to be light in weight 150

,, to be readily taken to pieces .. 154 ,j J, to be simple in construction . . 149 )) „ to be worked with low pressure 154

„ „ to occupy little space 150

„ „ to possess few parts 150

„ „ to strike the rock direct .. .. 151

„ „ tripod stand for 156

„ „ variation in stroke necessary ,. 153

„ „ velocity of 151

II J, violent shocks to be avoided among

parts 152

„ „ V. hand-drilling 146

„ „ Warsop 165

„ „ water reservoirs for 189

„ „ weight of 169

Machines for compressing air, construction of .. .. 178

Magnesian limestone 7,23,47

Management and accounts 521

Manager, duties of 525

Marble, black 45

„ statuary 5,22

„ saccharoid 25

Marl 21

clay 21

„ red 47

„ shell 24

„ stone 49

„ slate 47

Marwood beds 44

Master-joints 30

McKean rock-drill 161

Measurement of dip 28

„ and strike of rock-beds .. .. 53

Mechanical rocks 2

,, suspension 2

Melaphyre 12

Mercury, coefficient of expansion 476

Mesozoic period 38

Metal 22

Metallurgy, coal for use in .. .. 73

Metamorphic rocks 3,7,24

Mica 6

„ schist 6,20,25

Micaceous 6

„ limestone 23

„ sandstones 19

Microscope, preparation of rock-sections for .. .. 8

Microscopical examination of rocks 8

Millstone grit 19,46

Pack

Minerals, the chief rock-forming 4

Miners, houses for 519

„ intelligent working of 143

„ knowledge of character of rocks essential to . 143

„ regulations for 529

Minette 11

Mining, explosive compounds for 190

„ importance of cleat in coal 61

„ geological Imowledge in .. .. 50

)) „ geological surveys 52

n „ knowledge of fossils .. .. 50

I, „ knowledge of palaeontology .. 50

„ influence of geology on 1

Miocene period 50

Moisture in coal, estimation of 69

Mono-nitroglycerine, formula for 196

Moor rock 46

Mortar for shaft walling 240

Moss-box, Kind-Chaudron's 267

Mountain limestone 45

Mowbray's electrical machine 213

„ electric fuses 210

Mud 21

Mudstone 21

Mueseler lamp 504

Muschelkalk 23,48

Muscovite 6

Naphtha 63

Narrow work 277

New red sandstone 48

„ „ period 47

„ „ variety of thick ess of 48

Nip 29,31

Nipping-fork or tiger 102

Nitrocotton 201

Nitrogen 457

„ absorbed by water 459

„ proportion in atmosphere 457

., specific gravity 457

Nitroglycerine and guncotton, comparison of .. .. 201

„ Brain's powder 200

„ causes of accidents 195,197

„ defects of 196

„ dynamite 197

„ effects on the system 195

„ formulae for 196

„ Horsley's powder 199

„ importance of purity in 195

„ lithofracteur 198

„ merits of 196

„ or glonoin 195

J] preparation of 195

„ signs of impurity in 195

Nodular rocks 3

North Wales coal field 537

Nummulite 23

4 B

d54

Index.

Page

Oblici0b Sections 55

„ „ table of 55

Obsidian 13

Oil, use of, in hardening steel 137

Old red sandstone period 44

„ „ characteristic fossils of .. 51

Oligoclase ., .. 5

Oolite, inferior 49

„ period 48

„ series 49

Oolitic limestone or oolite 22

„ rocks 4

Order of formation of rocks 38

Organic remains 50

„ „ variety of 51

„ rocks 3

Origin and classification of rocks 2

Ormerod's safety link 399

Orthoclase 5

Outcrop 28

„ inferior quality of coal at 87

„ of coal seams 84

„ „ evidence of 85

„ „ proving 85

Overlap 37

Overman, duties of 525

Overwinding, precautions against 423

Oxford clay 49

Oxygen 455

„ absorbed by water 459

„ proportion in atmosphere 457

„ quantity to support combustion 457

„ specific gravity 457

Pack, conveying material for 331

„ material for 329

„ obtaining, from surface 332

„ quantity of material required 329

„ sources of obtaining 330

Packing 335

Page, Dr., influence of geology on mining 1

Palseontological identification of rock-beds . . . . 50

Palseontology, importance of knowledge of, in mining 50

Palfeozoic period 38

Paris, plaster of 5

Partings 59

„ influence of, on quality of coal 59

Pass-bys 368

Pearlstone 18

Peastone 23

Pegmatite 10

Peldon 20

Pennant rock 46

Permian period 47

„ „ characteristic fossils of 52

Period, cainozoic or tertiary 38

., cambriaa 42

,, carbon 38,45

J J ,, characteristic fossils of 51

Period, cretaceous 50

„ devonian 44

„ „ characteristic fossils of 51

„ eocene 50

„ Jurassic 48

,, laurentian 42

„ mesozoic or secondary 38

,, miocene 50

„ new red sandstone 47

,, old „ 44

„ „ „ characteristic fossils of .. 51

„ oolitic 48

„ palfeozoic or primary 38

„ permian 47

„ „ characteristic fossils of 52

„ pliocene 50

„ pleistocene 50

„ Silurian 42

„ „ characteristic fossils of 51

„ triassic, characteristic fossils of 52

Perthite 5

Petroleum 63

Phonolite 11, 13

Pick helves, choice of wood for 133

„ „ cost of 133,134

„ „ duration of 133

„ „ making 133

„ „ or handles 126,132

„ „ supply of 132

„ „ rate of making 134

Picks, Burys and Co.'s interchangeable 128

„ cast-steel 128, 130

„ choice of iron for 129

„ cost of 128

„ lining 129

„ making 129

„ objections to cast-steel 130

„ proper forms of 126

„ rate of making 129

„ rate of sharpening 129

„ re-sharpening 126, 128

„ sizes of 126-128

„ tempering 128,137

„ various kinds of 127

„ weight of 126-128

Piling through quicksands 258

Pillars, dimensions of 309

„ removal of 309,337

Pindy 22

Pipe-clay 21

Pipes 57

„ contents of 451

„ for pumps 438

,. joints 440

lining 440

„ pressure of water in 452

„ thickness of 439

„ weight of 440

Index,

Pisolite' 23

Pistons of pumps 435

Pitch, mineral 63

Pitohstone H

Pit-head frames 400

construction of 404

dimensions of timbers 403

height of 400

strains in 401

wroiight-iron 405

Pit-headman, duties of 525

Pits, trial 88

Pit work, cost of 450

Plagioclase 5

Planes of stratification 26

„ self-acting 321, 322, 328, 366

brakes 369

friction of ropes 370

laying out 367

pass-by 368

reels and sheaves 370

working 370

Plans, geological, directions for making 52

Plaster of Paris 5

Plate 22

Pleiocene period 50

Pleistocene period 50

Plungers for pumps 435

Pockets 29

Porcelain clay 20

Porous rocks 4

Porphyrite 10, 11

tuff 12

Porphyritic felstone 11

„ granite

„ rocks ,

Porphyry

Portland stone

Post

„ and stall, details of working

„ „ dimensions of

„ „ direction of workings 307

„ „ division into districts 310

„ „ in thick seams 324

„ „ jerking 338

„ „ removing pillars 309,337

„ „ timbering 337

Pot-bottoms 57,336

Potash felspars 5

Pounson 22

Powder and sawdust mixed for blasting 224

„ Horsley's 199

Preston Grange pit, sinking at 273

Primary period 38

Produce of coal seams, calculation of 77

Proto-carburetted hydrogen 463

„ „ „ danger of 463

„ „ „ specific gravity ., .. 463

Protogine 10

Page

Puddingstone 19

Pulleys 404

„ Fowler's clip 369, 370

Pumice 13

Pumping engines, Cornish 444

jj „ cost of 450

!, „ direct-acting differential .. .. 446

Pumps, angle-bobs 438

„ balance-bobs 437

„ calculation of efficiency 440

„ Cornish system 442

„ cost of 450

„ cylinders 431

„ defects of rod system 438

„ delivery per minute 452

„ delivery per stroke 452

„ determining resistances in 442

„ diameter of pipes 439

„ discharge of 431

„ erection of 449

„ force 430

„ formulfe, memoranda, &c. 451

„ friction of piston 440

„ friction of water in rising main 441

„ inertia of water 441

„ joints of pipes 440

„ length of sets 450

„ lift 430

„ lining pipes 440

„ lowering pit work 449

„ pipes 438

„ piston rods 436

„ pistons 435

„ plungers 435

„ pressure on pistons 435

„ requirements 429

„ sinking 449

„ strength of pipes 439

„ stroke of piston 436

„ thickness of pipes 439

„ timber for rods 437

„ valves 431

„ V-bobs 438

„ velocity of piston 436

„ vibrating rods 438

„ weight of pipes 440

„ weight of rods 437

„ working on air 450

Putters, duties of .. .. 530

Putting the coal along the face 346

Pyroxene 6

Pyroxenic rocks 9

Pyroxilin 201

QuAERiES for obtaining stowage 330

Quartz - 5

Quartzite 25

Quartz rock 25

Quicksand, Belgian method of sinking in 268

4 B 2

Index.

Quicksand, examples of sinking in 261

„ French method of sinking in 265

„ shaft-sinking in 257

Eails 379,383,384,386

„ forms of 363

Eainford colliery, sinking in quicksand 261

Rammers 140

Receivers for compressed air 188

Reddsmen, duties of 530

Red marl 47

„ rock 48

„ sandstones, lower 47

Reels and sheaves 370

Regulating tools for bore-holes 93

Regulators in air-ways 490

Relation between inclination and direction of fault .. 36

Remains, organic 50

„ „ variety of 51

Resistance of, to traction 358

Retinite 11

Ring curb 242

Rise .. .. , 28

,, workings 320

Roads 360

„ construction of 362

„ gradient of ;. .. 362

„ importance of 360

„ influence of inclination on traction 362

„ influence of, on force of traction 360

Roadsmen, duties of 527

Robey and Co.'s winding engine 243

Roche 20

Rock 20

„ farewell 46

„ moor .. 46

„ pennant 46

„ red 48

„ rough .. .. 46

Rock-beds, alternation of 29

„ boundaries, determination of 53

„ change of character of 53

„ determination of character of 52

„ dip and strike of, determination of .. .. 53

„ extent of 27

„ formation of 25

„ inclination of 27

„ means of identification of 50

„ thickness and depth of, determination of .. 54

Rock drills, cost of 138

sizes of 136, 139

„ steel for 135,136

„ tempering 138

„ weight of 139

sets of 138

„ hand 134

„ defects in ISy

Fagb

Kock drills, making , ,. 136

„ rate of repairing 138

„ hardening 137

„ machine, regulation of automatic feed .. 154

„ „ provision against accidents .. 189

„ „ economy of 168

„ „ high piston speed undesirable . . 151

„ „ automatic v. hand feeding . . 149

„ „ borer-bits for 167

„ „ Burleigh 159

„ „ drill to rotate automatically .. 153

„ „ diamond 166

„ „ dimensions of 169

„ „ Darlington 166

„ „ Dubois-Frangois 152

„ ,, comparative merits of .. .. 167

„ „ comparative table of 169

„ „ conditions to be fulfilled by .. 148

„ „ conditions of work 147

„ „ Brain's system of boring .. .. 249

„ „ Eainotomon 160

„ „ to strike the rock directly .. 151

„ „ to be worked with low pressure 154

„ „ to be readily taken to pieces .. 154

„ „ tripod stand for 156

„ „ to occupy little space .. .. 150

„ , to be light in weight .. .. 150

„ „ to possess few parts 150

„ „ advantages of 146

„ „ action of 147

„ „ w. hand drilling 146

„ J, n ethods of using in shaft-sinking 248

„ „ striking part to be heavy . . .. 151

„ „ supports for 155

„ „ stretcher bar for 168

„ „ Sach's 157

„ „ supports, conditions to be fulfilled by 148

„ „ strength required in 150

„ „ supports for, in mines .. .. 155

„ „ stretcher bar for 156

„ „ violent shocks among parts to be

avoided 152

„ „ variation in stroke necessary .. 153

„ „ velocity of 151

„ „ Warscip 165

„ „ to be simple in construction .. 149

„ weight of 169

„ „ water reservoirs for 189

Rock-forming minerals, the chief 4

Rocking levers for boring 99

Rock-joints, cause of 30

„ formation of 30

„ importance of, in mining 31

Rocks, acicular 4

Index.

Paoe

Bockii, aerial 3

„ amorphous 4

„ amygdaloidal 4

„ analysis of 8

„ aqueous 2, 7, 18

„ associated with coal 56

„ cellular 4

„ chronological order of, formation of .. .. 38

„ classification of 2

„ „ of, for excavation 143

„ colour of 8

„ columnar 4

„ compact 2,4,7

„ concretionary 3,4

„ crystalline 2, 3, 4, 7

„ cuboidal 4

„ definition of 1

„ determination of 6

„ felspathic 9

„ fibrous 3, 4

„ fracture of 8

„ fragmental 12

„ glassy 4

„ granitic 9, 14

„ granular .. ' 4

„ hardness of 3,4

„ hornblendie 9

„ igneous 2, 7, 9

„ „ mode of occurrence of 14

„ knowledge of character, essential to miners .. 143

„ lamination of 26

„ mechanical 3

„ metamorphic 3, 7, 24

„ microscopical examination of 8

„ nodular 3

„ oolitic 4

„ order of superpos tiou 38

„ organic 3

„ origin of 2

„ porous 4

„ porphyritic 4

„ pyroxenic 9

„ quartz 25

„ saecharoid 4

„ sedimentary 3, 24

„ „ relative extent of 27

„ specific gravity of 8

„ stratification of 26

„ stratified 3

„ streak of 8

„ structure of 3,4

„ sub-crystalline 4

„ table of hardness of 4

„ tabular 4

„ texture of 3,4

„ trachytic 13

„ trappean 9, 10, 14

Page

Eocks, veinous 3

„ vesicular 4

„ volcanic 9, 13, 14

„ Toredale 45

Eock-sections, preparation of, for microscope .. .. 8

Eods, pump 436

„ for boring 93

„ sliding joints in 95

9) „ guides for 95

„ hoUow, for boring 92

„ for boring, objections to the use of iron .. ., 94

Eoe-stone 22

Eolls 32

Eonchamp collieries, air compressors at 184

„ dimensions of air compressors .. 185

Eoof, to ascertain strength of 145

Eopes 384, 386, 405

„ coUing on drums 411

„ comparative strength of 407

„ durability of 409

„ duration of 390

„ fastening to drums 411

„ flat 406

„ formula for strains 408

„ formula for strength of 407

„ friction of 370

„ protection of 409

„ precautions against rupture 442

„ sizes and weights of 407

„ strains in 408

„ strength of 405

„ wire 406

Eotche 20

Eottenstone 45

Eough rock 46

Eound-mouthed shovels 125

Eubble 20

Saccharou) Limestone 22

„ marble 25

„ rocks 4

Sach's rockdriU 157

Safety doors in air- ways 491

„ fuse, Bickford's 142

„ ,, cost of 143

„ „ rate of burning 142

„ hook. Walker's 399

„ lamps 501

„ lamp, Clanny .. .. 503

„ lamps, cleaning 502

„ „ cost and weight of 503

„ lamp, Davy 501

„ lamps, locks for 502

„ lamp, Mueseler 504

„ lamps, sources of danger „ 501

„ lamp, Stephenson 504

„ link, Ormerod's 399

Index.

Sands, Hastings 50

Sandstone, felspatliic 19

St. Bees 47

Sandstones 18, 56

„ altered 24

„ argillaceous 19

„ calcareous 19

„ calciferous 46

„ lower red 47

„ micaceous 19

Sarrebriick collieries, air compressors at 178

„ „ dimensions of air compressors .. 179

Satin-spar 5

Scaur limestone 45

Schist, chlorite 20

„ hornblendic 20

„ mica 6,20

„ talcose 20

Schistose 4

Scoria 14

Scottish coal fields 537

Scrapers 139

Seam

Seams of coal, determination of existence of

Searching for coal, cost of labour

„ materials

„ production

determining continuity of seams .. 88

difficulties attending 84

evidence afforded by borings .. 88

„ „ streams .. 84

„ of local traditions .. .. 85

general commercial questions .. 81

„ engineering questions .. 80

„ survey of district .. .. 83

hasty conclusions to be avoided .. 83

horizontal headings 88

in a new locality 83

in a partially known locality .. 85

market 81

means of conveyance 81

outcrop of seams §4

preliminary considerations ..

side drifts

special survey of district

trial headings

trial pits

Secondary period

Sections, geological

„ „ directions for making

„ oblique

„ „ table of

„ of strata from bore-holes

Sedimentary rocks

„ „ relative extent of

„ strata, table of

Selenite ..

Self-acting planes 328

advantages of 866

brakes 369

friction of ropes 370

laying out 367

pass-by 368

reels and sheaves 370

working 370

Self-detaching hook, Walker's 399

Semi-bituminous coal 63

Serpentine 25

„ limestone 23

Shaft fittings 272

„ pillars 278

„ „ dimensions of 278

Shafts, air 230

„ designations of 230

„ dimensions of 232

„ distance apart of 234

„ division of 272

„ downcast 230

„ drawing or winding 230

„ engine 230

„ form of 231

„ importance of 230

„ number of 231

„ operations of sinking 234

„ position of 232

„ „ questions determining 232

„ up-cast 231

Shaft-sinking 124

„ backcasing 256

„ „ advantages of 257

„ „ cost of 271

„ boring shot holes with machine drills .. 248

„ causes of explosion 241

„ contracts 271

„ corves 235

„ cost 271

„ curbing 236

„ drainage 244

„ drawing engines 243

„ „ the stuff 242

examples of .. .. 235, 254, 261, 267, 273

„ excavating tools 124

„ explosives 190

„ fitting up the mouth 242

,, head-gear 243

„ in quicksands 257

„ in quicksand, Belgian method .. .. 263

„ „ brick-drum 259

„ „ cast-iron drum for .. .. 261

„ „ examples of 261

„ „ French method .. .. 265

„ „ Kind-Chaudron system .. 266

„ piling 258

„ journal 270

„ kibbles 235

Index.

Shaft-sfuking, laying out pit-eye 272

„ operations of 234

„ position of shot holes 248

„ preservation of verticality 236

„ rock-diills 145

„ sinking in compact rock 247

,) „ through loose rock 257

J) „ to the stone head 236

„ South Staffordshire 242

„ sump 272

„ surface erections 235

„ tools for 235

„ tools used in excavating 124

„ tubbing 250

„ „ cost of 271

„ ventilation 245

„ walling 238

Shaft- ventilation, air-box for 246

Shafts, ventilative capacity of .. .. 489

„ „ cost of 271

„ water-bearing beds 250

Shale 4, 21, 56

bituminous 21, 57

carbonaceous 21

lias, spontaneous ignition of 49

limestone, lower 45

„ upper 45

Shaly 3,4

Sharpening picks 126,128

Shear-legs, simplest forms of 97

Sheaves 879, 383, 384, 386

Shell limestone 23

„ marl 24

Shells or wimbles 91

Shifts, apparent .. 34

Shiver 22

Shovels 124

„ cost of 125

„ sizes of 124

„ various kinds of 125

„ weight of 125

Shropshire coal field 585

Signalmen, duties of 529

Silicates 2

SiUcions limestone 23

Silt 21

Silurian period 42

„ „ characteristic fossils of 51

Sines and tangents, value of tables of, in geological

surveying 54

Sinking for coal, abortive 29,50

Sinking pumps 449

„ shovels 125

Skips 400

Slate 21

„ clay 21,25

„ flinty 25

„ marl 47

en i. PAGE

blates, Denbighshire 43

Slaty '' " "

Sledge handles or helves, length of 131,132

Sledge helves, cost of 133,134

„ making 133

), rate of making 134

Sledges 347

„ and hammers .. 180

11 „ making 132

„ cast steel , 132

„ cost of 132

„ rate of making 132

„ sizes of 131 132

„ various kinds of 131

„ weight of 181,132,189

Slickensides 31 33

Slide '33

Slig 22

Sliggeen 22

Slip 33

Sludgers 92

Slyne 60

Soda felspars 5

Solution, chemical 2

Somersetshire coal field 536

Sommeiller's air compressor, table of useful effect .. 177

South Wales coal field 536

Spar, calc 5

„ calcareous 5

„ Iceland 5

„ satin 5

Special systems of boring II7

Specification, Cornish engine and pumps 451

Specific gravity, carbonic acid 458

„ „ hydrogen 462

„ „ nitrogen 457

„ „ of coal 62-68

„ „ „ determination of 9, 70

„ „ of rocks 8

„ „ oxygen 457

I, „ proto-carburetted hydrogen .. .. 463

„ „ sulphuretted hydrogen 462

teat 172

Spontaneous combustion, causes of 610

„ „ prevention of 511

„ ignition of lias shales 49

Spring poles for boring 101

Square work 323

„ „ dangers of 324

„ „ waste of 324

Staffordshire coal field 534

Stalactite 24

Stalagmite 24

Stalls, dimensions of 309

Standage for water.. .. 272,429

Statuary marble 5,22

Steam and water, table of relative volumes 419

Index.

Steam coal 62,63,75

„ „ Admiralty Commissioners' Report on .. 75

Steel, hardening 137

„ tempering 137

Stemmers , 140

Step faults 35

Stephenson lamp 504

St. Gothard tunnel, air compressors at 180

„ „ dimensions of air compressors .. 182

Stinkstone 23,45

23,49

„ blasting gear, double-hand 139

single „ 139

„ „ dimensions of 288

„ „ machine boring 287

„ for shaft walling 239

„ head, sinking to 236

„ Lydian 25

„ picks 127, 128

„ Portland 23

„ wedges 130

Stones, water 48

Stoppings in air-ways 490

Stowage, conveying material for 331

5, material for 329

J, obtaining from surface 332

„ quantity of material required 329

„ sources for obtaining 330

Strains in pit-frames, determination of 401

Strata, definition of 26

„ sections of, from bore-holes 93

„ sedimentary, table of 39

Stratification, effects of currents on 26

„ of rocks 26

„ planes of 26

Stratified rocks 3

Stratum 3

Streak of rocks 8

Streams, geological evidence afforded by 84

Stretcher bar for rock drills 158,168

„ „ methods of using, in boring holes .. .. 248

Strike 28

„ faults 35

„ joints 30

„ of rook-beds, determination of 53

Stringing deals 237

Stroke counters for boring ,, ,. 101

„ of boring rods, length of 100

Structure of rooks 3, 4

Sturgeon's high-speed air compressor 186

Stythe 460

Sub-crystalline rocks 4

„ divisions of coal measures 46

Sulphur in coal, estimation of 70

Sulphuretted hydrogen 462

„ „ effects on animal system ., .. 462

Sulphuretted hydrogen, specific gravity 462

Sump 272,429

Supports for rock drills 148, 155

Surface erections 235

„ works 518

„ „ coke ovens 519

„ „ dwellings 519

„ „ engine house 519

„ „ landing stages 518

„ „ tramways 519

Surveying for coal seams 83

„ geological 52

„ „ difficulties of 52

„ underground 521

„ „ value of tables of sines and tangents in 54

Suspension, mechanical 2

Swab-stick 140

Swells or swellies 32

Syenite 6, 10

„ granite 10

Synclinal, axis of 29

„ curves 29

Systems of working the coal 305

Table op Aie Pebssure shown by water gauge .. 481

„ of composition of various British coals .. .. 68

„ of flow of water 453

„ of oblique section 55

„ of relative strength of explosives 207

„ of sedimentary strata 39

„ of temperature correction for barometer .. .. 479 Tables of signs and tangents, value of, in geological

surveying 54

Tabular rocks 4

Tachylite 17

Tail-rope system 376,379

„ „ arrangement of ropes , 380

„ „ duration of ropes 382

„ „ engine plane 379

„ „ working 381

Talcose limestone 23

„ schist 20

Tamping 191,216,218

„ best material for 219

„ broken brick for 220

„ clay for 219

„ errors respecting 219

in coal blasting 219

„ preparation of clay for 219

„ sand for 220

Taniping-irons 140

Tangents and sines, value of tables of, in geological

surveying 54

Temperature, increase of, in sinkings .. , 493

„ of compressed air 171

Tempering picks 128,137

„ rock drills 138

Index.

Page

Tempering steel 137

Tertiary period 38

Texture of rocks 3,4

Thermal unit 172

Thermometer 475

„ action of 476

„ air 476

„ mercurial 476

Thickness of rock-beds, determination of 54

Thirling .. .. „ 285

Throw of fault 38

Thi'ust, cause of 308

Tiger or nipping-fork 102

Tilestones 43

TiUers or brace-heads 102

Timbering 296, 336

„ arrangement of 298

„ cutting up timber 298

„ distance between sets 300

„ forms in which used 297

„ French methods 301

„ importance of 301

„ kinds of timber used 297

„ means of economy 298

„ removal of 336,338

„ repairing 303

„ sizes employed 298

„ special forms of 301

„ storing timber 298

„ various methods of 299

Timber, strength of 403

Time, geological, divisions of 39

Tools used in blasting 134

„ „ boring 90

„ „ „ auxiliary 139

„ „ excavating, blasting gear 139

„ „ „ borers or drills 134

„ „ „ hammers 130

„ „ „ picks 125

„ „ „ rock drills 145

„ „ „ shovels 124

„ ,, „ sledges 130

„ wedges 130

Torbanite 66

Trachyte 13

tuflf 14

Trachytic rocks 13

Traction, influence of roads on 360

Tramways 351, 360, 519

„ construction of 362

„ curves in 352

„ forms of rails 363

„ gradient of 362

„ importance of 360

„ influence of inclination on traction .. .. 362

,, „ of, on force of traction 360

„ joints in rails 363

„ junctions 351, 364

Tramways, space between sleepers 364

„ weight of rails 364

Trap-conglomerate 12

„ hornblendic 11

tuff 12

Trappean breccia 12

„ rocks 9, 10, 14

Trial headings or drifts 87

„ pits 88

Trias 47

Triassic period 47

„ „ characteristic fossils of 52

Tri-nitroglycerine, formula for 196

Tripod stand for rock drills 156

Trouble 32

Trough faults 35

„ „ explanation of formation of 35

Troughs 32

Tubbing 250

„ bearing curbs 252

„ cast-iron 252

„ „ cost of 271

„ „ merits of 254

„ „ examples of 254,262

,, „ fixing 253

„ „ formula for 254

„ „ protection of 254

„ concrete backing 252,256

„ fixing cast-iron wedging curbs 253

„ fixing wooden wedging curb 251

wedging curbs .. .. 238, 251, 252, 255, 256

„ wooden 250

„ „ cost of 271

„ for bore-holes 104

Tubs 348,379,383,384,386

„ advantages of 348

„ bodies of 355

„ capacity of 356

„ cost of 358

„ dimensions of 357

„ height of 356

„ importance of lubrication 358

„ iron 357

„ number required per cubic yard 78

„ qualities requisite in 356

„ resistance of, to traction 358

„ special forms of 357

„ tramrailsfor 349,351

„ wheels and axles 350

„ wooden 357

Tuff 12

„ basalt 14

„ doleritio 14

„ felstone 12

„ greenstone 12

„ porphyrite 12

„ trachyte 14

„ volcanic 11

Index.

Unconformity

Underground fires 1"

„ „ causes of 510

„ „ extinguishing 512

„ surveying ' 21

Units of heat

Upcast or upthrow 33

Upcast shafts 231

Upper lias

Uses of coal 73

VALtTB OP Coal, large and small, comparative .. .. 78

Valve-gear, differential pumping engine 446

Valves, clack 432

lift of 434

of pumps 431

seatings 434

slip of 432

spindle 432

velocity of flow through 434

Vegetable origin of coal, evidences of 58,67

„ remains in coal 57

Veinous rocks 3

Velocity of flow through valves 434

Ventilation, after-damp 468

„ air-pipe for 293

„ air-ways in goaf 492

area of air-ways 489.490,492

„ arrangements for ,. .. 488

„ atmosphere of coal mines 454

„ atmospheric measurement 475

,, calculation of air pressure 480

„ calculation of cm-rent 475,487

„ causes of vitiation 454,471

„ choke-damp 461

„ coefficient of friction of air 484

„ comparative cost of fan and furnace .. 499

„ „ results of fan and furnace ., 498

„ coursing 493

„ diffusion 469

„ direction of current 492

„ discharge of vitiated current into shaft .. 493

„ distribution of current 488

„ doors 491

„ dumb-drift 493

„ effects of blasting 472

„ „ of contractions in ways 487

„ „ of pressure of air 479

„ „ of velocity on friction 483

„ effects of velocity of current . . . . . . 490

fan 496

„ fire-damp 463

„ force necessary to overcome friction . . 484

„ friction of air in ways 481

„ furnace 495

„ Guibal fan 497

„ means of producing current 493

Ventilation, obstructions to current 485

„ of levels 285

„ of shafts 245

„ „ air-box 246

„ „ bratticing 246

„ of working faces 293

„ „ places 285

„ position of regulators 489

„ regulation of currents 489

„ „ furnace fires 495

„ relative advantages of fan and of furnace 496

„ safety doors 491

„ short runs necessary 482

„ splitting the air 488

„ stoppings 490

„ white-damp 461

Ventilative current, artificial 495

„ „ calculation of 475,487

„ „ capacity of shafts 489

„ „ crossings 492

„ „ determination of velocity .. .. 490

direction of 492

„ „ effects of surface temperature .. 494

free flow of 489

„ „ height of motive column .. .. 493

„ „ intakes 492

„ „ loss by leakage 490

„ „ means of producing 493

„ „ motive column 493

„ „ natural 495

„ „ regulators 489

„ „ returns 492

„ „ velocity of 490

„ „ volume of 471

Verde antique 23

Verifying tools for bore-holes 93

Vesicular rocks 4

Vitiation of atmosphere of mines 454

Volatile matters in coal, estimation of 69

Volcanic agglomerate 14

„ breccia .. .. .. .. .. 14

„ conglomerate 14

„ rocks .. .. 9,13,14

„ tuff 14

Wackb

Wad-hook

Walker's self- detaching hook Wall face, direction relative to dip

Walling 238

backing 241

bricks for 239

cement or mortar for 240

construction of 240,304

cradle for builders 240

danger in removing timbering 241

iu levels 303

in shaft, cost of 271

Index.

Page

Walling, methods of ,. 304

„ outlet for water 241

„ ring curb for collecting water 242

„ stone for 239

„ thickness of 240

„ curb 238

„ „ fixing of 238

Warrant .. .-, 22

Warsop rock-drill 165

Warwickshire coal field 535

Wastes, draining 505

„ searching for 505

Water, absorption of gases by 458

bearing strata, sinking through 257

blast 506

boring for 504

flow of, in suction pipes 436

friction of, in pumps 441

inertia of 441

percentage of, in coal .. 69

preventing influx of, underground .. .. 428

pressure of, in pipes 452

specific heat of 172

table of flow of 453

and steam, table of relative volumes .. .. 419

underground 425

gauge 480

,, table of air pressure 480

level 28

reservoirs for rock boring 189

stones 48

Wealden beds .. .. 50

Wedge driving sledges 131

Wedges 130

„ sizes of 130

„ weight of 130

Wedging curb 238

„ curbs, cast-iron .. .. 252,255,256 „ ,, wooden .. 238, 251

Weigher, duties of Welsh coal fields .. Wenlock beds . .

„ limestone . . Wheels and axles . .

„ coned

diameter of

348, 355

„ durability of 354

„ fixed 350

„ form of flange 354

„ influence of friction 354

„ loose 351

White-damp 461

„ lias 49

„ rock 14

Width of fault 33

Winding 385

„ accessory arrangements 421

„ cages 398

Winding chains 409

cost of 423

counterweights for load 413

drums 409

„ arranging lengths of ropes .. .. 411

„ coiling ropes 410

„ conical 415

„ diameter 410

„ position of 412

„ putting on ropes 411

engines 415

„ and accessories 409

„ boilers 417

„ brakes 421

„ dimensions of 243

„ „ cylinder 418

„ examples 424

„ power required 420

„ requii-ements in .. .. ..416

„ Eobey and Go's 243

engine-room regulations 423

guides 396

head gear 400

indicators 421

keeps 397

precautionary measures 421

precautions against overwinding 423

„ „ rupture of ropes .. .. 422

regulation of load 412

safety hooks 399

shaft 230

skips 400

Winstanley and Barker's coal-cutting machine .. .. 339

Wire ropes 406

„ disadvantages of 408

Wooden tubs 357

Work, loss of, in compressing air 175

Working faces, direction relative to cleat 316

„ „ to dip 320

„ length of stalls 315

„ importance of direction 316

„ supporting roof at 336

Working places, pressure on wall face 317

Working the coal, systems of 305

Workings, advantages of different systems 306

„ choice of system 312

„ influence of direction 322

„ in thick seams 323

„ lighting 500

long-wall 310,314

„ old, danger of approaching 504

„ post-and-stall 307

„ precautions against inundations .. .. 504

rise 320

Workmen, regulations for 529

Toeedale Eocks ..

Yorkshire coal field

LONDON : PRINTED BY WILLIAM CLOWES AND SONS, Limited,

Stamfoed Steeet And Chaeikg Ckoss.

J-ug

Fi.g

INCHES t=rFr

n e Q 7

s c

to

£& F.N. Span, L

Plate 37.

Is

Id

-I I r P -,-

G.G.Andre

idon & New York .

Plate 38.

n 3 e 3 €

I N r H c 1 1 1 1 1 1 I 1 1 I II 1 1 1 I I 1 1 1 ;t?I

E & F.N. SpaiijXandon lib Hew York,

Plate 39

411

J'zg 4T3

-m-M

JF tg 4-1 S

Ftq 4-16

G. G ftNDRE

E &.F ¥ Spoil Lonaon ScNewYort

Ftg 4-19

Ftg 4-ZO

Fxq 421

Ft a 4Z4-

F L cj 4-Z6

F-vq 4-ZZ.

Ftg. 423

o

r

F-L a 4ze

n 6 -I

INCHPSf I I I I

S C A L E S

Figs 1-25 8. 4-25.

FIGS tl9 TO +24.

l UXU I f -I 1 t .

G. G Andre.

E &.E K Landon New

Plate 41.

G.6 .andre:

E 8c FN Spon Lan.dan.JbiTewYork,

Plate 42

F I a 436

Fi.g 432

n

r"

(J : : o d

Ftg. 438

of bottom/

'.y

%

J

"S

Pn

Ftg 439

JPloTv of GiUde A.

Scales

Fiss 431 & 432

I 1 I feft

Figs 4-36 To 439

-A V-

G.G Andre

E IS?.'S. SpoaLondan &. New York.

Y'.ate

Foff. 4-33

D

am

6 ; <)i 0', o; 6: Oj f"

Frorub

Ftg 4-34

u

Scale

3:

H T pi

G. G ANC't't

E 8tF N. Spon. London 8cN"ewYork.

Plate 44.

Scale

3=:r.ET

E & F. N Span . London &,Hew Yor>

G G Andre

Plate 45.

T r. it 441

F t g 4-4-2

443

F.g

/

j

Jb

/

y

A

Scale

G G Andre

E&FN" Sfon London 8c TTew York

Plate 46.

1 :

'-X

3r:

3:

G G Andre

E S..F N. Spon LondDii iKewYork

Pla?,c 47

Fly. 44S.

J-',: a. 449.

f

f

cfa

45 C.

s

Hi

v>.

'.V0-,

\"n

V,-

:.

S C A L E .

-i=r

G G Andre

E iHSpoTi.landim&HewTfork.

Plate 48.

Ft a 4-5 5

:F -L g 45 6

Scale

iNCHEs m-rT I T I 1 I 31

G. G. Andre

£ 8cF. N. Sp on . L ondon 8c Ifew York .

Willi'

ui

O

I?"

Plate 50.

F-Lg 460

F-tg 46 Z

Ft J S63

F-ug

S

'"

Fog 46-

F-Lg 4-65

Fig 4-66

G. G. Andre

E 8cF. R. Spon. London &.New York.

Plate 51.

F tg 4-6 1

Fz.

F

4-G9

F -v q .

F y g

G. G. Andre

E F-K-. London g.lfewTork,

Plate 52

J'vg 47 Z.

Fiq . 473

T-bg .jf75

Kvq. 474.

Fig 47 e.

G. 6. Andre.

H &F.1T. Spoil. London &.lTewTi!brk.

P late bj

Is

G. G. ANDRf

E &.KN. Spon- London ScIfew'Siri.

P-tate 54

f

G. G. AiJDRE.

£ &F.H". Spoil. Xoudon &_N York.

Plate 55.

G. G. Andre

E &iF.If. Spon. London 8L New Yor"k

Plate 56

Ms

E&FN.Spon London 8<. New 'Sort-

Plate 57.

"EX.FW Upon LottdoTL 8<."PrewTork.

G. G. Andre

Plate 68,

G. G. An Dre

E SlEM". Spon. LcmdoiL&.New'Xorlc

L-late 59.

'''ni.m)

ss

r

G. G. Andre

", &,F W Spon LondoTi 8>.Ne" Yovk

Hate 60.

G. G. An Dre

E ScEIT. Span. Icmaon Wew'Xark

Plate 61

G. G. Andre

IE &F K" Spaa Londrm. StKewlSjrk

21ar,K 62.

Gg. Andre

E &F.N. Span. London & Wewyoric.

Plate 63

Ftg 49Z.

777777/

TiTii TTTTTi I 11 I I '

Ti.q . 4-3G.

G G Andre

E F.TSI. Span. laruiQn&, New York.

Plate 64.

F lyg 49 7

Fi.g 'i-9S

Fiyg . 4-3 9.

Fi,g . 500.

G.G. Andre.

E &r.N. Spon.landon &JIevT"&rk

I? g J g

FIG. SOI -f—

.f , , f , , f

3 Feet

G.G.Andre

F rVN T.,rm.don*l!ewVTrX

F x.g 503 .

Plate 66.

1 2 3 e 3 c

INCHESi I I I I I I I I I I I I

Scale

G G.Andre

E

Ftg 505 .

JF-Lg .50 7

Fia 603.

'9

F-bg 510

J

UJjl

On

Scales

F I G. 505 .

Fid 506.

Fvg 508.

FOg . 511 .

Fvg 51Z

m 3 6 J

Fig6 506 To 512.

E *.T "N Spon.Laricbn &14i3w York

G.G. Andbe

F i/ g 5 13

Fi.g 515.

F i' g 5 16

G.G.Andre .

E & I iJ Span london iStHswlork .

Plate 69.

-Fvg. 517.

F vg. 51 S.

jFi. 51 d.

F-og . 5 ZO.

F ig . 5 ZZ.

F'i.g 521.

Fiyg 523.

- ij- s e J P

Scale Figs 520 To 523.

E & P.N. Span landon S'Spv-r York.

G.G.Andre..

Plate 70.

-v

ig . 5Z4-

F -0 g :. 52 6.

Ti.

S27.

Fvg . 52S .

F i/ a . 523

/ frf, , f , ,f ,, y

S C A L E S

Fig* 52* To S27

Fig 528 523

I f I I I I I f I I I I I Tl I I I TT lNCMt

E AT N. Spoil London Ifork

Ph

6 G Andre

Plate 71.

Fi.g . S6C.

Fig 56 2

F-Cg 56 3

Fiyg . 5 65

A

S C A L E S

Pig9 560 To 561 .

INrHF.' F [ ill iT. iTlli

Figs 562 To 56*

f, , f , , f

lAFN Spcai.Lcindan.(fe New "York

G.G Andre..

F i/q 6 66

F t a S 6 S.

IIMf.MF.g Fi I I I I I , . I I , I

S C A

Fig? 561

NCHEs fe I f I I f , , f , , '

E&P.3SI. Span.Lon

Hate 72.

F-ig 569

Ti.q . 571 .

G.G.Andre.

Fiyg . 6 7 4-

Ftq 576

T-ug 577

F-Og 57d

F-ug 57 S.

Fvg 58S.

E&i'.N.Span.Lon

Hate 73.

i/g 5SZ

vs. &,New"Kark .

G.G. Andrl

Plate 74.

E A T N , STMn london <flew-York

:f-i() 51

F-Lg . 5tS1 .

-t 1 Span.Lono;

Rosscut Way

n&lTewl&rk.

G. G .Andre.

Fi.q .538.

Fiyg 5 97

F-ug

6dd.

E&F.N.Spon.Lcn

Hate 76.

Bridge. Pit

Boilers

G.G.Andre.

n A/New Ycjrk.

F i. ij . o

:f-ci

I I (°i

m ? e 3

S C A

F1G5 sols,

A- F N Spoil Lonv-

Plate 77.

I'tq. 614

D

E .

Tig CIO

M 1± 7J

I I

G.G. Andre

Fvg G1S.

F-Lg 619

C A

n

s

1S

F 1 G5 2S

NCHESlHH f— 1

M

1 — 1

1— 1

1— 1 1—1

1— 1 1— 1

1— 1

H 1— 1

1— 1 1— 4 1— 1

1 — .

INCHESlHI&Z

1

Fiyg 6ZZ.

Plai 78.

F vg G2C.

F-vg . 621

L e s .

18 To 621. , 62 2.

40 -K Bo Ss W

—I I-

3: 1:

G.G.Andre.

don. &Bew York.

F-bg GZ

Ftq eZd .

Inchesehz

10 Is

I— I I— I i-r-F=

F V

S C A

F I G i

I? a 6 3 INCHES IHHHMHH '

Fig? S24-.

EAF.il.SpcirL;

Plate 79.

F-Cg 625.

F ij q G 2 G

JFlg eZT.

G Z9.

G 623 . m 36

a M M M 1-H

24 To 63 0.

45 iO ss en

I— I KH I— I I— I I— I I— I I— I T=l FEET.

Fxy 630.

G G.Andre .

ndon (icNew Yorls..

iyQ . 631.

Ftg

63Z .

S C A

Pig? 63

n i 3 4 i M ii x li ,

iNCMEs tmrM I— I K-i"1='1= r - t— I l-HT- l t— I 1-41— II— iTh MZ EJ

n 9 6 i a

t NCH ES I I' I I ' I I I I I 11

Fig? 634

Tiaie 80

:Ft.a 634

xjq 636.

L E S

I To 633.

isis

ifersz

-M-

.e

I— I I— I Feet.

I- To 636 .

e

mdoa (jkTJew'iork.

G, G.Andre

1Z G 3

iNr-.HFR l-h-l l-l l-l >-H M t-r-

n d e 3

INCHES I- M t-l l-l H l-r T=t-

E.'i:.F.N,Spon.Lc

Frg 64 5

G-G. Andre

Plate 82.

aeo 1 Z 3 1-5 10 .

Scale

Gg Andre.

EAT N. Spon. landon &BewYar"k.

EilJ..lS

Plate 83.

r/.j.'j

Lanaan &. Ifevy "Krk.

G.G.Andre.

riaie

&<!New1&rk .

G.G.Andre.