An Elementary Class-book of Practical Coal-mining: For the Use of Students Attending Classes in ...

Thomas Hansom Cockin · 1905 · Historical

An Elementary Class-book of Practical Coal-mining: For the Use of Students Attending Classes in ... by Thomas Hansom Cockin (1905). Full text and reference…

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

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WBAtrS SCIENTIFIC & TECHNICAL SEBIES.

MECHANICAL ENQINEERINQ. &c.— conW, Sewing Machinery. J, W, Urijohailt . Power of Water. J. Glynn Power in Motion. J. Armodu Iron and Heat. J. Aouotrs Mechanism and Machines. T. Bakbb J. N&sjitth

Mechanics. C. ToHLiHaaH

Cranes and Machinery. J. Glysn Smithy and Forge. W. J. E. Ckane Sheet-Metal Worker's Guide. W. J. K. Gbahb . Elementary Electric Lighting, A, A. C. Swihion

MINING & mETALLURQY. Mining Calculations. T. A. O'Dukahl-b

Mineralogy. A. Kaubat

Coal Mining, Sir W. W. Smyth iiT. F. liicu.s- .

Metallurgy of Iron. H. Bauekman .

Mineral Surveyor's Guide. W. Listbbn

Slate and Slate Quarrying. D, C. Davieb

Mining and Quarrying. J. H. Collins

Subterraneous Surveying. T. Fbhwios & T. Bakkci

Mining Tools. W. Morgan's .

Plates to ditto. 4t0. .

Physical Geology. Poktxook & Tai b

Historical Geology. B. Tatk

The above 2 toIs., bound togothtr , Electro-Metallurgy. A. Watt

NAVIGATION, 5HIPBUILD1N0, &C Navigation. J. GasEHWOOD k W, H. Rokser Practical Navigation. Gbekswood, Rosbkk & Law , Navigation and Nautical Astronomy, J. R. Youno Mathematical & Nautical Tables. Law k Yohnq Masting and Rigging, K. KrppiMo . Sails and Sailmaking. R. Eippinq Marine Engines. R. MirnRAy & G. Carlisle , Naval Architecture. J. Pbakb Ships, Construction of. H. A. SouURRFELnr .

Plates to ditto, 4to

Ships and Boats. W. Blast

I CROSBY LOCKWOOD 4 SON. 7, Staii

' HaU Court, !

9S.

The New York

Pubuc Ubrart

An Elementary Class-Book

Of

Practical Coal-Mining

For The Use Of

Students Attending Classes In Preparation For

The Board Of Education And County

Council Examinations

Or Qualifying For First Or Second Class

Colliery Managers' Certificates

Ijy

T. H. Cockin

Member Ok The Institution Of Mining Engineers

Certificated Colliery Manager

Lecturer On Coal'Mining At Sheffield University College

eSTttfi aqp of it %xiix Coal- atOr 200 mniXxntimH ijpcrmnj) IBraton anlr iiitsrabclr for

1 /

New York

The Norman W. Henley Publishing Co.

132 Nassau Street Jl O N D O N

Crosby Lockwooi) And Son

The New York

Public Library

A8T0R, LENOX aKO

TMDEN FOUNDATIONi.

Printed By

William Clowes And Sons, Limited,

London And Decclbs.

Preface.

The Author's experience as a Mining Lecturer in Yorkshire and Derbyshire leads him to believe (although excellent textbooks by experienced writers are already available) that there is still an opening for an Elementary Class-hook which shall give a student not only a general grasp of the principles of Coal-Mining, but also some insight mto allied subjects such as Chemistry, Mechanics, Steam and the Steam Engine, and Electricity.

The tendency of the times is towards a higher standard in all branches of Technical Education, in consonance with which a higher state of efficiency is now being demanded of - those who present themselves for Colliery Managers' and other Mining Examinations. It is with the view of meeting these conditions that the Author has carried this work to a rather more advanced stage than has hitherto been considered necessary for an Elementary Class-book.

In dealing with the various topics of the volume, the Author has endeavoured to start at the very commencement, and has assumed no previous knowledge on the part of the reader; at the same time, obsolete methods have not been described

Preface.

except where they illustrate principles or point out the trend of modem improvements; and in this way space has been economized, with the result that probably in no text-book on Coal-Mining published at so moderate a price will be found such a complete and advanced treatment of the subject.

While not adhering to the formal syllabus of any mining examination, the Author has covered the ground required by the Board of Education and County Council Examinations, and the student who is qualifying for his First or Second Class Colliery Manager's Certificate will find that this volume will supply him with the theoretical knowledge he needs, and in addition, furnish him with many and varied examples of actual mining practice, drawn from some of the largest collieries, and those best equipped with modem appliances, in the country.

The illustrations in the text are for the most part from original drawings specially prepared for this work, all unnecessary complications being avoided, so that the diagrams may be easily understood and used as examples for sketching.

A large number of arithmetical examples have been introduced, the working out being shown in detail in order to enable students to readily grasp the principles involved.

The Author has not ventured to undertake the preparation of this work without a practical connection with collieries in several counties, extending now over many years; and he cannot too strongly express the opinion that the closest study of eveii the best text-books, and those of the most elaborate kind, will be of little avail to the aspiring colliery manager unless coupled with practical experience in the mine; and BS the conditions of Coal-Mining vary so widely, some

Preface. V

degree of knowledge of as many coal-fields as possible is also desirable.

Finally, the Author has pleasure in acknowledging the assistance afforded him by Mr. Herbert Perkin, who has kindly revised the text and made many valuable suggestions. He is also indebted to several manufacturing firms for information given in answer to his inquiries, and, in some instances, for the loan of blocks of illustrations.

Sheffield,

September i 1904.

Contents.

Chapter I. Geology.

I'A(;e

The earth's crust — Classification of rocks — Stratified and unstratified rocks — Metamorphic rocks — Order of succession of stratified rocks — Carboniferous system of rocks — Permian and Triassic rocks — Formation of coal i

Chapter H.

Structure Of Stratified Rocks.

Strike, dip, and outcrop of beds — Methods of measuring and expressing gradients — Bedding and jointing — Conformability — Rolls — Thinning out of beds — S wellies— Overlap of strata — Normal faults — Step faults — Reversed faults — Efifect of faults upon outcrops — Dykes — Wash-outs — Geological maps . . . .16

CHAPTER ni.

Coal And Coal-Fields.

Statistics — Produce of coal-seams — Produce of inclined seams — Occurrence of coal— Peat — Lignite — Bituminous coal — Anthracite — Brief description of each of the British coal-fields ... 33

Chapter Iv.

Search For Coal.

Preliminary operations — Boreholes — Method of finding true thickness of inclined seams — Finding rate and direction of dip from three boreholes — Percussive method of boring — Lining boreholes — Mather and Piatt's method of boring — Diamond method of boring — Davis-calyx method of boring 48

Contents.

Gobert's methodSinlting by the aid of

Chapter Vi.

SINKING {eenlinatd).

AlTangements at sinking-pit top — Winding and capstan

Calculating weight capable of beinE raised by steam capsians — Ventilatioa of sinking pits — Winding the dSris—'ExQa.vsiiaa — HupportiEg the shaft sides — Walling curbs — Scaffolds— Bricking shafts— Sinking with rock drills— Walker's patent sinking frame

Chapter Vii.

SINKING [cefiitmeJ).

Presence of water in shafts— Tubbing — Cotfeiing— fi sinking pits — Winding water — Hanging lifts Suspended sli pumps — Electric sinking-pumps — Kind-Chaudron process sinking — The Pattsberg method of sinking — Deepening and widening existing shafts — Sinking upwards Sinking "

Chapter Viii. Opening Out.

Chapter Ix.

Miners' Tools.

Picks — Wedges — Hammers — Shovels — Drills — Hand-boring niDchinesSharpening and tempering steel — Blasting tackle — Sylvester's patent prop withdr a wer Mechanical wedges .

Chapter X. Explosives.

Is

Contents.

Chapter Xl Methods Of Work.

Chapter Xh.

Working By Longwall.

Longwall in seams of moderate inclination — Modificatio

wall — Longwall in inclined seems : examples from the Barnsley, Atlej-, and Silltstone scams — Longwall with gates in the solid — Longwal] rclrealing: example froni Ihe main

Chapter Xiii.

Methods Of Working By Pillar And Stalu

Durham meihoJ of pillar and stall — Barnsley Bank method — Botd and pillar work — Double-tail method of work — Working coal in liftsCalculating proportion of whole and broken coal .

Chapter Xiv. Special Methods Of Work.

Methods of working steep seams by longwall— North Staffordshire metliDd of working nearer coais — South Staffotdshiie square work Diethod— Working contiguous coal-seaiaa — Warwickshire method 167

Chapter Xv.

Timbering.

Preservation of timber — Props — Cogs or chocks— Bars— Calculations IS to strength of bars — Spraga and cockermegs — Tapered props — Steel girders — Masonry — Spiling ihrougl' loose ground — Courrieres system of timbering 176

Chapter Xvi. Coal-Cutting By Machinery.

Il Statistics — Advantages and application of machine holing — Diamond L machine Rigg-and.Meiklejohn '' r- -

L machir " '

H machii

B naacbii

Chami

, - machine — Jeflrey disc machine — Clarke - and - Steavenson machine — Hurd machine — Lee machine — Morgan-Gardner — Stanley heading machine — Ingersoll machine — Champion mHchinc , ,

Coxtexts.

Chapter Xvii.

Units of vesg po ver, and coer — Vanocs forms of lereis — Calcolatiocs rciaiing to Icrcrs — bdi piiI2eTs aad toothed vbeels — Calmlations as to gearing — BIoc pcillers — Tbe isdied plazic — Screws — HTdrsalic machiaeiy — Fricnco of sohiis — Fnctioii of fluids 209

Chapter Xvih.

Heat — Units of heat — Specific heat — Transfer of heat — Properties of steam — Expansion of steam — Richards' indicator — Indicator diagrams — Steam-ei;ine, simple and compound — Jet condenser — Surface condenser — The Lancashire bofler — Water-tube boilers — Economizers — Compressed air — Calculations relating to aircompressors — Air-compressing in stages — Air-mains — Driring air-compressors by electricity 225

Chapter Xix.

Gases.

Chemical elements and compomids — The atmosphere — Oxygen — Nitrogen — Carburetted hydrogen — Carbon dioxide — Carbon monoxide — Sulphuretted hydrogen — After-damp . . . 249

Chapter Xx.

Ventilation.

Charles's and Boyle's laws — Motive column — Friction of air in mines, rules and calculations — Co-efficient of frictioa — Power of ventilation, rules and calculations — The fiimace — Dumb drifts — Natural ventilation — Steam jet — Schiele fan — Guibal fan — Walker's fan — Waddle fan — Capell fan — Calculating size of engine necessary to drive fans — Closing in upcast shafts — Ventilating the workings — Stoppings — Doors — Air-crossings — Brattice —Splitting the air 256

Chapter Xxl Instruments.

Barometer — Verniers — Aneroid barometer — Thermometers — The water-gauge — Hygrometer— Anemometer — Measuring the air and caTcuUting the quantity 279

CONTENTS, xi

Chapter Xxii.

Lighting,

Naked lights— Snfety-l amps ; Davy, Cknny, Sleplienson, Marsinl, Mueseler, Hepplewhite-GtHy, ThDrneburry — niimunanls for lamps— Locts— Relighting lamps in Ihe workingsElectric safety-iainps — Fire-damp indicators : Fieler, Clowes, Stokes, Beard-Mackie ' . , aSg

CHAPTER XXni.

Winding.

Ilead-geac— Pulleys— Cages— Props— Conductors ; timber, rails, and ropes— Windmg ropes: ordinary lay, Lang's lay, and locked coil — Calculations as to weight and strength of ropes- Capping wire ropes — Chains — Equalizing load on winding engines — Spiral drums— Balance ropes— Chain and staple — Detaching hooks — WiniiiDg from two fevel. — Calculating siie of winding engines .

Chapter Xxiv.

Haulage.

ives— Setting out curves — Calculations as to frictiou of corves — Horse haulage — Self-acting inclines, calculations as tn gradient, jinn eying from two or more levels — Single- rope haulage, drags, calculations as to power required — Main and tail rope haulage — Endless-rope bandage : calculating ratio of engine gearing, rope wheels, tension pulleys, junctions, friction clutches, branches, attachment of cores to ropeFisher's clip— Branches— Calculations as to size of engines , i

Chapter Xxv.

Pumping.

Memoranda — Source of feeders underground — The syphon — Bucket pumps, calculations as to quantity of water delivered — Ram pumps — Pumping by several lilts — Balance bobs — Driving pumps by reciprocating and rotary engines— Double-acting pamps, pistons and rams — Air-vessels — Calculating siie of pumps for a given duly — Siie of pipes required — Worthiogton pumps — Three-throw pumps — Hydraulic pumps — Pulsometers — Centrifugal pumps — Pumps for sinking pits — Winding water — Ricdler

Contents,

Chapter Xxvi, Surface Arrangements.

EDgine-houses and boilers — Shops and stores — General anangemeiil of snrbce works — Sidings — Arrangement of roads on pit bank —Tipplers — Futed-bai and jibing screens — Picking bands — Coal washeiies ; trough, MortoD, Elliot, Robinson, and Baum . 366

Chapter Xxvh,

Coke-Uaking.

Analyses of coal and coke — Beehive ovens — Firing boilers 60m waste gases — Retort ovens — Simon -Carves ovens — Charging and compressing machinery — By-producis 383

CHAPTER XXVIll.

Accidents.

Statistic* — Explosions — Coal- — Pneumataphor — Falls of n

and sides— Shaft accidents — Miscellaneous accidents: on haulage '1 roads, from suffocative gases, from the use of explosives, fiat ¥ eruptions of water — Spontaneous ignition — Dams against gob- 1 lires — Boriog against accumulations of water — Dams agaitut ] water, calculations as to pressure — Miners' diseases ; phlhias, 1 ankylostomiasis, nystagmus

Chapter Xxix.

Electricity.

Electric lermi : volt, coulomb, ampere, ohm, vfatt, unit — Calculations as to Board of Trade unit series, shunt, and compound winding — Cables : calculations as to size — Motors— SwitchesCut-outs — Electric lamps : incandescent and arc — Systems of wiring — Polyphasi plants— Dangers of electricity — Calculations as to size of electric I machinery

Coal-Mining.

Chapter I.

Geology.

Scope and Value of Geology. — Geology is that branch of ] science which investigates the history and construction of our globe. It examines and classifies the various materials which form the crust of the earth as far as they are accessible ; and inquires into their modes of formation, and the changes that they have undergone since deposition. Although geology is one of the newest of the sciences, it is of vast practical and industrial importance, and has of recent years made very great advances.

A knowledge of geology is of great value to all engaged in. mining. It points out where to look, and where not to look for the various valuable minerals, and indicates the position and extent of irregularities and disturbances in the strata.

The Earth's Crust.— The earth is supposed to have been at one time a molten mass ; the exterior of which has gradually cooled down and solidified, forming what is known as the (r/ir/of the earth, whilst the interior is beheved to be siill intensely hot That ihe interior of the earth is extremely hot is proved to some extent by volcanoes, by the presence of igneous rocks, and by the fact that the deeper we penetrate the earth's crust, the higher the temperature becomes.

As the crust of the earth cooled, the atmosphere would be

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Geology.

to the action of heat. Fig. i illustrates the mode of o of the igneous or unslratified rocks. The earth's crust seems to have been rent asunder, and the material which has formed the igneous rock, forced through in a molten condition. In the figure the molten material is shown to have overflown upon the surface, forming a boss and overlying the stratified rocks. At C, the igneous rock is iiitcrsfrarijUd, that is, it has been i forced into the stratified rocks, running along the bedding , planes ; this is frequently the case, especially where the stratified rocks are composed of some soft material such as coal. some coal-fields much coal is destroyed by the intrusion of Igneous rocks in this manner ; the molten material having i

P

f'fJjmiTn

Fig. 1. — Igneous and aqueous cocks,

practically taken the place of the coal over large areas, burning and coking the coal at the points of contact.

Examples of igneous rocks overlying coal-measures, somewhat after the manner shown in Fig. i, are to be found in Leicestershire and South Staffordshire, in both of which districts shafts have been sunk to coal through a considerable thickness of igneous rocks, which has been forced to the surface and spread over large aieas. Unstratified rocks are not very frequently met with in coal-mining ; but where they are mej with, they are a source of trouble and expense. In some of the largest of the British coal-fields igneous rocks are entirely

r

4 Coal-Mining.

Aqueous, or Stratified Rocks. — These occur in parallel layers or strata ; they have a definite line of dip and cleavage, and are non-crystalline. Stratified rocks being formed by the agency of water, are known as ajiteoiis, or sedimenlary. All stratified rocks are built up from the waste of older rocks ; thus, in order to form new rocks, older ones have to be destroyed. Some of the stratified rocks are built up of the waste of older stratified rocks, others from the waste of igneous rocks. The process by which the stratified rocks have been formed, and by which they are still being formed, is as follows : The existing rocks are continually wasting away, or denuded, chiefly by the action of rain and frost, assisted in some cases by the wind, sea, and running water. The dibris, or waste material, gradually makes its way down to the streams and rivers, which carry it out to sea, in the shape of mud, sand, and shingle. As the river widens out and enters the sea, its velocity is checked, and the mud, sand, and shingle are deposited at the bottom — the heavier falling first and the lighter being carried further out. In course of time, these beds become solidified by the pressure of the material deposited upon them, and stratified rock beds are formed, the mud, sand, and shingle becoming beds of shale and fine- and coarse-grained sandstone.

Rocks formed in this manner are known as mechanically formed rocks, and embrace the sandstones, shales, clays, etc. ; some stratified rocks, however, have been formed chemically and some organically. Travertine, or tufla, is an example of a chemically formed rock ; springs charged with carbonic acid gas pass through crevices in limestone, and the water, owing to the presence of the carbonic acid gas, carries Hme away in solution ; but when the spring breaks out into the open air, the carbonic acid gas escapes, and the lime is re-deposited, forming a newer rock bed. Other examples of chemically formed rocks are gypsum, rock-salt, and some limestones.

Organically formed rocks are those built up from the remains of once living vegetable or animal organisms. Some limestone, for example, is composed almost entirely of the remains of marine plants and animals. The plants and animals had the

Geology.

property of extracting lime from the water in which they lived ; as they died, their remains, which consisted chiefly of carbonate of lime, sank to the bottom, and in the course of lime built up rock beds of immense thickness. Coal is also an organically formed rock, being composed of the remains of vegetable substances.

Metamorphic Rocks. — Rocks which have been so much changed since their deposition as to have lost all traces of their original character, are known as melamorpMc, or altered rocks. The alteration is, in most cases, due to heat and pressure, which has usually destroyed the lines of stratification and caused semi-crystallization. Some metamorphic rocks merge intojgneous, others into stratified rocks.

Age of Rocks. — It is, of course, impossible to arrive at the exact age of any group of rocks; but the relative age of the stratified rocks has been determined. This has been done by ascertaining their relative positions ; thus, if one group of rocks is always found above another, it follows that the group which occupies the lower position is the older. Information as to age has also been gathered by studying the fossil remains found in the various rocks, and the character of the rocks themselves.

The relative age of igneous rocks is difficult to determine, but may be roughly estimated ty finding the newest rocks which they intersect, and the oldest faults which intersect them. For example, if a bed of basalt intersects coal-measures, it is obviously newer than the coal-measures ; and if this basalt was found to be affected by a fault that also affected the coal- i measures, the basalt would have been formed earlier than the fault, and later than the coal-measures.

Order of Succession of Stratified Rocks.— The stratified rocks have been divided into four main groups, the classification depending upon the fonn of life which existed during th% period when the groups were being formed, a record of which is preserved in each by the fossils.

These main groups

Cainoroic, or Tettiaries (recent life). Mesozoic (middle life).

Pal;em:oic (ancient life).

Azoic (without life).

These main groups are subdivided into the following

stems : —

„ . - f Post-tertiarv.

I Cretaceous. Oolitic. Lias. Trias. f Permian. Carboniferous. Devonian, or Old Red Sandstone, Silurian. Cambrian. Laurent! an.

f Rocks older than Laurentiai), mostly Azoic Cr>'5tailine and Metamorphic.

Each of these systems may be subdivided into rock groups, and the rock groups into beds.

The rocks shown in the table would have a thickness of .ibout twenty miles if they were all present together, but this is never thq case. The surface is sometimes composed of the rocksofonesystem, and sometimes of another. If, for example, the surface is composed of Carboniferous rocks, all the rocks above the Carboniferous system would be absent ; the lower systems might, or might not be present, but where they did occur, they would be in their proper order. In short, though rock systems are frequently missing, they are never out their proper order unless under very extraordinary conditions which are never met with in coal-mining.

The order of succession of the stratified rocks is of the

Geology.

greatest importance ; it shows us, for example, that k would be useless to bore for coal in any district whose surface was composed of rocks belonging to any period earlier than the Carboniferous ; whereas, if the surface consisted of rocks higher up in the scale, the Carboniferous system might exist, though it by no means follows that it would, as frequently many of the systems are entirely absent, and rocks high up in the scale are found reposing on rocks quite low down. A detailed description of the whole of the different systems is beyond the scope of this volume, but the economic value of each is briefly as follows : —

Terliaries. — Clays, building-stones, marbles, sand, grave!, lignites, J

Cretaceous. — Qialk, flints, iron ore, inferior coal.

OoliUs. — Clay, iron ore (Northamptonshire), building- si one (Bath).

Lioi. — Ironstone (Cleveland), limestone, alum shales, jet, inferior

Trias. — Gypsum, rock-salt, clay (Peterborough), Permian. — Building-stone, magnesian limestone. CarbaiiifcrOTis. — Coal, ironstone, fireclay, building-stone, limestone 1

lead, inc, copper, barytes, chert, umber, manganese. De-Donian. — Marble, iron ore, Siiurtan . — Limestone.

Cambrian a?id Pre-Cambrian. — Gold (Dolgelly), copper, granites, marbles, slates.

The Carboniferous and Adjacent Systems.— The

Carboniferous system is overlaid by the Permian, which, in its turn, is covered by the Trias, when all three systems are present As most of the undeveloped coal in Great Britain lies in measures which are covered by one, if not by both, of these formations, it follows that most new shafts will have to be sunk through them. Both these systems are, therefore, of . great interest to the coal-miner. J

The Trias. — This system occurs above the Permian, 1 being, in some places, conformable, and, in other places, unconformable with it. The system in Great Britain is divided

COAL-MtNING.

into tiro main series of rocks, tu, tbe Keupcc and the Bunter. The Keupo' consists of red and green mails and sbales, with occasional beds of sandstone. In Cheshire valuable beds of rock-salt are found in this series, and in Nottinghamshire impoitant deposits of gypsum have been worked in it for manj years.

The Bunier scries of rocks consists of soft variegated sandstones and mails with thick pebble beds. Its chief industrial importance is its value as a water-bearing tocfc, large suppUes of excellent watei being obtained from boreholes in it. Its watei-bearing quabties make it veiy costly to sink through.

Rocks belonging to the Triassic system cover a large area in the centre of England, usually forming rich undulating pasture land, with few hills of any importance.

The Permian System. — The rocks forming this system consist of sandstones, marls, and magnesian limestones. In Yorkshire and Derbyshire the Permian rocks form a long narrow band lying along the whole of tbe eastern boundary of the coal-field, and carrying two beds of magnesian limestone, both of which are extensively quarried for lirae-making and building purposes. The stone used for building the Houses of Parliament was obtained from quarries working these rocks.

of

The Carboniferous System. — The main divisions the Carboniferous system, as it occurs in Great Britain, are

Upper coal -measure.

Middle do.

Lower do.

Millstone grit.

Yoredale shales and limestone.

Mountain, or Carboniferous limestone.

!

The tipper coal-measures consist of shales and sandstones, with thin beds of limestone and thin seams of coaL This

Geology. 9

scries is not represented in the Yorkshire and Derbyshire coalfield, and is nowhere of great industrial importance.

The middle or true coal- measure arc the series of rocks from which the great bulk of our coal is derived. The measures consist of sandstones, shales, and clays, with numerous beds of coal and ironstone. The sandstones vary in texture, but are usually fine grained ; their colour is white, yellow, or pale blue, though sometimes stained a reddish tint owing to the presence of iron.

The shales are mostly blue or black in colour, some merge gradually into sandstones, and others ate highly bituminous, and may contain a considerable quantity of oil. The clays are usually of a hard character ; some contain much silica, and are valuable as fire-clays ; other clays are carbonaceous, and contain stigmaria rootlets, tMs being frequently the case with the "spavin," which is usually found underlying the seams of coaL

Formation of Coal. — There are two theories as to the formation of coal-seams ; both agree that coa! is formed from the vegetable remains of dense forests, or, more probably, of thick low-lying swamps covered with great masses of luxuriant vegetation,

The difference of the two theories is that, while the one I considers that the coal-seams occupy the exact site of the I swamps, the other maintains that they do not. The former is known as the in si/ii theory, and the latter as the drift theory.

The in situ theory appears to be the more generally I accepted of the two, but neither accounts in a very satisfactory j manner for the whole of the phenomena which present themselves in connection with the formation of coal-seams.

T/ie"iH situ" theory, — According to this theory huge swamps or marshes covered the area now occupied by coal-seams, this area subsided, or sank below water-level, owing to the gradual movements of the earth's crust, and was covered with water, which formed the medium for the conveyance of mud, sand, etc. This mud and sand covered the vegetable deposit, and,

Coal-Mining.

by becoming hard and solid, formed beds of shale, sandstone, etc., which, in course of time, filled up the shallow waters in which they were deposited, other marshes of dense vegetatioD grew on the site, subsidence again took place, more mud and sand was deposited, forming more beds of rock and shale, and so on throughout the whole series.

T/ie "drift" theory. — This theory holds that coal-seams were formed in exactly the same manner as the shales and the sandstones which surround them. According to it, the swamps and forests grew elsewhere, probably on the banks of large rivers, and vast masses of decomposed vegetation were transported by water and deposited in their present position, which may have been a large inland lake, or, more probably, the mouth of some great river.

In considering these two theories, the following questions naturally suggest themselves ; —

1. Is coal being formed at the present day? and if so, how?

(Will not the large peat-bogs, in course of time, become beds of coal ?)

2. Are not the rootlets, which are found in the under-clay,

the roots of the vegetation which formed the coal ?

3. How is it that coal-seams are so regular in extent and

thickness ?

4. How are the " bats" and carbonaceous shales formed,

some of these being half coal and half dirt, and others being shale at one place and coal at another?

5. Ail coal-seams are " laminated," that is, they are divided

by partings into various bands and quahties. How is this to be accounted for ?

It may be that some seams were formed iu situ, and others by drift. It is a subject which presents many difficulties, but the student may form his own opinion by studying the questions suggested with reference to the coal-field with which he is most familiar.

The Uw coal-mmsums or ganisler series consists of flagstones, shales, and gritstones, with thin seams of coal, ironstone, ganister, and fire-clay.

Geology.

The ganister, from which the series sometimes takes itsl name, is a veiy hard, fine-grained, and highly siliceous sandstone; it contains, in some cases, up to 98 per cent, of sihca. ' In the Yorkshire coal-field the most important seam of ganister is found underlying the Halifax Hard, or Ganister seam of coal. It varies in thickness from a mere trace up to 5 or 6 feet, and is used in the manufacture of refractory bricks for steel furnaces, The lower coal-measures also contain the ironstone from which the well-known Lowmoor and Farnley iron are made.

The millstone grit is best developed in Yorkshire and Derbyshire. It consists of massive grits, made up chieSy from I granite dihris. These grits vary greatly in texture, some being very fine and others quite coarse. In Derbyshire there are four beds of gritstone separated by shale ; most of the wellknown " edges " of the Peak district are formed by the escarp- J ment of the third bed of grit. Thin seams of coal have been f worked fiom the shales accompanying these grits, and the finer I grits make excellent building and ashlar stones, otherwise the J millstone grit is of little industrial importance. The c grits are made into millstones for grinding oats, cork, etc 1 hence the name of the series.

The Yoredale and Carbo/ti/erous limestones are very well 1 developed in the northern counties, covering a consider able portion of north Derbyshire, Lancashire, Durham, and ' Northumberland. They are very well represented i Peak district of Derbyshire, where they form some of the well-known " Dales " around Matlock, Bakewell, and Buxton.

The mountain limestone in Derbyshire consists of massive 1 beds of grey limestone, and attains a great thickness. In the J north of England and Scotland the limestone splits up, the j bottom group of rocks being known as the Calciferous sandstones, and containing the valuable seams of coal and oilshale which are extensively worked in the neighbourhood of I Edinburgh.

Both mountain limestone and millstone grit are absent in J

Coal-Mining.

Warwickshire, Leicestershire, South Staffordshire, and Shropshire, and the coal-measures are found reposing on the very old Silurian and Cambrian rocks.

Fossils of the Carboniferotis /icriad.—The coal-measure fossils are very numerous, and consist chiefly of plant remains, some of which attain a great size. Freshwater sliells are also

frequently met with in some districts. The mountain limestone contains a large number of fossils of marine shellfish and plants, whilst the millstone grit contains few fossil remains.

Figs. 2 to 5 show some of the more common fossils which occur in the coal-measures.

large centres

Geozogv.

Eeo7tomicva/iii-. — The Carboniferous system is of i possible industrial importance, and most of the large of industry are found clustered around our coal-fields. From the coal-measures we get coal, ironstone, ganister, fire- and pot-clays, building-stones, and alum shales, all of which are found in beds or seams. From the mountain limestone we get veins of lead, zinc, hiematite iron ore, barytes, umbers, copper, and manganese, as well as beds of limestone, marble, and chert.

The following is a list of the minerals now being worked in the United Kingdom, abstracted from the Government returns of igoa : —

Alitm Shale. — Worked from the middle coal-measures in West

Yorkshire from a bed lying between the two seams of the

Stanley Main coal. Formerly largely worked from the Lias,

near Whitby. A rienicai Pyrites.-— in small quantities from some of the

mines in Cornwall and Devonshire. Baryies. — From the Silurian and Carboniferous limestones in

Northumberland, Shropshire, Durham, etc. Used as an

adulterant of white lead. Bauxite. — Mined from between sheets of Tertiary basalt in county

Antrim, Ireland. Used for the manufacture of aluminium. Bog Ore. — From open works in Ireland, An ore of iron used in

the purification of gas. CArt/*.— Used for the manufacture of Portland cement ; very

largely worked in Kent and Essex. Chert. — Used in the manufacture of porcelain, and mined from j

the Carboniferous limestones of Derbyshire and Flintshire. C/fl.— Brick-clays occur in most districts, and fire-clays are

chiefly wrought from the middle or lower coal-measures. China Clay. — Derived from disintegrated granite, and worked in

Cornwall and Devonshire. Gw/.— See Chapter III. Copptr Ore. — Worked from veins in Cornwall, Devonshire, ar

Wales. Fluor spar. — Worked in Derbyshire and Durham. Used

making ornaments. Fuller's Earth.— 'Worked in Bedfordshire.

Coaimining.

Ganisler. — Worked in South Yorkshire from the lower coalmeasures. Used in the manufacture of refractory bricks.

Gold Ore. — Worked from the lower Cambrian rocks in Merionethshire. In 1902 the value of gold worked amounted to 12,621.

Gypsum.— OzQM.r& in the Keuper division of the Trias, and is mined in Cumberland, Nottinghamshire, Staffordshire, etc. Used in the manufacture of plaster of Paris.

[gneous Rocks. — Quarried in Leicestershire, Aberdeen, Ireland, Wales, etc. Employed for paving, building, and monumental purposes.

Iron Or.— Quarried in Lincolnshire, Northamptonshire, and Leicestershire from the inferior oolite, and rained in Cumberland and Lancashire (hematite) from the Carboniferous limestones ; also worked from the middle coal-measures in Scotland and Staffordshire.

Iron Pyrites. — Small quantities picked out at some coal-mines ; worked also in Ireland. Used in the manufacture of sulphur.

Lead Ore. — Worked in many places, but chiefly from the Carboniferous limestone in the Isle of Man, Derbyshire, Durham, and Flintshire.

Livtestmie. — Quarried in most counties, and mined in Scotland, Wilts, Staffordshire, etc.

Manganese Or.Small quantities worked in Devonshire and Wales.

Mica. — Obtained as a by-product in the preparation of China clay in Cornwall.

Ochre, fOTi?-, e/c— Obtained from many locahties. Used in the manufacture of paint.

OilShaU. — Largely worked in Edinburghshire and Linlithgowshire from seams in the Calciferous sandstone at the base 0/ the Caboniferous limestone.

Petroleum. — Small quantities are occasionally found in coal-

Phosphate of Lime. — Largely wrought at one time, but now only

worked on a very small scale. Salt. — Chiefly produced from brine in Cheshire, Durham,

Lancashire, etc. Sandstone. — Found in most localities, and chiefly used as building-

Slate. — Largely mined and quarried in Wales, Argyll, Cumberland, and Westmoreland.

Geology. 15

Sulphate of Strontia, — Dug from shallow pits in the Keuper beds

of Gloucestershire and Somersetshire. Tin, — Mined from veins in the granites of Cornwall. Uranium Ore, — Worked at one mine in Cornwall. Wolfram, — Found in the tin mines of Cornwall. Zinc. — Often accompanies lead ore. Worked from the Palaeozoic

rocks in Cumberland, Wales, Isle of Man, Derbyshire, etc.

stratified Rocks. — The stratified rocks were originally deposited horizontally, but they are now usually found lying at a more or less steep inclination. This is due to the pressure to which they have been subjected owing to the shrinkage and movements of the earth's crust. The older rocks are usually found to be much more disturbed than the newer ones, as they have been longer exposed to pressure, and the disturbing influences were probably more violent in the earlier history of our globe.

The main result of the pressure has been to force the rocks into a series of folds. Fig. 6 shows strata folded by pressure.

A one m h trata w e flat, bu no mou p ure at A and B n he d e on of he arrows has gradua y o ed A and B owa d ea h o he bending he o k. a hown he

Structure Of Stratified Rocks.

dotted lines above the surface indicate the position of the beds after being curved, but the dotted portion has been worn away or denuded. At the point C (Fig. 6) the beds dip away on both sides, forming what is known as an anticline ; and at d the beds on either side dip towards each other, forming a syncline, the centre in either case is known as the axis.

The size of these folds varies very greatly, they may be only a few feet across or they may be many miles.

Pressure exerted from the east and from the west would result in the formation of a series of folds having their axes running north and south, whereas pressure exerted from the north and south would produce folds lying the other way. Hence, if pressure were exerted from all sides, a double series of folds would be formed, running at right angles to each other; the result of which would be the production of basins, in which the beds would outcrop all round and dip towards a central point. Most of our coal-fields are found in basin-like deposits, though in many cases parts of the basins are hidden by the rocks of a later period.

Strike, Dip, and Outcrop.— The inclination at which beds lie is extremely variable ; in some cases beds are found vertical or even inverted, and in other cases horizontal. These variations may take place in short distances, but, on the other hand, the dip is frequently found to be very regular over large areas. As a general rule, beds that lie at a high inclination near their outcrop become flatter as their depth increases.

The Strike of a seam is its level line, and the full dip must be measured at right angles to the strike. The inclination of a seam may either be expressed in degrees (thus a seam is said to dip io° when it makes an angle of io° with the horizon), or it may be expressed as a vertical fall in a horizontal distance, e.g. if the seam dips 6 inches vertically for every yard measured horizontally, its dip would be said to be 6 inches to the yard, or i in 6,

Dip may be measured with a clinometer, one type of which is shown in Fig. 7. It consists of two brass straight-edges

Coal-Mining.

Iiinged together, on tht: upper is fixed a spirit-level, and on the lower a quadrant divided into degrees from which the angle made by tlie two pieces of metal can be read off. To measure an incline with this instmmenl, the lower limb is [daced upon the seam, or upon a long wooden straight-edge, to obtain the average dip, and the upper limb is opened on the hinge until the bubble of the spirit-level is in the centre of its run ; the angle is then read ofi" from the quadrant.

Another method of measuring inclinations is that shown in Fig. 8, that is, by means of a straight-edge lo feet long and an ordinary spirit-level. One end of the straight-edge is raised until the spirit-level indicates that it is level, then the height that it has been raised is measured, and the measurement gives the amount of fall in lo feet. For e.tample, if the fall is

Fig. 7.- ) inches, the rate of inclination is 10 inches ii

3 feet, that

It is often necessary to convert dip measured in degrees into a vertical rise or fall in a horizontal distance. This may be done approximately by dividing the number of degrees into 57-3, which gives the horizontal distance for a fall of i.

Example—

,5713

1-4 nearly.

This rule becomes incorrect when the inclination is more than about 20°, and a more accurate method is to take the cotangent of the angle which gives the horizontal distance for a fall of I. Example : The cotangent of 28° is rSS, hence 38° dip corresponds to an inclination of i in i'88,

1" urther information on this subject is given in ChapterXVll.

In measuring the dip of a seam, care must be taken to make the observations along the line oi full dip, that is, at j right angles to the strike, otherwise the dip will appear to be less than it really is. This will

understood by reference to 'S- 9i where ab represents the line of strike, and (d the full dip. If the dip of the measures IS 6 inches per yard, and cd measures exactly i yard, the erid of the line ed will be exactly

inches below ab. Suppose

Structure Of Stratified Rocks.

now that the inclination is

measured along cf instead of cd, the point / is higher up than so that the dip per yard in that direction is less than 6 inches. The direction of dip, as well as the rate of inclination, is always required. Thus a seam may dip N. 62" W., at

rate of 3 inches per yard. On geological and other plar tile dip is shown by arrows, thus, 8", the arrow head always points downhill, and its direction shows the correct line of full dip.

The Outcrop of a seam is the edge exposed to the surface. If the surface is level, the outcrop is a straight line, ; cides with the line of strike, otherwise it does not. The form of the outcrop of a bed depends chiefly upon the contour of the surface ; hence outcrops may be seen running round hills fl-od along valleys.

The width of an outcrop depends not only upon the thickness and inclination of the bed, but also upon the surface i contour. This will be understood by reference to Fig. 23, where the outcrop of the rock bed at a is much wider than at b, although the thickness and dip of the bed are the same in both rases.

It is difficult for an untrained eye to trace outcrops, but "le outcrops of all the principal coal-seams have been mapped ny the geological survey for the whole of their exposed length,

r

20 Coal-Mining.

and In most cases with great accuracy. Coal-seamvIw very inferior at the outcrop, being usually found as a mere bed

of smudge.

Bedding and Joints. — Stratified rocks are made up of beds, and beds of Inyen or lamina. These laminations cause the rocks to split more or less readily along the bedding planes, The vertical divisional planes, which occur in most stratified rocks, are called joints. These are not nearly so regular as the horizontal bedding planes, and are much more strongly marked in some beds than in others. Two sets of vertical joints running at right angles to each other traverse some rocks and cut them up into cubical blocks. Joints or backs are strongly marked in some coal-seams, and very slightly in others.

Conformability. — Beds lying parallel to each other are said to be conformable, the beds in the same series are always conformable to each other ; but when rocks of different periods come together, the one series may have quite a

formabilily.

different dip to the other, as shown in Fig. lo, in which case they are said to be unconformable. The coal-measures are sometimes overlain by the Permian rocks, the two being unconformable.

Irregularities of Stratified Rocks.— Seams of coal, and all other stratified rocks, are subject to many irregularities

STRUCTURE OF STRATIFIED ROCKS iv

|nd disturbances. These may be divided into two classes, (A) Jrhose which were caused during the time the seams were in process of formation, and (B) Those which were caused after the seams were formed. It is important to distinguish letween these two classes, as those which come under class A iually affect one seam only, whilst those in class B generally iect the whole series of seams.

Irregularities caused contemporaneously with the iFormation of the daaX.—SpUUing, — Coal-seams are much iven to splitting and coming together ; sometimes the split-ofF portions of two adjacent seams unite and a third seam is formed, lying between the two original seams and composed of the upper part of one seam and the lower part of the other. One of the best examples of splitting is found in the ten-yard , coal of South Staffordshire, which splits up into nine distinct seams of moderate thickness in the northern part of the coalfield. The Silkstone seam in South Yorkshire usually contains a band of dirt about a foot in thickness, but a mile or two north of Sheffield it splits into two seams, with about 30 yards of strata between them ; still further north these two seams reunite, forming one seam.

The Barnsley Bed is lo feet thick in the neighbourhood of Barnsley, but near Sheffield it is only half that thickness ; the thinning being chieSy due to the fact that layers of coal, which are a part of the seam in the Barnsley district, have split off and are some distance from the main bed in the roof or floor. Many other examples might be given; in fact, splitting is more or less common in all coal-fields.

Reck faults, or liorsebaeks. — These usually occur in seams having a rock roof; examples on a large scale may be seen in the Parkgate and Deep Hard seams of Yorkshire and Derbyshire. A cross section of a small example is shown in Fig. n. From this it wiH be seen that the roof has gradually come down until it almost touches the floor. Some of these rock fanlts are small, being only a few feet across and taking only a portion of the seam ; but others are very large, and may take

w

Coal-Mining.

the whole of the seam out for a width of several hundred yards and extend for some miles. The Dumb fault at Alfrelon washes out the Deep Hard seam for a width varying between 200 and 500 yards, and has been proved to extend for a length of several miles from the outcrop of the seam.

Rock faults appear to have been caused by a river or Blrearn flowing through the coal-seam just after it had been deposited and whilst it was still in a plastic condition. This has eroded or cut out the coal-seam, and filled in the space with sand and mud, which has in course of time hardened and become rock. In some seams rock faults are quite common, in others they are never met with ; they only affect the one seam.

Rolls. — As shown in Fig. 12, a roll consists of a mass of rock taking the lower part of the seam out. Rolls are probably due to the coal-seams being deposited on an uneven surface or floor. Small rolls are fairly common, but large ones are seldom met with.

Thinning Out. — Some coal-seams and rock beds thin very rapidly and even disappear altogether. This may be due to their being deposited on a sloping floor, or to a failure in the supply of the material from which they were formed. As a rule, coal-seams are more " persistent " than the rocks which accompany them ; but the thickness of some coal-seams varies very greatly over quite a small area.

Structure Of Stratified Rocks,

A Swelly or Swiliy is an abnormal thickening of the coal-seam. This may be caused by a depression of the surface upon which the coal was deposited, as shown in Fig. 13, in which case ihe increase in thickness will be from llie bottom. Swillies are frequently due to the plastic material forming the coalseam being partly washed away in one place and piled up in another ; pic. 13.— sweiiy.

or to extraordinary pressure on one

part of a seam squeezing the bed thin in one place and forcing the material to another.

Overlap of Strata. — This occurs when a system of rock beds is deposited on a sloping surface. In Fig. 14 the top seam A overlaps the lower seam B, owing to the ancient

hill upon which the coal-measures were deposited. This overlap is of great importance, as it shows that the top seams might be present and the bottom ones absent ; it may have considerable bearing upon the extent of some of our hidden I coal-fields.

Irregularities caused long after the Formation of the Coal-seams. — Faults. — The most important irregularities I to which coal-seams and other stratified deposits are liable are

Coal'Mtntng.

" faults." A fault is a fracture in the measures, usually at a slight angle from the vertical, and throwing the measures on one side cither up or down from their original position. The line of fracture is usually very smooth and polished, and the fissure, when one exists, is usually filled in with debris, or "fault muck" as it is tenned. Most faults have not been caused by a violent upheaval, but by the gradual movement of the earth's crust ; the displacement they cause varies &om an inch or two up to many hundreds of feet. Mineral veins are generally the contents of faults. This, however, is very rarely the case in the tfoal-measures or newer systems, but frequently in the Mountain, Limestone, Cambrian, and older systems.

Faults may continue in almost a straight line for many miles, with little variation in the amount of" throw," bat oflen the displacement varies, a large fault gradually diminialiing and dying away. Sometimes a fault which is an upthrow in one place will change to a downthrow in another. Lae faults frequently have smaller ones branching off them in all directions, and often bend about in an apparently erratic

The larger faalts frequently ran roughly parallel to the line of hills and valleys in the district. Fig. 15 shows an ordinary or norma/ ' ' ' fault of small dis-

placement. The fiadc is the inclination the fault makes with the vertical, and is expressed in degrees. The average Imde of a coal-measure fault is about 10°,

The widl/i is the horizontal distance between the fractured ends ; it depends upon the size of the fault and upon its hade. larger the throw and the gre.ater the hade, the greater will te width.

STJiUCTC/JiE OF STRATIFIED ROCKS.

The throw or size of a fault is the vertical distanc*] between the fractured ends, that is, the amount by whicli thi seam has been displaced from its original position. If thi fault shown in the sketch were approached from B, it would be: called a downthrow, whereas, if struck first from A, it would be said to be an upthrow.

It is very important to notice that if the seam is thrown down, the fault is first hit in the roo/oi the working ; but if the fault is an upthrow, it is first struck in the Jioor. So that by observing the direction of the hade of a normal fault it is easy lo see whether the coal should be sought above or below. When proving coal across a fault by boring, it is very necessary lo drive in right across the width of the fault before commencing to bore, otherwise the seam could never be hit. Quite erroneous results have sometimes been arrived at by not driving in far enough before boring, as it is impossible tq estimate the exact width of a fault unless both size and hade are known.

Slep Faults. — Faults do not always affect their full amount of displacement in one operation, but often throw the coal up

Fig. i6,— Siep faulca.

or down in a series of steps. In Fig. i6 the total displacement is the vertical distance AB, the coal being thrown down by a series of faults in the same direction, these are termed step faults. A large fault often changes into a series of step faults.

rroiigh fa

26 Coal-Mining.

and sometimes even into a bend in the strata, whi3? fractured, the displacement talking the form of an extremelsr steep dip in the measures.

Trough Faults. — These are formed by a pair of parallel faults dipping towards each other. They may have beeBz* caused by the strata breaking ir. two places at the top of a fol<:3 and allowing a wedge-shape <r3. mass to sUp down. The strip= of coal is wider in the uppeiseams than in the lower, anc3 the two faults may run each other out altogether deep down, as shown in Fig. 17; or if one of the faults is larger than the other, as is commonly the case, the displacement in the beds below their intersection will be equal to their difference ; thus, if one fault were 70, and the other 60 yards, the displacement below their intersection would probably be 10 yards only.

Reversed or Overlap Faul/s.—This class of fault is very rare in the coal-measures, but may be frequently seen in the rocks belonging to the older systems, where the strata have been subjected to much greater pressure. In reversed faults the strata on one side of the fracture have not only been lifted above the strata on the other side, but have also been pushed over them, thus doubling the beds for some distance, as shown in Fig. 18. The rule as to finding the direction of the throw of a fault from its hade, as given on page 25, has to be reversed when it is applied to these faults, but they are so seldom met with that it is fairly safe to assume that any fault met with in coal-mining is "normal," and not "reversed."

The best-known example of a reversed fault is the " slide fault " at Radstock, in Somersetshire, where the vertical throw is 72 yards, the top seams being doubled for 120 yards, and the lower beds for 330 yards. It should be noticed that the beds on either side of a normal fault are /w&i asunder, causing

Structuke Of Stratified Rocks.

a strip of barren ground, but when the feult is reversed the beds are pushed over each other. In other words, normal

T "

faults appear to have been caused by a tenshnal strain, and reversed faults by a compressive strain.

Effect of Faults on Outcrops, — When a fault runs paraUel to the strike of the measures, it is called a strike fault. The effect of a downthrow may be to double the outcrop, as shown in Fig. 19. An upthrow strike fault may throw

Fig. 19. — Strike faolt repealing

a seam of coal out altogether, so that it will not outcrop at all in the neighbourhood of the fault.

A fault running parallel to the dip of the measures is

tJi

Coal.Hining.

lamed a dip fault When a fault crosses the outcrop of a seam, such outcrop is broken or dislocated, the amount of the dislocation depending upon the inclination of the seam and the size of the fault. It is of great importance to understand this, as the direction and size of the throw of a fault may often be calculated from its effect upon the outcrop of a seam. Fig. ao shows dJagrammatically the plan and section of a fault cutting an outcrop ; in the figure the fault throws the measures down to the north, and the outcrops are shifted towards the rise of the beds. Had the fault been a riser or upthrow north, the outcrops would have been shifted towards the dip.

Interseclion of Fauln. — When two faults intersect one

another, the line of the older fault is broken at the point of intersection ; the same reasoning applying as in the case of a fault intersecting an outcrop,

Dykts. — The strata are sometimes intersected by masses of igneous rock, as shown in Fig. i, these are termed "dykes." They have the appearance of walls of granite or basalt, and the coal is coked or charred for some distance on either side, proving that the material forming the dyke was forced through the strata whilst in a molten condition. Dykes do not usually displace the coal at either side. Some districts arc much affected by dykes, others not at all ; one of the best-

Structure Of Stratified Rocks.

known is the great whin dyke in thy north of England, which can be traced for scores of miles.

Wash-outs, — Fig. 21 shows the Team wash-out. Several seams have been denuded, evidently long after they were formed, a large valley being scooped out and filled in again with boulder clay, probably by glacial action. The depth of boulder clay is about 300 feet, and the width across the top of the old valley varies from about 600 to about Soo feet

Variations in Inclination, — In most of the larger coal-fields the dip is regular over large areas ; but occasionally great variations exist.

sral H

nf

I'll

r-

-

Fig. 21, — Team wash-out.

When the strata are very much twisted, they are said to be contorted. Contorted strata are uncommon in the British coal-fields, but are frequently met with in France and Belgium.

Geological Maps. — The geological features of a district are shown upon geological maps. These maps show by colours the period to which the strata forming the surface belong. They also show the position and size of all the known faults, the rate and direction of inclination of the strata, and the outcrop of any beds or veins. In addition to this, they should have marked on them the depths of all shafts and

Coal-Mining.

boreholes, and any other geological information which mayl obtainable.

Fig. az shows a geological map delineating on a smaJl scale a part of a coal-field. On the west will be seen tte millstone grit dipping to the east, and bounded on its eastern side by tlie coal-measures, the latter in their turn being laid by the Permian, and the Permian by the Trias. Thie information given on this map will perhaps be more clearly

— Geological p!t

understood by reference to the section which has been constructed from the plan. In preparing this section the contour of the surface is first drawn. This is done by making use of the contour lines, which are shown on all the geological maps drawn to a scale of six inches to the mile ; these contour lines are level lines marked on the maps, every twenty-five feel, vertically, the height above sea-level being marked

'Tructure Of Stratified Rocks.

DTi each. The boundaries of the various rock-groups are then projected from tlie plan as shown by the dotted lines ; and the TKUte of dip of the beds is laid down on the section, as given by arrows on the plan.

It will be noticed that the millstone grit is shown to extend Tinder the coal-measures, and the coal-measures under the Trias the whole length of the section. There is no actual proof of this, but it is reasonable to assume tliat they do so, and in geological sections the lower beds of a series are usually assumed to follow the upper, unless there is evidence to the contrary. On examining the plan and section, it will be observed

23. — Oulcrop caused by valley.

that when the surface is level, and the beds not faulted, the I boundary of a bed, on its rise side, is its outcrop, and Its , dip boundary is formed by the edge of the beds which overlie it. It should be noticed that 'if the surface is hilly, the outcrop may be Co the dip of a bed, this will be understood by reference to Fig. 23, which represents an outcrop caused by the erosion of the strata by a valley,

From this it will be understood that the geological information given on plans must be studied in conjunction with the surface contour lines, otherwise erroneous conclusions may be arrived at.

32 Coal-Mining.

The Government have published geological maps of tlwhole of England and Wales, on a scale of one inch to a mil and of some districts, on a scale of six inches to a mil These maps and the sections which accompany them will h found of the greatest value in studying the geology of ar district

oUowing table shows the great increase in the output of om Great Britain and Ireland which has taken place ; the last fifty years : —

'854

64,661,401

80,042,698

110,431,193

146,969,409

i8go

181,614,288

225,181,300

219,046,945

227,095,042

'903

230,334,469

this table it will be seen that the output is now more J times as much as it was fifty years ago. Almost every hows an increase on the preceding one; the year 1901 a decrease, which is accounted for by the fact that that as a period of exceptional prosperity and of high wages, tier being usually accompanied by a decreased output m employed.

'Oduce of Coal-seams- — The specific gravity of ry bituminous coal averages about r'aS, The specific r of a substance is its weight as compared with an equal )f water; and as a cubic foot of water weighs 63'5 lbs,, eight of a cubic foot of any substance is obtained by lying its specific gravity by 6z'5. Thus the average t of a cubic foot of coa] is I'aS X 62'5 80 lbs.

COAL-MINmG.

15557 tons.

The weight in tons of an acre of coa! 4840 X 9 X 80

This quantity is, however, never realized, as there is always a certain amount of coal lost in working. The Royal Commission on Coa! Supplies of 1903 took the tonnage to be 1500 per foot per acre, but this was subject to deductions for waste in working, and for pillars, barriers, etc.

Taking the present annual output of coal from the United Kingdom to be 230,000,000 tons, and assuming the average thickness of the seams from which it is produced to be 4 feet, and the yield per foot per acre, 1500 tons, the number of acres worked out per annum amounts to the enormous total of 38,333 ; that is, to nearly 60 square miles.

Produce of Inclined Seams. — Where a seam is inclined the number of tons under an acre measured on the plan is, of course, more than if the seam were level. The increase on die tonnage depends upon the inclination of the seam, and the tonnage of a seam when level bears t!ie same proportion to the tonnage of the seam when inclined, as the base of a rightangled triangle does to the hypothenuse.

In Fig. 24 is shown a seam dipping at the rate of i in 3 ; the length of the hypothenuse AC, which represents the inclined seam, AW BC, so that as AB I and BC 3, the length of AC is Vi + Vio 3'i6z. Then the tonnage per acre (on plan) in the level Fici. 24. area bears the same proportion to

the tonnage when inclined as 3 bears to 3'i6a. Hence, if the yield when level is 1500 tons per foot per acre, the yield, when inclined at an angle of i in

A simpler method, to those familiar with trigonometry, is . to multiply the tonnage calculated as for a level seam by the secant of the angle of dip.

COAL AND COAL-FIELDS. i%m

Modes of Occurrence of Coal— Coal is very widely distributed among the stratified rocks, being found in almost every division from the Cambrian upwards.

In Great Britain coal is mined almost entirely from the Carboniferous formation, being obtained from the middle or true coal-measures, except in Scotland, where there are large collieries working coal from strata corresponding to the Carboniferous limestone. Coal is, or has been, worked to a limited extent, in England, from the newer measures, and there are very large deposits of such coal abroad.

Coal-seams differ very greatly in character, their main differences being as follows ; —

Thickiuss. — The thickest seam in England is the South Staffordshire thick coal, which attains in some places a thickness of about 33 feet of clean coal ; whilst in other districts seams of under one foot in thickness are bemg profitably worked. In districts where no thick seams exist, it is possible to work very 'hin seams to a profit ; but, generally speaking, thin seams can- i*Ot compete with thick ones in the same district,

Indination. — Seams occur at all inclinations, from vertical to 'horizontal. The flatter seams are the more cheaply wrought, 3*d a much larger output is possible from a flat seam than from steep one. In some districts the measures have no regular dip, but are undulating ; this adds to the cost of haulage, and greatly increases the cost of dealing with water if any be present. Furity. — Coal is subject to two classes of impurities— one Consists of shale, iron pyrites, and earthy matters, which can be "ashed out ; and the other class consists of chemical impurities, <liiefly sulphur and phosphorus, which cannot be removed.

The cleaner and better seams are becoming exhausted, and, Ul order to make the dirtier seams marketable, very elaborate *nd costly cleaning plants are being introduced.

A coal-seam usually consists of layers or bands ; these may sll be coal of various qualities, o r one or more of these bands iwy consist of dirt. The following are typical examples, taken Irnm various districts :—

Coal-Mining.

Barnsley Bed. (South Yorks.)

Coal.

Dirt.

"Bags"

Top softs

Clay dirt

Clay seam

Hards

Bottom softs

ft. ins.

1 O

ins.

Total

Black Shale. (Derbyshire.)

HuTTON Coal. (Durham.)

Coal.

Dirt.

Top coal

Top dirt

Tinkers (inferior)

Bottom dirt

Bottom coal

ft. ins.

ins.

Coal.

Dirt.

Top coal Bottom coal ...

Dirt band

Inferior coal (not worked)

ft. ins.

o 8

4 lo

o 5

ins.

Coal And Coal-Fields.

Seven-feet Mine. (West Lancashire.)

Coal.

Dirt.

Top coal ( inferior)

Dirt band

Bottom coal .. .

tt. ins. 2 O

ins. lO

Main Coal. (South Derbyshire.)

Coal.

Dirt.

Rider coal

Lower rider coal ...

Dirt

Over coal (inferior)

Dirt

Tops ...

Best hards

Middle dice

Spires

Grounds (inferior)

ft. ins.

3 o o 6 6 o

ft. ins.

The over coal is left for a roof, the workable portion of this seam that portion between the grounds and over coal.

Hardness. — Seams differ very greatly in this respect, some exceedingly hard, and others of a tender nature. The coals are usually more expensive to work, but naturally 'ake much less small. Generally speaking, the deep seams more small than the shallow ones, and coal mined from deep seams is apt to decrepitate on reaching the surface.

Coal-Mining.

The method of working has a. great influence on the amonat of small coal, but some seams invariably make much more smaJ.1 than others.

Cleavage. — -The "cleavage," "bord," or "face" lines are vertical joints in the coal ; they occur every few inches, and their effect is to divide the coal-seam into vertical layers or slabs.

Bord lines are very strongly marked in some districts, and may run with perfect regularity for hundreds of yards ; they are generally more strongly marked where the bord line is parallel to the strike of the seam. When the bord lines are very distinct they have a great inHuence on the method of working the coal, as the coal is got much more easily " on bord," that is, when the working face is parallel to the cleavage planes. In house-coal pits, the coal is often worked " on end," that is, at right angles to the bord ; or " on the cross," that is, making an angle with bord and end, as by working in this manner much more round coal is obtained. In some districts the bord liaes are very indistinct, and are disregarded in working the coal.

Varieties of Coal. — Coal consists of carbon, volatile matters, and ash. Several classifications have been suggested* but the most convenient depends upon the relative proportions of carbon each variety contains. The different varieties coal gradually merge one into the other, there being no well defined line between any two of them, so that there is cor>' siderable variation in the chemical composition of the differen* coals belonging to the same class.

Peat. — This is considered to be the first step in the chang* of vegetable matter into coal ; it is a brown fibrous materia-I very light and friable. It is found in peat bogs, sometimes up to 60 feet in thickness, and occurs in many places, notably> Ireland, Scotland, Lancashire, Lincolnshire, etc. It is use" locally as fuel, but owing to its bulk and to the large amou"* of water it contains, it has never become a commercial product as a fuel, though efforts have been made to find a market for by drying it and compressing it into blocks. The average chemical composition of peat is —

Coal And Coal-Fields.

Caiban. Hytlrogen. Uiyecn

55 to 65 per cent 5 to 7 per cent, 30 to -

Lignite, or Brown Coal. — Lignite is the next link between vegetable matter and true coal. It is of a woody fibrous texture, and is brown, or brown is h-blaci; in colour ; it contains much water, and burns with much smoke and smell. Lignite has been worked on a small scale in Devonshire, from a seam found in Lower Tertiary strata, and is largely worked in several places abroad. The chemical composition of lignite is —

Caiban. Hjilrogcn. Osysen and nilroBsn.

'5 to 75 per cent. 5 to per cent. 15 to 30 per cent.

Lignite gives off little heat, and contains a large amount of h, sometimes as much as 30 per cent.

Bittiminoiis Coal. — Nearly the whole of the coal worked in 'feal Britain belongs to this variety, which has many subdivisions, such as house, gas, and steam coal ; cannel or parrot ''al, etc. Several of these varieties are often found in the seam, each variety forming a distinct band ; thus, in the of the Barnsley bed given earlier in this chapter, the hards " are best steam coal, whilst the " softs " are often sold

fc Caking coals fuse or cake together when burning, and

F-Jjpear to be more highly bituminous than the non-caking or |*"e-buming variety, though there may be little difference in tieir chemical composition. Caking coals make good coke, *V-ee-burning coals do not.

(Td'jw/.— This is a dull hard variety of coal, showing no igns of cleat ot lamination, it is found chiefly in the Lancaliire and Scotch coal-fields.

Sometimes a seam is cannel throughout ; at other times a 1:>ortion only of the seam is cannel; and seams which are iioroposed wholly of cannel in one place may consist entirely ordinary coal a short distance away.

Cannel is very rich in hydrogen, and is of great value gas coaL A ton of good cannel coal should yield from 14,01 to 16,000 cubic feet of gas of about 40 candle-power.

tre

COAL-MINING. The average chemical composition of bituminous coal

Carbon.

About 85 per cent.

Hyiiroi

5 to Si psr cent 8 to 12 per cent

Anthracite.— 'W\\'& variety of coal is not extensively worked in Great Britain, though large quantities exist in South Wales-

In Pennsylvania it is worked on a very large scale, and is used as a house and steam coal. In England it is mainly for malting and other purposes which require a smokeless fuel.

Anthracite is very hard and black, it does not soil fingers, and breaks up into cubes.

It is supposed to be the last stage in the formation of coaand is no doubt bituminous coal altered by heat and pressur- In Wales it frequently happens that seams which are anthracite- e in one place gradually change into ordinary steam coal L another. Anthracite bums without smoke and gives off heat. It requires a strong blast for combustion, and has t=- " be broken up into small cubes before use.

The chemical composition of anthracite is —

90 to 95 per cent, to 5 per cent, s- to 5 per cent It will be noticed that the gradual conversion of vegetabBmatter into coal is accompanied by a loss of the volatiL matters, leading to an increased percentage of carbon. ThS is clearly shown by the following table, which is taken froi* j Andre's " Mining Engineering " {E. and F. N, Spon) : — j

Specific

Carhoo.

Hjidmgen

gr y

Wood

34'iS

i-as

72'37

23'45

Cannel coal

S007

'it

Bituminoas coal

Sem!-liltu mi nous coal

Anihracite cool

37S

Coal And Coal-Fields.

' Calorific Value of Coal. — The heating properties of ferent kinds of coal depend mainly upon the amount of rbon they contain. The oxygen present in coal is usually ind combined with a portion of the hydrogen in the shape of iter, so the oxygen has no heating value, neither has the drogen with which it is combined. In gas coals there is Pays an excess of hydrogen present ; this is known as disposable hydrogen," and it is only this disposable portion

the hydrogen which is available for heating purposes. The ating power of coal is measured in " heat units," the British at unit is the amount of heat required to raise i lb. of water

i" Fahr. A good steam coal should give from 14,000 to ,000 units per pound.

Uses of Coal. — House coal should take fire readily, be lan and free from white ash, leave no clinker, and give a, ght fire with little smoke. It should be fairly hard, so as to ike little slack. Gas coal should yield at least 11,000 cubic t of gas of 16 or 17 candle-power, and should give a good i coke. Cannel coal gives gas of a much higher candlewer, but the coke produced from it is of little value. Steam al should be hard and hot-burning, be fairly free from Iphur, and not too liigh in ash. The free-burning varieties ! preferable to the caking coals, as the latter hinder the light by clogging the firebars, and put more work oti to the ters. Coal' for metallurgical purposes must be very free m sulphur and phosphorus, and should give off great heat iliout much smoke or flarae.

The following is a brief descripti Etish coal-fields.

British Coal-fields.

of the most i

The Northern Coal-field. — This coal-field extends from 6 river Coquet nearly down to the river Tees, the length lim QOTtfa to south being about 50 miles, and the width

Coal-Mining.

varying between 5 and 30 miles. It lies partly in the county ' of Durham and partly in Northumberland. The strike of the measures is roughly north and south, and the dip is towards the east.

The coal-measures outcrop towards the west, where tliey are hounded hy the millstone grit, to the east dip under the sea, towards the south are overlain hy Permian rocks. The only extension of this coal-field is towards the south and under the sea, and mining is being vigorously prosecuted in these directions, both hy the old collieries of Seaham, Ryhope, Monk Wearmouth, etc., and by the new winnings at Easington and Horden.

This coal-field is not much troubled by faults, and the seams are found regular in thickness and lying at a light inclinatitHi. Several large Whin dykes traverse the district in a souAeasterly direction. '

The Cumberland Coal-field.— This coal-field lies along the Cumberland coast, extending from a little below Whitehaven up to Wigton, and having a length of about 25 miles and a width of about 5. The coal-measures dip towards the west under the Irish Sea, and arc bounded on the east; by the millstone grit. Towards the north and south they arC' overlain by the Permian rocks, under which extensions maybe expected.

The principal seams are the Bannock Band, Main Band, Ten Quarters, and Metal Band. The Whitehaven Collieries have already worked the inain band for a distance of over three miles under the sea. The Workington Colliery waa also working the main band under the sea until the year 1837, when, by the injudicious removal of pillars, the water broke in with disastrous results. This coal-field is much cut up by faults.

The Midland Coal-field.~This great coal-field extends from below Nottingham to Leeds, having a length of about 65 miles, and lying in the counties of Nottingham, Derby, and

Coaz And Coal-Fields. 43

'York, The strike of the beds is about north and south, and the measures dip gently towards the east, where they are overlain by the rocks of the Permian, Trias, and Lias formations. On the west and north the coal-seams crop out one after the other, and are bounded by the millstone grit, and on the south they rise and crop out under the Permian rocks. The only direction in which extension can be looked for is towards the east, and there great developments may be expected, and indeed are taking place. The coal-measures have ; been proved to extend for 10 miles to the east of Doncaster by the South Carr borehole, which struck the Barnsley bed at a depth of logo yards. How far the coal-measures actually , extend to the east is not known ; some authorities believe that they come to an end by rising to the east and outcropping I under the Permian, whilst others hold that they extend as far as the North Sea. They may terminate either by thinning out or by being cut off by the thickening of the Permian measures. The principal seam is the Barnsley bed, which is found at its best in the neighbourhood of the town from which it takes its name. In the South Yorkshire district this seam has a thickness of from 7 to 10 feet. In Derbyshire it is known as the Top hard coal, and is of excellent quality. It has been worked continuously from Nottingham to Barnsley. Towards the north the Barnsley bed splits up and takes the name of Warren House, and is only a second-class seam. Other important seams are the Parkgate and Silkstone, the former being the Deep hard and the latter the Blackshale of Derbyshire.

The lower coal-measures also contain thin but valuable Kams of coal, accompanied by excellent beds of ironstone and fire-clay.

Taken as a whole, this coal-field is not greatly troubled by faults, and no intrusions of igneous rock have been met with, The inclination of the beds is generally moderate.

The Lancashire Coal-field. — This coal-field is separated from the Midland coal-field by the Pennine chain anticlinal,

Coal-Mining.

and at one time the two wre connected ; the Ganister and

Silkstone scams of Yorkshire probably representing the Mountain and Arley mines of Lancashire. On the north and east the Lancashire coal-fidd is bounded by the millstone grit, but to the south and west the coal-measures are overlain by Permian rocks, which have not been thoroughly explored. There are many valuable seams of coal, at some collieries as many as ten being worked. In the St. Helen's district the Ravenhead, Rushey Park, and St. Helen's Main delfs are most 1 sought after ; whilst in the neighbourhood of Wigan, the Wigan and Orrell mines have been extensively wrought, and contain excellent cannel.

The coal-field is much intersected by faults, and the inchnation of the measures is, as a rule, very considerable.

The North Wales Coal-fields. — These coal-fields occur in the counties of Denbigh and Flint. On the west they are bounded by the millstone grit and mountain limestone, but dip under tlie Permian rocks to the east, in which direction further extension is probable.

On the Flintshire coast the coal-measures extend undei the Dee, and are worked on the Wirrall peninsula. The chief coal-seams in the Ruabon district are the Main, Yard Bench, and Quaker, and in Wirrall the Six-feet, Five-feet, and Seven-feet.

The North Staffordshire Coal-field.— This coal-field underlies the Pottery district of North Staffordshire, the chief towns upon it being Stoke and Hanley. It is bounded on the east by the lower Carboniferous rocks, but the coal-measures extend to (he west and south under the Permian rocks.

The coal-field is extremely rich, but somewhat irregular, ib seams being frequently very highly inclined (when they ar known as " readers "), and in some cases even vertical.

The Leicestershire Coal-field.— This little coal-field is

situated around the town of Ashby-de-la-Zouch, and probably

one time formed part of the Midland coal-field, being separated by an anticlinal having an axis running from west to asL On the north-west it is bounded by lower Carboniferous strata, but on the west and south it is covered by the new red sandstone under which it extends. Six or eight seams have seen vigorously worked, the most valuable being the Main, Eureka, and Stanhope seams in the Moria district, and the Wain and the Roaster Main in the Coalville area.

The Warwickshire Coal-field. — The exposed portion of this coal-field extends from Tamworth on the north to Bedworth on the soutii. It is almost entirely surrounded by Permian strata, and recent winnings appear to point to the <oaI-measures extending under these Permian rocks up to the South Staffordshire coal-field, a distance of about 12 miles.

The principal seams are the Slate, EU, Rider, and Twoyard coals; and at some collieries these are found separated by only a few feet of strata, and are worked together.

The South Staffordshire Coal-field.— The exposed portion of this coal-field extends from Cannock to the Clent Hills, but as it is bounded on all sides by the new red 'andstone, it is probable that great extensions will be made. Collieries which have been sunk through the new red lieasures on the east and west, afford evidence which renders 't probable that the coal-field joins up to the Warwickshire and Sljropshire coal-fields. The chief feature is the presence of the Ten-yard coal, which is found in the southern portion of the *rea. This seam is at its best in the neighbourhood of Dudley,

*here it is 33 feet in thickness, Igneous dykes occur in

pliices.

The Shropshire Coal-field.— The Shrewsbury, Coalbfookdale, and Forest of Wyre coal-fields, extend in a broken line from Shrewsbury to the river Terae ; towards the west the coal-measures terminate against Pre-carboniferous rocks, but extensions may take place under the new red sandstone,

1. COAL-MlNflfG.

which tonus the nonhem and eastern boundary of the C rnal-ndd.

The Bristol and Somerset Coal-field.— This coalflplil lto If the north-east of the town of Bristol. The exposed U miall. but a much larger area is covered by newer tontutioat. One of the chief features of this coal-field is tlie IUnmm of the seams, some which are being worked are od iftM iU duckness.

Tt of Dean Coal-field.— This little coal-field hu .lit aioi of squacc miles, and is situated around the IMiM \ii And Cindeiford, in Gloucestershire. Ui the tcTiii of a perfect basin, the seams dipping to the centre from all aides. The seaoas are thin, and the most valuable litpidly becoming

The South Wales Coal-field,— This important coal field lies in the fomi of a basin, its length being about %Z miles from east lo west, and its width from north to south about i6. A large anticlinal traverses almost the whole of the basin, bringing the deepest seams to a work.ibie depth at its crest, but at the lowest parts of the basin the deeper scams lie beyond the reach of present methods mining. Towards the south-east the seams are bitumincuSj bill [bey gradually change their character until they become jiilhiacitc in the north-west. The coal-measures are divided liilo an upper and lower series by a great thickness of sandkioiies, known as the Pennant grit.

The Scotch Coal-fields,— These lie in a long strip es-

(rn4i"K the Firth of Forth and the Firth of Clyde, the

' .'inua area being divided into the Midlothian, Clyde,

, Aj-shire, and other basins. The coal-measures are

into the upper and lower series, which are divided

Mitbtonc grit. The lower series are in the Carboni

f/Dt;glove, and contain valuable beds of coal and

ftetow sre the Calciferous sandstones, whidi

Coal And Coal-Fields.

contain ihe oil shales, lately worked in the neighbourhood of Edinbuih.

The Irish Coal-iields. — These are small and u portant. They occur in Antrim, Leitrim, Leinster, Tipperary, and West Munster.

The Dover Coal-field. — Little is at present known of the character and extent of this coal-field. Several boreholes have been put down, and shafts are now in process of sinking (1904). The boreholes proved several seams of coal, principal one, 4 feet in thickness, being found at a depth of aaa5 feet. It is supposed that a line of detached coal-basins extends across England, from the Bristol coal-field to Dover, and probably runs under the sea and joins up to the Belgian coal-fields.

The relative importance of the various coal-fields may be estimated from the following table, which gives the output for the year igoi : —

Tons.

thecal

'. Scotch coal-fields

34.115.309

2. Korthem „

46,427,487

3. Yorkshire, etc., coal-fields

52,136,750

23'o

4. Lancashife and Cheshire coal-fields

24,879,391

shi/e, elc.) /

20,264,442

S-9

Small detached coal-fidds

4,674,054

7. Nonh Woks „

3.Ij3.I18

". South Wales ,

41,305,583

% Irish coal-fields

108,737

Preliminary Operations. — Before making any detailed search for coal in any particular locality, it is first necessaij to ascertain the geological period to which the rocks forming the surface of that district belong. If the rocks are found to belong to a period older tlian the coal-measures, further search will be useless, as no workable coal is likely to be found; if the surface rocks are much newer than the Carboniferous, coal may be present, but probably at a great depth ; but if the coal-measures themselves are found on the surface, a detailed examination for outcrops should be made. If no geological map of the district exists, the explorer must make one for himself, and to do this will require considerable geological knowledge. An ordinary map of the locality must first be procured, or, if necessary, made ; and upon this map must be marked the nature and dip of the rock beds wherever they are exposed. Sections of the beds may usually be seen on the banks of streams or rivers, in railway or other cuttings, in quarries and wells, and sometimes on the hillsides; by examining all these, and by carefully recording the information upon the map, the general geological features of the district will be gradually determined.

Fossils are of the greatest assistance in determining the geological period to which rock beds belong, and any that are found should be carefully preserved, as their accumulative evidence may definitely determine the system of the rocks in which they were found.

Search For Coal.

seam of coal is usually thin, and always of inferior quality a.t its outcrop. To test its true character, trial headings should "be driven into the seam at intervals along the outcrop ; these will not only prove the seam itself, hut will also test its continuity and reveal any dip faults which may be present, if more convenient, trial shafts may be substituted for the headings.

Before a decision can be arrived at as to whether or not a coal-seam is likely to be workable at a profit, many factors have to be noted and considered, chief among which are the following :—

Thicktiess. — The minimum thickness of coal which can be worked at a profit is almost entirely a matter of locality. Usually it is impossible to work much thinner seams than are worked at neighbouring collieries. In some districts seams of i3 inches and under in thickness can be profitably worked, whereas in other districts this would be quite impossible,

Quality. — This, too, is to some extent a matter of locality. A coal-seam, to be worked at a profit, must be as good as those ilK which it will have to compete; otherwise there wilt be no sale for it when trade is depressed, except at ruinous prices,

Nature of Roof and Floor. — Rocks, strong binds, or coals nake the best roofs, and the nature of the roof has the greatest influence on the cost of working a coal-seam. The floor should not be too soft, or it will " heave," and cause the roads to be very expensive to maintain. The presence of water in roof or floor is almost fatal to economical working, when they consist of'binds," or "lunches."

Quantity of Water present. — It is generally very difficult W estimate the quantity of water which may be made in the *orkings. The expense of deahng with water does not so BWch depend upon the quantity present, as upon the difficulties |l$i$ may be met with in concentrating it, and the general Mjufitioiis of each mine.

P FmSs. — In an unproved coal-field, faults are often quite Wiexpected until they are actually struck in the workings.

so COAL-MINING.

They may be a source of enormous trouble and expense ; they not only entail the cost of crossing them, but they disarrange the haulage and upset the whole scheme of the workings. Faults may occasionally be of advantagCj by acting as a barren and keeping back water ; they frequently form a dividing line between two collieries.

Avtulabli Area. — The capital expended upoti a modem colliery is so great that very large areas are now the rule. In the Midland district the viewer royalties are seldom less than four or five thousand acres. The royalty rent paid per acre averages about 30 per foot thick, which works out to abonl <,d. per ton on the output.

Labour. — Most new collieries have to provide dwellinghouses for their workmen ; this increases the capital required) but money spent on cottages yields good interest.

Markets. — The railway rates to the largest markets have, of course, a very important bearing on the profits ; if possible, a large colliery should be In communication with at least two railways, as the competition between them leads to much better facilities for traflic. In the neighbourhood of large towns the land sales may be be and remunerative. Canals also aSbrd a means of transport to many important centres.

Boreholes. — Vhen a coalfield is overlain by rocks of a newer period, as is the case with most of our undeveloped areas, surface explorations are of little value, and boring has W be resorted to.

It frequently happens that the coal-6eId is proved on one or more sides by other collieries, and the borehole is only required to complete the information thus gained. When this is the case one borehole only may be required.

At other limes it is desired to prove lower seams imder ao area from which the upper seams have been worked ; this best done by putting down a borehole from the bottom of at* existing shaft. If the district is quite unexplored, several bor&' holes arc required to prove a large area, and the sites have be \-ery carefiilly chosen in order to obtain the most complete

Search For Coal.

$]

tellable information. A borehole should show the depth, thickness, and quality of the seams passed through.

A borehole only shows the true thickness of the seam passed through when the seam happens to be level; when it is inclined, the thickness is arrived at by multiplying the distance bored through by the cosine of the angle of dip. The following table gives the trae thickness of a seam per foot bored through when the seam lies at various inclinations ; —

Thiclm=sof™l

D" ofdieaiarH

Tide Ihicti.™ of

J

oot

S°

0996 feet

10=

985 „

iS°

20°

=5°

30°

S66

B19

40"

If a borehole passed through a seam dipping 20°, the thickness of coal in the borehole being 4' 3", the true thickness w-ouldbe4-z3 X 0-940 3'ii"-94. Ofcourse, such calculations s*e only correct when the borehole is vertical.

When boreholes are required to prove the thickness, rate, Hd direction of dip and depth of a seam of coal in a totally proved district, at least three are necessary; they might be set out as in Fig. 25. Their distance apart would depend Olirely upon local conditions.

To find the direction and rate of dip of a coal-seam from information obtained by three boreholes, proceed as follows ; —

First, prepare a plan of the three boreholes, A, B, and C, fig. 25, in their correct positions to any convenient scale. In the present case, A is 130, B 205, and C 170 yards deep;., these may not be the actual, but are the corrected depths after makiBg allowance for the variations in surface levels. The J coal-seam is 75 yards deeper at B than at A, and as the

Coai.-Mining.

horizontal distance AB is 300 yards, the inclination of t measures from A to B is 75 in 300, or i in 4.

The seam at C is 40 yards deeper than at A, and the dis tance AC is 360 yards, hence the dip from A to C is 40 in 36 or 1 in g.

Now, the dip of AB is i in 4, so that at a point 4 yards from A measured along AB the seam will be exactly i yar deeper than at A ; and the dip along AC is i in g, so th 9 yards from A measured along AC the seam will again exactly I yard deeper than at A ; hence it follows that a poin~ 4 yards from A measured along AB is exactly !evel with point 9 yards from A measured along AC. To put this lev -

ifj-

Fli5. 25.— Method of Endine true dip from three boreholes.

line upon the plan, mark off on AB any four equal parts and nine similar parts along AC ; Join these points and the line between them {ax on sketch) will be the level line of the seam, and a line drawn from A at right angles to it (hk. Fig. 25) will show the line of full dip. To get the rate of inclination, measure tlie line kk, using the same scale : in the figure this line measures 3-2, and ax is exactly i below A, so that at full dip the seam gained i vertically in %-2 horizontally, and its dip is i in 3-2, or about 17°. Having thus found the rate of inchnation, the true thickness can he calculated from the thickness bored through, in the manner previously explained. The direction of full dip can be read off the plan by means of a protractor. Of course, if any faults exist between these boreholes

Search For Coal.

iCtions will be incorrect ; this is the weak point reliability of the results obtained by boring.

Boreholes may be put down by one of two systems — ths, pifcnssive and the rotary ; the former is the older of the two, but for important work in connection with mining is now almost entirely superseded by the latter.

Tlte Fercussive System of Boring. — This system of boring is only suitable for unimportant holes of moderate depth, very deep holes it cannot compare with the rotary system, either as regards cost or speed. Moreover, the results cannot be considered satisfactory, because the samples from the seams bored through are cut up into such small fragments that tl evidence as to their quality is never very reliable.

The process of putting down a borehole by the ordinary.' percussive system is as follows : — -

A guide pife is first driven vertically into the ground; <=onsists of a wooden or iron pipe, of the same diameter as the lole is to be started, and from 6 to 9 feet in length. It is fitted at its upper end with iron covers or shutters, which lave a square liole in them to allow the passage of the rods. "The covers are required to prevent anything from falling 3own the hole, and can be moved clear of the liole when "*-e quired.

Exactly over the guide pipe a derrick qx head-gear erected. in its simplest form this consists of three poles, forming a Vriangle at their base, and coming together at the top. The derrick carries a pulley, as shown in Fig. 26, and a windlass is fitted across two of the legs. A piece of hoop iron is nailed around the legs near the top, to form a guide for the rods when Xhey are raised out of the hole.

The rods are sometimes worked by means of a lever or brake, in which case they are suspended to its short arm, and the power applied through the other. For shallow holes a spring-pole is frequently employed ; it consists of a larch pole about 30 feet in length, arranged as shown in Fig. 26. When the end of the pole is depressed, the blow is struck, and the rods are raised by its elasticity.

ler

b. i

S4

Coal-Mining.

The hole is bored hyc/Usils ; the chisels are attached to the bore rods, which are screwed to the braceluad, and hung from the kver or spring-pok through a stirrup.

The chisels (a and b, Fig. 27) are about iS inches long, and made of best tool steel. The flat chisel (a) is the most common, and is suitable for the strata usually met with in the coalmeasures ; for exceptionally hard ground chisels shaped in the form of a cross are employed. The ends of the chisels are fitted with bosses and screws, by means of which they ar attached to the rods.

Fig. 26. — Surface arrangements for percussive bori

The reds (c, Fig. 27) are of best wrought iron, and vary in size from to I5 inch square, i inch square being the most common; they are made in lengths of up to 18 or ao feet. The ends are provided with bosses of about double the diameter of the rods themselves, and one end of each rod has a male screw, and the other a female screw.

Wooden rods are also employed, but are not common in this country.

The hraeehead (d, Fig. 27) consists of four wooden arms, each about 18 inches in length, fitted into an iron socket. At

Search For Coal.

ttie top of the bracehead is a swivel, and at the bottom a short* length of rod terminating in a screw.

The stirrup (e, Fig. 27) consists of a bridle of iron and tog screw; its position is between the bracehead and lever, or spring.pole.

la boring a hole, the tools are hung from the lever or sprinpole in the following order : stirrup, bracehead, rods.

Fro. 37. — Boring tools.

anfl chisel. Two or four men each take an arm of the bracenead and lift the rods up, allowing them to fall sharply; as do this the men walk slowly round in a circle, so that at WEh blow the chise! is moved through a small angle, and 'tfikes the bottom of the hole in a fresh place ; this prevents chisel from jamming, and keeps the liole circular. I As the hole gets gradually deeper the rods are automatically wngthened by the lowering of the screw in the stirrup, and

Coal-Mining.

when this has reached its limit, a short rod is added top of the other rods, and the screw in the stirrup is run After a few inches have been bored, the bottom of the gets ful! oidibrisy which has to be removed. To do this, the bracehead is unscrewed, and the hook at the end of the windlass rope {a, Fig. aS) is slipped under the boss of the top rod, the windlass is turned, and the rods raised slowly out of the hole to the height of the derrick. A fork {b. Fig, 28) is then sHpped underneath the lowest boss above the guide pipe, lo prevent the rods from descending the hole, and the rods above are unscrewed bj a spanner ; this process is repeated until all the rods have been raised from the hole, A shell or sludger (0 Fig. aS) is then screwed on to the end of the rods and lowered down to the bottom of the hole.

The sludger consists of an iron pipe, closed at the bottom by a valve opening upwards, but open at the top. It is allowed to strike the bottom of the hole violendy several times; this forces the debra into the pipe, where it is retained by the valve, \Vhen all the debris has been collected by the sludger, it is raised lo the surface and emptied ; the chisel is again screwed on to the rods, sent down the hole, and the boring continued. These operations succeed each other until the borehole is completed.

The nature of the strata passed through is ascertained by examining the contents of the sludger. The master borer is able to tell the principal variations of the strata by noticing the jar upon the rods, which he marks whenever he believes

— Boring tools.

Search For Coal.

that a new sort of stratum has been reached, possible to get a very accurate section of the strata by this method of boring, as small bands may be passed through without being detected, although the thickness of any beds of coal can be almost exactly determined by a careful and experienced borer.

When the borehole is very deep, the time absorbed in

lifting and lowering the rods in order to clean the hole and

change the chisels is very great ; in some cases only an hour

ot two out of the twenty-four have been occupied in the actual

process of boring, the remainder being taken up by raising and

Wering the rods. In deep holes accidents may occur very

frequently, the most common being the fracture of the rods.

I'arious tools are used for catching and lifting broken rods ;

'f the fracture is a clean one, the bell-box {d. Fig, 38) may be

rtiployed to catch the broken end. This is an arrangement

*ith 3 bell-shaped end made of hard steel, having a thread

't inside the bell. The apparatus is screwed on to the rods,

lowered down the hole, and moved about until the broken end

Of the rod is caught in the bell. The rods to which the bell-

t*ox is attached are then turned slowly round, until the bell

1 attaches itself firmly to the fractured rod end by cutting a

*crew thread on it, and the whole lifted together to the surface.

; "Vhen the fractured end is ragged and bent, a special tool may

a-ve to be made to clutch it. An impression of the fractured

Hd may be obtained by lowering a lump of soft wax on to the

fracture, and keeping it there until it hardens ; a special tool

then be made suitable for the particular condition shown

, the impression in the wax. Fragments of chisels which

tave become broken have sometimes been drawn from the

Vole by means of magnets lowered down to the bottom,

lAning Boreholes. — Boreholes have usually to be lined to prevent their sides from falling in. This is done by forcing wrought-iron tubes down the hole in the following manner : The tube is first driven as far as possible down the hole by striking it with a hammer. When it can be driven no further liy the hammer, a length of rods is let down the hole through

Coal-Mintng.

the tube, the top rod being gripped by a strong clamp, whidi prevents it from slipping down the hole. The rods are then raised a few feet by the windlass and dropped, when the clamp comes into violent contact with the top of the tubes, and forces them down. The tubes have screwed joints, and should be put down in as long lengths as possible, for eadi succeeding length of tubes will be smaller than the previous one, as it will have to pass through it. This reduces the aiie of a borehole as it gets deeper, and many holes have been so reduced that they have had to be abandoned before reaching the required depth.

Boring from Colliery Workings. — When boreholes aie pat down from the workings, a small shaft should be sunk for a few yards, to give room for the rods to be raised and unscrewed. Rubber bands may be substituted for the lever or spring-pole; they are made out of rubber about r inch square, extra bands bemg added as the hole gets deeper and the rods heavier.

When deep holes are bored by the percussive method, the rods should be raised and dropped by mechanical power instead of by hand This may be done by means of pins which project from a revolving wheel driven by a steam-engine; these pins depress one end of the lever, to the other end of which the rods are attached, and so raise the rods and let them fall. Another method is to attach a hemp rope to the rods ; the rope is taken over a pulley in the head-gear, and makes two or three turns round a revolving drum. When tension is put on to the loose end of the rope it binds on the drum, and the rods are raised, and when the rope is released it slips on the drum, allowing the rods to fall.

Bori7ig by Ropes. — Many of the disadvantages of the ordinary method of percussive boring are overcome by the use of a rope instead of rods ; in this way holes can be put down much more quickly, but it is difficult to keep them vertical, and not easy to get an accurate section of the strata.

The most elaborate method of rope boring is Mather and Piatt's arrangement ; an outline of the necessary surface arrangements is shown in Fig. ag.

to Fig 29, a is a vertical cylinder having a pulley, b, fitted a fork at the top of its piston-rod. The flat rope to which boring tool is attached passes over b, through the clamp c, round the guide pulley e, on to the drum d. When horing 1 progress, the clamp c is tightened and holds the rope fast ; m is then turned into the cylinder a, which works the sy 6 up and down at the rate of about twenty-five strokes minute. The effect of this is to raise and drop the rope I the heavy tool which is hung on to its end ; this cuts into tock at the bottom of the borehole.

Fig. 29. — Mather and Piatt's method of .

When the hole has to be cleaned out, steam is shut off n 0, the clamp c is loosened, and the rope is raised by the Ira d; the sludger is then lowered down at the end of the e. The boring tool is a heavy iron bar 6 or 8 feet long, ing guide blocks at either end. The upper blocks are pro- Ed with a rachet arrangement which twists the drill slightly very stroke, and so forces the chisels to strike every blow 1 difiereot place. The bottom block carries a number of kIs, which form the cutting tool.

Coalmining.

The sludger is sometimes of special design, or it may be an ordinary " shell " divided into several compartments, each of which has its own valve. This system of boring is not very suitable for proving minerals, as a good section of the strala passed through is not obtainable. Holes can he bored uplo 1 8 or 24 inches in diameter ; the cost is said to average aboni per foot. Round ropes are largely employed for boring in the oil-fields of the United States.

The Rotary System of Boring. — This is now generally acknowledged to be the best system of boring to prove minerals, and all the important boreholes which have been put down of late years to prove coal-seams have been made by one or other of its modifications. The great advantage of this method is that the strata passed through are not cut up into small fragments, but a " core " is extracted. The amount of core actually obtained depends upon the size of the borehole and the hardness of the rock bored through ; the larger the hole and the harder the rock, the more perfect is tlie core.

The holes are bored by abrasion. A ring, made <rf material harder than the rock which is to be bored through, is rapidly rotated, and is at the same time pressed against the rock. This grinds the rock away where it is rubbed by the ring, leaving a solid column of material, known as a core, in its centre, which is broken off and extracted in short lengths.

There are two systems of rotary boring in genera! use, one known as the Diamond system, and the other as the Davis -calyx.

The Diamond System of Bering. — In this method of boring, the cutting is performed by diamonds of the black variety. The boring-piece is shown in Fig. 30. it is a wrought-iron tube about 3 inches in external diameter. It extends to the top of the hole, and the rotary motion is conveyed through it from the engine and gearing on the surface, a terminates in a block, c ; this block forms the division between the sediment tube b and the core-box d; bis an open-topped cylinder rather

SEARCH FOR COAL. 6i

in diameter than the borehole, and d is another cylinder

f the same size, having the crown screwed on to its lower

nd. The boring-crown is a wrought-iron ring, the bottom and

oih edges of whicti are set with diamonds. As the crown

evolves, these diamonds, which project slightly beyond the

oelal of the crown, cut away an annular space around a solid (entral core. Whilst the hole is being bored, water is pumped

brough the tube a j it passes underneath the crown through

proves provided for the purpose, and back to the surface

trough the borehole. The object of the

liter is to keep the crown cool and carry

Way the divis made in boring. As the

nier passes through the restricted area

lieiween the boring-piece and the sides of

iie hole its velocity is very great so that

Scarries all the debris with it; but as soon

Bit teaciies tlie unrestricted area above the

Op of the sediment tube, the .velocity de-

Beases, and the debris falls and settles in

Hie sediment tube.

The pressure upon the crown is regupted by means of balance weights, and can K either increased or reduced at will. [When the holes are shallow, and the tubes pich act as rods light, extra weight is acquired ; but when the holes are very deep, Fig. 30.— Diamond

tl of the weight of the rods must be mcihod of boring.

DUB terbala need. The cores are broken off by means of a split wedge-shaped ! 6xed in the inside of the crown. Wlien a few feet have

een bored, the boring is stopped, and the rods are lifted by a

Kam-winch. As soon as they are raised, the split ring is iwn down an incline and wedges the core tightly in the

-box. It then breaks off, and is drawn to the surface with

K boring-piece. Many very important boreholes have been put down by

62 Coal-Mining.

this system. At Soutbcar, in Lincolnshire, a hole was down to a depth of 3195 feet. Its diameter at the surfece was 13 inches, which was gradually reduced, the core at the bottom being about inch in diameter. A borehole at Snaith commenced 14 inches in diameter at the top, and finished inch at 1600 feet. Another at Ruddington had a core of about 4! inches at a depth of i3ao feet.

The Diamond system js suitable for boring through verj hard rocks, but the rocks of the coal-measures are not, as a rule, very hard, so that there is no necessity for using so pensive a material as the diamond to pierce ihem ; properij tempered steel will serve the purpose equally well, and in many cases even better.

The Davis-calyx System of Boring.- — This method of boring differs little in principle from the Diamond system. Its chief features arc the substitution of a steel cutter for the crown set wild diamonds. The sediment tube is made very much longer, and is called the " calyx ; " its length may be up to 100 feet.

The cutler is shown in Fig. 31. It consists of a cylindrical steel shell, the lower end of which is formed into a series of long sharp teeth. The front edges of these teeth arc vertical, and the backs slope at an angle, in order to give the greatest strength in one direction. They are set slightly in and out alternately, like the teeth of a saw. The outside set is to make the hole large enough for the boring tool to pass, and the inside set to dress the core sufficiently small to enable it to pass into the core-box. These teeth have a chipping rather than an abrasive action ; they sink into the rock and revolve with a series of jerks, chipping out small pieces of the rock in front of them. The number, size, and shape of the teeth are varied to suit the nature of the ground to be bored through, and the cutters are driven at a

ri/ixyi

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iHch slower rate than when diamonds are employed. The toerage speed for a large hole is four or five revolutions per minute.

I When the rock is very hard, a plain steel shell, without teeth, is substituted for the cutter described above, steel shot tre poured into the cut, and 8ie tool revolved rapidly apon them, thus wearing lway an annular groove, as done by the diamond. ; The surface airangelinents are shown in Fig. 32. a is a derrick 50 or 60 feet 'liigh, from which is suspended a set of blocks, b, the block rope being led to the drum g. To the top .of the rods e, which are

hollow and about 3 inches

in diameter, is attached the

swivel and water coupling

lij to which is connected the

pump by a hose, c is an

hydraulic cylinder, by means

of which part of the weight

of the rods can be carried,

for when the holes are very

deep the full weight of the

rods could not be safely

borne by the cutter. The

driving-wheel/ has a hole in

its centre, through which

the bore-rod pass. It also carries two arms, m, m', which engage

irith a clamp on the rods, and so force them to revolve with

he driving-wheel. By this arrangement the rods are free to

lide vertically through the driving-wheel, and so are able to

allow the borehole down as it gradually increases in depth.

Coal-Mining.

Both drum and driving-wheel are driven by a small pah of engines, and can be thrown in and out of gear when required by means of clutches. Water is forced down tlie rods through the hose-pipe by a small pump. About 50 gallons per minute are required. The same water can be used repeatedly, after it has passed through a small settling pond.

Boring operations are conducted as follows : Part of the weight of the rods is held by the block ropes, the exact weight upon the boring tool being regulated by the hydraulic cyiindei c. The pump is kept going at a regular speed, forcing water down the rods, under the cutting tool, and back up the boceliole. The engine is put into gear with the driving-wheel, which rotates the rods through its arms, which catch the clamp on the rods. As the boreJiole deepens, the clamp, being fixed to the tods, slides down and has to be moved up every foot or so.

The length of the core-box varies from 8 feet in large holes up to 15 feet in small ones. When the core-box is sufficiently full, the engine and pump are stopped, and the rods raised by means of the drum and block ropes, and unscrewed in sectionSi the length of the sections which can be unscrewed at once depending upon the height of the derrick. To break the core off, gravel is thrown down the bore-rods, causing the core ta bind in the box.

One hundred feet per day have been bored by this process, but this was in chalk, where the drilling would be unusually easy.

Surveying Boreholes. — Boreholes frequently iodine very considerably from the vertical. The deflection maybe so serious as to render a survey of the boreholes necessary. This may be accomplished in several ways. MacGeorge's clinometer is an instrument sometimes used for this purpose, It consists of a brass cylinder containing hquid gelatine, in which are suspended a plumb-bob and a magnetic needle. The apparatus is let down the borehole, and after a short time the gelatine congeals and holds the needle and plumbbofa in the same position that they occupied when in the hole, so that its exact inclination and bearing can be ascertained.

Chapter V.

Sinking.

Site of Shafts. — The choice of the position of the shafts is governed by a variety of circumstances, as both surface and Underground conditions have to be taken into account.

In former years, shafts were always sunk to the deep of the coal, because the appliances for pumping and hauling wer&so crude that it was almost impossible to work dip coal ; the shafts too, being shallow, were sunk close together to save the cost of haulage and of keeping long roads in repair. In districts that have been worked out many years ago, long lines of shafts can be traced. The oldest have won a narrow strip of coal alongside the outcrop of the seam ; the next line would be deeper and have worked a long narrow strip to the dip of the first, and Soon.

The haulage appliances at the present time are so good that . dip coal can be worked almost as cheaply as rise coal, except ; where water is present. Water is much less common in deep I pits than in shallow ones, and can be much more cheaply dealt ; with than formerly by the aid of electric pumps, so that at the Ipresent time it is not necessary that the shafts should beat the I dip of the royalty.

In selecting the site of a new winning, the following points Should be considered : —

(i) There must be ample room for surface works, sidings, Coke-ovens, workmen's houses, spoil heaps, etc.

(a) Access to one or more railways must be readily available, and the surface contour should be suited for the necessary

66 Coal-Mining,

branch lines. The question of landsales and communication with a. canal should also be considered,

(3) A supply of good water must be obtainable, as a large quantity will be required for steam. raising, coal-washing, cottages, etc.

(4) If large faults are known to exist, the position of the shafts may, to some extent, be governed by them.

(5) The shafts should be as nearly as possible in the centre of the royalty.

(6) Surface beds of sand, moss, etc., should, if possible, be avoided, as they may add enormously to the cost of sinking and of the foundations of the various surface erections.

It is obviously very seldom that a site can be chosen 10 comply with the whole of the above conditions, and frequently the choice is limited to certain areas by the terms of the leasE.

Number and Size of the Shafts. — At one time large collieries were worked with one shaft only, which was divided by a brattice for ventilation ; but since the accident at Hartley Colliery in i86z, the Coal Mines Regulation Act (§ 16) has stipulated that every mine shaU have at least two shafts outlets in communication with every seam, and not less than 15 yards apart. When several seams are to be worked at ' once, three or more shafts are sometimes sunk. '

Shafts may be either rectangular, polygonal, oval, or circulu in form. In England the latter are almost always adopted, being stronger, cheaper to sink, and much superior to the other forms, when tlie shaft has to be lined with cast-iron tubbing.

In Scotland rectangular shafts are still sunk, and are lined with timber instead of brickwork.

Among the advantages claimed for rectangular shafts, one is that there is little vacant space in them, and another, that they are more easily divided by a brattice, if one is required. The surplus space which occurs in circular shafts is, however, by no means wasted, being required for the passage of the air- Rectangular shafts are frequently employed for staple pits, and

Sinking.

te almost universal in metalliferous mines ; there are several . wal shafts in South Wales, and many polygonal shafts have sunk upon the continent. The size of shafts is gradually Bcreasirig, owing to the fact that royalties are larger and outputs increasing ; most modem shafts are between and 23 feet in Siameter. It is not usual to have more than one pair of cages a shaft, though occasionally two pairs are employed when Vera! seams have to be worked. In many of the old collieries in the county of Durham, two winding engines and two pairs of cages pull from one shaft ; examples of this may be seen at Murton, Hetton, and many other places. This practice increases the winding capacity of the shafts, but is hardly to be Kmm ended for new places.

In some districts there may still be seen one winding Kipne drawbg from two or three shafts, with one cage in each ; not a desirable arrangement, as it limits the output from each shaft.

Sinking through Loose Ground. — Strong rocks and shales are frequently found right up to the surface, but in some districts the measures for a considerable depth are composed of rery loose, wet ground, such as running sand, gravel, and toss. Special methods liave to be adopted for sinking through such material. When the loose ground is not of great depth, it Bay be got through by means of piles ; but when the thickness is very great, sand tubbing or some other system of sinking has to be resorted to,

Sinki'ig by Files. — Before commencing to sink through loose ground by piling, a borehole must be put down to prove the lUckness of the measures which will have to be piled through ; tills is necessary, because in the ordinary system of piling the size of the shaft is gradually decreased, so that the length of piling required has to be known before commencing operations, in order that the initial diameter may be arrived at.

The surface soil is first removed, and the ground levelled. A curb (o, Fig. 33) made of oak, 6 inches square in section, is Ihcn laid on the ground in a perfect circle, as shown in Fig. 33,

Fig. 33. — Sinking through lo

Coal-Mining.

and the piles h are driven down behind it. A wooden mallet is used to drive the piles down, and great care must be taken to keep them vertical.

The piles are about 15 feet in length, 6 to S inches wide, and 3 inches In thickness. They are sharpened at the bottom, and bevelled slightly at the edges, so that when the circle is completed there is a close joint between them. After the whole ring of piles has been driven about 5 feet down, 3 or 4 feet of the sand is dug 'out from inside them ; another curb, f, is then laid in position at the bottom of the excavation, the piles are again driven down, more sand is dug out, a fresh curb laid, and so on. \Vhen the first ring of piles has been driven down to its full length in this manner, and the sand dug out to a depth of about 12 feet, another set must be started, as the first will have reached its limit. This is done by laying 1 fresh curb, r, in the bottom of the shaft; this is made 18 inches less in diameter than the formO curbs, so that, when placed inside the last curb laid, there will be a space of 3 inches tween them. The second set of piles is driven down in ths space, step by step, and supported by curbs in the manner indicated above until it reaches its limit, when another sO will be started in the same manner, and so on, until the " stone head" or solid ground is reached.

It will be observed that the diameter of the shaft is reducoi by twice the thickness of the piles and curb for each set of pils* that have to be driven, and with piles 15 feet long a fresh s( is required for about every iz feet sunk through; so that, in order to obtain the initial diameter of the excavation, thej'

ed diameter at the "stone head "must be increased by ;hes for every is feet that has to be sunk through by

les are sometimes driven with a slight outward inclination

lid the large reduction in size of excavation which takes

when they are driven vertically.

lese inclined piles are made much smaller than the

il ones, being only 3 or 4 feet long.

le drawback to inclined piles is tliat there is a small space

en them, at the bottom of the length, and

sand is very loose it leaks through into the

inking through Loose Ground by

as. — Pile-driving is both costly and un- n when the beds of loose ground are of thickness, in which case the sinking is

performed by forcing a drum or cylinder n, limber or brickwork right through the f sand into the hard rock beneath it. le most suitable cylinders arc made of wrought iron, as wlicn timber and brickare used, the cyjicider walls have to be hick to resist the great pressure to which ire subjected. The operation of sinking a on drum is conducted as follows. be cylinder is built up of cast-iron plates, y ribbed and bracketed ; these plates are ;h outside, to enable them to slip easily jh the sand, and are bolted together '' '"ubbbl""'' , as shown in Fig. 34. The bottom of the t ring of plates is brought to an edge to form a cutter, as I in the figure. The joints between the segments are

watertight by strips of soft lead-sheeting, the edges of lates being planed. To sink the cylinder, the surface it levelled, and the bottom ring built up by bolting ments together. The sand is then dug out from the

r

70 Coal-Mining.

inside of the ring, which gradually sinks, its weight forcing the cutter through the soft sand. After It has sunk a foot or two, the second ring is bolted on to its top, more sand is dug out to ease the passage of the tubbing. Again a fresh segment is bolted on at the top, and so on until the hard ground is reached. Should the cyhnder stick, as it usually does when the sand is of great thickness, it may be either forced down from the top by Jiydraulic jacks, or it may be weighted with pig-iron, placed on girders put across the cylinder, and supported by the flanges. The most difficult part of the operation consists in keeping the cyhnder vertical ; it does not usually sink gradually, but in a series of jerks, and unless great caie is taken, one side may sink faster than the other. To guard against this, the cylinders may be either hung from strong timbers by four lifting screws, or a timber guide frame may be built up on the surface. In some cases the sand is dug from inside the cylinder by hand, the water being pumped out to allow the men to work. But in case the sand is very quid, Priestman's or other excavators are employed, and then the water can be left in. These excavators or dredgers are hung on ropes or chains and dropped heavily into the shaft ; as thej are pulled up they close, when they are raised by a small engine, bringing the sand with them. Care must be taken nol to allow the excavation to get in advance of the cylinder, for if this happens, the sand and water are liable to burst out from the sides and bottom and throw the cylinder out of plumb.

The general arrangement of sinking a cast-iron drum or cylinder will be understood from Fig. 35. a is the guide frame, which will be about 6 or 8 feet high ; b is one of the hydraulic jacks ; and c, the dredger. When the hard ground is reached, the cutting edge may be removed, and the permanent j lining of the shaft brought up to the cylinder, or iron plates may be placed under the cutter for it to rest on, and the permanent lining carried right up the shaft inside the cylinder. The great advantage of cast-iron cylinders is that they occupy very little space ; so that if it should be necessary to sink a second cylinder inside the first, as sometimes happens, it can

Sinking.

done without greatly reducing the diameter of the shaft. it iron, however, has one rather serious drawback— that is, liability to crack. Wrought iron, steel, or brick cylinders y be bent or squeezed out of shape with the pressure, but y seldom actually break.

Wrought-iron or Sieel Cylinders, — These are composed of o or steel plates about half an inch in thickness, riveted ether, with an inside of thick brickwork. The brick-

FlG 35 —Sand tubb ng— general arrangement

fk is built up on a ledge inside the cylinder and a few feet 3Q the bottom. The steel plates are doubled at the cutting je, and the inner plate is belled inwards till it reaches the ide of the ledge upon which the brickwork rests. This vents the brickwork offering a flat surface to resist the sand, I so aids its passage downwards. The process of sinking Be cylinders is similar to that described above. and lumber Cylinders. — These are constructed in the

72 Coal'Mining.

following manner: A timber curb about 18 inches wide tt laid down upon the site of the shaft, and brickwork is built upon it. When the brickwork has reached a height of 3 or 4 feet, a second curb is laid on the top of the brickwork, another 3 or 4 feet of brickwork is built up, a third curb is laid on its top, and so on.

The whole fabric is bound together by iron tie-bolts pa& ing from curb to curb, and the back of the brickwork is closely lined with planks, in order to form a watertight casing.

To form a cutting edge, the lower curb is bevelled off, and a steel plate is nailed behind it. Brick cylinders are sunk in the same manner as iron ones, the brickwork and cuifas beiag added at the top as the cylinder sinks.

Poetsch's Method of freezing Shafts.— This method of sinking through thick beds of very wet quicksand has met with great success; it is one of the recognized systems of sinking on the Continent, and has recently been employed in some very difficuh sinkings in the North of England.

The principle of the Poetsch system is to freeze the ground around the shaft into a solid block, the effect of this being to consolidate the sand and hold the water back whilst the shall is being sunk and lined through the wet ground.

The first step in sinking by this method is to put boreholes down in a circle all round the shaft, and in some cases inside it.

The number of boreholes varies according to the size of the shaft and nature of the ground; about zo are usually required, and they are put down about a couple of feet outside the circumference of the shaft. After the boreholes are completed, two tubes are inserted in each, one tube being placed inside the other ; the bottom end of the outer tube is closed, but the inner tube is left open. To freeze the sand, brine at an extremely low temperature, from — S to 5 degrees Fahr., is circulated through the boreholes, being pumped down the inner tubes, and back to the surface up the outer ones ; small cylinders of frozen ground are soon formed around each

borehole, and these gradually increase until they join, and finally a solid wall of frozen ground encircles the whole shaft. To reduce the temperature of the brine, ammonia is compressed and passed through a condenser, where it is cooled by water and is in the form of a liquid. From the condenser it passes into the refrigerator, where it expands and changes again to a Kas, the expansion resulting in an extremely low temperature.

The brine is kept circulating through the refrigerator and j boreholes by means of a small pump, the heat it gains in passing through the boreholes being absorbed as it passes through ' the coils in the refrigerator.

b

, c

L'

hM

'

a, Refrig £, Comp

e, ISoreliok.

d. Uond d. Brine-

pump.

Fio. 36.-PDEt;

of sinking .

Fig. 36 shows diagram matically the circulation of the ammonia and the brine.

The following description of the sinking of the Washington shafts in the county of Durham by this system is abstracted &om a paper by Mr. Ford {Trans. I.M.E., vol. xxiv.) :—

The strata sunk through consisted of from So to 90 feet of wet sand and boulder clay.

Two shafts were sunk, the winding shaft having a finished liimeterof i4feet. To get the position of the boreholes, a circle "15 drawn with a loi-feet radius, and the boreholes, twenty- two m number, were set off at equal distances around its circumfence. No holes were bored inside the shaft itself. To bore

Coal-Mining.

the holes, tubes 6 inches in diameter were forced through the sand with screwjacks. When they reached the clay, the holes were continued with chisels and rods in the usual manner. Much difficulty was experienced in keeping the holes straight in passing through the boulder clay, as they were apt to be deflected when they struck a large boulder.

The vertical directiou of the holes was tested from time to time by lowering plumb-lines down them. As soon as the holes reached their intended depth, the freezing- tubes were inserted, and the 6-inch tubes withdrawn. Special precautions were taken to make the joints of the outer tube perfectly tight, so that no leakage could take place through them.

The refrigerating plant for the two shafts consisted of the following ; —

Two horizontal compressors, compressing the ammonia to i5olbs. per square inch.

Two condsiuers, each lo feet high by 5i feet in diameter, containing 1600 feet of i-incb tubes for the ammonia, around which were circulated 4000 gallons of water per minute,

TTiree refrigerators, each 10 feet high by 7 feet in diameter, containing aooo feet of i-inch tubes, around which the brine was circulated.

One brine pump, with two 6-inch rams, producing a flow of 144 gallons of brine per minute through the refrigerators and boreholes.

The refrigerating agent was anhydrous ammonia, and the brine consisted of a solution of chloride of magnesia.

The excavation of the frozen ground was begun forty-three days after the freezing commenced. The sand was easily got through, but the boulder clay proved more difBcult, as blasting had to be resorted to, and especial precautions had to be taken so as not to disturb the freezing-tubes.

As there were no boreholes in the shaft itself, a soft core of unfrozen ground remained in its centre. The permanent lining consisted of brickwork set in cement. The brickwork consisted of two 9-inch rings, havmg a space of 2 inches between them, which was filled in with cement. To prevent the

Sinking.

cement mortar from freezing, the mixing water contained perl cent, of caustic soda.

The special difficulties in connection with the Poetsdi j system are as follows ; —

(i) When the boreholes have to be very deep, it is very difficult 10 keep them straight, and if they get much i out of plumb, wide spaces may be left between them which cannot be frozen.

(2) If the outer tube leaks, the brine escapes into the sand

and prevents it from becoming frozen.

(3) Where quicksand is met with at a considerable depth 1

from the surface, the whole of the ground right down to it would have to be frozen.

Gobert's System of freezing Shafts.— This i

important modification of Poetsch's system, the essential

difference being that no brine is employed.

Boreholes are put down, as in Poetsch's arrangement, and

are fitted with two tubes. The outer tube is similar to Poetsch's, liut the inner is serpentine in form, and is provided with apertures at intervals in the wJiole of its length. The ammoDia is compressed to a liquid, and forced down the inner tube; as it escapes through the apertures it vaporizes, owing to the heat of the strata, and to the pressure upon it being reduced. It is then drawn back by the gas pump, compressed gain to a liquid, and so on. In the act of vaporizing— ifhich takes place in the borehole— intense cold is produced, wd this freezes the strata around the boreholes. The advantages claimed for this system areThe danger from brine leaking into the strata is avoided; and, where necessary, the lower part of a shaft can be frozen without freezing the upper portion.

Sinking by the Aid of Compressed Air.— In this iWhod of sinking, a cast-iron cylinder is sunk through the 1 "ds of sand in the usual way. The cylinder is closed at the top and compressed air is forced in, to keep back the water,

Coal-Mining. V

and lo enable the men to work in the pit bottom, essential features of the system are illustrated in Fig, 37, v shows a section through a shaft in course of sinking by process.

a is a timber frame erected upon the surface, and for 3 guide to keep the cylinder vertical b is the outer or cylinder ; it is built up of cast-iron segments bolted tog in the usual way. c is an inner tube, kept always i pressure by compressed air ; it is belled out at the botto shown, to enable the men in the shaft to work right unde main cylinder walb. d is an air-lock, having double d through which men material pass up and 1 the shaft. It is mac small diameter, so i reduce the loss of a much as possible, cylinder is forced dow the weight of iron or b placed between b ai and, if necessary, hydraulic jacks split the top. The men work in the bottom ; the descent of the cyl by removing any bou or hard material v may be found under the cutting edge.

The water is kept from coming into the cylinder solel the pressure of the air, hence it follows that the air must ' a greater pressure than that of the water.

The pressure of the water depends upon its vertical h or depth. One cubic inch of water weighs o'036i7 lb., so a column of water 1 inch square and i foot long wi 12 X o'o36i7lb, o"434lb. This gives us the rule tha pressure in pounds per square foot due to a head of wati Jiead in feet X o'434'

Sinking. 77

It has been found that the greatest pressure under which men can work is about 45 lbs. per square inch, and this

corresponds to ahead of . 103 '6 feet, so that the greatest

epth to which a shaft can be sunk by this system is about 100 feet.

Tunnels under river-beds are sometimes driven by this tnethod, but it has not been largely applied to the sinking of shafts.

One of the drawbacks of this method is that when the pressure of the air is high, the men employed in the cylinder can only work very short shifts ; in some cases they have had to be changed every two hours.

Chapter Vi.

SINKING {fw//ww./).

Surface Arrangements.— After the " stone head" has been reached by one of the methods described in the last chapter the lining of the shaft is carried up some distance above tbe surface to provide a tipping ground for the sinking-dirt. the ground is strong right up to the surface, a few yards aX usually sunlc and bricked before the engines and pit top are erected ; solid brickwork should be built up around the shaft

Fio. 38. — Arrangements at a sinking pil lop.

as shown at g, Fig. 38. This forms the foundation for the headgear, and archways must be provided where necessary for fan drifts, haulage ropes, steam and water pipes, etc.

T/ie pit top is usually arranged as in Fig. 38. A frame,

consisting of four strong timbers, aa, is placed across the shaft,

anil the whole boarded over except the square aperture c.

blanks, are set at an angle, as shown in sketch ; and

Sinking.

Fig. 39.— Lifting doors for sinking pit

a lorry, or rolling bridge, arranged to run on rails, so that it can be made to either cover the shaft or leave it open. In the figure the shaft is shown covered, but the lorry can be run back clear of it. A fence, /, is erected to guard the mouth of the shaft ; its sides and back are fixed, but the front is attached to the lorry, and moves with it- Lifting doors are sometimes used instead of the siding lorry; they are arranged as in Fig. 39, and, when open, form the fence to two sides of the shaft, as shown by the dotted lines. These doors can be raised

by a hand lever when they ' ' - .- ' '

are properly balanced, or '., / :

they may be operated by a steam cylinder.

Winding Ettnes for Sinking. — These are usually a pair of horizontal engines, having cylinders from 16 to

So inches in diameter. To enable them to lift heavy loads the Jfum should be on the second motion, the ratio of gearing being ut a or 3 to I. Engines for sinking must be easily handled, lin steadily, and be provided with a powerful foot brake. If the saaftis to be very deep, the main winding engines are frequently eted whilst the earlier part of the sinking is in progress, and "'Uized for the latter part

Capstan Engines. — In all important sinkings — especially ''''ere large volumes of water have to be dealt with — very heyy weights have to be raised and lowered in the shafts, for this purpose a capstan is required. A capstan engine ' have several strong cast-iron drums, any of which can "e worked whilst the others remain stationary. The gearing "'ay be about 25 or 30 to i ; that is to say, the engines make or 30 revolutions to each revolution of the drum, so that, * the engines are traveling at a high speed, the drums We moving quite slowly, the reduction in speed being compensated by a corresponding increase in lifting capacity. The following example shows the manner of calculating the weight

CHAPTER VI. SINKING {co„time.i).

Surface Arrangements. — After the " stone head " has beeal reached by one of the methods described in the last chapter the hning of the shaft is carried up some distance above the surface to provide a tipping ground for the sinking-dirt If the ground is strong right up to the surface, a few yards are usually sunk and bricked before the engines and pit lop are erected ; solid brickwork should be built up around the shaft

Fig. 3S. — Arrangemcnl

inking pit top.

as shown at g, Fig, 38. This forms the foundation for the headgear, and archways must be provided where necessary for fan drifts, haulage ropes, steam and water pipes, etc.

The pit top is usually arranged as in Fig, 38. A frame, consisting of four strong timbers, aa, is placed across the shafl, and the whole boarded over except the square aperture c. Guide-planks, d, are set at an angle, as shown in sketch ; and

Sinking.

Fig. 39,— Lifting doors for sinking pi

Ig bridge, arranged to rua on rails, so that it

can be made Co either cover the shaft or leave it open. In

the figure the shaft is shown covered, but the sorry can be run

back clear of it. A fence, /, is erected to guard the mouth of

the shaft; its sides and back are fixed, but the front is attached

to the lorry, and moves with it,

I Lifting doors are sometimes used instead of the sUding

; lorry; they are arranged as in Fig. 39, and, when open, form

j, the fence to two sides of the shaft, as shown by the dotted lines.

ij These doors can be raised

I "by a hand lever when they I " ' - ,- ' ' ;

, are properly balanced, or / :

they may be operated by a steam cylinder.

Winding Engines for Sinking, — These are usually a pair of horizontal engines, having cylinders from 16 to

so inches in diameter. To enable them to lift heavy loads the drum should be on the second motion, the ratio of gearing being boat 3 or 3 to I. Engines for sinking must be easily handled, luasteadily, and be provided with a powerful foot brake. If the sliaft is to be very deep, the main winding engines are frequently Ottted whilst the earlier part of the sinking is in progress, and utilized for the latter part.

Cafsian Engities. — In all important sinkings — especially '"lere large volumes of water have to be dealt with — very heavy weights have to be raised and lowered in the shafts, ™d for this purpose a capstan is required. A capstan engine should have several strong cast-iron drums, any of which can he worked whilst the others remain stationary. The gearing be about 25 or 30 to t ; that is to say, the engines make '5 or 30 revolutions to each revolution of the drum, so that, liilst the engines are travelling at a high speed, the drums moving quite slowly, the reduction in speed being comptnsated by a corresponding increase in lifting capacity. The ihilowing example shows the manner of calculating the weight

Coal-Mining.

that a pair of capstan engines should lift : A pair of capstan engines having cylinders 1 2 inches in diameter by 24 inches stroke are geared down to drums 4 feet in diameter, the ratio of the gearing being 25 to i. Calculate the weight they should lift when the average steam pressure in the cylinders is 40 lbs. per square inch ; and find also the speed ai which such weight would be raised, when the engines are making 75 revolutions per minute.

First, find the area of the cylinders. This is done by squaring the diameter and multiplying by o"7854; so that the area of each cylinder is tz x 12 X o'78S4 ii3'i sq. inches, and as there are two cylinders, their combined area is SUS'Z sq. inches. On each square inch there is a pressure of 40 lbs., hence the total pressure on the pistons is 226-2 X 40 9048 lbs.

The engines make 75 revolutions per minute, and as tlieir stroke is 2 feet, each piston travels 4 feet per revolution; so the piston speed is 75 X 4 300 feet per minute. The rado of gearing is sj to i ; therefore the number of revolutions that the drum makes per minute is 3.

The diameter of the drum is 4 feet, and the circumference of a circle is found by muhiplying its diameter by 3'r4i6 ; this makes the circumference of the drum 4 x 3'i4i6 iz'56 feet. As the speed of the rope is exactly the same as the speed of the circumference of the drum, the speed at which the rope, and the weight upon it, travels is 3 x 12*56 37'68 feet per minute. Now the pressure on the piston is 9040 lbs., and the space it moves through per minute is 300 feet, whilst the weight lifted only travels through 37'68 feet; so that the weight the capstan should raise bears the same proportioD Co the pressure on the piston as the distance the weight moves bears to the distance the piston moves; or as 37"68 : 300 : : 9048 to weight lifted ; or, in other words —

distance it moves j weight capable of ' being raised 9048 X 300 37-M " '

pressure on piston

distance weight n

a Uiat the weight raised should be

2,038

Sinking.

large deduction must be made from this, because a c

ierable amount of power is required to overcome the friction

the engines and gearing. This deduction may be taken at

-third of the whole; so that the engines would raise about

Doo lbs. or over at tons at a speed of 37 '68 feet per minute.

Ropes used /or Sinking.— Th. special requirements in

lopes used for sinking are that they must not "spin" or twist.

Ordinary steel ropes are usually employed, but locked coil ropes

preferred by many, because they run more steadily than ropes

Bade of round wires. Flat ropes have been used, but they

hive not met with any great success, for if they do spin at all

dieir oscillations are very violent.

Calculations as to the weight and breaking strain of wire Mpes are given in Chapter XXIII.

Ventilation. — Sinking pits are ventilated by small fans, A . of air-pipes made of sheet-iron, and 18 or 24 inches in diameter, is spiked on to the side of the shaft, down which the is forced, or up which it is drawn by the fan, the former by preference, as the bottom of the shaft is more efficiently ventilated. Ample ventilating power should be provided, as it is ' to clear the shafts very quickly of the smoke given off when a heavy round of shots is fired; moreover, gas is wmetimes met with in considerable quantities, especially in fte vidnity of coal-seams.

iVig'.— Important sinking pits are usually lit by electric lamps. When gas is made safety lamps only should be employed. A recent disastrous explosion in a sinking pit was Uiribuied to the flame given off by an electric-lighting cable, hen it was accidentally severed by being struck with a fliovel.

Winding Ike De&ris.— The stone is wound to the surface

iii"hoppits" or "kibbles;" Fig. 40 shows their usual form.

The dimensions given are about the average, but the tendency

towards increased size. The bow of the hoppit is pivoted

Dn trunnions, a in sketch. These trunnions are set below the

of gravity, so that the hoppit can be easily tipped right

by withdrawing the cotter J, and lifting the hoop c clear

Coal-Mining.

of the pin. The hoppit is attached to the rope by spring hook and swivel.

To wind the debris two hoppits are required. One always in the shaft bottom being filled, whilst the Other is travelling the shaft and being emptied. The full hoppit drawn a few feet above the surface, the rolling bridge carrying, tip waggon is run over the shaft, and the contents of the hoppit emptied into it. The rolling bridge is then run back clear of the shaft, and the hoppit lowered to within a few yards of ihe bottom, and held there by the engine-man until it is signalled

lit /

Fig. 40.— Hoppit for

for by the sinkers, two of whom await its arrival, and push it into a convenient spot. The winding rope is then uncoupled and attached to the full hoppit, which is raised about 6 feet J it is there steadied by the sinkers, who signal it away, satisfying themselves that it is properly loaded and has no loose stones adhering to the sides or bottom.

Excavation. — The whole of the excavation is effected by

The shot-holes are usually bored by striking-d rills.

e drills are made from octagonal steel, forged chisel-shape

: ends — three of varying lengths forming a set One

Sinkiivg.

holds the drill, and one or, in hard ground, two men strike the head with heavy hammers. At every blow the drill is turned through a small angle, great care being taken to keep the holes round and of even diameter all through. The holes . are cleaned out by scrapers, and, if dry, water must be poured I down to keep the drills cool, and bind the dust so that it can ] be cleaned out by the scraper.

I The shot-holes should be arranged as in Fig. 41. The ' ring of holes marked a is first fired. These holes are termed " summers," and are deeper and more heavily charged than the others ; they should blow out that portion of the ground marked a. After they are fired the loosened material is filled out, and the second ring, d, is drilled, charged, and fired. This ring of shots should lift the ground marked i", and make a " loose end " for the next ring, c.

The best explosive for hard ground is dynamite or blasting gelatine ; owing to their high specific gravity and great strength, much smaller holes are required for these explosives than would be necessary for blasting powder. Moreover, the work required of an explosive is not merely to iifl the rock, it should also break it up into pieces small enough to be conveniently handled by the sinkers.

Shots should be fired by an electric battery, through a cable tiiken from the surface. The battery should be strong enough to fire several shots simultaneously, to reduce the time that is lost by withdrawing the men from the shaft during the process of shot-firing. When blasting powder is employed or the shots are fired by ordinary fuses, the fuses of shots which are fired together should always be cut of different lengths, so that the Dumber of detonations can be counted ; otherwise, a shot might hang fire without being detected, and explode whilst the sinkers at work.

Method of temporarily supporting the Shaft Sides.

— Formerly it was the custom to leave the hard beds of rock unsupported until the permanent lining was built, but it is now becoming usual to support the whole of the sides of the

Coalmtning.

ihan the thickness of the trickwork. In the sketch the brickwork is shown to be of more than ordinary thickness at the curb. This is not always the case, but it is good practice, as, if the shaft should at any time run in, these thick belts of brickwork would probably limit the injury to one length. When sinking is resumed below the curb-bed, the shaft is gradually belled out to its full diameter, leaving a- bracket of rock all round it to support the curb.

As a length of brickwork approaches the curb above, th* bracket of rock is removed in short lengths, and the brickworl; carried right up to the underside of the curb, or the curb be left partly supported on natural ground.

The centre line is a galvanized wire cord carrying a weight. When it is required, a beam is placed across shaft at the surface, from a mark on which the centre line i 3 hung. There is no necessity to use the centre line except t when setting a curb, as the brickwork is kept vertical by lin s hung from curb to curb. Foulstone's centre-line apparatims consists of a girder which can be run out over the shafl 13' means of a rack and wheel. The centre line is hung over a pulley at the end of this girder, and can be raised or by means of a small winch. When not in use the centre Iitre is hung down the shaft, but racked back close to the side, so that when it is required it has only to be racked forward to th e centre and, if necessary, lowered a few feet. This arrang-e- meat saves considerable time, as in a deep shaft it may take an hour or more to lower an ordinary line, and to steady ft after it is lowered,

A good curb-bed is not always obtainable. If the ground is too soft to afford the necessary support, the curb may Ije hung on chains from baulks fixed in the shaft some little distance up. A better method is to support the curb by driving in iron plugs all round the shaft side, and laying the i curb upon them. Sometimes a square or octagonal timber i frame is let into the sides, and the curb built upon it.

Scaffolds. — As the brickwork is being built, the workraenH

Sinking.

equire a scaffold to work upon. Fig. 44 shows the ordinary lalf-raooQ scaffold. It is made in two pieces for convenience lifting, and is constructed of 3-inch planks bolted to a tiong framework. It is provided with a flap to enable it to iss the air and water pipes, the whole forming a circle 6 or inches less in diameter than the shaft.

The scaffold shown in the figure is supported by the bolts . These are driven out and rest on the top of the brickwork, which is then built up for another 4 or 5 feet. The scaffold fcen has to be raised. To do this, the rope from the capstan ►i winding engine is hung on to the bridle chains attached to lie scaffold, the bolts are knocked back, the scaffold raised just the brickwork, and sup- >tried thereon by the bolts, which lie again driven out

The scaffold is frequently carried by chains instead of upon bolls, these chains being hung Flora timbers placed across the sliift. One very neat arrangement is to hang the chains from the curb above. When this is <ione, the curbs are built upon four pieces of fiat bar iron, which are bent back behind the curbs. These bars are spaced at equal distances around shaft, and their ends, which project a few inches from the ' ''urb, are forged into bows, from which chains are suspended. , The chains hang down the shaft close to the sides, and are I provided at equal distances with large links, from which the ' scatTold chains are hung.

When a half-moon scaffold is not in use, it may either be

lung up in the shaft in halves, or it may be taken to bank.

j Some consider the latter the safer, as if anything should fall

doirn the shaft and hit a scaffold suspended in it, it might

throw the scaffold down the pit. This happened some years

I 3go at a Derbyshire colliery.

A very good scaffold is shown in Fig. 45. It consists of

J. 44.— Sinking scaffold.

Surface Arrangements. — After the " stone h reached by one of the methods described in the last ch; the lining of the shaft h carried up some distance abovi surface to provide a tipping ground for the sinking-dirt the ground is strong right up to the surface, a few yards usually sunk and bricked before the engines and pit tO] t erected ; solid brickwork should be built up around the

as shown at g, Fig. 38. This forms the foundation foi headgear, and archways must be provided where necessai fan drifts, haulage ropes, steam and water pipes, etc.

T/k fit top is usually arranged as in Fig. 38. A fr consisting of four strong timbers, aa, is placed across the £ and the whole boarded over except the square apertu Guide-planks, d, are set at an angle, as shown in sketch

Sinking.

Fig. 39,— Lifting doors for sinking pi

or rolling bridge, arranged to run on rails, so that it 1 can be made to either cover the shaft or leave it open. In ] the figure the shaft is shown covered, but the lorry can be Tim back clear of it. A fence, /, is erected to guard the mouth of 1 tbe shaft ; its sides and back are fixed, but the front is attached to the lorry, and moves with it.

Lifting doors are sometimes used instead of the sliding J lorry; they are arranged as in Fig. 39, and, when open, form the fence to two sides of the shaft, as shown by the dotted lines. These doors can be raised by a hand lever when they aie properly balanced, or they may be operated by a steam cylinder.

Winding Engines for Si nAing.— These are usually a pair of horizontal engines, having cylinders from 16 to 2o inches in diameter. To enable them to lift heavy loads the ] drum should be on the second motion, the ratio of gearing being about B or 3 to r. Engines for sinking must be easily handled, nin steadily, and be provided with a powerful foot brake. If the shaft is to be very deep, the main winding engines are frequently Efected whUst the earlier part of the sinking is in progress, and lililized for the latter part.

Cspstan Engines. — In al! important sinkings — especially where large volumes of water have to he dealt with — very heavy weights have to be raised and lowered in the shafts, ind for this purpose a capstan is required. A capstan engine should have several strong cast-iron drums, any of which can w worked whilst the others remain stationary. The gearing "isy be about 25 or 30 to i ; that is to say, the engines make 'J or 30 revolutions to each revolution of the drum, so that, hilst the engines are travelling at a high speed, the drums W6 moving quite slowly, the reduction in speed being com- ' by a corresponding increase in lifting capacity. The

'ing example shows the manner of calculating the weight

w

f tha

Coalmining.

that a pair of capstan cngjnes should lift : A pair of capstan

CDgtoes having cylinders ix indies in diameter by 34 inches stroke aie geared dovn to 4 feet in diameter, the ratio of the gearing being 35 to i. Calculate the weight they should lift when the average steam pressure in the cylinders is 40 lbs. per square inch ; and find also the speed at which such weight would be raised, when the engines are making 75 reTolutions per minute.

First, find the area of the cylinders. This is done by squaring the diameter and multiplyicig by o'7854 ; so that the area of each cylinder is 12 x 12 x 07854 1131 sq. inches, and as there are two cylinders, their combined area is 286'S sq. inches. On each square inch there is a pressure of 40 lbs., hence the total pressure on the pistons is aaS'a x 40 9048 lbs.

The engines make 75 revolutions per minute, and as their stroke is z feet, each piston travels 4 feet per revolution; so the piston speed is 75 X 4 300 feet per minute. The ratio of gearing is 25 lo i ; therefore the number of revolutions that the drum makes per minute is 3.

The diameter of the drum is 4 feet, and the circumference J of a circle is found by multiplying its diameter by 3"i4i6 ; this

i makes the circumference of the drum 4 x 3' 141 6 i2*56 feet.

As the speed of the rope is exactly the same as the speed of the circumference of the drum, the speed at which the rope, and the weight upon it, travels is 3 X i3'56 37-68 feet per minute. Now the pressure on the piston is 9040 lbs., and the

space it moves through per minute is 300 Uitx, whilst the weight lifted only travels through 37-68 feet so that the weight the capstan should raise bears the same proportion to the pressure on the piston as the distance the weight moves bears to the distance the piston moves; or as 37-6S : 300 : : 9048 to weight lifted ; or, in other words pressure on piston x distance it moves J weight capable of distance weight moves t being raised

Sinking.

A large deduction must be made from this, because a con- Bderable amount of power is required to overcome the friction of Ihe engines and gearing. This deductioji may be taken at one-third of the whole ; so that the engines would raise about 48,000 lbs. or over 2 1 tons at a speed of 37 5S feet per minute. Jiofies used /or Sinking. — The special requirements in lopes used for sitting are that they must not "spin" or twist. Ordinary steel ropes are usually employed, but locked coil ropes preferred by many, because they run more steadily than ropes mide of round wires. Flat ropes have been used, but they liave not met with any great success, for if they do spin at all their oscillations are very violent.

Calculations as to the weight and breaking strain of wire KpM are given in Chapter XXIII.

Ventilation. — Sinking pits are ventilated by small fans. A Em of air-pipes made of sheet-iron, and 18 or 24 inches in diameter, is spiked on to the side of the shaft, down which the forced, or up which it is drawn by the fan, the former by preference, as the bottom of the shaft is more efficiently ventilated. Ample ventilating power should be provided, as it is necessary to clear the shafts very quickly of the smoke given when a heavy round of shots is fired j moreover, gas is Mmetimes met with in considerable quantities, especially in Ihe vicinity of coai-seams.

Lighting. — Important sinking pits are usually lit by electric Umps, When gas is made safety lamps only should be employed. A recent disastrous explosion in a sinking pit was itlributed to the flame given off by an electric-lighting cable, *hen it was accidentally severed by being struck with a shovel.

Winding tlie Dibris.—Ths. stone is wound to the surface iii"hoppits" or "kibbles;" Fig. 40 shows their usual form. The dimensions given are about the average, but the tendency is towards increased size. The bow of the hoppit is pivoted on tninnions, a in sketch. These trunnions are set below the wntieof gravity, so that the hoppit can be easily tipped right over by withdrawing the cotter b, and lifting the hoop c clear

of the pin. The hoppit is attached to the rope by means i spring hook and swivel.

To wind the debris two hoppits are required. One always in the shaft bottom being filled, whilst the ot is traveUing the shaft and being emptied. The full boppil a a few feet above the surface, the rolling bridge carryin tip waggon is run over the shaft, and the contents of the hop emptied into it. The rolling bridge is then run back clear the shaft, and the hoppit lowered to within a few yards of i bottom, and held there by the engine-man until it is signal

for by the sinkers, two of whom await its arrival, and pusl into a convenient spot. The winding rope is then uncoup and attached to the full hoppit, which is raised about 6 fe it is there steadied by the sinkers, who signal it away, at satisfying themselves that it is properly loaded and has no loi stones adhering to the sides or bottom.

Excavation. — The whole of the excavation is effected

asting. The shot-holes are usually bored by striking-dri

The drills ate made from octagonal steel, forged chisel-sh:

at the ends — three of varying lengths forming a set. One n

holds the drill, and one or, in hard ground, two men strike 1 the head with heavy hammers. At every blow the drill i turned through a small angle, great care being taken to keep the holes round and of even diameter all through. The holes are cleaned out by scrapers, and, if dry, water must be poured down to keep the drills cool, and bind the dust so that it can be cleaned out by the scraper.

The shot-holes should be arranged as in Fig. 41. The J ' of holes marked a is first fired. These holes are termed "summers," and are deeper and naore heavily charged than the others ; they should blow out that portion of the ground marked d. After they are fired the loosened material is filled out, and ihe second ring, b, is drilled, charged, and fired. This ring of shots should lift the ground marked b', and make a " loose end" for the next ring, c.

The best explosive for hard ground is dynamite or blasting gelitiae; owing to their high specific gravity and great strength, much smaller holes are required for these explosives than would necessary for blasting powder. Moreover, the work required of aa explosive is not merely to lift the rock, it should also tireak it up into pieces small enough to be conveniently handled i'y the sinkers.

Shots should be fired by an electric battery, through a cable tjlfen from the surface. The battery should be strong enough to fire several shots simultaneously, to reduce the time that is lost by withdrawing the men frorei the shaft during the process of shot-firing. When blasting powder is employed or the shots fired by ordinary fuses, the fuses of shots which are fired : should always be cut of different lengths, so that the of detonations can be counted ; otherwise, a shot might re without being detected, and explode whilst the sinkers at work.

Method of temporarily supporting the Shaft Sides.

—Formerly it was the custom to leave the hard beds of rock unsupported until the permanent lining was built, but it is now becoming usual to support the whole of the sides of the

Coal-Mining.

excavation as the sinking proceeds, because the hardest of rocks may be shaken by the blasting, and portions may break away without warning.

Under ordinary conditions the shaft sides are temporarily supported by iron rings and planks, al! of which are drawn out as the permanent lining of brickwork or tubbing is built up. The arrangement will be understood by reference to Fig. 42, which shows two views of part of a sinking pit timbered with planks and iron rings. The rings marked a are made of fiat

iron bars from 3 to 4 inches wide by inch thick ; they ar made up of segments, which have several bolt-holes in eacl"* end, so that the size of the rings can be varied to suit th irregularities in the uneven shaft sides. The planks b are or 7 inches wide by inch thick ; they are set against strata all round the shaft, and held in position by being wedgetBbetween the sides and the rings, the wedges c being used foC that purpose. The rings are kept in place by the hangers dr made of iron about 1 inch square, their distance apart varying according to the nature of the ground. Formerly woodeO

Sinking.

rings, termed curbs, made of oak about 6 inches square, were employed instead of iron rings. They are stronger than the iron ones, and more costly, but not so convenient, and are now

not often employed, except where the ground is unusually .

heavy. I

Bricking the Shaft. — Shafts are usually lined with tricks of the ordinary size, that is 9 by ij by 3 inches, xnoulded to the circle of the shaft. In some cases large ;ffireclay lumps are employed, but well-burned red bricks give satisfactory results except under exceptional circumstances.

The brick lining is built up in sections, the operation

tieing conducted as follows : The shaft— which has, of course,

fceen sunk large enough to allow for the brickwork — is reduced

to its finished size, leaving a ledge all the

round it ; this ledge, which is termed

the curb-bed, forms the foundation upon

rhich the brickwork is built. It is most

important that the curb-beds should be

perfectly level, and that their centres

sliould be the exact centre of the shaft ; to

ensure this they must be carefully tested

bymeans of the spirit-level and centre hne.

The curbs may be made of oak or of

cast iron, the latter being preferred for

ei shafts, as oak is liable to rot. Cast-iron

curbs vary ftom 12 to 16 inches in width,

Wd are about inch thick, made in

right or ten segments.

The curb is laid on the bed, and edged tightly from behind with hard ood wedges ; whilst being wedged up.

Fir.. 43. — Seelion ihrongb brickwork and curb.

should be tested *ith spirit-level and centre line, great care being taken to 'ay it perfectly true. Fig. 43 is a section through a curb- W and short length of brickwork ; a is the curb-bed, and the curb. The shaft is shown to be belled out a little at the Wtb-bed; this is necessary, because the curb is made wider

n

Coal-Mining.

than the thickness of the brickwork. In the sketch the brickwork is shown to be of more than ordinary thickness at the curb. This is not always the case, but it is good practice, as, if the shaft should at any time run in, these thick belts of brickwork would probably limit the injury to one length. When sinking is resumed below the curb-bed, the shaft is gradually belled out to its full diameter, leaving a bracket of rock all round it to support the curb.

As a length of brickwork approaches the curb above, the bracket of rock is removed io short lengths, and the brickwork carried right up to the underside of the curb, or the curb may be left partly supported on natural ground.

The centre line is a galvanized wire cord carrying a heavy weight. When it is required, a beam is placed across the shaft at the surface, from a mark on which the centre line is hung. There is no necessity to use the centre line except when setting a curb, as the brickwork is kept vertical by lines hung from curb to curb. Foulstone's centre-line apparatus consists of a girder which can be run out over the shaft by means of a rack and wheel. The centre line is hung over a pulley at the end of this girder, and can be raised or lowered by means of a small winch. When not in use the centre line is hung down the shaft, but racked back close to the side, so" that when it is required it has only to be tacked forward to the=

centre and, if necessary, lowered a few feet. This arrange

ment saves considerable time, as in a deep shaft it may taks an hour or more to lower an ordinary line, and to steady iM after it is lowered.

A good curb-bed is not always obtainable. If the is too soft to afford the necessary support, the curb may bS hung on chains from baulks fixed in the shaft some littles distance up. A better method is to support the curb driving in iron plugs all round the shaft side, and laying th? curb upon them. Sometimes a square or octagonal timbe*" frame is let into the sides, and the curb built upon it.

Scaffolds. — As the brickwork is being built, the workmen

Sinking.

J require a scaffold to work upon. Fig, 44 shows the ordinary

bI half-moon scaffold. It is made in two pieces for convenience

c in lifting, and is constructed of 3-inch planks bolted to a

strong framework. It is provided with a flap to enable it to

piss the air and water pipes, the whole forming a circle 5 or

S inches less in diameter than the shaft.

The scaffold shown in the figure is supported by the bolts f. These are driven out and rest on the top of the brickwork, ivhich is then built up for another 4 or 5 feet. The scaffold lien has to be raised. To do this, the rope from the capstan Or winding engine is hung on to the bridle chains attached to the scaffold, the bolts are knocked back, the scaffold raised just 3bove the brickwork, and sup- Ported thereon by the bolts, which are again driven out

The scaffold is frequently

rried by chains instead of upon

these chains being hung

'fcim timbers placed across the

Slkaft. One very neat arrange-

*iient is to hang the chains from.

*he curb above. When this is

*ione, the curbs are built upon

*our pieces of flat bar iron, which are bent back behind the

urbs. These bars are spaced at equal distances around

tVie shaft, and their ends, which project a few inches from the

Curb, are forged into boils, from which chains are suspended.

'I'he chains hang down the shaft close to the sides, and are

proTided at equal distances with large links, from which the

Scaffold chains are hung.

When a half-moon scaffold is not in use, it may either be Viung up in the shaft in halves, or it may be taken to bank. Some consider the latter the safer, as if anything should fall down the shaft and hit a scaffold suspended in it, it might ftiiow the scaffold down the pit. This happened some years at a Derbyshire colliery.

A very good scaffold is shown in Fig. 45. It consists of

;. 44.— Sinking scaffold.

CHAPTER Vr. SINKING {contimted).

Surface Arrangements. — After the " stone head " has been reached by one of the methods described in the last chapter the hning of the shaft is carried up some distance above the surface to provide a tipping ground for the sinking-dirt If the ground is strong right up to the surface, a few yards are usually sunk and bricked before the engines and pit top are erected ; solid brickwork should be built up around the shaft

as shown at g, Fig. 3S. This forms the foundation for the headgear, and archways must be provided where necessary for fan drifts, haulage ropes, steam and water pipes, etc.

The pit top is usually arranged as in Fig. 38. A frame, consisting of four strong timbers, aa, is placed across the shaft, and the whole boarded over except the square aperture c. Guide-planks, d, are set at an angle, as shown in sketch ; and

Sinking. 79

I' a lorry, or rolling bridge, arranged to run on rails, so that it can be made to either cover the shaft or leave it open. In the figure the shaft is shown covered, but the sorry can be run

back clear of it. A fence, /, is erected to guard the mouth of

the shaft; its sides and back are fixed, but the front is attached to the lony, and moves with it

Lifting doors are sometimes used instead of the sliding

illoxry; they are arranged as in Fig. 39, and, when open, form

jthe fence to two sides of the shaft, as shown by the dotted lines.

rrJiese doors can be raised

fbya hand lever when they ,-'' ;

[(are properly balanced, or '

|they may be operated by a

I steam cylinder,

I Winding Engines for J f'

£ Sinking. — These are usually

I haling cylinders from 16 to

20 mches in diameter. To enable thera to lift heavy loads the drum should be on the second motion, the ratio of gearing being alMut 2 or 3 to I. Engines for sinking must be easily handled, run steadily, and be provided with a powerful foot brake. If the ftis to be very deep, the main winding engines are frequently *tected whilst the earlier part of the sinking is in progress, and utiliMd for the latter part.

Capstan Entries. — In all important sinkings — especially "here large volumes of water have to be dealt with — very heavy weights have to be raised and lowered in the shafts, ™<1 for this purpose a capstan is required. A capstan engine SMQld have several strong cast-iron drums, any of which can worked whilst the others remain stationary. The gearing nsy be about 25 or 30 to i ; that is to say, the engines make or 30 revolutions to each revolution of the drum, so that, "nilst the engines are travelling at a high speed, the drums "e moving quite slowly, the reduction in speed being com- PSDsated by a corresponding increase in lifting capacity. The fciuowing example shows the manner of calculating the weight

Coal- Mining.

that a pair of capstan engines should lift ; A pair of" capstan engines having cyUnders 12 inches in diameter by 14 inches stroke are geared down to drums 4 feet in diameter, the ratio of the gearing being 25 to i. Calculate the weight they should lift when the average steam pressure in the cylinders is 40 lbs. per square inch ; and find also the speed at which such weight would be raised, when the engines are making 75 revolutions per minute.

First, iind the area of the cylinders. This is done by squaring the diameter and multiplying by 07854 ; so that the area of each cylinder is 12 x 12 x o'7854 ii3'i sq. inches, and as there are two cylinders, their combined area is '8 sq. inches. On each square inch there is a pressure of 40 lbs., hence the total pressure on the pistons is 2z6'z X 40 9048 lbs.

The engines make 75 revolutions per minute, and as their stroke is a feet, each piston travels 4 feet per revolution ; so the piston speed is 75 x 4 — 300 feet per minute. The ratio of gearing is 25 to t ; therefore the number of revolutions thai the drum makes per minute is 3.

The diameter of the drum is 4 feet, and the circumference of a circle is found by multiplying its diameter by 3"i4i6; this makes the circumference of the drum 4 X 3'i4i6 i2'56 feet. As the speed of the rope is exactly the same as the speed of the circumference of the drum, the speed at which the rope, and the weight upon it, travels is 3 x la'S 37'68 feet per minute. Now the pressure on the piston is 9040 lbs., and the space it moves through per minute is 300 ftet, whilst the weight lifted only travels through 37'68 feet; so that the weight the capstan should raise bears the same proportion to the pressure on the piston as the distance the weight moves bears to the distance the piston moves; or as 37'68 ; 300 : : 9048 to weight lifted ; or, in other words —

pressure on piston X distance it moves 1 weight capable of distance weight moves ( being raised

so that the weight raised should be - - 72,038

Sinking.

large deduction must be made from this, because a con-

flerable amount of power is required to overcome the friction

the engines and gearing. This deduction may be taken at

ae-third of the whole; so that the engines would raise about

(8,000 lbs. or over zi tons at a speed of 37 '68 feet per minute.

Ropes used for Sinking. — The special requirements in

opes used for sinking are that they must not "spin" or twist.

Ordinary steel ropes are usually employed, but locked coil ropes

preferred by many, because they run more steadily than ropes

made of round wires. Flat ropes have been used, but they

bve not met with any great success, for if they do spin at all

their oscillations are very violent.

Calculations as to the weight and breaking strain of wire ropes are given in Chapter XXIII.

Vmlilation. — Sinking pits are ventilated by small fans. A line of air-pipes made of sheet-iron, and 18 or 24 inches in "liamEter, is spiked on to the side of the shaft, down which the sir is forced, or up which it is drawn by the fan, the former by reference, as the bottom of the shaft is more efficiently ventilated. Ample ventilating power should be provided, as it is ary to clear the shafts very quickly of the smoke given off when a heavy round of shots is fired ; moreover, gas is Bmetiraes met with in considerable quantities, especially in tile vicinity of coal-seams.

LighCiTtg. — Important sinking pits are usually lit by electric lumps. When gas is made safety lamps only should be employed. A recent disastrous explosion in a sinking pit was iUlributed to the ilame given off by an electric-lighting cable, then it was accidentally severed by being struck with a shovel.

Winiiirig the Dtbris,- — The stone is wound to the surface lfi"hoppits" or "kibbles;" Fig. 40 shows their usual form. The dimensions given are about the average, but the tendency towards increased size. The bow of the hoppit is pivoted on trannioDS, a in sketch. These trunnions are set below the Mtiire of gravity, so that the hoppit can be easily tipped right fw by withdrawing the cotter h, and lifting the hoop c clear

r

Coal-Mining.

of the pin. The hoppit is attached to the rope by means ofi spring hook and swivel.

To wind the dibris two hoppits are required. One is always in the shaft bottom being filled, whilst the other is travelling the shaft and being emptied. The full hoppit is drawn a few feet above the surface, the rolling bridge carrying tip waggon is run over the shaft, and the contents of the hoppil emptied into it. The rolling bridge is then run back clear of the shaft, and the hoppit lowered to within a few yards of the bottom, and held there by the engine-man until it is signalled

F:g. 40. — Hoppit for sinking.

for by the sinkers, two of whom await its arrival, and push it into a convenient spot. The winding rope is then uncoupled and attached to the full hoppit, which is raised about 6 feet; it is there steadied by the sinkers, who signal it away, after satisfying themselves that it is properly loaded and has no loose stones adhering to the sides or bottom.

Excavation. — The whole of the excavation is effected by blasting. The shot-holes are usually bored by striking-drills. The drills are made from octagonal steel, forged chisel-shape at the ends — three of varying lengths forming a set. One man

Sinking. 83 '

holds the drill, and one or, in hard ground, two men strike the head with heavy hammers. At every blow the drill is turned through a small angle, great care being taken to keep the holes round and of even diameter all through. The holes are cleaned ouE by scrapers, and, if dry, water must be poured down to keep the drills cool, and bind the dust so that it can be cleaned out by the scraper.

The shot-holes should be arranged as in Fig. 41. The ring of holes marked a is first fired. These holes are termed " siimpers," and are deeper and more heavily charged than the others ; they should blow out that portion of the ground marked a. After they are fired the loosened material is filled out, and the second ring, b, is drilled, charged, and fired. This ring of shots should lift the ground marked and make a " loose end " for the next ring, c.

The best explosive for hard ground is dynamite or blasting gelatine ; owing to their high specific gravity and great strength, much smaller holes are required for these explosives than would be necessary for blasting powder. Moreover, the work required of an explosive is not merely to lift the tock, it should also break it up into pieces small enough to be conveniently handled by the sinkers.

Shots should be fired by an electric battery, through a cable taken from the surface. The battery should be strong enough to fire several shots simultaneously, to reduce the time that is lost by withdrawing the men from the shaft during the process of shot-firing. When blasting powder is employed or the shots are fired by ordinary fuses, the fuses of shots which are fired together should always be cut of different lengths, so that the number of detonations can be counted ; otherwise, a shot might hang fire whhout being detected, and explode whilst the sinkers were at work.

Method of temporarily supporting the Shaft Sides. —Formerly it was the custom to leave the hard beds of rock unsupported until the permanent lining was built, but it ia now becoming usual to support the whole of the sides of the

Excavation as the sinking [proceeds, because the hardest oC rocks may be sliaken by the blasting, and portions may beat: ,'ay without warning.

Under ordinary conditions the shaft sides are temporarily

supported by iron rings and planks, all of which are drawn ou J

i the pemianent lining of brickwork or tubbing is built up. The arrangement will be understood by reference to Fig, which showfl two views of part of a sinking pit timbered witl — planks and iron rings. The rings marked a are made of fia-_

"b:

J~iG. 41.— Supporting (he sides of a sinking pii.

iron bars from 3 to 4 inches wide by inch thick ; they are I made up of segments, which have several bolt-holes in eacb I end, so that the size of the rings can be varied to suit the I irregularities in the uneven shaft sides. The planks b are 6l or 7 inches wide by inch thick ; they are set against thel strata all round the shaft, and held in position by being wedgcfT between the sides and the rings, the wedges e being used fJ that purpose. The rings are kept in place by the hangers T made of iron about i inch square, their distance apart varyifl accordinjj to the nature of the ground. Formerly woo(|

Sinking.

H

ings, termed curbs, made of oak about 6 inches square, were taployed instead of iron rings. They are stronger than the ron ones, and more costly, but not so convenient, and are now lot often employed, except where the ground is unusually

Bricking the Shaft. — Shafts are usually lined with bricks of the ordinary size, that is 9 by 4 by 3 inches, moulded Co the circle of the shaft. In some cases large fireclay lumps are employed, but well-burned red bricks give satisfactory results except under exceptional circumstances.

The brick lining is built up in sections, the operation being conducted as follows; The shaft — which has, of course, been sunk large enough to allow for the brickwork — is reduced to its finished size, leaving a ledge all the

ffay round it ; this ledge, which is termed the curb-bed, forms the foundation upon which the brickwork is built. It is most important that the curb-beds should be perfectly level, and that their centres should be the exact centre of the shaft ; to ensure this they must be carefully tested by means of the spirit-level and centre line. The curbs may be made of oak or of Cast iron, the latter being preferred for Wet shafts, as oak is liable to rot. Cast-iron Curbs vary from iz to i5 inches in width, and are about inch thick, made in tight or ten segments.

The curb is laid on the bed, and Wedged tightly from behind with hard wood wedges ; whilst being wedged up, it should be tested with spirit-level and centre line, great care being taken to \vj it perfectly true. Fig. 43 is a section through a curbbed and short length of brickwork ; a is the curb-bed, and h the curb. The shaft is shown to be belled out a little at the curb-bed ; this is necessary, because the curb is made wider

r

86 Coal-Mining.

than the thickness of the brickwork. In the sketch the brickwork is shown to be of more than ordinary thickness at the curb. This is not always the case, but it is good practice, as, if the shaft should at any time run in, these thick belts of brickwork would probably limit the injury to one length. When sinking is resumed below the curb-bed, the shaft is gradually belled out to its full diameter, leaving a bracket of rock all round it to support the curb.

As a length of brickwork approaches the curb above, the bracket of rock is removed in short lengths, and the brickwork carried right up to the underside of the curb, or the curb may be left partly supported on natural ground.

The centre line is a galvanized wire cord carrying a heavy weight. When it is required, a beam is placed across the shaft at the surface, from a mark on which the centre line is lung. There is no necessity to use the centre line except when setting a curb, as the brickwork is kept vertical by lines bung from curb to curb. Foulstone's centre-line apparatus consists of a girder which can be run out over the shaft by means of a rack and wheel. The centre line is hung over % pulley at the end of this girder, and can be raised or lowered by means of a small winch. When not in use the centre line is hung down the shaft, but racked back close to the side, so that when it is required it has only to be racked forward to the centre and, if necessary, lowered a k'v feet. This arrangement saves considerable time, as in a deep shaft it may take an hour or more to lower an ordinary line, and to steady it after it is lowered.

A good curb-bed is not always obtainable. If the ground is too soft to afford the necessary support, the curb may be hung on chains from baulks fixed in the shaft some little distance up, A better method is to support the curb by driving in iron plugs all round the shaft side, and laying the curb upon them. Sometimes a square or octagonal timber frame is let into the sides, and the curb built upon it.

Scaffolds. — As the brickwork is being built, the workmen

tSinire a scaffold lo work upon. Fig. 44 shows the ordinary aJf-moon scaffold. It is made in two pieces for convenience 1. lifting, and is constructed of 3-inch planks bolted to a :Tong framework. It is provided with a flap to enable it to ass the air and water pipes, the whole forming a circle 6 or inches less in diameter than the sbaft. The scaffold shown in the figure is supported by the bolts . These are driven out and rest on the top of the brickwork, rhich is then built up for another 4 or 5 feet. The scaffold hen has to be raised. To do this, the rope from the capstan winding engine is hung on to the bridle chains attached to he scaffold, the bolts are knocked back, the scaffold raised just the brickwork, and sup- >orted thereon by the bolts, which LTe again driven out

The scaffold is frequently carried by chains instead of upon bolls, these chains being hung from limbers placed across the shaft. One very neat arrangement is to hang the chains from tte curb above. When this is done, the curbs are built upon four pieces of flat bar iron, which are bent back behind the curbs. These bars are spaced at equal distances around the shaft, and their ends, which project a few inches from the curb, are forged into bows, from which chains are suspended. The chains hang down the shaft close to the sides, and are provided at equal distances with large links, from which the safTold chains are hung.

When a half-moon scaffold is not in use, it may either be lung up in the shaft in halves, or it may be taken to bank. jSome consider the latter the safer, as if anything should fall rdovn the shaft and hit a scaffold suspended in it, it might jtiirow the scaffold down the pit. This happened some years tgo at a Derbyshire colliery. I A very good scaffold is shown in Fig, 45. It consists of

—Sinking scaffold.

Coal-Mining.

a strong circular frame made of timber, having a hole 6 or 8 feet in diameter in the centre. This central aperture can be closed, when desired, by a timber platform. It is hung from two ropes wound round the drums of a capstan engine. These drums are capable of independent motion, to enable the scaffold to be kept straight. The outer portion, a in the figure, is always left in the shaft, and when sinking is in progress it partially shelters the men from anything that right fall down. When sinking is stopped, and the brickwork or tubbing is

-Sinking scaRold,

being put in, a central piece is dropped into position, fOTHUBf I a solid platform upon which the men work. The whole ' scaffold can be very easily raised or lowered by means of the capstan, without withdrawing the men. Tlie two capstan ropes e, in addition to carrying the scaffold, form guides to steady the lioppit when in the shafi, the arrangements for guiding the hoppit being as follows : rf is a wrought-iron guide bar, haying a pair of slides or thimbles at each end, and an aperture in its centre just large enough to pass the detaching hook. At the end of the winding rope is the cone <r, which is rather larger

Sinking.

diameter than the widest part of the detaching hook /. When the hoppit is in the shaft, the guide bar d is carried by the shoulders of the cone e. As the hoppit descends it leaves the guide bar at the scaffold, and picks it up again on its return journey.

As the brickwork is built up and the scaffold gradually raised from the bottom, the space below is sometimes allowed to fill with water. When this is the case, care must be taken thit the water does not cut off the ventilation ; if it rises above the bottom of the air-pipes, a joint must be broken above the water-level.

Sinking and Bricking simultaneously. — When sinking and bricking are carried on as described above, the sinking must be stopped whenever a length has to be briefed ; this is the usual practice, but several shafts have been sunk and bricked simultaneously, thereby avoiding the delay occasioned by tlie stoppage of the sinking whilst the lining is being built. Galloway's scaffold for sinking and bricking simultaneously consists of a platform having a circular aperture, through which the hoppit to serve the sinkers passes. This opening is surrounded by a circular iron fence 7 or 8 feet high, which prevents men and materials falling from the bricking platform On to the sinkers. The bricklayers work on the annular space between the fence and the shaft-sides ; they are served bya separate engine, and protected bya sheet-iron roof. The scaffold is suspended in the shaft, and raised or lowered by capstan ropes, which are arranged to form guides for the lioppits serving both sinkers and masons.

Sinking with Rock Drills. — These are usually driven by compressed air, and may be either rotary or percussive. For sinking purposes, percussive drills driven by compressed air are almost exclusively employed. A rock drill of this description consists of a cylinder 3 or 4 inches in diameter, with a 5 or 6 inches stroke. In this cylinder is fitted a piston having a very strong rod, into the end of which is fixed the drili Compressed air is admitted into each end of the

cjrttnder atteraatelf, going the piston and the drill which it carries a rapid ledprocating motkm. At each stroke the drill is turned throtigh a anall aoe hj means of a rachet arrangement fitted into the top of the jHstoo. As the drill works and the hole becomes deeper, it is fed forward either automatically or by hand, the latter by prefereDcc, as there are fewer complications, and the rate of feed can be varied to suit the difierent kinds of ground which are met with. Rock drills are either mounted on tripods, or upon a frame fixed in the shaft There are many types of rock drills, differing chiefly in thei valve gear, which b nsually actuated by some form of tappi struck by the drill at either end of its stroke.

For very hard rock the drills should be + Ot X shaped Those shaped thus 4- are the more easily sharpened, but th )( drills are better suited for extremely hard ground.

In sinking with rock drills, all the holes in a round shouli be drilled in a definite pattern, which should be so arranged as to clear out a given length of ground. The inner ring, known as " surapers," should be first simultaneously fired by an electric battery ; the dirt is then filled out, the second ring fired simultaneously, and so on.

Fig. 46 shows Walker's patent drill frame arranged for rotary drills, a is a stand of cast iron, forming a receiver for compressed air, which is supplied to it through a pipe from an air compressor on the surface. At intervals along the outside of the stand are eight rotary motors, i, t, which are driven by compressed air, taken from the receivers through the pipes

The radial arms d, d are fixed to the top of the stand, and are provided with a long slot, in which the drills f, e can be secured in any position. The arms are adjustable, to enable them to be run out against the sides of the shaft in order to hold them firmly in position. The drills are driven by the motors through the flexible shafts f, f, or, if desired, any of 1 can be worked by hand through rachets. To raise or r the frame in the shaft, a capstan rope is attached to the , and the arms d, d are swung round into a vertical The lower part of the receiver a contains water,

lich, being under pressure, can be used to flush the drill-

Walker's patent drill frame for use in conjunction with percussive drills consists of a heavy cast-iron ring-shaped &Mne carrying adjustable arms, upon which the drills can be

Fig. 46.~Walker's patent sinking frame.

Wtaehed in any desired position, the compressed air being listen from a circular receiver fitted to the underside of the liame.

Rock drills are of no great advantage except in very hard ground, where they affect great economies, as the holes can be deeper and much more quickly than by hand.

Chapter Vii.

SINKING {conHmied).

Presence of Water in Shafts.— Some of ihe beds f the earth's cnist are porous, and some impervious. The rocks may hold large volumes of water, especially i " lain and underlain by impervious or watertight beds of clay

Frc, 7.— Occurrence of

Inking pi [I

shale. The manner in which water makes its way into sinking pits is indicated by Fig. 47. ff is a thick porous rock outcropping in a valley, both overlain and underlain by the im- Lpervious beds i>, b. A stream is shown to traverse the outcrop

Sink/Ng.

ffthe porous rock, and water from it will percolate into the lock and saturate the whole of its pores. If no stream be Resent, the rainfall may be quite sufficient to form a heavy ittder of water. As soon as the rock a is struck in the sink- k$ shaft, a feeder of water will be encountered, which, if not pWnped or tubbed back, will rise in the shaft to the level of be outcrop of the bed.

Another bed of rock is shown at c, but this does not outttop, as it is thrown out by a fault. It is reasonable to expect Ibt no permanent feeder of water will be met with in passing [trough c, as there is no source of supply ; but the rock may pntain a store of water, which will gradually diminish if [limped. Faults usually form a barrier against water, facially when they throw a porous rock against an impervious one.

It will be noticed, from the above, that water may be met either as a permanent feeder or as a pound or reservoir, rile former should be tubbed off if possible, but the latter lay be pumped, as it will gradually diminish, and finally cease Utogether.

Tubbing. — The operation of tubbing consists of inserting watertight lining through the water-bearing strata in such a maimer as to dam back any feeders of water which may be bnsent.

Tubbing usually consists of cast-iron segments, but when She pressure of the water is not very great, brickwork and Wmetit may be used. A segment of cast-iron tubbing is wown in Fig. 48. The segments are usually about 4 feet in , 3 or 3 feet in depth, and of a thickness varying accordpg to the pressure to which they are to be subjected. The fences are made from 4 to 5 inches wide, the top and tee side flange being provided with a projecting rib to keep K adjoining segments in position and to provide something 1 wedge against Each segment is divided into panels by

js-ribs, and one or more holes are cast in each to enable B water to escape from behind the tubbing whilst it is being

Coaimining.

excavation as the sinking proceeds, because the hardest of rocks may be shaken by the blasting, and portions may break away without warning.

Under ordinary conditions the shaft sides are temporarily supported by iron rings and planks, all of which are drawn out as the permanent lining of brickwork or tubbing is built up. The arrangement will be understood by reference to Fig. 42, which shows two views of part of a sinking pit timbered with planks and iron rings. The rings marked a are made of flat

l'"iG. 42. — Supporting the sides of a sinking pi

iron bars from 3 to 4 inches wide by inch thick ; they made up of segments, which have several bolt-holes in eaclwend, so that the size of the rings can be varied to suit irregularities in the uneven shaft sides. The planks b are fr or 7 inches wide by inch thick; they are set against the strata all round the shaft, and held in position by being wedged between the sides and the rings, the wedges c being used foC that purpose, The rings are kept in place by the hangers made of iron about 1 inch square, their distance apart varying according to the nature of the ground. Formerly wonder*

Sinking. 85

rings, termed curbs, made of oak about 6 inches square, were employed instead of iron rings. They ate stronger than the iron ones, and more costly, but not so convenient, and are now not often employed, except where the ground is unusually

Bricking the Shaft. — Shafts are usually lined with bricks of the ordinary size, that is 9 by 4 by 3 inches, moulded to the circle of the shaft. In some cases large fireclay lumps are employed, but well-burned red bricks give satisfactory results except under exceptional circumstances.

The brick lining is built up in sections, the operation being conducted as follows : The shaft— which has, of course, been sunk large enough to allow for the brickwork — is reduced to its finished size, leaving a ledge all the way round it ; this ledge, which is termed the curb-bed, forms the foundation upon which the brickwork is built. It is most important that the curb-beds should be perfectly level, and that their centres should be the exact centre of the shaft ; to ensure this tbey must be carefully tested liymeans of the spirit-level and centre line. The curbs may be made of oak or of cast iron, the latter being preferred for wet shafts, as oak is liable to rot. Cast-iron Curbs vary from 12 to 16 inches ia width, ind are about inch thick, made in eight or ten segments.

The curb is laid on the bed, and wedged tightly from behind with hard wood wedges; whilst being wedged up, it should be tested "ith spirit-level and centre line, great care being taken to liy it perfectly true. Fig. 43 is a section through a curbbed and short length of brickwork ; a is the curb-bed, and h the curb. The shaft is shown to be belled out a little at the CBib-bed ; this is necessary, because the curb is made wider

IG. 43, — Section tlirougii brickwork and curb.

" Honeycombs " may be quite cmcealed from view, and to discover Ihem the tubbing should be all over with , . pointed hammers ; by doing this any defect is discovered by tie sound of the blow, even if the hammer-point does not break through the crust into the hollow space. Each smell of tubbing is sent down the pit on a large D link, which is hung on to the winding rope, the pin of the D link passing through the centre hole in the tubbing. As soon as the engine-man lowers the segment to within reach of the sinkers, several of them seize it and swing it into its place, the weight being carried by the winding rope. Tha pin of the D link la then withdrawn, and it is sent back on the windmg rope for another segment. Layers of fir sheeting about I nch m thickness are placed between the curb and the tubbmg, also between the segments, the grain of the sheetmg pomUng towards the centre of the shaft, Afler a ring of tubbmg has been placed in position, it is wedged np from behmd bv folding wedges, as shown in Fig. 50. These

Fig. 49. — Curb (or tublwng.

wedges are about 2 feet long and 6 or 8 inches wide. After i ring has been wedged up, a layer of sheeting is laid on its top flange, and another ring of tubbing built up on it. The vertical joints are broken ; that is, the joints between the segments in one ring come in line with the centres of the segments in the rings above and below. The tubbing is carried on in this naanner, either up to the surface or to the

Sinking.

require a scaffold to work upon. Fig. 44 shows the ordinary half-moon scaffold. It is made in two pieces for convenience in lifting, and is constructed of 3-inch planks bolted to a strong framework. It is provided with a flap to enable it to the air and water pipes, the whole forming a circle 6 or S inches less in diameter than the shaft.

The scaffold shown in the figure is supported by the bolts

These are driven out and rest on the top of the brickwork,

"-hich is then built up for another 4 or 5 feet. The scaffold

tlien has to be raised. To do this, the rope from the capstan

Or winding engine is hung on to the bridle chains attached to

*Tie scaffold, the bolts are knocked back, the scaffold raised just

ffittove the brickwork, and sup-

.i:o"ed thereon by the bolts, which

I Eire again driven out

' The scaffold is frequently

carried by chains instead of upon

" , these chains being hung

from timbers placed across the

shaft. One very neat arrange-

1 nient is to hang the chains from

vhe curb above. When this is

done, the curbs are built upon

four pieces of flat bar iron, which are bent back behind the

cubs. These bars are spaced at equal distances around

tbe shaft, and their ends, which project a few inches from the

irb, are forged into bows, from which chains are suspended,

I'he chains hang down the sliaft close to the sides, and are

provided at equal distances with large links, from which the

Kaffold chains are hung.

When a half-moon scaffold is not in use, it may either be fcHag up in the shalt in halves, or it may be taken to bank. Some consider the latter the safer, as if anything should fall down the shaft and hit a scaffold suspended in it, it might liirow the scaffold down the pit. This happened some years jgo at a Derbyshire colliery.

A very good scaffold is shown in Fig. 45. It consists of

Fig. +(,— Sinking scaffold.

r

Coal-Mining.

and owing to its thickness, a much larger excavation is required than is necessary for cast-iron tubbing.

Tubbing is usually considered more economical than cofTering when the depth of the shaft exceeds loo feet

Cast-iron tubbing is subject to corrosion by acid water and by the fumes given off from a furnace, when one is employed Several cases are on record where tubbing has burst, or has become so thin as to be dangerous.

Furnaces have a very detriinental effect upon tubbing, not only on account of the wearing of the plates, but when tiie shaft has to be cooled down for examination or repairs, the plates contract, leading to leakages and blown-out sheeting. The tubbing of a furnace shaft is sometimes lined with brickwork. This protects the plates, but renders it impossible to examine the tubbing and wedge leaky joints.

Pumping from Sinking Shafts. — The feeders of water met with in sinking shafts have to be pumped or wound to the surface until they are tubbed off. The following are the three principal methods of doing this : (a) By water-barrels ; (i) by hanging lifts worked by an engine on the surface; and (f) by steam or electric pump' suspended in the shaft. Each of these methodi has its own advantages and drawbacks, and frequently a combination of two of them is employed.

Winding Water in Barrels. — In its simplest form this method is suitable only for dealing with small volumes of water. The water made in the shaft is caught by water-rings oi garlands. These (Fig. 51) consist of a curb, the front of which is formed into a gutter or water-ring, the brickwork being set back the width of this gutter at the curb, and gradually regaining its proper position. The water which is made above the carb flows into the water-ring through holes left in the brickwork, and is led down the shafl in pipes. These pipes terminate in

Fig. 51,-

a legible hose, which is taken to the water-barrel, which is ound up when full. The water which is made in the shaft bottom is " laded " into the water-barrel by scoops or buckets. Galloway's Pneumatic Waier-hard. — This arrangement was tised at the sinking of Llanbradach Colliery, where feeders of over a hundred gallons per minute were dealt with. When water-barrels are filled by hand, only a very small quantity can be raised, but by Galloway's arrangement much larger feeders lean be drawn, and at considerably less cost and inconvenience, pit consists of a close-topped iron tank, into the bottom of which is fitted a large valve opening upwards. The tank is also provided with a glass gauge to indicate the depth of the ifater it contains, and an iron pipe, which passes through the de and rises within it almost up to the top. An air-pump is fixed upon the surface, and from it a range of 3-inch iron pipes is taken down the shaft, terminating with a flexible hose. The barrel is lowered into the water in the pit bottom, and the hose coupled on to the pipe in the barrel by means of an instantaneous coupling similar to those used for the vacuum brakes on railway trains.

The action of the air-pump forms a partial vacuum in the tinel, and water is drawn in through the bottom valve. When the tank is full, the vacuum pipes are uncoupled, and the tank is sent away to the surface and there emptied.

Hanging Lifts. — -This method of pumping water from sinking pits consists of hanging bucket-pumps in the shafts, the buckets being operated through rods driven by an engine on the surface. This method is still very largely employed, but it appears to be gradually giving place to self-contained steam or electric sinking-pumps, hung in the shafts and supplied with tieam or electricity through steam-pipes or cables.

The ordinary arrangement of a hanging lift is shown in Fig. 52. (T is a set of timbers sufficiently strong to carry the "hole weight of the lift, and upon a are mounted two sets of Cast-iron pulleys, 6, b. The lift c is carried by ground spears, i,i, which are secured to the bottom of the lift, and the whole together by the clamps e. Attached to the top of the

4.7-I50&

loo COAL-MINING.

ground sp sheaves, w sheaves.

sars are two sets o hilst the sets of

f puUeys, g, g, each having three pulleys b, b have each fir

Block ropes ate threaded through these pulleys in the usual way, and led to the dnims on a capstan engine, by which the lift can be raise and lowered at will. The bottom of the lift terminates in a windbore, j. This, in its ordinary form, consists of a bulb cast in the bottom of the lowest pipe, having holes in it through which the water passes and is strained. A stuffing-box is also provided, by means of which the windbore can be lowered a few feet without altering the position of the pumps. As the shaft is deepened, the pumps are lowered by means of the capstan, until the blocks have been run 'out their full length ; they are then raised, and another pipe added at the top. Additional ground spears and pump-rods are attached to the top of the others as required. The pumps are driven by bell cranks, the horizontal leg being attached to the pump-rod by a clamp, and the vertical leg to a connecting-rod, which isdriven by the crank on the secondmotion shaft of an engine, g engines are put down before to drive the pumps during the

.A ;

p

A

J-

L=J

I'r

g

dir

Lzec

1

riG.s

Some the si

a.— Hanging lift for sinki pit

times the main wir aft is sudI:, and util

Sinking.

sinking. If more water is made than can be dealt with set of pumps, other lifts have to be added.

An ordinary bucket-pump cannot work to advantage the height of the lift is more than So to loo yards, and when this is exceeded, two lifts have to be employed, the lower one, which follows the sinking down, delivering its water into a cistern, from which the upper lift pumps to the surface.

The bottom of the shaft just below the pumps is kept a little in advance, so that the water drains into it, keeping the remainder of the shaft comparatively dry. The windbore should be raised clear of the ground when shots are being fired, to lessen the risk of injury from flying masses of rock ; and even when this precaution is taken, windbores are apt to be fractured.

At the Maypole sinking near Wigan, a short" length of itmoured hose was introduced between the pumps and windbore. This gave the suction pipe a certain amount of elasticity, and prevented its being broken by the sudden shock of the shots.

Steam-pumps hung in the Shafts. — In this method of draining sinking pits, self-contained pumps of special design are hung down the shaft on chains or capstan ropes. The advantages of this method are as follows : more water can be dealt with, as the pumps take up less room in the shaft than Wing lifts of equal capacity ; the pumps are light and handy, and 50 can be raised or lowered easily, and swung to one side when required ; each pump works independently of the others, and can be controlled from the surface. They are also more Konomicai in first cost, as no foundations are necessary, and ibe pumps and pipes can be easily disposed of when they are 10 longer required. There are several types of pumps specially dtsignedfor sinking, the "Denaby"and "Evans" being notable implies.

Sinking-pumps have no bed-plates, but are bung in the afts by ropes or chains. It is very important that they should occupy little room, and be reliable in working, and not ttsily put out of order. The steam-cylinder is fixed above

Coal-Mining.

the pump, which is worked direct from the engine piston-tofl. Wrought-iron are much superior to cast-iron pipes for this class of work, being much lighter, more easily fixed, and less likely to fracture.

Fig. 53 shows the arrangement adopted for hanging the sinking-pumps at tlie sinking of the Cadeby Main Colliery." IT, a are old steel winding ropes, which are attached to the pump, taken up the shaft, and over pulleys at the surface, W the capstan drums, b are stretchers made of flat bar iron, to which the delivery, steam, and exhaust pipes are secured hy the staples c, e, c, and the ropes by the collars e, e. These stretcher are placed about 9 feet apart, and by binding the pipes to the ropes, steady the whole arrangemenL

The pumps are provided with sliding suctions, and the steampipes are taken through stuffingboxes at the surface, so that the pumps can be lowered the length of a steam-pipe without breatiog the joints As the shaft is deepened the pumps are lowered by the capstan, and new pipes added at the top. Vhen the limit of the lift is reached, cisterns are placed lO I the shafts, and the pumping done in two lifts. The suspension- ' ropes are clamped at the pit-top, and coupled to the ropes oo the capstan drums when it becomes necessary to raise or lowcf the pumps.

At Cadeby, over 400,000 gallons per hour were pumped by this system, from a depth of about 130 yards, eight " Denaby' sinking-pumps being employed.

One drawback to this method of pumping from sinking pit& is the very heavy consumption of steam. It is impossible IC keep the steam-pipes properly covered, and as the shafts ar Tram. I.M.E., vol. iii. p. 51S.

I king-pumps hung

aiily wet, the loss of steam by condensation is exces- ; sive.

Economy of steam is not of paramount importance in . temporary work such as sinking, and the advantages possessed hy this method of pumping are so great as to render its uni- . versa] adoption, in preference to hanging lifts, almost certain.

Puhomeiers {see Chapter XXV.). — These pumps are fre-

j quently employed in sinking. They pump large volumes of

1 water, and are in no way a/Tected by sediment or even small

Stones ; moreover, they are very light and compact, condense

' flieir own steam, and, having no moving parts except the

valves, require but little attention. The serious drawback to

. the use of pulsometers, in sinking pits, is the limited height to

which they can raise the water. With ordinary steam-pressures

this is about 30 yards, so that several lifts are required when

the feeders extend to a considerable depth. Pulsometers are

very useful for pumping from the bottom of a sinking pit to a

lank, from which a ram-pump delivers the water to the surface.

They can be lowered, to follow the sinkers down, much more

easily than an ordinary pump, and, when they are used in this

manner, the main pump has only to be lowered once for each

so to 30 yards that is sunk.

Electric Sinking-pumps. — Pumps driven by electricity are now being used for sinking. A strong steel frame carries a motor, which drives three single-acting ram-pumps through gearing, the whole being arranged to work when suspended, iind take up as little room as possible in the shaft.

The motor is enclosed in an air and watertight casing, and tile cables, from the dynamo at bank, are wound on a reel, and Wnbelet out as required. These pumps are much heavier than steam-pumps of equal capacity, but the cables are lighter lad more easy to deal with than the steam and exhaust pipes which they replace. There is also a saving in steam consumption as compared with steam sinking-pumps, for the latter work under the worst possible conditions as regards economy.

Special Systems of Sinking. — These special systems

r

104 Coal-Mining.

of sinking are mostly of Continental origin. Until recently the shafts sunk in Great Britain (with several notable exceptions) have had no unusual difficulties to encounter; tut in France and Belgium many shafts have had to be sunk through ground of such a character as to render special systems ot sinking absolutely necessary.

The Kiiid-Chaudron System, — In this method of sickiiig the shafts are Sored by percussion, and no water has to be pumped. In the original arrangement, the sliaft was hored in two operations, a hole of small diameter (6 to 8 feet) being bored first, and afterwards enlarged. The boring tools, known as trepans, were lifted and dropped by a beam engine, and turned through a small angle at each blow, by men working on a scaffold at the pit-top. As the small shaft was bored, ii was cleaned out by means of a large cylindrical sliidger> similar to that used in the ordinary process of boring, which has already been described.

When enlarging the shaft to its full diameter, a tank wss suspended in the smaller hole, to catch the dlMs made during the enlargement, the tank being raised when full by an engine, and emptied. The tubbing was made in cylindrical rinp, having no vertical joints. As these rings were too large to be carried by rail, they had to be cast in a foundry erected close to the shafts. The rings were bolted together at the sarfece, and lowered down the pit, after it had been sunk through the water-bearing strata, into impervious ground. Before lowering the tubbing, a bed was prepared to receive it, this being done by a special tool attached to the bore-rods. A watertight joint at the bottom of the tubbing was secured by fitting the two bottom rings with flanges turned outwards, the lower r being made small enough to allow the second ring to slide upon it. Moss was introduced between these two lower flanges, and as the lowest ring reached the curb-bed, it rested upon it, whilst the others slid down and compressed the moss by their enormous weight.

TAe Pattsberg Method of Sinking.— method is noff being employed (1903) in sinking two shafts at the Rhein

Sjn-Kitg.

fBsen Collieries. It is similar to the Kind-Chaudron method in principle, but differs in very important details. rThe tubbing is forced down by hydraulic rams as the shaft is Iseing sunk, and not lowered down afterwards as in the Kind- Chaudron method. The shaft is bored in one operation, and the debris is raised to the surface by a " mammoth " pump, no sludger being required. The mamraolh pump consists of a Jiipe about 6 inches in internal diameter, extending from the lotlom of the cutter to the surface ; alongside this is another

Pallsberg method of sinking

pipe, inch in diameter. Air at a very high pressure is 'ofced down the smaller tube and ascends the larger one, writing the rffim— which is ground into mud — with it.

The general arrangement of this method of sinking will be "nderatood from Fig, 54.

The cutter is carried by the bore-rod a, which is a pipe, about 6 inches in diameter. Water, at a pressure of 1000 lbs. square inch is forced down this pipe, and issues from the tdes J, i in the bottom of the cutter blades. This water >titB the sediment into mud, and enables it to be lifted to the

io6 COAL-MINING.

surface by the mammoth pump c. is a guide-frame, woiiiiig in guides fixed to the lower rings of the tubbing, Recipto catory motion is obtained by the engine e, the disc / being driven by it through a crank and connecting-rod. The disc/ is clamped to the small drum, part of the weight of the cutler and rods being balanced by the steam- cylinder li. The rope from the drum passes over a pulley in the headgear, and is coupled to the bore-rods, as shown, guides being fixed in tht headgear to steady the rods. As the pits deepens, the drum is undamped from the disc, and additional rope run off. A rotary movement is given to the tool by men, through a turning lever. To raise the rods when the cutters have lo be changed, the drum is undamped, and turned by means of a worm, not shown in sketch. The tubbing is forced down by the hydraulic rams r, r; if it sticks fast, smaller rings of tubbing have to be forced down inside.

At the Rhein Preussen sinking, the cutter which vras finally adopted was ig feet in diameter, and weighed 12 tons; from 60 to 70 strokes per minute were made, the length of stroke being from S to 12 inches. The cutter-blades were changed about every fortnight, the operation taking about is hours. The rate of boring was from 2 feet 8 inches up to as much as 2o feet in one day.

Deepening Shafts. It is frequently necessary to deepen a shaft whilst the upper part is in use for winding. When tbe winding shaft is only worked one shift, and there is no necessity for speed in sinking, the shaft may be deepened during the night. This is done by fixing up a sliding lorry at the pit bottom, in such a manner that the winding is not impeded ; a length of rope is kept in the shaft, and coupled on to one of the winding ropes when sinking is in progress. After winding is finished for the day, the flat sheets which are in the way of the lorry are moved, and the loose rope is coupled up to one of the winding ropes, by passing it ihrougli a hole in the cage bottom. The sinking d'debris is not wound to the surface direct, but tipped into corves at the landing,

ifl either gobbed in the workings, or sent out

When sinking and winding have to be done simultaneously, a separate engine has to be provided for the sinking, and the dibris wound to a level below the landing of the cages. Rg. 55 shows an arrangement recently adopted at a Yorkshire

Fig. sj. — Deepening shafts.

Mlliery, which proved safe, efficient, and economical. The sin king- engines were placed on the surface, the rope being tiilceQ through the wrought-iron pipe a, fixed close to the shaft iide, to be out of the way of the cages. A strong timber Erame, b, was built into the shaft sides, just below the landing, ud a bed of puddle rammed on its top, to keep back any

r

io8 COAL-MINING.

water made in the shaft. The winding-rope ' centre of the sinking pit by the guide pulleys plate for the detaching hook, and the rolling short length of level road,/; was driven in the stone stand room for the corves, into which the divis was emptied from the hoppit. The corves, when full, were drawn up a staple pit to the winding-pit bottom landing, by a small steamwinch.

Frequently a few yards of solid strata are left in betwEen the bottom of the winding pit and the top of the extension, a borehole being put through to ascertain the exact centre of the shaft, and for the passage of the rope. The object of tiiis is to guard against injury to the sinkers in case a cage broke loose and fell down the shaft. An inclined plane is sometimes driven from the landing instead of a level and staple pit ; and often the sinking engines are fixed at the top of the extension instead of at the surface.

Widening Shafts. — This is a very troublesome operation when the shaft has to be used during the process of widening either for winding or for ventilation. The widened shaft is usually made concentric with the original one, an equal area being blown oat all round. The difficulties of widening shafts are greatly increased by the presence of pipes, conductors, or cables, which must not be disturbed by tbe blasting ; and sometimes it is found to be more economical to take the whole width of the increase from one side.

When the shaft is not in use, a scaffold is hung some distance down it, and ashes are tipped on to it till they reach the surface. The men stand on these ashes whilst at work, and send them out as the widening proceeds. When the scaffold is reached, it is lowered another length, and asheS tipped on it again until the bottom of the widening is reached- This method is found to be both quicker and safer than th employment of a suspended scaffold.

Sinking Upwards. — Occasionally shafts have to

Sinking. 109

Ink for a short distance from the bottom tjpwards ; this ccurs more frequently in metal than in coal mines. The £ual method is to divide the shaft by a strong brattice ; the pace on one side is kept filled with the stones from the excavaion, and forms a platform for the men to work on. After the haft is completed, the brattice is removed, piece by piece, Mginning at the top, the stones being thrown down at the me time.

Sometimes shafts are divided into three parts by two brattices, the middle compartment being kept full, and used IS a platform, and the two outer ones forming the intake and tatum airways.

Sinking Contracts. — Shaft-sinking is usually let by contract, the contractor being paid a fixed sum per yard. If much w.iter is present, the risk may be too great to admit of a contract, and the sinking has to be done by day work. The following is an epitome of a recent sinking contract : —

[. The shaft to he sunk from the surface to the coal — an csiimated depth of 700 yards.

2. The inside diameter, after the brickwork is put in, to be feet ; the shaft to be of an exact circle, and sunk perfectly plumb by the use of a centre line and ten side lines,

3. The shaft to be lined with brickwork 9 inches thick ; any spice between the back of the brickwork and shaft sides to be filled in solid with ashes or brickwork as required.

Curbs to be set perfectly level, notice to be given to the colliery engine- Wright, so that he may examine and test them.

5. No shots to be placed within i foot of the sides, except by special consent.

6. The contractor to secure the shaft sides with timber and tioEs, and carry out the provisions of the Coal Mines Regulation Aci,

The shaft to be sunk as quickly as possible, the men working oij and night continuously, with never less than ten sinkers and a iiargeman at work in the shaft.

!. The work to be done to the satisfaction of the colliery ™Eineer, and in the most approved manner.

Coal-Mining.

g. The contractor to find banksmen, and deliver the nkiil3 laterial into wagons, after which the company will deal with ii.

ID. The company to find all materials except those afterward: mentioned ; contractor to return the same in good condition.

II. The contractor to lade out a reasonable quantity of waler but if more than rooo gallons per hour is made, the company ar* to provide a pump.

13. The contractor to provide all explosives, fuse and detonators, as well as all tools used by the sinkers.

13. No money to be paid to the contractor without a cerlificaie from the company's engineer.

14. The contractor to supply the company with a sample and correct measurement of each stratum passed through.

15. 10 per cent, of the money due to the contractor to be Itepl back until the completion of the work.

The following are a few contract prices paid for sinking I various shafts in the Midlands :—

( in 1890, per yard ;£8 o

'897 £6 'S °

igoo „ IS

£n JO

Opening Out.

ds of Opening Out. — When the seams to be worked moderate gradient, the main roads are made in the ut if the seams are very steep they are usually won by ifts driven across the measures, as shown in Fig. 56. are first sunk to a, and

coal in the various seams Jt

the drift worked uphill, e become exhausted, the deepened to i, and other riven to win the striji of ,ng between a and i, and

Bottom. — The mouthhe pit bottom are secured cs, the shaft being belled I obtain the necessary Often pit bottoms are iry wide — -30 feet and s — and sidings are probe both full and etnpty

side by side. These wide pit bottoms necessitate very masonry and extensive excavations ; and when empty I corves run side by side, it is difficult to grade the .nd control the traffic. The best arrangement for a pit

is to have some roads entirely for full and others for

— Opening om in sleep

112 Coal-Mining.

empty corves ; all the traffic has then a definite direction, can be automatically controlled. As much siding room as possible should be provided, so that the winding engines can be kept at work for an hour or two, in case the haulage should fail, and also to ensure a good start in the mornings. Someof the modern collieries have siding room for four or five hundred tons in the pit bottom.

The cages at large collieries always have several decks, and arrangements should be made for loading them simultaneously, There are several methods of doing this ; one very common plan, when double-decked cages are employed, is to have two landings, one level with the upper and the other with the lower deck ; the corves from one district serve the upper, and those from another district the lower deck. It is preferable W arrange the roads so that the corves from any district can be sent to either deck.

Fig. 57 shows a simple method of loading three deds simultaneously. The whole of the full corves are brougliE along the road marked ah, which is level with the top deck; the corves for the second and third decks are lowered by tli' drop-cages c and e respectively. Each drop-cage is connected to another small cage on the other side of the shaft, so that the weight of the descending full corves raises the empties to the main level Each cage is served by its own road, whidi is used solely for it. The cages for the empty corves are made heavier than those for the full ones, so that when both cagffl are empty they run back to their proper landings ready for the next load.

The roads for the full corves should dip towards the shift, and the roads for the empty ones from it. This means that the empties are delivered at a level considerably below the main haulage road, and mechanical arrangements must be provided lo raise them. A gradient of i in 60 is usually found to worlt well at a pit bottom.

Shaft Pillars. — When coal is worked at a moderate deli from under any considerable area, the surface invariably sinks.

Opening Out.

the amount of subsidence being from 50 to 70 per cenCoT

Ihc thickness of the seam, so that if a seam 6 feet ia thickness worked, the level of the surface above it will sink between

3 or 4 feet. Subsidence always extends beyond the excavation, and the a subject to this " pull " varies with the depth of the s

peace, when pillars are left to protect shafts or buildings, they

r

'

t

h

M

,c

Fig. 57.— MeLhod of Bimultaneously changing the corves on three decks.

Bust be larger for deep seams than for shallow ones. It is of ll* utmost importance to protect shafts from the effects of ice, and pillars have to be left for this purpose. If :s are too small the shafts may be crushed and it of plumb, and if they are tubbed, the tubbing may pictured with disastrous results; moreover, the roads jh the pillars will be difficult to maintain. There are

Coal-Mtntng.

several rules for determining the size of shaft pillars, but iht pillars provided by most of them are quite inadequate.

The following are examples of shaft pillars left in collieries recently sunk, all working coal by the longwall system. 1. Depth, 750 yds., thickness of seam, 7 ft., diam. of pillar, 600 yds. ii 54° „ „ „ „ „ ., „ „ 520 „

3- .. 240 „ „ „ „ 5 „ „ „ „ 250 „

4- .. 500 „ „ „ „ 4i,' :. " -, 500 11 The general practice is to leave rectangular pillars having their sides equal in length to from two-thu-ds to the full depth of the shaft : thinner seams, of course, require less pillars than thicker ones. Theoretically, a shaft pillar in a level seiin should be circular, but in practice it is found more convenient to make them rectangular.

A pillar, 700 yards square, has an area of over 100 acres. This may ajDpear very large, but it must be remembered tiat the shaft pillar has to support the engine houses, chinmeys, etc., as well as the shaft.

At one time it was thought that the line of fracture or break, resulting from coal workings, ran vertically to the surface, as shown at im, Fig. 56. This was found to be incorrKt when the seam was inclined, as also was the theory that the line of fracture tuns at right angles to the dip of the seam, as at nm. It is now generally recognized that the break runs about midway between these two lines, as pm, Fig, 56. This shows that in inclined seams it is necessary to arrange tie pillars in such a manner that more coal is left to the rise of the object to be supported than to the dip, in order to support the object equally on all sides.

Water Levels. — When much water is made, water-levels have to be driven to form standage for the pumps and to catch the rise water and prevent it following the workings down as the coal is got to the dip. Water-levels should be driven on the dip side of the main roads, so as to drain them ; and if it can be conveniently arranged, the top of the water-level should be lower than the floor of the main level, otherwise the water

Opening Out.

ow from it into the main level before it is full For ;e, if the seam dips i in lo, and the water-levels are 5 igh, the distance between the main and water levels

not be less than 5 X 10 50 feet When water-levels ed as standage for pumps, they must be driven dead ir they will overflow at their lower end before tlie tipper full, and so will not be able to contain an amount of :qual to their full capacity. When a water-level meets a he level must be turned either to the rise or to the dip h the coal at the same level on the other side of the If the fault is a down-

the level must be

to the rise until it e coal, and if an upit must be turned to ). Fig. 58 shows a nd section to illusle method of crossing ; with a water-level, section ab shows the n of the seam above It, and cd'\\.% position

the fault. If the ' were continued in a t line it would have

to regain the seam, turning it to the rise, a gisal level maintained.

have sufficient lodge

Fig, 58.— Waler-lovel

s shown, the coal can be won and All important pumping engines hold at least a couple s' water. If the feeder amounted to 400 gallons per , and the water-levels were 6 feet 6 inches wide and 5 ;h, the length of levels necessary to hold the water made lOurs would be 5671 feet. This is calculated as follows ; umber of gallons made in 48 hours is 400 x 60 x 48, ; there are gallons in one cubic foot, the number or divided by gives the cubic feet of space required, ca of the road is x 5 feet, so that the required length

Coal-Mining.

'5iir6fxT

5671 feet.

For a large quantity like the above, it would be necessary to drive several parallel levels connected by slits.

Direction of Main Roads. — The direction of the main roads depends upon the dip of the seam, the position of any known faults, and the shape of the royalty ; it is also to some extent governed by the system of working the coal, and ibc method of haulage. The output of some of our large coUienes reaches from 250 to 300 tons per hour, and to deal with this large quantity sever.al independent main roads are ahsnluttly necessary. They should be carefully laid out from the commencement of the colliery, so as to divide the whole area of the royalty among them: and as far as possible they should be perfectly straight. The bratkch roads should leave the mroi roads by regular curves of large radii. In longwall work ibe gates should be systematically cut off by cross gates or levels The direction of the gates depends upon the dip of the seaffli and upon the line of the faces, which, in its turn, is usually governed by the cleavage lines of the coal. Seeing that ever)' yard of road may be expected to cost something per year for maintenance , it is obviously desirable to keep down the lengtl' of the roads as much as possible, but, on the other hand, ins a very serious evil to have too little pit room, leading, as it does, to a diminished output.

After the direction of any road is decided, it is necessary W fix tines or marks in the road, for the guidance of the norltmen. Lines are usually hung 6 or 8 feet apart. A greate distance between them would be preferable, but if they an much further apart they cannot be illuminated by one lamp, and two men have to be employed to take a sighL To hang pair of lines, a dial is set up, and its sights clamped at the correct angle as read off from the magnetic needle.

The approximate position of each line is then marked on the roof, by observations taken through the dial sights, and

Opening Out. 117

drilled a few inches into the roof. Soft wooden plugsire driven tightly into these holes, and the pivots carrying Ilie lines are knocked into them and very carefully adjusted to the exact line of the dial sights. To take sight, a lamp is held in Ihe face and moved about to the instructions of the observer, who stands behind the lines and notes when they and the lamp wein exact alignment. A mark is then made on the roof over the lamp, and the series of mark? made day by day in this runner keeps the workmen in the right direction.

Lines are often hung from the bars which support the roof. These, however, are apt to be moved by the pressure, which mold throw the road wrong.

When the roof is good and even, chalk bnes may be marked on it and carried forward as the road advances. To mark the line, the ends of a chalked cord are held tightly in the correct position, and its centre is pulled down ; this causes the cord, when released, to rebound smartly, leaving a chalk mark on the toot

Roada driven in the coal have to follow the inclination of the seam, but stone drifts driven across the measures must be Mianged with a fixed gradient. This gradient is maintained bjmeans of a templet, which consists of a spirit-level or piumbbob mounted on a straight-edge. A tapered strip of wood is Miied to the bottom of the straight-edge, the amount of the taper being equal to the required inclination of the drift. If the road had to dip or rise i in 6, and the straight-edge were 4 feet long, the tapered strip nailed to the bottom would be 8 ihes deep at one end, and come to a point at the other. To test the gradient, the templet is placed on one of the rails of the drift, one end of which is raised or lowered until the bubble of the spirit-level is in the centre of its run.

When a road is to be used for horse haulage alone, it is more important to keep it level than straight, and it is usual to maintain a favourable gradient by slightly altering the direction of the road to suit the undulations of the strata. Roads used Tor mechanical haulage, however, should always be kept Kraight, and undulations disregarded.

(

k

Coal-Mining.

It frequently happens that cross-measure drifts have to be driven, either to win coal cut off by faults, or to connect two seams for haulage or ventilation. The length of such drifts may be calculated as follows : —

A seam dipping i in 5 is thrown 20 yards down by a fault, what length will a drift dipping i in 3 be to win the coal on the other side of the fault? -iJ

Dip of drift is 1 in 3 5 in 15

„ 'seam „ i in 5 3 in 15 '

So that the drift gains 2 yards vertically upon the seam for every 15 yards measured horizontally, hence the 20 yards will

be gained in — 150 yards.

To calculate the length of the drift measured on the incline.

Flc. 59.

the total fall must first be found. As the seam dips at the rate' of I in 5, the fall in a horizontal distance of 150 yards is - — 30 yards, hence the total fall of the drift is zo + 30 50 yards.

The actual length of the drift is equal to the hypotenuse of a right-angled triangle, having base and perpendicular 150 and 50 yards respectively, and -j -(- 50 -f- 158-1 yards. The method by which this is arrived at will be understood by references to Fig 59, in which n- represents the drift, and the seam.

Chapter Ix.

Miners' Tools.

feii. — These are the most widely used of all the tools cm- P'oyed in mining ; they vary considerably in shape and weight, wd are employed for a variety of purposes. For coal holing Or cutting, the blades are from to 3 lbs. in weight, and itioui 15 inches long; tiie shafts or helves being of ash or 'licliory, and about 2 feet 6 inches long. The blades are straight, or very slightly curved ; they should be made of steel throughout, and the ends should be square in section, and 'aper gradually to the point. The helves may be fixed to the blade ; but " interchangeable " picks, in which the blades are loose and can be changed, are the most common, as during a shift a workman may " mar " several blades, and these interchangeable picks greatly lessen tlie weight he has to carry to a-tid from his work, a, Fig. 60, shows the " Universal pick," made by the Hardy Patent Pick Company, in which the helve is slipped through the eye of the blade and secured by becoming wedged on the ferrule.

The picks used in stone are much heavier than those used in coal. They are from 4 to 7 lbs. in weight, and the helves are made both longer and stronger ; the blades are square or octingular in section, and made thick almost up to the points. Dressers. — b, Fig. 60, shows a dresser. They are employed for breaking up, or pulling down, large masses of coal or stone ; snd are also used by plate-layers. One side of the head forms abammer, and the other a curved pick. As they are used almost entirely for wrenching, the helve is curved, and strengthened by iron bands where it (its into the eye.

Coal-Mining.

-These are used for breaking down coal or stone, and for cutting up large pieces after they have fallen. The coat wedge, c. Fig. Co, is S to 12 inches long, and about a couple of inches wide, and ij inch thick at its head, with a flat chisel point. For use in stone, the wedges are smaller; they are similar in shape to the coal wedges, but come to a point at the end.

Hammers. — These vary very greatly in size and weight, in accordance with the work for which they are employed. They should be made of steel, tapering slightly from the eye, and

F;g. (JD.~A, " Universal " pick; 13,

C, wedge.

hampered off towards the faces. The weight of the head is from about 5 lbs. for use in coal, to about 10 lbs. for stone,

Shpveh. — The plates are of steel, slightly turned up at the edges, and coming to a point at the ends, to enable ihera to easily enter loose heaps of stuff. The centre of the plate is strengthened by being bent into a crease, terminating in the straps by which it is attached to the helve. The helves or handles are about 2 feet 6 inches long, and are set at an angle of about 150° to the plates ; they are circular in section, so as to be comfortably handled, and terminate in a crutch or boxhandle. The size of the plates vary from lo inches wide, when

Misters' Tools.

in stone, to i6 inches in width, when used for shovelling

Drills. — Shot-holes may he either bored by percussion, or by a rotary hand-boring machine. For coal or soft rock, "jumpers" are sometimes employed. Tliese consist of a bar iron 5 or 6 feet long, having a steel bit at one end, and sometimes an enlargement or bulb on the bar near the other. The Korkman grasps the bar near the bulb and works it backwards and forwards in the hole, making the bit strike the bottom of the hole at a different place by giving the bar a slight turn between each blow. This method is only adapted for soft material, and when the rock is hard, striking drills have to be employed. A set of striking drills consists of two or three drills of different lengths, the drills being made from octagonal bars of steel, forged into a chisel-shape at one end, A singlebaaded set consists of two light drills, one being about ao and tbe other about 40 inches long. To use these drills, the miner holds the drill in one hand and strikes the top with a light bammer which he holds in the other, turning the drill through a small angle at every blow. The shorter drill is used at the commencement, and when the hole becomes too deep for it the long one is employed. Small holes only can be bored by single-handed drills, and they are not suitable for hard rocks. In the double-handed set there are three drills of about 20, 30, and 50 inches long respectively. One man holds the drill, laises it slightly, and turns it between each blow, whilst another — or, if the ground is very hard, two men — strike the lop trith heavy hammers. The bit of each drill is made rather Smaller than the one it follows, to enable it to pass easily down 'he hole, care being taken to keep the holes circular and of *"en diameter all through.

Holes can be drilled by this method in extremely hard Etound ; in fact, the one advantage it possesses over the rotary tteihod is that it will face harder rocks, and so can be applied lisiraia too hard for the rotary machines.

Striking drills are now nearly always made of steel through- ™t ; formerly they had iron shafts and steel bits. Steel drills

full exi

Coal-Mining.

are lighter than the iron ones, and steel transmits a blow better than iron.

Rotary Hand-boring MaMnes. — For ordinary colliery work, rotary machine drills have almost displaced striking drills : they are quicker, bore a hole with less labour, and in ordinary ground only require one man to work them. A very good type of machine is shown in Fig. 6i, which is an illustration of the " Elliott " drill made by the Hardy Patent Pick Company. It consists of a drill or auger {a), worm {b), standard {c), ratchet and handles {i), and worm-wheel The drills are made of flat bar steel, twisted into a spiral ; from two to four of increasing lengths forming a set. The worm or screw is provided with a socket at one end, into which the drill is fitted : the other end is forged square to receive the ratchet The pitch of the screw is about half an inch — that is, the screw advances at the rate of half an inch for every revolution. The screw works on a worm-wheel, having teeth cut in its outer edge. This worm-wheel, is carried by a split ring provided with hinges and tightening screw. When the tightening screw is quite slack, the drill, when turned, does not advance, hat moves the worm-wheel round in the split ring, so that when the drill is working, sufficient friction has to be applied to the split ring by the lightening screw to prevent the wheel from taming with ordinary pressure. If extra pressure be applied, the wheel moves, instead of the drill advancing to the full extent of the pitch of the screw. The effect of this is to make the feed partly automatic and prevent breakages, as when, ing to the hardness of the ground, extra pressure is applied, " of the strain and motion is taken by the worm-wheel.

ElUolt Ji'tilting machine

J

Miners' Tools. 123

The machine is provided with two ratchets, one being fitted 10 each end of the screw ; by the use of ratchets the toand-fro movement of the handles gives a rotary movement in one direction to the screw and drill. The end ratchet can , also be used as a crank handle when required.

Ratchets are slower than cranks, but more power can be applied through them, and they can be used when a hole is being drilled loo near the roof to allow a crank to be turned. The standard is made telescopic, as shown in Fig. 61, It consists of a double frame of steel, having notches to carry the pin, attached to the sleeve of the split ring. Rough adjustment for height is made by drawing down the outer frame and securing it in a position by the screw /; after this is done the machine is fixed in position, and tightened up by the bottom screw g.

To use the Elliott or similar machine : a hole a few inches is first stamped into the coal or stone with a pick ; 'aiachine is then erected and tightened up, the correct ditttnce from the face being obtained by a rough measurement. The shortest drill is fitted into the socket, and the ratchet is worked until the screw has advanced its full length. The lightening screw of the split ring is then slackened, and the screw b is pushed right back, turning the worm-wheel as it moves. A longer drill is then fitted into the socket, and the operation repeated imtil the hole has reached the required iJeplh.

When the rock is very strong both ratchets are used, but for soft ground only one is required. A simple form of drill, "hich is much used in stone, consists of a worm working ibrough a nut in a barrel ; no standard is employed, the barrel being set against a prop. The screw thread is of small pilch, so that the drill advances slowly, but will penetrate Wd rock.

Sharpening and tempering Tool Steel. — Drills ad picks are sharpened by being heated to redness and lanimered on an anvil. After they are sharpened they must

Coal-Mining.

chain e. The block is kept from sliding backwards by means of the catch-bolt g, which can be drawn clear of the notches when required. To draw a prop with this appliance, the chain b is secured to a prop or other firm object and the longer chain, is lashed round the prop which is to be withdrawn, e is then pulled tight, and one of the links slipped into the recess in the block ; the lever is moved backwards and forwards, drawing the block, chain, and prop along the bar towards the fixed prop. The block can be freed and slipped back to the end of the bar by drawing the catch-bolt clear of the notches. The advantages of this apparatus over the ordinary ringer and chain are that the leverage is very much greater, being 30 to i

as against 7 to i, and that the strain is not released when the weight is taken off the lever. The use of these prop withdrawers is not confined to pulling out props ; they may be employed with advantage for drawing the ends of ropes together when they have to be spliced, separating corves which have got off the road and become jammed, and for a variety of purposes which require the moving of heavy loads.

Mechanical Many mechanicalappliances have been patented for breaking down coal or stone in order to avoid the use of explosives.

As yet none of these machines have been widely adopted, though some do very good woik when the conditions are favourable. They frequently fair, when used in soft tough coals, as the result of the expansion's to crush and grind up the coal round the hole in which the wedge is inserted, , instead of rending the coal and it down.

Mm EMS' TOOLS.

" squibs," and not by fuses. The process of firing a shot by squib is as follows :—

After the hole has been cleaned, the end of the needle is forced into the Wasting powder cartridge, and carefully into the end of the bole. The hole is then stemmed by ramming it tightly with clay or other suitable material by means of the slemraer. This is done until the hole stemmed to the end, when the needle is carefully withdrawn, leaving a small hole right through the stemming to the charge. A squib, which_ is a straw, or paper tube filled with powder, having a piece of touch-paper at one end, is then fixed in the mouth of the hole. When the touch-paper is lighted it sets fire to the powder, and a train of sparks is projected along the small hole left by the needle, and fires the charge. This method of firing shots is now becoming obsolete.

Hinger and Chain, — r'or drawing timber fi'om goaves, a *"inger or dog and chain must he used. This, in its simplest form, is an iron or steel bar from 3 feet 6 inches to 4 feet long, with one end bent into a claw, about 6 inches from hich a length of chain is attached. The chain is secured to the prop which has to be drawn, and the end of the claw fixed against another prop, which must be sufficiently firm to bear the strain.

The leverage is 6 or 8 to i, so that if a pull of i cwt. is applied to the long end of the bar, the strain on the prop and chain will amount to 6 or 8 .

Sylvester's Palent Prop Withdrawet: — This implement, *hich is a great improvement on the ordinary dog and chain, is shown in Fig. 62.

u is a notched steel bar, 3 feet long, inch deep, and finch thick, the notches are 1 inch apart and about half an inch deep. At one end of this bar is a swivel carrying a light cfian, b, and at the other end a stop, to prevent the sliding tlock e moving too far. The sliding block is propelled along Ae bar by means of the lever d, tlie short end of which mgages with the notches as shown. The back of the block is (iiovided with a recess, shaped so as to grip any link in the

The block is ftom siding bacbrards by means of Ibe <atdt-bdt g, wbkli can be drawn dear of the notches when Feqnired To diaw a prop whh this appliance, the chain b is seemed to x prop or other firm object and the longer chain, is bsfaed round the pn which b to be withdrawn, c is then pulled tit, and one of the links slipped into the recess in the blodc ; the Icro' is march backwards and forwards, drai>- ing the block, chain, and piop jixa% the bai towards the fixed

. prop. The block can be freed xnd pped back to the end oT

the bai bj diawii the catch-bob gtiieai of the notches The advantages of this appantns over the ordinary ringer and

' chain are that the Icrerage is verf nnidi greater, being 30 lo 1

I as against 7 to i, and that the strain is not released when the

f weight is taken off the lerer. The use of these prop with-

drawers is not confined to pulling out props ; they may be employed with advantage for drawing the ends of ropes together when they have to be spliced, separating corves which have got off the road and become jammed, and for a variety of purposes which require the moving of heavy loads.

Mahanical IVeJgirs. — Many mechanical appliances have beer* patented for breaking down coal or stone in order to avoitJ the use of explosives.

As yet none of these machines have been widely adopted,

though some do very good work when the conditions arc

favourable. They frequently fail when used in soft tough

as the result of the expansion b to crush and grind up

1 round the hole in which the wedge is inserted

of rending the coal and bringing it down.

FtG. 61.— Syircslers pauoic prop withdraw'er

M/NEJiS' TOOLS.

Yvg. 63 shows the ffardy Patent Pick Company's Multiple Wedge. — These wedges are made in sizes varying from 18 Ches in length and ii inch in diameter to 4 feet in length Itad 2 inches ia diameter. To use them, a hole is first bored [in 1 similar position to that which would be necessary if an leiplosive were to be used; the depth of the hole should be sbout 6 inches more than the length of the wedge, and its liiameter should exceed that of the wedge by about inch. he feathers a are first placed in position, and the split-wedge

driven up between them. If the expansion is not sufficient J bring down the stone or coal, the other wedge, c, is driven between the halves of the split wedge b, and furtlier expansion obtained. This apparatus is lighter and cheaper than most mechanical wedges, and requires a mucJi smaller hole.

Hydraulic wedges are sometimes employed ; in some forms llie rending action is accomplished by drawing lonj wedges between pairs of feathers, whilst in others small rams are forced igunst the upper side of the hole.

Chapter X.

Explosives.

Explosives. — An explosive is a substance which contains within itself all the ingredients necessary for complete and rapid combustion, the gases resulting from such combustion occupying a much greater volume than the explosive itself. The action of an explosive is simply this : The charge is lil or detonated, and is instantly changed to gases ; this causes it to expand with extreme rapidity and, if there is not ample room for expansion, great pressure is generated.

The power of an explosive depends upon the quantity and density of the gases produced, and the rapidity of its action upon the speed with which the explosive is changed into gas. Some explosives are much quicker in action than others. For example, if blasting powder be placed on a stone and Sred, the stone will be undamaged, because the change from solid to gas takes place comparatively slowly, and the expansion relieves itself in the air. But if dynamite be fired in the same manner, the stone will be shattered, because the expansion takes place so rapidly that it has not time to spend itself entirely in the air, the action being more in the nature of a blow than of gradual pressure.

The chemical change which takes place at an explosion is accompanied with great heat, which adds to the expansion of the gases. An explosion may be regarded as extremely rapid combustion, as when any substance bums, gases are generated, although the action may be very slow. An ordinary combustible requires a supply of oxygen from external sources,

Explosives. 129

the air, but an explosive contains oxygen usually in the form of a nitrate.

Explosives are employed in mining for breaking down coal, ripping, etc., and for driving stone drifts, and sinking "When used in coal the explosive should be slow in action, so ss not to shatter the coal, and should " spread " well, so as to bring down a large area; the same qualities are required for ripping and similar work. For driving stone drifts, and sinking in hard ground, a high explosive which is quick in action is usually preferred, one advantage being that a smaller hole is required.

Legislation. — The great dangers resulting from the use of explosives in dusty or gaseous mines (see Chapter XXVIII.) are now fully recognized ; and the " Explosives in Coal Mines Order of 1S99," with subsequent modifications, has been drawn up to meet them. Tlie chief provisions of this Order are —

I. (i) " Permitted " explosives only must be used in all mines in which a dangerous quantity of gas has been found within the previous three months.

(z) "Permitted" explosives only must be used in all roads and in every dry and dusty part of any mine which is not wet throughout.

(3) In all such coal-mines as mentioned above the use of " permitted " explosives is absolutely prohibited, unless the following conditions are observed :—

{a) 'S.yi.Tj charge of explosive must be placed in a properly

drilled shot-hole, and be properly stemmed, (i) Every shot to be fired by electricity, or by some other means

equally secure against the ignition of gas or dust, (i-) Every charge shall be fired by a competent person appointed in writing, and not being a person whose wages depend upon the amount of mineral to be gotten. i/i) Each explosive to be used in the manner prescribed in the

schedule. 3. All explosives are prohibited in the main haulage roads and intakes, unless all workmen have been removed from the seam, and ail others communicating with the shaft at the same level, except the men engaged in firing the shot, and not more than ten other persons who may be employed in attending to engines, horses,

Coal-Miniig.

a inspecting the mine ; or unless a permitted explosive is used, and every part of the roof, floor, and sides of the main haulage road or intake are thorougMy wet within a distance of 20 yards from the shot.

This section does not apply to such portions of the iiaiii haulage roads or intakes as are within 100 yards of the coal face. A "main haulage road" means any road which has been or is being used for moving trains by gravity or mechanical power.

Detonators are to be issued only to shot-firers, and must bs kept by them in a locked case.

A list of " permitted " explosives is added as an appendii to the Order, giving composition, number or strengtli of detonator to be used with each, and method of firing.

Cotnposition of Explosives. — Ttie principal explosives usel in coal-mines may be roughly divided as follows ; —

(a) Gunpowder, and similar compounds, (i) Nitro- glycerine compounds, (c) Ammonium nitrate compounds.

Gunpowder is a mixture containing —

Saltpetre (potassium nitrate) from 65 to 75 per cent.

Charcoal 15 percent.

Sulphur from 10 to 20 per cent.

For blasting in coal, there is no explosive equal to gnupowder. It is much slower in its action than the high plosives of the nitro-glycerine and ammonium nitrate class, and therefore brings down the coal in larger lumps, and iBakes much less slack. It also has the great advantage of no' requiring a detonator to lire it, a simple fuse or squib being all that is necessary.

The use of blasting powder in coal-mines is now greatly limited by the " Explosives in Coal Mines Order," as it is not upon the permitted list.

Nitro-Glycerine Compounds. — Nitro-glycerine is a very powerful explosive, very rapid in its action ; it is of high .specific gravity, and is not affected by water. Nitro-glycerine

Explosives.

compounds are very suitable for blasting hard rock, as only small holes are required; and, owing to their density and pbilic nature, they do not fill up much of the shot-hole, but lie in the bottom, and can be pressed down to fill up the wfioie of that portion of the shot-hole which they occupy.

Dynamite. — In its liquid state nitro-glycerine is dangerous

and inconvenient to use, but it is commonly employed when

mixed with some absorbent substance. Dynamite consists of

nitro-glycerine absorbed by kiesclikr, which is a porous

earth found in Hanover. The proportion of nitro-glycerine

present depends upon the strength which is required, and

Varies up to as much as 75 per cent, (by weight) of

the whole compound. In common with the other high

explosives, dynamite must be fired with a detonator, and is

liable to explode if subjected to a very severe shock or blow.

It is not on the permitted list, but is much used for sinking,

quarrying, etc

The list of " permitted " explosives contains the names of several nitro-glycerine compounds, of which carbonite may be ta.ken as an example,

Carbonite. — The authorized composition of this explosive IS, for every hundred parts.by weight of the finished explosive, —

Kot more than 27 parts, or less than 35 parts of purified nitro-

Not more than 36 parts, or less than 30 parts of r barium or nitrate of potassium.

Not more than 37 parts, 1 Not more than 5 parts, o With or without not mori With or without not mon carbonate of calcium.

less than 34 parts of wood meal, less than 4 parts of moisture, than part sulphuretted henzol. than part carbonate of sodium ai

h must be used in a non-porous wrapper, and fired t detonator of not less strength than that known as No. 6. If b a firoien condition, it must be thawed in a safe and suitable manner. Nitro-glycerine freezes at about degrees Fahr , that is,

f

r

132 Coal-Min/Ng.

when the temperature is about 144 degrees above the fteezingpoint of water ; its compounds are dangerous when frozen, md should be thawed in a can having an outer case to contan warm water. In no case should cartridges be exposed to the direct heat of the fire.

The majority of the " permitted " explosives belong the ammonium nitrate class. Ammonium nitrate is a vay powerful explosive ; it " spreads " more, and is not quite so quick in its action as nitro-glycerine, and is in consequence more suitable for blasting coal or ripping. Its compounds ire light and bulky, which renders them unsuited for very hard ground. It does not freeze, but is affected by moisture, and must be used in watertight cases when the holes are wet,

Wcstfalite, No. i. — This is a good example of a nitrate of ammonium explosive ; its authorized composition is, for every hundred parts by weight, —

Not more than 96 parts, or less than 94 parts nitrate of

Not more than 6 parts, or less than 4 parts rosin. Not more than part moisture.

The explosive must be used in {a) a wrapper of stout paper, thoroughly waterproofed with paraffin wax ; or (b) a case made of an alloy of lead and tin, waterproofed with paraffin wax; or (c) a n on- waterproofed wrapper of paper, the outer waterproofed paper having been previously removed,

The explosive is only to be used with a detonator of not less strength than that known as No. 7.

" Safety" Explosives.- — A perfect explosive, for use in coal, should break down the coa! in large masses without shattering it ; should have a temperature of detonation so low as to render the firing of gas or coal-dust impossible ; and should not give off poisonous or unpleasant fumes when it explodes. None of the explosives now on the market come quite up to this standard. All the high explosives shatter the coal moie or less, none are absolutely safe when fired in a dangerous atmosphere, and the reek from all, though perhaps not dangerous.

Explosives.

tainly unpleasant. All " permitted " explosives are

less liable to fire gas or dust than blasting powder, as

they produce tend to quench the flame and lower

Ehe temperature of detonation.

A committee of the North of England Institute of Mining Engineers, after making a series of tests of "flameless*' nplosives," came to the following conclusions :—

All high explosives upon "detonation produce evident flame, and are liable to ignite mixtures of air and fire-damp or coaldust, though they are all safer than ordinary blasting powder. The proportion of coal-dust in air necessary to form an explosive mixture is much less than has hitherto been thought to be the case.

The risk of an explosion, when using high explosives, is Only diminished, and not abolished.

Explosives alter in character if they are improperly kept. In view of the changes in the composition ofan explosive which a.re made by the makers from time to time, the composition siiid date of manufacture should be printed on the wrapper of ] each cartridge.

JDe/onators. — High explosives have to be fired with ds- Collators, These are hollow copper cylinders, closed at one end, and containing the detonating agent, usually a mixture fulminate of mercury and chlorate of potash, which explodes With a strong local action when fired by a spark. It is very important that perfect detonation should be produced, otherwise the explosive may burn away slowly rather than explode, the result being a great or total loss of power, accompanied by unpleasant fumes. Some explosives (more especially those of tile ammonium nitrate class) are very liable to incomplete detonation when damp, or improperly made. In some cases pan of the explosive only is detonated, the remainder being compressed into a hard mass. To ensure perfect detonation, the detonator must contain sufKcient fulminate, and the cylinder containing it must be strong enough to offer considerable resistance to the shock of its explosion. The detonator has a better chance of doing its work well when '

r

134 Coal-Mining.

placed at the back of the hole ; or, if several cartridges are employed and fired by electricity, it may be placed in tlie middle one with advantage.

The explosives on the permitted list have to be fired mlh detonators varying in strength from Nos. 6 to 8. A No. 6 detonator contains 15 grains of a composition containing 80 per cent of fulminate of mercury and so per cent, of chlorate of potassium. A No. 8 detonator contains 30'g grans of a composition containing 80 per cent, of fulminate of mercury and 20 per cent, of chlorate of potassium.

Detonators deteriorate very seriously if allowed to become damp ; even when they are sufficiently dry to explode they may be so much weakened as to fail to completely detonate the charge. When the detonator is exploded without firing the charge, the failure is usually attributed to a fault in tbe explosive, although it may be entirely owing to the detonator.

To fire a high explosive with an ordinary fuse : First cut off the end of the fuse obliquely, then carefully examine the detonator to see that it is quite clear of dust or dirt of any sort ; next push the fuse into the open end of the detonator, and nip its edges on to the fuse to hold it firmly in position, Then make a hole in one of the cartridges to be fired, using a sharp wooden peg for the purpose, and push the detonator into the explosive in such a manner that it cannot be pulled out if reasonable care be employed. Next push the cartrit into the hole with a wooden or copper stemmer; stem very lightly at first with clay, and very heavily in the later stages. The shot is then fired by lighting the end of the fuse, after making certain that all men and ponies are out of the way of any flying pieces of stone or coal.

Detonators should be handled with the greatest caie, Otherwise they are CNtremely dangerous. If dust or fluff gets into the open end, it should be shaken or blown out, and on no account should it be removed by the insertion of a piece of wire or anything else. Every explosive gives the best results only when properly stemmed, although good stemming is not so necessary with the high explosives as with blasting powder.

Explosives.

Fuse is made in several qua.lities : only good fuse should iwused, as niisshots are very costly. Ordinary fuse burns at Hie rate of about 30 inches per minute. It is usually lighted lian open light, or Bickford's igniters may be used. These Consist of tin cylinders, rather larger than ordinary detonators. They are open at one end, and the closed end contains the igniting mixture.

One of these igniters is slipped on to the end of the fuse which projects from the shot-hole, and held in place by being nipped at its open end. The closed end is then nipped with special pincers; the pressure on the mixture fires it, and this in its turn lights the fuse. It is desirable, when firing several sTiots simultaneously with safety fuse, that the lengths of fuse should vary, so that a misshot may be detected.

Shot-firing: by Electricity. — In mines where " perimitted " explosives are used, shots are usually fired electricity. The advantages of electric-shot firing are as 4 follows : —

I. No sparks are given off, and no naked lights are required.

a. Several shots can be fired absolutely simultaneously.

3. Shots can be fired from a distance, which is of great advantage in shafl-sinking, etc.

4. When a shot misses fire, the workmen can go straight back to work ; whereas, if ordinary fuse has been used, a considerable delay is necessary.

5. The cartridge containing the detonator can be placed St the back of the hole, which is the most favourable position, 3S it tends to complete detonation of the charge.

On the other hand, the apparatus required for electric shotfiring is heavy and cumbrous. Electric fuses are more expensive than ordinary tape fuse ; and when blasting in very Wd stone, the cables are cut and damaged by almost every shot.

There are two systems of electric blasting in general use, - high tension and low tension. I

Coal-Mining.

In high-tension blasting a very small current at a high pressure is employed, and in low-tension blasting a comparatively large current at a low pressure is necessary. Neither of these systems has any very great advantage over the other. Low-tension are much more easily tested than high-tension fuses, and the cables for low-tension firing need not be so well insulated, and are therefore more efficient when worn or datnaged than would be the case if the high-tension system were employed. The apparatus required for electric blasting are : Batteries, cables, electric detonators or fuses.

Batteries. — Electric exploders may be of two kinds: — (i) Primary, voltaic, or dry cells ; (z) mechanical exploders.

Primary Cells consist of certain elements placed in jars containing an exciting liquid; usually metals and acids are employed, the electricity being generated by the chemical action of the acid upon the metal. These batteries are seldom, if ever, used for shot-firing, owing to their weight and cost, and to the inconvenience of carrying the liquid about,

£)ry Cells. — These are cells which contain no liquids, and in which electricity is generated and given off when a circuit is

A well-known type is the Obach dry cell : it consists of a cylinder of zinc containing a central rod of carbon, together with depolarizing and exciting mixtures in the form of paste. These cells are made in various sizes. Size o is 6 inches by inches by 45 inches, and costs about 2s, 6rf. Each cell gives off electricity at about volts pressure, so that when two are coupled in series, the total pressure is 3 volts. Two or three are generally employed, being coupled in series and placed in a light box for convenience in carrying them about. As they are used, the discharge of electricity gradually decreases. One set will fire about looo shots before it becomes too weak and has to be discarded. As the voltage of these cells is low, they can, of course, be only employed in conjunction with lowtension detonators.

Mechanical Exploders. — These are small dynamos (Chapter XXIX.), worked by hand. The poles are usually permanent

Explosives.

magnets, and the armature is very rapidly rotated, by means of the handle, through gearing. The high-tension machines generate a very small quantity of electricity at a pressure of from loo to goo volts, and low-tension machines genera,te a larger quantity at a much smaller voltage.

Cables. — These consist of two insulated strands of copper we, forming a single cable. A similar cable is used for higher low-tension blasting.

Cables are snbject to much rough usage, being frequently cut and damaged by the material dislodged by the shots. The insulation, too, gets worn away by their being dragged about from place to place. Broken strands can be roughly repaired by twisting the broken ends together, care being taken that the two strands cannot come Whether where both are bare.

Eetter insulation is requited for high- than for low- Knsion blasting and for wet ibn for dry places.

fftdrU Fuses. — A, Fig. iffa .shows a high-tension a is the copper cylinder containing the fulminate of mercury b, the priming of gunpowder c insulated wires e, e.

wires, which ate sunounded by the priming where 'tt terminate, do not quite touch each other, but are ted by a very small space, as shown. The electric went, which is generated by the exploder, passes from the Wploder along one of the wires and back along the other.

As the ends of the wires do not touch, the current has to jump from one to the other, and pass through the priming, "liich offers high resistance. The interruption of the current thus caused results in a spark, which lights the priming and fires the fulminate.

Low-tension detonators (B, Fig. 64) are similar to those iMd for high-tension firing, except that the ends of the fiise

B, Iqw-

and the

Coalmining.

inecied by a " bridge " of very fine platinum mre, as shown at e. The platinum wire, being very thin, offers great resistance lo the passage of the electric current, ihe result of which is that the wire is heated to redness, and so fires the priming. High-tension fuses may be compared with arc lamps— a small quantity of electricity is necessary, but It must be at a high pressure in order lo leap from one wire W the other. Low-tension detonators may be compared wilh ordinary electric incandescent lamps, the wire being healed by the passage of a considerable quantity of electricity at a low pressure.

Low-tension detonators are tested by putting the fuse in a weak electric circuit. If the bridge is broken the cuireat will not pass.

To make the test, the detonator should be slipped down a pipe through a hole in the wall of the room in which the tests are made ; or it may be put through a small hole in an iron bos, sufficiently strong to resist the force of an explosion, should the detonator explode by any mischance. The fuse wires are connected with a small battery and galvanomeier. If the bridge is perfect the current passes through the fuse, and the needle of the galvanometer is deflected.

Firing Shots. — The process of firing shots by electricity is as follows : The detonator is carefully pushed into Ihe cartridge, and the wires are bent bad and hitched round the cartridge, as show at a, Fig. 65. This is not always done, but it is a good practice, as it prevents the detonators becoming withdrawn from the charge. Tlie cartridge is next pushed gently into the hole, which has previously been cleaned by means of the scraper. The shot-firer then holds the wiiej in one hand and stems with the other, using the stammer veiy lightly for the first few rounds. The wires are then connected with the cable in the manner shown at b, Fig. 65. The cable

Fig. 6s. — Charging shot-holes.

Explosives.

should be turned round a prop or secured with a weight a few jards from the hole, so that any pull on it will not affect the connection to the fuse. The cable is let out until a safe place is reached ; the end is then connected to the exploder and the shot fired.

Misshols. — These may result from defective materials or from a short circuit. When a short circuit is formed, the current goes back to the exploder without passing through the detonator. When a shot misses, the battery should be discoQnected from the cable, and the shot-firer should tirst carefully examine the connection between cable and fuse, to find out whether bare wires are touching each other at any point, or whether both bare wires are touching any conducting medium, such as water. If the junction between fuse and chile is good, the cable should be examined and raised out of any wet places there may be in the roadway. If a high tension battery is employed, it may be tested by making and breaking the contact between the terminals and a short piece of fuse wire. The cable can also be tested in the same way by uncoupling it from the fuse and sending a current through il. If these details are found to be in order, either the detonator is bad or the fuse wires may have become kinked in . the hole and the insulation rubbed off.

When a good brand is used, the proportion of bad fuses is very small, being not more than one for every two or three thousand. When a miss-fire occurs, another hole must be drilled and fired, not nearer than 6 inches. The direction of all shot-holes should be indicated after boring, so that the second hole may not strike the first. The end of the fuse that baa missed should be tied by a cord to a prop, so that it can be recovered after the coal or stone has been blown, otherwise it may be accidentally struck and exploded.

Simultaneous Blasting, — When several shots are to be fired simultaneously, they may be arranged in two ways. A, Fig. 66, shows the method of firing several shots arranged in series by means of a low-tension battery. The direction of the current is indicated by the arrows. It will be noticed that

Coal-Mining.

the whole of the current goes through every shot in turn, connection between the fuse wires is usually made with fuse wires, which the shot-firers save for the purpose.

Fig. 66. — Simultaneous blasting : A, in series ; B, in parallel.

the high-tension system of blasting is employed, the shots arranged inparalkly as shown at B, Fig. 66. In this case current splits at the end of the cable, a part of it only go through each shot.

ce of a Method of Work. — The two chief methoiSs irking coa! are by " ioiigwaU" and by "pillar and stall" : are many modifications of each of these methods, some lich partake of the characteristics of both to such an t that it is difficult to say to which class they belong. ; purest form of longwall, the whole of the coal is taken

one operation, and no pillars are left, the roads to the eing maintained through the goaf. In the pillar-andmethod of work, the coal is first cut up into pillars,

are subsequently extracted in " lifts ; " that is, by narrow being worked off them. The longwall method is gradually cing pillar and stall in almost every district, and in some tant coal-fields it is exclusively employed.

selecting the method by which a seam of coal is to be d, there are many important &ctors to be taken into leration.

le success of a colliery depends largely upon the under- d costs, and upon the quality— as regards size — of the fter it has been wrought, and both of these are greatly ced by the method of working,

often happens that the method of working suitable for art of a mine is quite unsuited for the same seam in a :nt part, but, notwithstanding this, a similar method is lyed throughout. The workings may become deeper, or :am may alter in character or thickness, but as the change place very gradually, the original method may be followed it has become quite unsuitable.

COAL-MfNING.

The choice of a method of work is governed by tfi I following considerations : —

{a) Localily of the Mine.— The choice of a method of worJt is affected by tlie locality in which the seam is found. If lie workmen and officials in the district are accustomed to any particular method, it would be unwise to make a new departure without good reasons, as it is very difficult to train men who have been accustomed to one method only to work efficiently in another. This difficulty is very serious, and can only be overcome by great patience, as men working under new conditions cannot at first get good results, and this leads to aa increased cost of working the coal just at the time when the price-list has to be settled.

(i) Markets, — The purposes for which a coal is to he used have a very important bearing upon the manner in which il should be worked. If it is a house-coal and non-coking, the slack may be of little or no value, and every effort must be made to obtain as large a proportion of round coal as possihie, which would be a very strong argument in favour of longwsH, for with no other method of work is the coal got in such good condition. At some collieries, however, the whole output is ground up and coked, so that there is no difference in value between large coal and slack, in which case cheapness in working is the main consideration.

(f) T/iiektiess.— Very thick seams are usually worked by some form of pillar and stall, though in some few cases longwall in two or three lifts is being practised, the lower portion being worked first and allowed to settle, and the upper portion being subsequently extracted. The thicknessof coal taken out in a longwall face is limited in practice to about 7 feet ; if the seam is thicker than this, the upper portion laty be left to form a roof in the stall faces, and got down in the goaves when the back timber is drawn. Very thin seams bK more often worked by longwall than by pillar and stall, though there are many exceptions. Seams between z and 3 feet ii [thickness are largely worked by pillar and stall in West STorkshiie and Lancashire.

Methods Of Work.

(rf) Character of the Seam. — When a seam is interstratified th dirt bands, it is better worked by longwall, as the dirt nds form packing material, and can be more easily disposed [than is the case in pillar-and-stall workings.

The disposal of the dirt is a very serious item in some Sams, as very large quantities may have to be drawn to ink.

If the coal-field is very faulty, the system of pillar-aad -stall roridng has certain advantages over longwall, for in longwall fork no preliminary opening out or exploration is necessary, lence an unexpected fault may cut off a large proportion of he faces with very little warning, which could hardly be the ase with the pillar-and-stall method.

(f) Character of Roof and Floor. — The nature of the roof nd floor of coal-seams varies very greatly, and has the greatest possible influence upon the cost of working the coal, and upon he choice of the most suitable method of work.

A thick seam without dirt bands, and having a strong rock Bof, is not adapted for longwall, as it makes no dirt for licking, and the cost of ripping down the hard roof for the pies is excessive. Moreover, the ripping will require blasting, ind when a mine is gaseous this is very objectionable, and, Swing to the Explosives Order, very inconvenient When the aal-seam is hard and tlie floor soft, the pillar-and-stall method is unsuitable, as the weight of the superincumbent strata upon ftie hard coal presses down the floor under the pillars and queezes it up wherever the coal has been extracted, causing Ihe floor of the roads to "heave," and adding enormously to Ite cost of keeping open the roadways. Some seams are of fitch a nature as not to stand well in headings ; sometimes the tea! at either side grinds and crushes out, leaving the roads of ftmormal width ; or it may be almost impossible to keep up ie roof owing to the grinding action breaking it up into small eces for a great height. Seams of this character should of Ourse be worked by longwall.

IndinoHon, — Seams lying at a high inclination may be looked cither by longwall or by pillar and stall, the former

COAL-MimNG.

being the moie common when the seams ue thin, and fti

latter when they are thick.

Dth. — The depth at which a seam lies has a vej important effect upon the system by which it should worked. As the depth increases, the pressure upon the coai becomes greater, which causes the coal to be crushed and the roof to be difficult to keep up.

It is now generally recognized that seams lying at a greal depth should be worked by longwall. There are still many colheries where deep seams are being wrought by pillar anil stall, but most of these are old places in which the method was commenced when the seam was comparatively shallow, and has been continued without regard to the changed

The proportion of slack made in working a seam is generally greater when deep than when shallow ; and as a nle the roads in deep mines are the more difficult to keep open. There are, however, exceptions to this, as the nature of the roof itself has to be considered.

The depth to some extent influences the choice of a method of work in another way. Owing to the high temperature of deep mines, it is of the utmost importance that tlie ventilation should be good, as by brisk ventilation only can the temperature of very deep mines be kept within working hmits. The ventilation in longwall mines is much simpler and more thorough than in mines worked by pillar and stall ; beW the temperature of the workings can be kept lower. The temperature of the strata is usually about 50 degrees Tahr. at a depth of about 50 feet, and the increase in temperaloK averages about i degree Fahr. for every 60 feet of inaeased depth. According to this rule, the temperature of the strata at ;t in depth would be nearly 66 degrees Fahr.; at 2000 . feet it would be Zi\ degrees Fahr. ; and at 3000 feet, 99 degrees I Fahr. The temperature of the mine is usually several degrees I lower than that of the strata, owing to the cooling action of tl mutilation. The temperature in which men are able to woA spends very greatly pon the dryness of the air. If the an is

Methods Of Work.

taid as well as very hot, it is impossible for men to work, hut if dry, very high temperatures can be withstood by men who iave gradually become accustomed to the conditions. Sufficient are not available to enable the limit of temperature to be itely fixed, but it is probably about loo degrees Fahr. The 'peatest depth below the surface that any English mine has .reached is 3483 feet, which is the maximum depth of the Rams mine workings at Pendleton colliery. At that point the iemperatureofthe strata is 100 degrees Fahr., and of the workings Wij degrees Fahr. At Agecroft colliery, at a depth of 2940 Ifcet the temperature of the workings is 84 degrees, and of the jlliata 92 degrees.

' It seems probable that the greatest depth at which coal can be economically mined with our present appliances is about 4000 feet.

The temperature is influenced by the nature of the overstrata and the contour of tlie surface. There is also widencc which tends to show that the increase in temperature not quite so rapid as the greater depths are reached. Special Conditions. — There may be special difficulties to be welcome in the working of a seam which necessitate the Kdoption of a special method of work to meet them. For ttample, seams liable to spontaneous combustion should, if fosable, be laid out and worked in such a manner as to reduce Ihk liability and to limit the effects of gob fires should they cur. When other conditions are favourable, this may be done by some system of longwall retreating.

Sometimes sears have to be worked which are overlain ty large volumes of water, either found on the surface, or contabed in the strata, and a special method of working has lo be adopted to prevent this water from making its way ilhrough the strata into the workings. In working under-sea it is usual for the proportion of the seam which may be icted to be settled by lease, and it has been found to be safe to extract the whole of the seam when the cover is It 100 yards thick, A strip of coal should be left alongeach fault, and in some cases, as an extra precaution, the

Coal-Mining.

coal-field has been divided into panels by barriers of solid

so that if the sea-water should percolate into the mine,

district can be shut off by dams.

When coal is worked from under valuable buildings, les3 damage is occasioned by longwall than by pillar and stall. ihe face advances regularly and continuously, the strata* gradually subside without breaking, and no damage is done but if the face stops, a break is formed, and great damage be done to any buildings that happen to be on the line of break. This is especially the case when the workings stop - an upthiow fault, in which case the line of break follows th -e. slope of the fault.

Comparative RcsnlU of Longioall and Pillar and Stall,

The objects to be aimed at in selecting a method of worlc are — to get the coal safely, economically, in good condition for the market, and to get the whole of it. Discussing in order —

Safety. — As regards safety, there is lite to choose between the two methods; but what little advantage there is, is certainly with longwall. The ventilation in longwall pits is much the simpler, and is more efficient, as there are no " dead ends," whereas in pillar and stall a large proportion of the men are dependent upon some form of brattice for their supply of air. The risk of outbursts of gas is also much lessened by the longwall method, which is a very important matter in working certain seams.

£eofwmy.'~The comparative cost depends upon th suitability of the seam to the method by which it is Some seams can be worked very cheaply by pillar and stal and others quite as cheaply by longwall. In the former systeiO the cost of heading and cutting has to be borne, as against th cost of ripping in the latter, and the relative cost of these items depends upon the characteristics of each individo**

Condi/ion of the Coal when looked. — It is under this he that the longwall system compares most favourably with i*-® rival, as there is no doubt that with ordinary conditions

Methods Of Work. 147!

B round coal is obtained by longwall than by pillar and

In districts where the slack is of little or no value, tbis

's of the utmost importance. The tendency is for slack to

become of more value than formerly, so tliat it is probable that

the great difference in value between large coal and slack will

not be maintained, Coal which has stood for a long time

in pillars is usually found to have deteriorated in quality,

irrespective of size.

Gelling llie Whole of ike Coal. — In seams of moderate J

tliickness the whole of the coal should be got out, no matter

what method of work is adopted; but in the piilar-and-stall

method small portions of coal are frequently lost, whereas in

the longwall system there may be absolutely no waste. When

! more than 6 or 7 feet in thickness there is nearly

always a considerable amount of waste. Frequently the upper

portion of the seam is left to form a roof in the face, and

though it is supposed to be got from the goaf, a large

percentage of h is unavoidably lost.

CHATTER Xn.

Longwali.

the face fa open bf bong sapporteA bf tW t

If tbe roof is strong, props iloae are set ; if weak, b placed at right angles to the &ce from prop to prop ; unusually bear, wood dicks may be set allemately i ordinary props. The ga:es ate kept open by means of "gaiepacks," wluch are built up of the material got from ripping

1 the roof in the gales. The gates require ripping, because j from under which the coal has been taken gradually

Working By Longwall.

sinks and crushes up the packs. Intermediate packs are built between the gale-end packs to steady the roof down as it sinks, the width and distance apart of these intermediate packs depending upon the amount of material available with which to build them.

The operation of getting coal at a longwall face is conducted as follows ; —

The coal is first "holed," or undercut, and is supported by sprags. It is then cut through or " broken into " opposite the gate, and several sprags are withdrawn ; then, if the coal does not fall, it is wedged or blasted down and filled into corves, a corf road being laid along the face as soon as sufficient room is made for it by the removal of part of the " web " of holed coal. As the face is cleared, a fresh row of timber is set and the back row drawn, and intermediate packs built up. After a part of the web is cleared, holing is commenced at the cleared portion, so that in one part of the "stall," or "benk," the coal is being holed, and at another part it is being filled out

The gate-roads are usually ripped and packed during the 1 night-time

I To carry on the longwall system to perfection, each stall I should be let to a set of men, who share their earnings and employ the holers and fillers. In some districts, where double shifts are worked, several men work independently in one stall, some working on one shift and some on the other. When this is the case, the proper holing and working of the stall is impossible, as the men on one shift naturally object to leaving coal holed for those who follow them to fill out and be paid for. In some seams the coal can be got without holing, and the practice of getting coal without systematically holing it appears to be on the increase, and has a detrimental effect upon the systematical carrying out of the longwall method of work.

Modifications of Longwall. — Seeing that the longwall

.method of working coal is employed under a great variety of xinditions, it follows that it must have many modifications. Direction of Face. — The direction of the face is mainly

[ the dip

Coal-Mining.

governed by the cleat of the coal ; it may also be iimui the dip of the seam.

when the cleat lines are strongly marked, the coal genemUy gets most easily when worked on "bord," that is, when the face advances parallel to the cleat lines. On the other hand, more round coal is made when the face advances either " on end," that is, at right angles to the cleavage, or on " the cross," which is a direction between bord and end. For this reason, where the slack is of little value, the coal is usually worked on end or on the cross, and where it is not important to get a large proportion of round coal, the faces advance on bord,

Dirfclion of the Gates and Headways. — Tlie roads in a longwall pit consist of main engine planes, main gates, cross-gates, ind ordinary gate roads. The gate roads are cut off at intervals by cross-gates, the old cross-gates by newer ones, and the miin gates by the engine planes. This is necessary in order to keep down the length of the roads as much as possible. When the seam is flat, the direction of these roads is entirely a matter of convenience, but where the seam dips the question of gradient has to be considered. Figs. 68 and 69 show methods of working inclined seams, in one of which the face is level, and in the other it is carried at full dip.

Distance apart of Grtto,— The distance apart of the gales depends upon the thickness of the seam, the nature of the roof and the custom of the district. In flat seams the gates are carried in the centre of the face, but when the faces are inclined the rise side of the stall should be the longer, so that most 0' the coal comes downhill to the gate end. In thin seams corves may have to be loaded at the gate end, as there may not be height enough for them in the face ; this necessitates the coal being thrown bick to the gate end, and when this has 10 be done the gates should not be more than ra or 15 yards apart.

Where the coal is sufficiently thick to allow the corves to taken into the face, the distance between the gates may iom 30 to 80 yards. If the gates are too far apart, the advances very slowly, and unless the roof is good, falls

Working By Longwall.

niaj occur ; on the other hand, by bringing the gates too close Mgether, the cost of ripping is increased. In the Midlands the arerage distance that longwall gates are apart is about 40 yards.

The distance apart of the cross-gates averages about 200 yaids; it depends upon the manner in which the ordinary gates stand. When the latter becomes bad, a new cross-gate is set :Et them off. Cross-gates are usually ripped and packed lal face advances, and are driven at an angle with the in some few cases it has been found preferable to scout

cross-gates through the goaf after it has settled.

In some methods of working inclined seams no cross-gates ate required, the gates being cut off by the level above, as shown in Fig. 69.

Fig. 67 shows the ordinary method of working a comparatively flat seam by longwall. The example is taken from the Bamsley Bed, as worked in South Yorkshire, at depths varying tietween 300 and 700 yards, and having the following section : —

Bags (coal) i' 7 '"'

Top softs 2 1

Clay seam dirt

Clay seam (poor) o i

Hards (best steam coal J 2 (

Bottom softs 2 I

The whole of the " bags " and about half of the top souls are kft up in the faces, and the gate-end packs are built under Ihem. They are ripped down in the gates to make height for the traffic, and are filled out of the goaves between the packs, "hen the back timber is drawn.

When the roof above the coal is bad, it is liable to come down with the roof coal when the timber is drawn, causing it to be buried with dirt, and consequently lost. The yield per acre from a seam having the above section is about 10,000 tons, which is rather less than 120a tons per foot thick per

Is2 Coal-Mining.

The gate roads (a, Fig. 67) are set out 33 yards apart, and are made 10 feet wide between the packs, which are about la feet wide. No intermediate packs are built, and all the back timber is drawn out, allowing the roof to break freely behind the second row of props. The cross-gates {e, Fig, 67) are put in when the ordinary gates begin to crush up ; their distance apart varies, being from 100 to aoo yards.

In the deeper collieries it is found to be impossible to maintain a good road right up to the face, owing lo the settlement of the strata, so that the main roads are not made to their full size at once, but are remade as the face gets about iQo yards in advance.

The thinner seams, when lying at a comparatively low inclination, are worked in a similar manner, except that the gates are usually rather further apart, intermediate packs are built, and, of course, no roof coal is lefi up in the faces. The ripping are usually made in two or three lifts ; the first ripping is made close up to the face, and as the roof gets low a second ripping is started, and a third follows, if necessary. If the whole thickness of ripping were taken at once, the gates would be unnecessarily high towards the face when cut off by the cross-gates, but by taking the ripping at twice, only the olda part of the gate has to be made the full height, as the end near the face is cut off by the cross-gate before it has had time to sink enough to necessitate a second ripping. In this system of workmg the opening out is automatic, as no roads are driven in advance, but all are made as the face advances. The only drawback to this is that in unproved ground an unexpected fault might cut off a large district with very little warning.

Longwail in Inclined Scajiu, — Fig. 68 shows a method of working by longwall when the incUnation is considerable and the line of face is level. This example is taken from the Bamsley seam, in the neighbourhood of Sheffield, where it has a section of about 4 feet 6 inches of good coal, A main engine plane is driven to the full dip of the seam, and from it levels are set out on either side. These levels are about 200 yards

Working By Long Wall.

the gate roads are 60 yards apart, and advance to the I the levels, The whole of the coal is taken out in ,s sfiown in the figure, and about 20 yards are taken ' oat beiow them, so as to allow the roof to settle down gradually without breaking. No cross-gates are employed, and the faces are "stepped " as shown ; that is, each stall is about 10 yards behind the one it follows.

The object of stepping faces is to localize the weight, so , that if the roof breaks away in one place, the damage may be :rTilined to the one stall It is probable that these "steps" -re a mistake, and the tendency is to do away with them. They increase the proportion of small coa!, and interfere with

— Longwall in inc!in

ihc proper regulation of the weiglit upon the face ; r il is very difficult to keep the cuttings anything like the proper leagth. If the men in one stall habitually send out more coal than tlieir neighbours, as frequently happens, their stall gets a bag way in advance of the others, and the cuttings gradually income very long, and are liable to break down and obstruct Ihe ventilation. The gate roads are made 10 feet wide, and the ripping is taken 5 feet thick, the full thickness being ripped at one lift. The haulage down the gates is entirely by self-acting inclines, so that it is expensive to take a second ripping, because the stuiT that is ripped down cannot conveniently be sent uphill into the stalls, but has to be sent

tS4 COAL-MINING.

downhill to the levels, and may have to be sent out of the

pit

In most collieries a really good gob road cannot be made until practically the whole of the road is in the roof. That is to say, if a road 6 feet high is required, it will not be satisfactory until about 6 feet of ripping has been taken down, and in some cases a good deal more may be necessary.

When the inclination is great, and the most favourable line for the faces, as regards cleavage, is steep, the method of work shown in Fig. 69 may be adopted. This example is taken from

%

im

Fig. 69.— Longwall in inclined seams, gate roads level,

workings in the Arley Mine in West Lancashire, the thicknes5of the seam being 3 feet, and the depth from the surface about 400 yards. The main levels are 100 yards apart, and from them cross-gates are set out at an angle of about 45 degrees. From these cross-gates the ordinary gate roads are set out parallel 10 the main level The gates are 1 5 yards apart, and each stall has 3 yards of face to the dip and 12 yards to the rise. The corves are not taken into the faces, but are filled at the gle 1 ends, the coal being cast back to them. When fiill, they ate imed to the cross-gate and lowered to the main level,

Working By Long Wall.

iSS '

self-acting inclines or by balance jigs. Very little s taken in the gales, as they are cut off by a new crossgate when they have advanced 60 yards, and as the stalls are t the advance is very rapid. This method is not suited mder coal, as much slack is made by casting back the coal P gates. In the example given above, about 50 per cent, e output is slack, although the seam is of a fairly hard nature.

A modification of this method is illustrated by Fig. 70, which is taken from workings in the Silkstone seam (South Vorkshire), where it has a thickness of 5 feet 3 inches, and lies

Fig. 70. — Longwall

an inclination of 1 in 5. In this modification the main levels are driven out in advance, and not opened out in the Worse of the working, as in the last example. Every 20D yards iong these levels " jinneys " are set out to the full rise of the Xam, and from either side of these "jinneys " level gates are set off. The gates are 20 yards apart, and each stall has 5 yards of dip and 15 yards of rise coal. Each stall goes a yards before it is finished by meeting the stall set off from lie next "jinney"; and as one pair of stalls finishes, another pairs started from theopening-out "jinney" as shown. This method requires a large amount of pit room, as it is not convenient to have more than three or four pairs of gates from one "jinney." The working of self-acting inclines or '' jinneys " is fully described in Chapter XXIV.

'54

Coal-Mining.

(downhill to the levels, and may have to be sent out of the

In most collieries a really good gob road cannot be made until practically the whole of the road is in the roof. That is to say, if a road 6 feet high is required, it will not be satisfactory until about 6 feet of ripping has been taken down, and in some cases a good deal more may be necessary.

When the inclination is great, and the most favourable line for the faces, as regards cleavage, is steep, the method of work shown in Fig. 69 may be adopted. This example is taken from

Fig. 69. — Longwall in inclined seams, gate roads level.

workings in the Arley Mine tn West Lancashire, the thicknessof the seam being 3 feet, and the depth from the surface about 400 yards. The main levels are 100 yards apart, and from them cross-gates are set out at an angle of about 45 degrees. From these cross-gates the ordinary gate roads are set out parallel 10 the main level. The gates are 1 5 yards apart, and each stall has 3 yards of face to the dip and iz yards to the rise. The corves are not taken into the faces, but are filled at the gate ends, the coal being cast back to them. When full, they are trammed to the cross-gate and lowered to the main level,

Working By Long Wall. 157

pillars, which is about 55 yards wide, is worked uphill In a longwall face. The face and headings are driven up simul- iMeously, the headings being kept a little in advance, and slits put through for the passage of the coal. These slits are about 25 yards apart, and the coal from the face is brought down the cutting side and along the top sHt into the gate. The gate road pillars are extracted after the stalls are finished.

In this method of wock no ripping is necessary, and the gate roads are protected from the weight by means of the pillars on either side. These pillars also serve to prevent the effects of a " weight " upon one stall spreading to the others. The cost of the headings is considerable, but against it must be set the cost of the ripping and packing, which would be required if the gates were taken through the goaf, as is done ia ordinary longwall. This modification of longwall is also applicable to seams having an unusually weak root It was adopted many years ago in working the VVathwood coal in South Yorkshire, where it was about 4 feet 6 inches in thickness, and lay very near to the surface. The roof was found to be so wet and weak that it was almost impassible to keep the gates open when all the coal was taken out, and they were carried on packs in the usual way. This difficulty was overcome by making the gates in the solid, as shown in Fig. 7 1.

Lengwall Retreating. — In this method, headings are driven to the boundary of the district, and the coal worked back by a longwall face, leaving the goaf behind. Longwall retreating is specially suitable for working seams which are liable to spontaueous combustion, as the goaf Is left behind, and is gradually compressed almost solid by the weight of the strata settling upon it A district must be headed out before any large output can be obtained, and this is necessarily a work requiring conaderable time. This is one of the objections to this method ; but it is not necessary to head out right to the boundary of the royalty, but only to the boundary of a district, the extent of which can be arranged to suit circumstances- It is only in certain seams that this system of work is successful, or even possible ; in some of the deeper seams it is

iS6

Coal-Mining.

Longwall with Gales in i/ic iVZ/rf,— When the roof of a coal-seam consists of a tiiick bed of hard rock, special difficulties present themselves in working the seam by longwall. All the rippmgs have to be blasted, and no material can be obtained with which to build the intermediate packs. It is also very difficult to regulate the weight upon the coal face, as the roof will not break when the timber is withdrawn, bul tiG.7(.— t-ongwauwungaLesinsoiideoal. stands for a long way back in the goaves, and comes down over large areas when it does fall, breaking all the timber and closing the stalls and gates. The method shown in Fig, 71 has been adopted to reduce the difficulty of making and maintaining the gateways in a seam having a roof of this description. This example Is taken from a seam which has the following section, the depth from the surface being about 300 yards : —

Inferior coal Dirt Brights Hards Bottom brights

The roof consists of beds of strong rock having thickness of about 30 yards.

The main levels consist of headings in the solid coal, and are driven about 150 yards apart. Rise headings are started off these main levels ; they are about 100 yards apart, and serve as gate roads. A pillar of coal 22 yards wide is left on either side of these rise headings, and the coal between these

WORKmC BY LONGWALL 149

sinks and crushes up the packs. Intermediate packs are built >etweeD llie gate-end packs to steady the roof down as it sinks, the width and distance apart of these intermediate packs de- Jieoding upon the amount of material available with which to build them.

The operation of getting coal at a longwall face is conducted a. follows:—

The coal is first "holed," or undercut, and is supported by sprags. It is then cut through or " broken into " opfiosite the gate, and several sprags ate withdrawn ; then, if the coal does not fall, it is wedged or blasted down and filled into corves, a corf road being laid along the face as soon as sufficient room is made for it by the removal of part of the " web " of holed coal. As the face is cleared, a fresh row of timber is set and the back row drawn, and intermediate packs built up. After a part of the web is cleared, holing is commenced at the cleared portion, so that in one part of the "stall," or " ," the coal is being holed, and at another part it is being filled out

The gate-roads are usually ripped and packed during the night-time.

To carry on the longwall system to perfection, each stall should be let to a set of men, who share their earnings and employ the holers and fillers. In some districts, where double shifts are worked, several men work independently in one stall, some working on one shift and some on the other. When this is the case, the proper holing and working of the stall is impossible, as the men on one shift naturally object to leaving "Ml holed for those who follow them to fill out and be paid for. In some seacns the coal can be got without holing, and the practice of getting coal without systematically holing it appears lobe on the increase, and has a detrimental effect upon the yaematical carrying out of the longwall method of work.

Modifications of Longrwall. — Seeing that the 1 of working coal is employed under a great variety of i, it follows that it must have many modifications. Diration of Face. — The direction of the face is mainly

Coal-Mining.

almost impossible to drive headings, as they crush up as soon as driven.

Fig, 72 shows the method of working the main coal in South Derbyshire. A section of this seam is given on p. 37. The workable onion is about 7 feet in thickness, and is that portion between the " grounds " and " overcod," Tliis seam is extremely liable to spontaneous combustion Formerly it was worked by the ordinary system of longwall, and attempts were made to isolate the goaves by building "was walls" on each side of the gate roads. These "km walls" were continuous walls, built up of plastic day; they were compressed by the weight into solid barrieiB of hanJ

clay, but only partially succeeded in keeping the aii from the goaves, and the method of work was altered to that shown in Fig. 72.

Parallel headings are driven 40 yards apart to serve as gaW roads, and slits are driven at intervals to connect then for ventilation.

The slits should be as few in number as possible, as they are expensive to cross, and cut up the faces. After the headings have reached the boundary, they are connected by a crossheading and the coal worked back, leaving the goaf behind The line of face should make an angle with the slits, so that they may be crossed gradually. The roof of the seam is the overcoal," which is of inferior quality, and is usually left 10

Working By Long Wall. 159

' pit ; all the timber is drawn from the goaves, and packs of il are built at the face to steady the roof down. As the advances, a considerable amount of weight is thrown ward on to the gate ends, and they have to be very well ibered to prevent their being crushed up.

Longwall retreating has been adopted in a few cases in in seams worked by coal-cutting machines, but, except under ecial conditions, it has not been largely employed.

Coal-Mining.

The gate roads {a, Fig. 67) are set out 33 yards apart, and. are made 10 feet wide between the packs, which are about 12 feet wide. No intermediate packs are built, and all the ha rlt — timber is drawn out, allowing the roof to break freely behindL-ii the second row of props. Tbe cross-gates {c. Fig. 67) are put in when the ordinary gates begin to crush up ; theii distanc apart varies, being from 100 to 200 yards.

In the deeper collieries it is found to be impossible tcB maintain a good road right up to the face, owing to the settler — ment of the strata, so that the main roads are not made to their full size at once, but are remade as the face gets abou. t 100 yards in advance.

The thinner seams, when lying at a comparatively low inclination, are worked in a similar manner, except that the j gates are usually rather further apart, intermediate packs aie I buiU, and, of course, no roof coal is left up in the faces. The 1 ripping are usually made in two or three lifts ; the first ripping is made close up [o the face, and as the roof gets low a second ripping is started, and a third follows, if necessary. If the whole thickness of ripping were taken at once, the gates would be unnecessarily high towards the face when cut oif by the cross-gates, but by taking the ripping at twice, only the older part of the gate has to be made the full height, as the end near the face is cut off by the cross-gate before it has had time to sink enough to necessitate a second ripping. In this system of working the opening out is automatic, as no roads are driven in advance, but all are made as the face advances, The only drawback to this is that in unproved ground an unexpected fault might cut off a large district with very little warning.

LoKgwail in Jndlned Seams, — Fig. 68 shows a method of working by longwall when the inclination is considerable and the line of face is level. This example is taken from the Bamsley seam, in the neighbourhood of Sheffield, where it has a section of about 4 feet 6 inches of good coal. A main engine plane is driven to the full dip of the seam, and from it levels are set out on either side. These levels are about aoo yaids

Working By Longwall.

apart; the gate roads are 60 yards apart, and advance to the e from the levels. The whole of the coal is taken out in the levels as shown in the figure, and about 20 yards are taken It below them, so as to allow the roof to settle down gradually I without breaking. No cross-gates are employed, and the faces are " stepped " as shown ; that is, each stall is about 10 yards behind the one it follows.

The object of stepping faces is to localize the weight, so thai if the roof breaks away in one place, the damage may be confined to the one stall. It is probable that these "steps" are a mistake, and the tendency is to do away with them. They increase the proportion of small coal, and interfere with

Fic. 68. — Xjingwall in inclined seams, faces level.

the proper regulation of the weight upon the face ; moreover, it is very difficult to keep the cuttings anything like the proper length. If the men in one stall habitually send out more coal than their neighbours, as frequently happens, their stall gets a long way in advance of the others, and the cuttings gradually become very long, and are liable to break down and obstruct the ventilation. The gate roads are made 10 feet wide, and the ripping is taken g feet thick, the full thickness being ripped at one lift. The haulage down the gates is entirely by self-acting inclines, so that it is expensive to take a second ripping, because the stuff that is ripped down cannot conveniently be sent uphill into the stalls, but has to be sent

Coal-Mining.

to the levels, and may have to be seat

la most collieries a really good gob road cannot be made iiiilil practically the whole of the road is in the roof. That is to say, if a road 6 feet high is required, it will not be satisfiictoiy until about 6 feet of ripping has been taken down, and in some cases a good deal more may be necessary.

When the inclination is great, and the most &vourable line lor the faces, as rards cleavage, is steep, the method of wort shown in Fig. 69 may be adopted. This example is taien from

in the Mine in West IaDca5lne,die UncknesoT the W4in beans 5 and tbe depth fiva the ss&oe about ipa yw Th* muB lewk 100 pods mt, and from them 4hh ta£-fUs Ae onliaairsWe taads ue set on ponUel to , Ttw8Mteiarei$piiA9Hadcaicii stall has t to te nd n psA to tbc rise. The ||tldkMHHAefaccbaI sr filled the gate itocktoAcK. Win fon, tbejr ue k clWJgite tmA kivered to dke main level,

either by self-acting inclines or by balance jigs. Very little ripping is taken in the gates, as they are cut off by a new crossgate when they have advanced 60 yards, and as the stalls are so short the advance is very rapid. This method is not suited toatendercoal, as much slack is made by casting back the coal lo the gates. In the example given above, about 50 per cent, of the output is alack, although the seam is of a fairly hard

A modification of this method is illustrated by Fig. 70, which is taken from workings in. the Silkstone seam (South Yorkshire), where it has a thickness of 3 feet 3 inches, and lies

-mM'"

P

1

'

fr 1

Fig. 70. — Longwail m iiii.ijii..U acidic, yalcs level

aa inclination of i in 5. In this modification the main 'evels are driven out in advance, and not opened out in the Murse of the working, as in the last example. Every 200 yards along these levels " jinneys " are set out to the full rise of the Kam, and from either side of these " jinneys " level gates are SI off. The gates are 20 yards apart, and each stall has 5 yards of dip and 15 yards of rise coal. Each stall goes 100 yards before it is finished by meeting the stall set off from tile next " jinney"; and as one pair of stalls finishes, another pair is sUrted from the opening-out "jinney" as shown. This method requires a large amount of pit room, as it is not convenient to have more than three or four pairs of gates from one "jinney," The working of self-acting inclines or " jinneys " is fuUy described in Chapter XXIV.

r

COAL-fINING.

are driven from the main level at intervals of about 40 yards. Bords are driven from ending to ending; they are set off narrow, but widen out to 5 yards within a few feet from the endings. The bords and endings are driven simultaneously, and the pillars between the bords, which are 40 yards square, are worked out in 5-yard lifts soon after they are formed, and before the endings have fallen in. The object of starting the bords narrow is to avoid the damage that would be caused to the endings by "setting them off at their full width, and the reason that they are widened

Fic. 75. — Bord-and-pi

s to decrease the cost of ihe " yardage " which has to be paid for driving narrow roads. Some of the thin seams which occur in the lowtr coal-measures are worked in West Yorkshire and Lanca- .shire by a method similar to the one illustrated in Fig, 75, the chief difference being that both bords and endings are driven rather nearer 10- gether. The corves used

carry up to about 5 . of coal, and stand about s feel high. In seams 30 inches in thickness, a few inches only of roof are ripped down in the bords and endings, and the corves are pushed or "trammed" from the face to the haulage roads. The men and officials travel about the pits on small flat-bottomed trams, as the roads are too low to admit of walking. This method, when applied to Ihin seams, results in a saving in the cost of ripping and packing, but the cost of tramming is very heavy, and much small coal is

The Douhk-stall Method of Work. — Fig. 76 shows the double-stall method of working coaL This method has been adopted to a limited extent in several of our coal-fields. IB

Working By Longwall.

pillars, which is about 55 yards wide, is worked uphill in a loDgwall face. The face and headings are driven up simultaneously, the headings being kept a little in advance, and slits put through for the passage of the coal. These slits are about 25 yards apart, and the coal from the face is brought down the cutting side and along the top slit into the gate. The gate road pillars are extracted after the stalls are finished.

In this method of work no ripping is necessary, and the gate roads are protected from the weight by means of the pillars on either side. These pillars also serve to prevent the effects of a " weight " upon one stall spreading to the others. The cost of the headings is considerable, but against il must be set the cost of the ripping and packing, which would be required if the gates were taken through the goaf, as is done in ordinary longwall. This modification of longwall is also applicable to seams having an unusually weak roof. It was adopted many years ago in working the Wathwood coal in South Yorkshire, where it was about 4 feet 6 inches in thickness, and lay very near to the surface. The roof was found to be so wet and weak that it was almost impossible to keep the gates open when all the coal was taken out, and they were carried on packs in the usual way. This difficulty was overcome by making the gates in the solid, as shown in Fig. 7 1 .

Longwail Retreating. — In this method, headings are driven to the boundary of the district, and the coal worked back by a longwall face, leaving the goaf behind. Longwall retreating is specially suitable for working seams which are liable to spontaneous combustion, as the goaf is left behind, and is gradually compressed almost solid by the weight of the strata settling upon it. A district must be headed out before any large output can be obtained, and this is necessarily a work requiring considerable time. This is one of the objections to this method ; but it is not necessary to head out right to the boundary of the royalty, but only to the boundary of a district, the extent of which can be arranged to suit circumstances.

It is only in certain seams that this system of work is niccessfiil, or even possible ; in some of the deeper seams it is

CHAPTER Xir.

Working By Longwall.

In the longwall method of working coal, the whole of the seam is extracted in a more or less straight face in one operation, the roof being allowed to sink as the workings advance. Access to the face is maintained by " gates," which are roads made through the " goaf," or old workings. Fig 67 shows the ordinary method of working coal by longwall. The road along

A

Fia. 67. — Longwall En se

the face is kept open by being supported by two i timber.

If the roof is strong, props alone are set ; if weak, t placed at right angles to the face from prop to prop ; unusually heavy, wood chocks may be set alternately ordinary props. The gates are kept open by means of "galeend packs," which are built up of the material got from ripping ' down the roof in the gates. The gates require ripping, because J the roof from under which the coal has been taken gradually j

WORKmC BY LONG WALL.

sinks and crushes up the packs. Intermediate packs are built between the gate-end packs to steady the roof down as it sinks, ihe width and distance apart of these intermediate packs depending upon the amount of material available with which to build them.

The operation of getting coal at a Longwall face is conducted IS follows; —

The coal is first "holed," or undercut, and is supported by sprags. It is then cut through or " broken into " opposite the gate, and several sprags are withdrawn ; then, if the coal does not fall, it is wedged or blasted down and filled into corves, a corf road being laid along the face as soon as sufficient i is made for it by the removal of part of the " web " of iioled coal. As the face is cleared, a fresh tow of timber is set and Ihe back row drawn, and intermediate packs built up. After a part of the web is cleared, holing is commenced at the cleared portion, so that in one part of the "stall," or "benk," the coal is being holed, and at another part it is being filled out

The gate-roads are usually ripped and packed during the night-time.

To carry on the longwall system to perfection, each stall should be let to a set of men, who share their earnings and ' employ the holers and fillers. In some districts, where double shifts are worked, several men work independently in one stall, some working on one shift and some on the other. When this is the case, the proper holing and working of the stall is impossible, as the men on one shift naturally object to leaving coal holed for those who follow them to fill out and be paid for. ia some seams the coal can be got without holing, and the practice of getting coal without systematically holing it appears lobe on the increase, and has a detrimental effect upon the systematical carrying out of the longwall method of work.

Modifications of Longwall. — Seeing thai the longwall method of working coal is employed under a great variety of conditions, it follows that it must have many modifications.

Direction of Face. — The direction of the face is mainly

r

i6S COAL-MINING.

of the workings of a thin seam of coal lying at a high indiM tion. The seam from which the example is taken is about 3 feet in thickness, and lies at an inclination of nearly 70 degrees from the horizontal. It should be remembered that A, Fig. jS, is not a plan of the workings, but a vertical section, and in dealing with excessively steep seams, a much better idea as to the character of the working is obtained from a vertical section than from a horizontal plan.

Levels are driven, 60 yards apart, from which the coil is

Fic, 7B.— Method of

worked to the rise, a pillar 20 feet thick being left above each level to keep back the goaf. As the seam is so nearly vertical, the coal-seam itself forms the roof and floor of the levels, as shown in the transverse section. Gate roads are set off every 3o yards along the levels, and are ripped and packed in the usual manner. These gate roads are divided longitudinally by a timber brattice, one side forming a travelling road to enable the men to pass from the levels to the faces, and the other forming a shoot for the coal. The shoot terminates in a wooden hopper, which is opened and closed at will by an iron

Working By Longwall.

roay occur ; on the other hand, by bringing the gates too close together, the cost of ripping is increased. In the Midlands the average distance that longwall gates are apart is about 40 yards. The distance apart of the cross-gates averages about zoo yards ; it depends upon the manner in which the ordinary gates stand. When the latter becomes bad, a new cross-gate is set out to cut them off. Cross-gates are usually ripped and packed as the coal face advances, and arc driven at an angle with the face. In some few cases it has been found preferable to scout the cross-gates through the goaf after it has settled.

In some methods of working inclined seams no cross-gates ate required, the gates being cut off by the level above, as shown in Fig. 6g.

Fig, 67 shows the ordinary method of working a comparatively flat seam by longwall. The example is taken from the Bamsley Bed, as worked in South Yorkshire, at depths varying between 300 and 700 yards, and having the following section : —

Bags (coal)... . Top softs ... Clay seam dirt Clay seam (poor) , Hards (best steam Bottom softs

The whole of the " bags " and about half of the top softs are left up in the faces, and the gate-end packs are built under Ihem. They ate ripped down in the gates to make height for the traffic, and are filled out of the goaves between the packs, when the back timber is drawn.

When the roof above the coal is bad, it is liable to come down with the roof coal when the timber is drawn, causing it to be buried with dirt, and consequently lost. The yield per acre from a seam having the above section is about tons, which is rather less than laoo tons per foot thick per acre.

Coaimining.

The gate roads Fig. 67) are set ot 33 yards apart, ami' are made 10 feet wide between the packs, which are abont 11 feet wide. No intermediate packs are built, and all the back timber is diawi] out, allowing the roof to break freely behind the second row of props. The cross-gales {c. Fig. 67) are put in when the ordinary gates begin to crush up ; their distance apart varies, being from too to aoo yards.

In the deeper collieries it is found to be impossible to maintain a good road right up to the face, owing to the settlemeet of the strata, so that the main roads are not made to their full size at once, but are remade as the face gels about 100 yards in advance.

The thinner seams, when lying at a comparatively low inclination, are worked in a similar manner, except that the gates are usually rather further apart, intermediate packs are built, and, of course, no roof coal is left up in the faces. The ripping are usually made in two or three lifts ; the first ripping is made close up to the face, and as the roof gets low a second ripping is started, and a third follows, if necessary. If the whole thickness of ripping were taken at once, the gates would be unnecessarily high towards the face when cut off by the cross-gates, but by taking the ripping at twice, only the older part of the gate has to be made the full height, as the end neat the face is cut off by the cross-gate before it has had time to sink enough to necessitate a second ripping. In this system of working the opening out is automatic, as no roads are driven in advance, but all are made as the face advances. The only drawback to this is that in unproved ground an unexpected fault might cut off a large district with very little warning.

Longwall in Inclined . — Fig, 68 shows a method of working by longwall when the inclination is considerable and the line of face is level. This example is taken from the Earnsley seam, in the neighbourhood of Sheffield, where it has a section of about 4 feet 6 inches of good coal. A main engine "'ane is driven to the full dip of the seam, and from it levels 'ct out on either side. These levels are about aoo yards

Working By Long Wall.

ipait; the gate roads are 60 yards apart, and advance to the rise from the levels. The ivhole of the coal is taken out in the levels as shown in the figure, and about 20 yards are taken oul below them, so as to allow the roof to settle down gradually without breaking. No cross-gates are employed, and the faces are " stepped " as shown ; that is, each stall is about 10 yards behind the one it follows,

The object of stepping faces is to localize the weight, so that if the roof breaks away in one place, the damage may be confined to the one stall. It is probable that these " steps " are a mistake, and the tendency is to do away wilh them. Tiiey increase the proportion of small coal, and interfere with

Fig. 68. — Longwall in inclined scans, faces level.

file proper regulation of the weight upon the face ; moreover, iit is very difficult to keep the cuttings anything like the proper length. If the men in one stall habitually send out more coal .than tlieir neighbours, as frequently happens, their stall gets a (long way in advance of the others, and the cuttings gradually jtecome very long, and are liable to break down and obstruct jlhe ventilation. The gate roads are made 10 feet wide, Itnd the ripping is taken 5 feet thick, t!ie full thickness being (ripped at one lift. The haulage down the gates is entirely If-acting inclines, so that it is expensive to take a second fcippiijg, because the stuff that is ripped down cannot con- RDiently be sent uphill into the stalls, but has to be sent

Coal-Mining.

several lifts, in whicli the seam is removed in several thicknesses, layer by layer.

The South Stafford Method of Square Work.—Qj this method the coal is worked in rectangular chambers or " ades of work," and as the Ten Yard Coal is extremely liable to spontaneous combustion, each side of work is enclosed hy a barrier of coal lo yards thick.

The inside dimensions of a side of work are about 46 yards by 64 yards. The roof is supported by six pillars of coal, each being 8 yards square, and surrounded on all sides by 10 yards of goaf. Fig, 80 shows a side of work when finished ; it would be opened out and worked as follows :—

Narrow gale roads, a, a, are first driven in the bottom part of the seam, andare con-

nected by the cross-road /'. As soon as the cobnection is made, the coal from li to tbe boundary is worked out by longwall, making b 10 yards wide This also is done in the bottom 6 or 8 feet of the Flg. Bo.— Souih stafTordshim square wurk, seam, as !S all the Opening out. Whilst this is being done, the piece of coal marked c is taken out, and the gate roads a, a are also widened out. The piece marked d is next removed, leaving the two pillars e, e % yards square, 10 yards apart, and 10 yards from the boundaries of the side of work. Whilst this is going on in the bottom layer of coal, the upper beds are being worked at b by cutting through and dropping the layers one by one. The remainder of tbe pillars are formed in a similar manner, and the coal surrounding them dropped and filled out until all has been worked except the pillars ; dams are then put in at m, m, and the side of work abandoned. Sometimes the pillars are got out by buildmg large wood chocks between them to carry the roof.

In practice, this method is modified very greatly to smt

either by self-acting inclines or by balance jigs. Very little ripping is taken in the gates, as they are cut off by a new crossgale when they have advanced 60 yards, and as the stalls are so short the advance is very rapid. This method is not suited toatendercoal,as much slack is made by casting back the coal lo the gates. In the example given above, about 50 per cent, of the output is slack, although the seam is of a fairly hard

A modification of this method is illustrated by Fig. 70, which is taken from workings in the Silkstone seam (South Yorkshire), where it has a thickness of 3 feet 3 inches, and lies

1

4;- 1

Fig. 70. -Long-all m iLidiiJ ,=,11,,, gains level.

at an inclination of i in 5. In this modification the main evelsare driven out in advance, and not opened out in the Course of the working, as in the last example. Every 200 yards along these levels " jinneys " are set out to the full rise of the seam, and from either side of these " jinneys " level gates are off. The gates are 20 yards apart, and each stall has 5 yards of dip and 15 yards of rise coal Each stall goes loo yards before it is finished by meeting the stall set off from the next " jinney " ; and as one pair of stalls finishes, another psir is started from the opening-out "jinney" as shown. This method req,uires a large amount of pit room, as it is not conwnient to have more than three or four pairs of gates from one "jinney." The working of self-acting inclines or "jinneys" Is fiilly described in Chapter XXIV.

Top coal Dirt Bottom coal

Coal'Mtntkg.

The gate roads are driven 20 yards apart, and are cut offwbtn they have proceeded 100 yards. The first working is in the I, the dirt band forming the roof in the faces, but being ripped down in the gates.

After a stall in the lower seam has reached the boundai)',

the top coal is cut through in the gate, a face opened out by ! heading and worked back by longwall, the coal being thrown back into corves which stand in the gate.

A, Fig, 81, is a section through the gale and face in th( first working, and shows the packs, ripping, upper coal-rool and face in the lower bed. E, Fig. 81, is a section througl the gate and face as it appears when the top coal is bein worked back.

Working By Long Wall. 137

pillars, which is about 55 yards wide, is woiked uphill in a longwall face. The face and headings are driven up simultaneously, the headings being kept a little in advance, and alias put through for the passage of the coal. These slits are about 25 yards apart, and the coal from the face is brought down the cutting side and along the top slit into the gate. The gate road pillars are extracted after the stalls are finished. In this method of work no ripping is necessary, and the gate roads are protected from the weight by means of the pillars on either side. These pillars also serve to prevent the effects of a " weight " upon one stall spreading to the others. The cost of the headings is considerable, but against it rust be set the cost of the ripping and packing, which would be required if the gates were taken through the goaf, as is done in ordinary longwalL This modification of longwall is also applicable to seams having an unusually weak roof. It was adopted many years ago in working the Wathwood coal in South Yorkshire, where it was about 4 feet 6 inches in thickness, and lay very near to the surface. The roof was found to be 30 wet and weak that it was almost impossible to keep the gates open when all the coal was taken out, and they were carried on packs in the usual way. This difficulty was overcome by making the gates in the solid, as shown in Fig. 71.

Lmgwall Rdnating. — In this method, headings are driven to the boundary of the district, and the coal worked back by a longwall face, leaving the goaf behind. Longwall retreating is specially suitable for working seams which are liable to sponinneous combustion, as the goaf is left behind, and is gradually compressed almost solid by the weight of the strata settling A district must be headed out before any large outbe obtained, and this is necessarily a work requiring ible time. This is one of the objections to this but it is not necessary to head out right to the boundary of the royalty, but only to the boundary of a district, Ihe extent of which can be arranged to suit circumstances.

It is only in certain seams that this system of work is successful, or even possible ; in some of the deeper seams it is

Chapter Xv.

Timbering.

Supporting the Roof and Sides. — In those parts of amine whicli have to be kept open for transit or for ventilation, the roof, when weak, must be supported by timber or some substitute. The supports in the roadways are of a permaneol cliaracter, but the supports in the faces are only temporary, and are withdraivn as the face advances.

The best timbers for mining purposes are Baltic, NgrwegUn, and Scotch pines, firs, and larches.

Timber should be dry when set, or a considerable portion of its strength is lost ; it is usually found to be more durable when set without the bark. The cost of mining timber varies from about 8d. up to about is. 6d. per cubic foot; andthecost on the output varies in different mines between about id. and &d. per ton. This great difference in cost is due to the nature of the roof and floor, thickness of seam, and method of working.

Preserving Timber. — In some mines the timber rots vwj quickly. It may be preserved by forcing creosote into the pores. Creosote isa mixture of pitch, creosote oil, naphtha, and ammonia ; the timber is thoroughly dried, and the creosote is healed and forced into it at a high pressure.

One drawback to this method of treating timber is, that it causes the timber to be highly inflammable.

Another method of preserving pit limber is that known M Aitkin's process, in which the timber, after being thoroughly dried, is boiled for two days in a solution containing 7 parts <rf

Working By Long Wall. 159

the pit; all the timber is drawn from the goaves, and packs of coal are built at the face to steady the roof down. As the face advances, a considerable amount of weight is thrown forward on to the gate ends, and they have to be very well timbered to prevent their being crushed up.

Longwall retreating has been adopted in a few cases in tMn seams worked by coal-cutting machines, but, except under special conditions, it has not been largely employed.

P the wei

j down

Coal-Mining.

the weight comes on, it tends to force the tops of the props downhill ; and if they were set perfectly square in the first instance, this might push them out, whereas by "undersetting" them a little, the effect of the pressure acting downhill is to tighten them. To set a prop, the workman "stamps" a depression into the floor with a pick, places the foot of tlK prop in it, and pushes lid and prop as nearly into position as he can by hand, and finally drives it up with a hammer. The length of the prop should be such that considerable force b required to drive it up into position.

Chocks or Cogs. — When the pressure to be resisted is veij great, chocks or cogs may be employed.

These are square pieces of timber built up two by two, placed crosswise. When used in the working faces they are built up on heaps of slack or dirt, so that they can be withdrawn by cutting away the support from underneath them. They yield at first to the pressure, but as the weight upon tliem increases, they become consolidated, and will then bear an enormous pressure.

Chocks or wood packs are also used in the gate-roads of longwall collieries, being built into the packs, more especially at the junction of one road with another.

Chocks vary greatly in size ; the smaller are built up out of timber about 2 feet long, the larger may be constructed of oW railway sleepers, or of broken props or bars.

The large chocks are often partly constructed of stone, which is packed up inside them.

Bars. — A bar is exposed to a strain acting at right angles to its length ; this is known as a transverse strain.

The strength of a bar may be calculated from the following formulse ;—

LW breaking load in .

B breadth of bar in inches.

.1

Orking By Pillar And Stall.

ly making the pillars much larger, and only taking out a small proportion of the coal in the first working, the pillars being afterwards got out in lifts.

There are ntiaoy variations of pillar-aod-sCall working, so of the most important of which are described in the following pages.

Fillar and Stall as practised in the Durham Coal-fidd, The first working, or "working in the whole," consists of ci

up the coal into rectangular blocks or pillars by means of roads driven at right angles to each other. These roads are termed " walls, or endings," and " bords," the endings being raids driven parallel to the cleat, and the bords roads driven & right angles.

In some cases the bords are driven wider than the endings,

I in otliers both are driven of the same width. The second working, or "working in the broken," consists of getting out the pillars formed by the first working.

collieries a large area is cut up into pillars, which My be left for many years before being extracted ; at other places the pillars are worked out soon after they have been formed, and before the bords and endings have had time to close up. This is known as " following up the whole with the broken." When pillars are left for a long time before being extracted the quality of the coal deteriorates, and the roads between the pillars become entirely closed up. These drawbacks have led to the practice of following up the whole with the broken becoming more common.

Fig. 73 shows the method adopted for working out the "irs al a Durham colliery. The seam worked is the main coal, which lies at a depth of about 300 yards, and has the 'ollowing section, post roof ; —

FfG. 75.— FOar dd =EiiL

lAonl 19 pa ceoL of th< wncric Jb tbe bords and end mgs fave &IleD Id before the Ibis MK attached skiitings, s, i, 3MK Anm aloDg two sides of tbc fSin wiiicfa is to be extracted m open it ooL A " siding over," i. is men dciTen as showD, 10 SDGTtea liie length of the ju6. Tbe pilhr is then worked out bi Sfa, or " ," 6 yards wide, iowa at p, J, etc Tbe hst Ax of coal is taken out in short lifts dnncB at ligM zns tn its length.

There are manj other methods of working pillars ; in soiw cases the ptibi is split, aod jods taken off in both diiectiooi' The size of the pillais varies conHderably ; they should be made larger as the depth increases, because the weight upon them, due to the pressure of the superincumbent strata, also becomes greater.

A road is kepi open to the face of the juds alongside tbe solid coal by means of props and bars. After a jud is finished, the road is pulled up and all the timber withdrawn, aUotnog the roof to fall. In taking out a large number of pillars, llie line of goaf should not be straight, but zigzag, so as to bisat the weight ; but care should be taken that no pillar lags behicid, or it may become crushed and lost

T/ie Bamsley Bank System. — Fig, 74 shows the method bj which the Bamsley Bed has been largely worked, where found at a moderate depth and inclination. Levels are driven in sets ofthree, leaving about 120 yards of coal between each set. The els which form a set are each 2a yards apart ; the lop " the purpose of opening the banks off, the nuddle haulage, and the third and lowest is used for vati for opening offthe return banks. From these leads

Ng By Pillar And Stall.

bents ao yards wide are set off uplnll, at intervals of 60 yards.

These banks are taken up to the lowest level of the set above,

mdivhen they reach this another 20-yard bank is opened off

from it, and brought downhill as shown.

This system of work was very successful where the coal "as shallow, and there was little weight. It is now, however, almost entirely superseded by the long-wall system of work,

irtuch is found to be much superior where the depth is con-

letable, and there is now very little Barnsley coal remaining

d at a depth of less than 400 yards.

amd-Pillar Method. — Fig. 75 shows an important

ford-and-pillar working.

example is taken from workings in the West Yorkshire

lon Bed, where it has a thickness of about 4 feet g inches,

1 wdliesatadepthofabout 200 yards. Endings about S feet wide

¥

Coal-Mining.

are drii'en from the main level at intervals of about 40 yards. Bords are driven from ending to ending; they are set ofl but widen out to 5 yards within a few feet from ihe endings. The bords and endings are driven simultaneously, and the pillars between the bords, which are 40 yards sqmre, are worked out in 5-yard lifts soon after they are formed, and before the endings have fallen in. The object of starting the bords narrow is to avoid the damage that would be caused tc the endings by "setting them off at their full width, and tin

%

Fig. 75.— Bord-and-p'

n that they are widen out is to decrease the cost Ihe '' yardage " which has ti be paid for driving nano roads. Some of the thin seaic which occur in the lowf coal-measures are worked i West Yorkshire and Lanci shire by a method similar 1 the one illustrated in Fi| 75, the chief difference bcin that both bords and ending are driven rather nearer t gether. The corves use

carry up to about 5 . of coal, and stand about a fd high. In seams 30 inches in thickness, a few inches only ( roof are ripped down in the bords and endings, and tl corves are pushed or " trammed" from the face to the haul| roads. The men and officials travel about the pits on sma flat-bottomed trams, as the roads are too low to admit ( walking, This method, when applied to thin seams, resul in a saving in the cost of ripping and packing, but the co tramming is very heavy, and much small coal I made.

TItc DoubU'Stall Mithod of Work.—V\%. 76 shows tl double-stall method of working coaL This method has bee doptcd to a limited extent in several of our coal-fields. I

Working By

PILLAR AND STALL. 165 that ventilation

chief advantage over the single-stall method ii is made easier and more complete.

The example is taken from the workings in a seam feet thick, lying at a depth of about 300 yards. The levels are drireii in pairs, and from these levels headings are taken up at the full rise of the seam in sets of three. These sets of rise headings are separated by about 350 j-ards of coal, and the headings in each set are 20 yards apart, The centre heading of a set is reserved for haulage, and the stalls are opened out fiiiQtbe outer ones. The headings are connected every 20

yards by slits, along which the coal is conveyed to die haulage road from the stalls.

The stalls are ao yards wide, and leave a pillar of coal 20 yards wide between them. They are driven up in pairs, and "ken they have reached their limitwhich is half the distance between the sets of headings — the 20-yard pillar is cut through and worked back. A road is made at each side of the stalls, iind is kept open by timber and pa-cks, but the timber is drawn tram the space between the roads, and the roof allowed to fall.

After a district is finished, the coal along either side of the laulage road is worked out to the level.

r

184 COAL-MmiNG.

Tapered Props. —The great breakage of props which occun ' at a longwall face, especially when the floor is hard, is due to the subsidence of the roof, whicli inevitably takes place as the face advances, the pressure which causes this subsidence being ! so great that no timber can withstand it. To reduce this breakage, Mr. Hepplewhite has recently introduced the employment of tapered props.

These are ordinary props, having one end tapered down lo . about half the original diameter, the tapered portion beizig about 12 inches long. As the weight settles on to a prop of this description, the tapered end burrs under the pressure as the roof subsides, thus saving the prop from being broken, A prop 6 inches in diameter begins to " burr " when the pressure upon it is about 16 tons and breaks under the same pressure as an ordinary prop of the same diameter, that Is, about 40 tons. After a prop has been set, and the end become burred, it is sent out of the pit lo be re-tapered ; when it can be used again, either for a thinner seam, or it maybe used for the same seam, being set with an additional lid.

Sud Girders. — Steel girders of H section are now frequently used instead of timber bars, for supporting the roof in main roads ; they are more costly in the first instance, but last much longer, and carry a greater weight with less loss of head room. They are also used in a few places for props, but they have not hitherto been adopted very widely for use at the coalface, as they are apt to get lost, and buried by falls of roof, The ends of steel girders used as props should be flattened; this is usually done by cutting a piece out of the web at each end, and bending the flanges over till they meet and form a flat surface. Steel props should always be set with soft wood lids on roof and floor. Cast-iron props have been tried at several places, but have not met with success, as sudden strains cause them to break without warning.

Asteelprop of H section 5 inches by4inches, weighing 50 lbs. per foot, and 5 feet in length, has a breaking strain of nearly 100 tons ; and a similar prop, 4 inches by inches, weighing 38 !bs. per foot and 4 feetiong,breakswithapressure of about 70 tons.

Special Methods Of Work.

The methods of work described in the previous chapters are I "liy suitable for working seams which occur under normal ; Conditions as to thickness, inclination, etc. But in various

pWs of this and other countries, seams are found to occur

Under such abnormal conditions as to render the adoption of

special method of work absolutely necessary.

Methods of working Steep Seams.— Seams which iie at an angle of about 45 degrees, or i in i, can be Worked by some modification of the methods already described ; bm when this rate of inclination is greatly exceeded, a special method of work has to be adopted. These very steep seams are termed "readers," and are found chiefly in North Staffordshire and locally in Somersetshire and parts of South Wales and Scotland. Steep measures are usually found at the edges of basins, and when followed down the inclina- I non gradually decreases. There are collieries in North I Staffordshire working seams which are both vertical and ' horizontal in a comparatively small area. When scams are nearly vertical, the method by which they are worked is somewhat similar to the methods adopted for working mineral veins, which are usually nearly vertical.

JTie cost of working steep seams is not necessarily much lueater than the cost of working the same seams when Sat, but bless the seam is of a very strong nature, much small coal is

Me-

In Fig. 78, A shows a vertical and B a transverse section

i68 COAIMINING.

of Che workings of a tttin seam of coal lying at a high inclioa' tion. The seam from which the example is taken is about j feet in thickness, and lies at an inchnation of nearly 70 degrees from the horizontal. It should be remembered that A, Fig. jS, is not a plan of the workings, but a vertical section, and in dealing with excessively steep seams, a much better idea as to the character of the working is obtained from a vertical section than from a horizontal plan.

Levels are driven, 60 yards apart, from which the coal a

Fig. 78.— Method of '

worked to the rise, a pillar ?o feet thick being left above each level to keep back the goaf. As the seam is so nearly vertical, the coal-seam itself forms the roof and floor of the levels, as shown in ihe transverse section. Gale roads are set off every JO yards along the levels, and are ripped and packed in the usual manner. These gate roads are divided longitudinally by a timber brattice, one side forming a travelling road to enable the men to pass from the levels to the faces, and the other forming a shoot for the coal. The shoot terminates in a wooden hopper, which is opened and closed at will by an iron

Special Methods Of Work. 169

slide, so that the corves can be filled by pushing them under the hopper and pulling out the slide.

The shoot is always kept full of coal, in order to reduce the greit breakage that would ensue if lumps of coal were dropped from the top to the bottom of the shoot. The men at the coal-face work on a platform built up of boards placed across limbers let into the strata. These platforms also serve to prevent the coal from falling into the goaves and being lost.

In some places where a similar method is employed, no pillars are left above the levels. When this is the case, the levels must be very carefully timbered, because the goaf, which SigK the roof of the levels, may be very small and loose, and,

Kd break through into the levels, may be difficult to thick seams in Pennsylvania, when lying at a high n, are Bonietinies worked by a method of pillar and easts 10 or 13 yards wide are taken up from the lerels, each breast being separated from the next by a pillar of coal 10 or 12 yards thick.

A small space on either side of each breast is timbered off fur a travelling road, and the remaining portion is kept full of loose coal. This loose coal forms a floor for the men to work upon, and avoids the use of scaffolding. After a breast is Goished, the loose coal is drawn off and the roof allowed to fall in.

North Staffordshire Method of working Rearer Coals. — A very interesting method of working steep seams is practised in North Staffordshire. The seams are won by " cuts," or level drifts, which are driven from the shafts, as shown in Fig. 56.

After the coal has been reached, levels are driven out in it to right and left in pairs, the upper being used for haulage, and llie lower for a return airway and for a water-level, these levels rise headings are started in pairs (Fig. 79), each pair being separated from the next by 200 yards of coal. The distance between the main levels is about 120 yards, and all 'he coi\ is worked to the rise of the upper levels before any of the pillars are removed from the levels below. The

J

headings are carried up to within lo yards of the goaf above,

which forms the boundary ol" the breadth of coal which is to be worked.

From these rise headings, three levels are driven on either side for a distance of roo yards ; the levels are lo yards apart, and ID yards of coal is left between the top level and the goaf. The coal is then worked in lifts uphill from level lo level. Operations are commenced at the top level first, by taking a lift almost up to the goaf above. The thin barrier of coal which is left next to the goaf is blown out by a shot, and the goaf comes sliding down into the lift. This is done to

n

n

,

n

Ul

'

"

Jl_

—

Fig, 79.— Melhod of working nearer coal-slams in North Staffordshire.

give the men something to stand upon whilst at work. The same method is pursued in the two levels below, the top levels being kept a little in advance, as shown in Fig. 79, which is a vertical section through a district. The coal is filled into corves, which stand in the levels and are not taken to the face. This method is somewhat similar to that illustrated in Fig. 77, except that in the case of these very steep seams the goaf is brought down from level to level, to give the workmen something to stand upon. The corves are raised and lowered in the headings by means of cage dips. Four lines of rails are laid in the headings, and a wheel fitted with a powerful brake is set up at the top. The cage, which runs on wheels and

Special Methods Of Work.

fairies one corf only, is attached to one end of a rope which passes round a wheel and has a balance weight secured to its other end. The cage and full corf are heavier than the balance weight, so that when the cage is loaded with a full corf, it runs to the bottom and pulls the balance weight up.

When the full corf is run off the cage and an empty one substituted for it, the balance weight is the heavier, so that it runs down to the level and pulls the cage and empty corf up.

The movement is controlled by the brake on the wheel, and the cage can be stopped at any of the levels. Whilst the pillars are being worked back in the manner described, fresh levels are being driven out below, as shown in Fig. 79. When tbe seams in a breadth are becoming worked out, the shafts uesunfc another 120 yards, and a lower breadth opened out by adrift.

Methods of working Very Thick Seams. — Excessively thick seams are always difficult :ind dangerous to work, and when, as is very often the case, they are liable to spontaneous combustion (see Chapter XXVIII.), both the difficulty and the danger are greatly increased. The thickest seam Borked in England is the Ten Yard Coal of South Statfordshire, which has a maximum thickness of about 33 feet of clean coal.

Thick seams are also found in other districts, but in most cases a pari only of the seam is workable, the remainder being left in the pit.

The working of a thick seam is usually attended by great waste: In Staffordshire, it is the custom to work the Ten Yard Coal two or even three times over. An area is worked and abandoned, and years after the same area is worked over again by systematically exploring the goaves, and extracting the pillars, ribs, and roof coal which were left behind in the first working.

There are two methods by which thick seams may be worked ; (i) By square work, in which the whole thickness of fte coal is worked in one operation ; (2) longwall work in

Coal-Mining.

several lifts, in wliicli the layer by layer.

Tlu South Stafford Method of Square Work.—'y thii method the coal is worked in rectangular chambers or " sides of work," and as the Ten Yard Coal is extremely liable to spontaneous combustion, each side of work is enclosed by a barrier of coal ro yards thick.

The inside dimensions of a side of work are about 46 yards by 64 yards. The roof is supported by six pillars of coal, each being S yards square, and surrounded on all sides by 10 yards of goaf. Fig. 80 shows a side of work when finished ; it would be opened Out and worked as follows : —

Narrow gate roads, o, ir, are first driven in the bottom part of the seam, andare connected by the cross-road b. As soon as the connection is made, the coal from b to the boundary is

H making b 10 yards wide This also is done in tin; bottom 6 or 8 feet of the

Fjg. So.— aouth Hiaffordbhire square work. Seam, as is all the Opening out. Whilst this is being done, the piece of coal marked c is taken out, and the gate roads a, a are also widened out. The piece marked d is ni removed, leaving the two pillars ,?, e 8 yards square, 10 yards apart, and 10 yards from the boundaries of the side of woit Whilst this is going on in the bottom layer of coal, the upper beds are being worked at b by cutting through and droppioE the layers one by one. The remainder of the pillars are formed in a similar manner, and the coal surrounding them dropped and filled out until all has been worked except the pillars ; dams are then put in at m, w, and the side of work abandoned. Sometimes the pillars are got out by building large wood chocks between them to carry the roof.

In practice, this method is modified very greatly to suit

Special Methods Of Work.

circumstances. Often the sides of work catch fire, and have lo be closed before all the coal is worked.

The proportion of coal which is lost depends upon the nature of the roof, the depth of the seam, and the skill and e which is exercised. As a rule, only about 50 per cent, of Ae coai is got out in the first working.

Working Thick Seams by Zongi'all in Lifts. — A thick seam

of coal is always made up of distinct bands or beds, so that it

may be regarded as a series of thin seams lying close together.

The bands which form a thick seam may be worked

separately by longwall, either in descending order by working

ihe top band first, or in ascending order by commencing with

ihe bottom bed. When seams are worked by lifts in this

manner, one band may be worked over a large area, and the

strata allowed to settle before attacking the next, or the face

in one band may be closely followed by the workings in

I another. In either case the method is very similar to the

I methods adopted for working several contiguous or nearly

I contiguous coal-seams.

Eethods of working Seams lying close to- :. — When two seams lie close together, or are separated hy a thin band of dirt, the lower seam may be worked by the ordinary longwall method, and the upper seam filled out of the goaf by being dropped between the packs when the timber ii drawn. This method results in much waste, as the upper seam is left over all the packs, and, if the roof above it is not very strong, it falls with the coal and buries it.

the seams are separated by a dirt band of several feet in thickness, the lower seam may be worked first by longwall, the din between the seams being ripped down in the gates. Aiier the workings in tlie lower seam have reached their limit, the upper seam is opened out and worked back, using the same gates as were employed to work the lower bed. This method is illustrated in Fig. Si, which shows the manner by which a seam is worked where locally divided hy a dirt band, and has the following section : —

r

Coaimining.

cases the output per man is about doubled, the propoitiooBtE increase being greater in thin seams.

4. The length of face required for a given output is lessened. This reduction in pit room leads to a reduction id the cost, as the workings can be concentrated and the length of roads reduced.

Description of Machines. — The machines cut a groove in or under the coal, and at the same time propel themselves along the face. The cut is made by means of chisels filed either in a disc, bar, or chain.

Disc Machines, — Machines of this class consist of a frame

mounted on small wheels carrying a pair of engines or an electric motor. A bracket projects from the machine, and carries the cutter wheel or disc, which has chisels set in its rim. Bevel teeth are cast in the wheel, and engage with a small bevel pinion driven by the engine through spur gearing- Fig. 92 shows an end view of a disc machine as it appears when making a cut. Whilst the disc revolves, and the machine cuts, it pulls itself along the face by means of a light steel rope. This rope passes from a drum on the machine round a pulley attached to a prop set in advance, and back to the machine, so that as the rope is woimd on the drum the machine is pulled along. Arrangements are always made for varying the

Special Methods Of Work. 175

Under suitable conditions, this method works very weU.

The upper seam makes good coal, and is little damaged by

Ae working of tlie lower bed.

Warwickshire Method of working Contiguous Coal-seams, —

In the southern part of the Warwickshire coal-field, several scams are found lying very close together, being separated frara each other by only a few feet of dirt. As the coal is very liable to spontaneous combustion, headings are driven dowii to the dip, and the coa! worked backwards uphill, the goaf being allowed to fill with water. In some of the colheries, the Two Yard, Rider, Ell, and Slate coals are all worked together ; in other collieries only two or three of the seams ire worked. The method of working is as follows : —

Roads are driven to the full dip of the measures in the lowest of the seams which is to be worked. These dip roads are about 150 yards aparl, and are driven for a distance of 500 or 600 yards. After the dip headings have reached their bonndaiy, a " congate," or level cross-measures drift, is driven to intersect the whole of the seams. Levels are then driven in each seam from either side of the congate, to open out stalls in each seam, all of which are worked simultaneously. The Eices Id each seam are kept 15 or 20 yards apart, and the Bate ends are allowed to hang back as far as possible, as when they advance a new congate is required.

r

194 Coal-Mining.

cut. In some seams, if deep cuts are taken, the coe the floor lifts until the cut is practically closed ; when this is so, the labour involved in breaking the coal up may be almost equal to the labour of getting the coal by hand and the number of shots required to break up the coal increased. The usual depth of the cut is from 4 to 5 feet

Width of Cut. — The width of the cut varies from scinches up to 6 or 8 inches. In coal the width should be small, otherwise a considerable percentage of the seam is ground up inta slack. Soraetimes the seam has a band of dirt in which the machine can be arranged to hole. When this is so, the width of the cut is modified to suit the width of the band. When there is no such band, and the seam is thin, the holing should, if possible, be done in the underclay. Some machines will hole on the floor level, in which case the cut is made horizontal, but, if the machines are not adapted for holing on the floor level, the machine should be tilted as shown in Fig. 9!, otherwise the " bottoms " will have to be got up by hand all along the face.

The following are brief descriptions of some of the principal disc machines; —

The Diamond Machine. — Fig. 94 shows this machine U arranged to be driven by electric motors. Two motors ate employed, one being fixed at either end of the machine, and the disc carried by a bracket in the centre. About ten bosses are cast into the periphery of the disc, the cutters fit into boxes, in groups of three, and the boxes are secured to the bosses by a pin. This cutter-box arrangement is a speciality of the diamond machine, and has greatly reduced the time required to change the cutters. The weight of a diamond machine is from 25 to 45 ., according to the depth] of the cut it is capable of making. These machines are arranged to work in either direction, that is, along a face and back again. They are made for very deep cuts, and are very strong and well suited for holing in hard ground. A fair shift's work for a machine, when holing to a depth of 4 feet 6 inches in hard ground, is from 50 to 60 yards. Three

Timbering.

common salt and i part of chloride of lime. Timber treated by tliis process will not bum, but is slightly weakened, owing to the presence of moisture, and is also considerably increased in weight.

The weight of pit timber varies between 40 and 50 lbs. per cubic foot.

Object of Timbering. — The object of limbering is not only to keep a roof up when it is bad, but to prevent it from becoming bad when it is sound. It is often cheaper in the end to pull loose stuff down rather than keep it up with timber, though, of course, there is a limit to this. Many roofs break in the form of a natural arch, after which they stand indefinitely with little timber. Wlien this is the case, the best roads are obtained by allowing them to arch themselves over in this manner. Timber in the working places has now to be set at stated intervals, these being fixed at each colliery by special lules. In some districts it is the custom for the coal-getters to set and draw the timber in their working places ; but in other districts this is done by men specially employed for the purpose.

Props. — Props are exposed to a compressive strain; their length is usually about ten or twelve times their diameter. Thus a prop 5 feet in length would have a diameter of about 5 or 6 inches.

The strength of a prop having these proportions depends upon its sectional area, and is about ih ton per square inch. Thus a prop 6 inclies in diameter has an area of X 6 X 07854 28-27 square inches, and a breaking strain o[ 38'27 X I'j about 42 tons. If the prop is much longer than 10 diameters, its strength is decreased, as it breaks by being buckled and not by being crushed. To get the maximum strength, a prop should have flat ends, cut off square, upon which the pressure should bear evenly ; it should be set It tight angles to the pressure, and should have a cap or lid of soft wood between it and the roof. In inclined seams props should be set almost at right angles to the roof and floor ; the tops should lean uphill a little from this line, because, when

r

178 Coal-Mining.

the weight comes on, it tends to force the tops of the propsai downhill ; and if they were set perfectly square in the firsl instance, this might push them out, whereas by " undersetting them a httle, the effect of the pressure acting downhill is tc=s tighten them. To set a prop, the workman "stamps" depression into the floor with a pick, places the foot of ths prop in it, and pushes lid and prop as nearly into position he can by hand, and finally drives it up with a hammer. Thes length of the prop should be such that considerable force required to drive Jt up into position.

Chocks or Cuj.— When the pressure to be resisted is very great, chocks or cogs may be employed.

These are square pieces of timber built up two by two, placed crosswise. When used in the working faces they aie 1 built up on heaps of slack or dirt, so that they can be readily withdrawn by cutting away tbe support from underneath them. They yield at first to the pressure, but as the weight upon them increases, they become consoHdated, and will then bear an enormous pressure.

Chocks or wood packs are also used in the gate-roads of longwall collieries, being built into the packs, more especially at Che junction of one road with another.

Chocks vary greatly in size ; the smaller are built up out of timber about 2 feet long, the larger may be constructed of old railway sleepers, or of broken props or bars.

The large chocks are often partly constructed of stone, which is packed up inside them.

Bars. — A bar is exposed to a strain acting at right aoglea ' to lis length ; this is known as a transverse strain.

The strength of a bar may be calculated from the following formulae :—

W breaking load in . B breadth of bar in inches. D depth „ L length „ „

K coefiScient of rupture.

Timbering.

- when load is in centre and ends of bar are

supported but not fixed, as at A, Fig. 8i.

— I when load is in centre and ends are nxea,

as at B, Fig. 83.

0Q00_000

Fees. Bi, 33, 84. 85.

distributed and ends supported C, Fig. 84.

when load is distributed and ends fixed, ; at D, Fig. 85.

- — j— when load but not fixed, as I2KBD-

J

1 98 Coal-Miming.

disc machines the wear of the pinions and other moving parts is very heavy, and may add considerably to the cost of holing. The rails upon which the machines travel along the face hive to be very carefully set and spragged, as there is considerable thrust upon them. Disc machines, as a rule, do not cut their way into the coal, but require " wheel-holes " to be made a! either end of the face to admit the disc at the commencement These "wheel-holes" usually take the form of headings kept a yard or two in advance of the face.

With the diamond machine there is a special arrangement by which it can cut its way into the coal. The machine is placed on cross rails and set at an angle to the face, the disc is revolved, and the machine gradually pushed up to the face by screwjacks placed under the rails. The last yard or two at each end of the face has to be holed by hand, as the frame projects beyond the disc at either end,

Longwall Ear Machines.- — These are similar in general design to the disc machines, except that the disc is replaced by a bar. This bar is studded with small chisels, and revolves at a high speed. Ka the machine pulls itself along the iace the chisels revolve and cut a groove in the coal or under-

Tlte Hurd Machine. — This machine consists of an electric motor mounted on a frame and wheels, driving a bar, together with the usual propelling gear. The bar is so arranged that it can be drawn out of the cut for examination and to change the chisels ; it can also be turned right over to enable the machine to make its cut higher up in the coal. The bar makes between four and five hundred revolutions per minute; it has a spiral groove turned along it to act as a conveyor for bringing the dibris out of the cut. Between thirty and forty chisels are fitted into the bar, which, in addition to the rotary motion, has a reciprocating movement of 2 inches in and out of the cut. This prevents the bar from clogging, and helps to clear the cut. The cut is taper, and not parallel, as is the case with disc machines ; it is usually 6 or 7 inches wide at the front, and J j or 4 inches at the back. The chisels can be either set in die

TIMBERfNG. i8i

iVhen set on its broad side, with a span of 8 feet, and having ends supported and weight concentrated in the centre.

[i) When set on edge, with a span of 6i feet and having ends fixed, and weight spread along its entire length.

4Kbd'

: 14 xj 96

In this case the formula for beams having ends supported and veight in centre must be used, and as the beam is laid on is broad side, its depth is 10 inches, which has to be squared.

Fig. 86. — Filed and supported

2Kbd'

: 14 X 14

30i5"4.

In this case the formula for beams with fixed ends and load distributed applies, and as the beam is set on edge, its depth is 14 inches, which has to be squared.

These examples show that by reducing the span and fixing ihe beam to the best advantage, the strength is increased from about 29 to about 150 tons.

Three methods of fixing bars are shown at A, B, and C, Fig 87. At A the bar is supported by the sides, which are notched to receive it. Bars of this description are known as "stretchers," and can only be employed when the sides are strong. With loose sides, bars supported by props, as shown at B, are set ; if the roof is very loose, it is supported between Ihe bars by " covering wood," which consists of timber slabs

Coal-Mining.

placed longitudinally from bar to bar. " Herringbone " strutting is shown at C, Fig. 87. This form of timbering is largely employed in the main roads of sone of the Midland collieries, when the sides of the roads are sufficiently strong to afford the necessary support to the struts. The balk a is long enough to enable several pairs of struts to abut against it, thus binding the whole together. The strength of timber set in this manner is due to the fact that the struts take the greater part of their load by compression and not transversely,

Fig. 87.— a, stretcher ; B, bar ; C, herringbone slruHing.

and SO act more like props than bars. Herringbone strutting looks well and is strong, but it is rather costly to set.

Sprags and Cockcrmsgs. — During the process of holing thecoal has to be supported by " sprags," their distance aparC beiog fixed by the Coal Mines Regulation Act at not more= than 6 feet.

In seams lying at a high inclination, and in some rhickr seams, sprags do not afford sufficient protection to the metmengaged in holing, as the coal may burst off from the face slabs. To prevent this, " cockermegs " are set. Fig 88 shows sprag and " cocker " set in position. When the floor is hard a hole should be stamped in it to receive the end of the sprags which should be wedged tightly against the coaL

Timbering.

The cockermeg consists of a piece of timber a or 3 feet long {a, Fig. 88) set horizontally and wedged to the floor and roof by the sprags b and c.

Timbering Zongwali Faces, — The object of timbering longwall faces is to steady the roof, and keep a temporary road open along the faces.

The timber should be set at

regular intervals, and systematically withdrawn when no longer required, coal face is partly supported by the timber, coal itself, and it is of the greatest importance to arrange the timber in such a manner that the coal has just sufficient weight upon it to cause it to work easily.

The packs only carry the gates, they do not assist in the support of the face, because they resist no great pressure until crushed and consolidated by the weight, and this does not happen until they are some distance back from the coaL The roof gradually sinks in the goaves as the face advances, the rate of subsidence amounting in some cases to about i inch per foot, so that 10 feet back from the face the roof has sunk about 10 inches. It is impossible to resist the enormous pressure which produces this subsidence, so that if props are left in the goaves, either they or the roof around them are broken, and extra weight is thrown upon the face and timber supporting it For these reasons all props should be drawn from goaves, packs, and, wherever possible, the gates.

When working by longwall, two rows of props should he Ittpt at the face, and the back timber regularly drawn, and the roof allowed to break behind the second row. When the roof is very bad, bankbars must be set in addition to the props, to prevent the roof from breaking down between the props.

The packs should be built entirely of hard lumps, as large as can be obtained ; and special attention should be given to ihe gate-end packs, which are built from the material got from Ihe tipping.

i84 COAL-MiyiNG.

Tapered Props.— "Wiz great breakage of props which occurs at a longTiall face, especially when the floor is hard, is due to the subsidence of the roof, which inei-itably takes place as the face advances, the pressure which causes this subsidence being so great that no timber can withstand it To reduce this breakage, Mr. Hepplewhite has recently introduced the employment of tapered props.

These are ordinary props, having one end tapered down to about half the original diameter, the tapered portion being about II inches long. As the weight settles on to a prop of this description, the tapered end burrs under the pressure as the roof subsides, thus saving the prop from being broken. A prop 6 inches in diameter begins to " burr " when the pressure upon it is about i6 tons, and breaks under the same pressure as an ordinary prop of the same diameter, that is, about 40 tons. After a prop has been set, and the end become burred, it is sent out of the pit to be re-tapered ; when it can be used again, either for a thinner seam, or it maybe used for the same seam, being set with an additional lid.

Steel Girders. — Steel girders of H section are now frequently used instead of timber bars, for supporting the roof in main toads ; they are more costly in the first instance, but but much longer, and carry a greater weight with less loss of head room. They are also used in a few places for props, but they have not hitherto been adopted very widely for use at the coalface, as they are apt to get lost, and buried by falls of root The ends of steel girders used as props should be flattened; this is usually done by cutting a piece out of the web at each end, and bending the flanges over till they meet and forma flat surface. Steel props should always be set with soft wood lids on roof and floor. Cast-iron props have been tried at several places, but have not met with success, as sudden strains cause them to break without warning.

Asteelprop of H sections inches by 4inches, weighing 5olbs.

nerfoot, and 5 feet in length, has a breaking strain of nearly 100

id a similar prop, 4 inches by 35 inches, weighing 38 lbs,

ind 4 feet long, breaks with a pressure of about 70 tons.

Coal-Cutting By Machinery.

Cutting the Coal. — From two to four men are required to work a machine, three being the usual number.

The work of the machine men is to start and stop the machine when required, see that it is properly lubricated, and not subjected to undue strain, change the cutting tools when ihey become blunt, lay the rails and sprag them properly into position, set the timber at the face and clean out the cut, arrange the haulage rope, look after tlie hose-pipe or cable and make the connections when required, and attend to the many small details upon which the success of machine- cutting so much depends.

Three or four lengths of rails are required, the back length being taken up, handed over the machine, and relaid in front. As there is considerable outward thrust on disc machines, the rails should be of strong section, and securely stayed in position. The simplest form of rails are steel bars to li inches square j holes are bored through each end, and are dropped onto pins fixed on the flat steel sleepers. Flat-bottomed rails weighing from 20 to 36 lbs. per yard are commonly employed ; they are carried by sleepers made of dished steel fitted with projections to hold the bottom of the rails.

Motive Power. — Coal-cutting machines are driven either by electricity or by compressed air ; at the present time compressed air is the more common motive power, but electricity is rapidly gaining ground. The advantages of electricity are that it is the more efficient, and therefore the more economical in steam ; and that the cables along which it is conducted are more convenient than air-pipes. On the other hand, compressed air has advantages which go a long way towards making up for its lower efficiency, and more inconvenient conductors. It is absolutely safe in an explosive atmosphere — which electricity is not. Tlie engine is cheaper, lighter, and simpler than the motor ; moreover, it will stand rough usage better, and is more readily repaired by the men and with the appliances usually found at collieries.

Cost of Machine Holing. — The cost of the machines varies from about to about each, including accessories,

longitudinal centre-piece against which they abnt being of timber.

Masonry. — Pit-bottoms and important main roads are frequently lined with brickwork ; brick arches, though costly, making the best permanent lining that can be obtained, but of recent years girders placed upon brick side walls have been often used as a substitute.

If girders become bent or broken, they can be replaced without much difficulty, but if an arch becomes crushed, it has to be taken out and rebuilt, which is rather a serious matter. The simplest form of arch consists of two vertical side wails carrying a semi-circu!ar, or elliptic arch ; but this construction is weak, as tiie side walls can be pushed in with a moderate pressure. All arches should be constructed so as to he subjected to a compressive strain ; a perfect circle would be the strongest form of arched road, but could not be employed owing to the large area of waste space. Unless the floor is very strong, an inverted arch should be turned at the bottom of tlie road, which, together with the main arch, forms a complete lining of brickwork. The brickwork should on no account be set to touch the strata, but should be separated from it by a space of a few inches, which should be tightly packed with sand.

Fig, 90 shows an arch suitable for a double road. It wDl be noticed that it has no straight walls, and that the result of weight upon it would be to compress the bricks, which must be crushed before the arch can give way. The crushing strain of good hard red bricks is about 3000 lbs, per square inch. Courses of wooden blocks, similar in size and shape to ordinary bricks, are sometimes built into arches ; being softer than bricks, they are compressed before sufficient pressure is applied to the arch to break the bricks.

To put in a length of arching similar to the one shown in Fig. 90. The ground is first got out for a short length, the main timbers used to temporarily support the excavation being arranged longitudinally instead of across the road. The floor is then dressed with picks to the shape of the invert, and a

Timbering. 187

layer of sand a few inches thick is laid upon it. The brickwork is then laid upon the sand, being kept in the correct shape by means of a wooden template.

The brickwork is carried up in independent rings ; thus an aich 14 inches in thickness would be constructed of three separate rings of bricks with no bond between them. After the invert is laid, the main arch is carried up, the sides being built by the aid of a template, and the crown upon centres. The centres maybe constructed either of timber or iron; in the figure, one of the iron centres, a, is shown in position. The laggings b, b are carried by the centres, and the brickwork is built up on them. All the rings of brickwork must be

Fig. 90. — Arch for double road. Fig. 91. — Spiling ihrongh loose ground.

carried up from both sides simultaneously to equalize the weight upon the centres, the inner rings being kept a course or two in advance. As the top of the arch is reached, short langs, known as blocking lags, are fixed at right angles to the main lags, and the few courses at the crown of the arch are built up on them. The whole of the timber used to support the excavation must be drawn out as the arch is built, and the space between the walls and strata should be filed in with sand. Arches should not be put in unless the road is perfectly settled, Otherwise they may be broken and have to be taken out and rebuilt.

Timbering through Loose Ground.- — Special means are required to drive roads through very loose ground. Fig. 91

Coal-Mtning.

shows the method of spiling or poling which is usually adopted for passing through very loose or wet ground, such as is sometimes met with when scouring through faulty ground, goaves, ot very heavy falls, a, a are props carrying the bars b ; over the bars, the boards c are driven in advance, and are 5 or 6 feet long and i inch thick. These boards are driven into the loose material, as shown, a portion of it is excavated, and another prop and bar set.

Tlie Courrih-es System of Timbering. — This method of timbering is in use at the large Courrieres collieries, which are situated near Lens, in France.

The death-rate from falls of ground at Courriferes during the ten years prior to 1899 was o'i5 per thousand persons employed underground, whereas in Great Britain the death-rate was 079 per thousand during the same period. The attention of the British coal-owners was called to this, in 1900, by a circular letter from the Home Secretary, and the question of adopting a similar method in England was discussed. The chief features of the method are : (i) The whole of the working places are timbered systematically; (2) each workman is supplied with three iron bars, each about I5 inch square and 4 feet 3 inches long, which he drives over the last bar to form a temporary shield in advance of tie timber.

The main bars are set in rows parallel to the face, the rows being 3 feet g inches apart. Each of these main bars is about 8 feet long, and is supported by three props. Smaller bus rest on these main bars, being fixed at right angles to them, and spanning the space between the rows. These smaller bars are placed about 12 inches apart. When the workman has cut away about 12 inches of coal in front of him, he drives the iroi bars over the main bars towards the face, to form a temporary support.

The iron bars are held in position by wedges from the back, and are driven forward as the face advances, being never more than 8 inches behind the coal. By this method every square foot of the roof is always supported.

COAL-CUTTING BY MACHINERY. zoj

to the percussive machines already described, except that it does not run on wheels, but is mounted upon a supporting column. It can be used either Tor shearing, holing, or drilling Ehot-holes, and, being light and portable, is suited for driving ngs. Fig. 98 shows a plan of this machine as arranged fcr holing, a is the vertical supporting column, which is iBcrewed tightly between roof and floor; it carries the machine ily means of a sleeve, which can be fixed at any height upon ithe column. The toothed segment h is carried by a bearing on the sleeve, and is so arranged that it can be turned Sorizontally, as shown in Fig. 98, when holing is to be done,

ing macbini

] ot vertically when a shearing is to be made. The machine can be swung through the arc of a circle by turning the handle which acts on the segment b. The bit strikes about 350 Hows per minute, and is advanced into the coal or stone by [turning the handle i/, which moves the whole machine forward Wn the column. After the machine is set up, compressed air ps admitted into the cylinder, and the bit commences to strike Bhe coal ; as it does so, the handle c is slowly turned, causing fthe machine to gradually move round, so that instead of [drilling a hole, it cuts a groove. After the machine has been ing through the width of the cut to g in figure), the d-3crew is advanced, and it is swung back again by reversing ; handle c Each cut is in the form of the segment of a

Chapter Xvi.

Coal-Cutting By Machinery.

The employment of coal-cutting machines lias increased] greatly during the laat few years ; this has been brought by the scarcity of labour and the approaching exhaust the best seams at many collieries. The following statenieiil. shows the number and type of the machines now in use in Great Britain (1903) : —

Tons of coal got by machines (1903)

Total number of machines in use

Machines driven by compressed

Machines driven by electricity .

Disc machines

Pick machines

Revolving bar machines ...

Rotary heading

Chain machines

Class not stated 3

Over one-half of the total output of machine-cut coal was obtained from Yorkshire and the Midlands.

At many colheries coal-cutting machines have been iutioduced and abandoned after a short trial, whilst at other places they are largely used, and are an unqualified success. Theit success or failure depends upon the suitability of the seam fw machine work, and possibly even more upon the skill and resolution of the management. Like all innovations, much trouble is usually experienced in the early stages, and it metiraes happens that they are given up before these initial

sullies have been overcome.

Coal-Cutting By Machinery.

Coal-cutting machines may be divided into three classes — 1. Machines designed to hole the coal in longwall faces. I. Heading machines,

J, Machines that can be used either for headings, for longirall faces, oi for short banks, as in pillar and stall.

Machines for holing Longwall Faces. — These machines have the greatest chance of success wlien working ID thin seams which are expensive to get by hand. If the getting price of hand-cut coal is low, little saving in cost can be efTected by machines, though they may be of advantage by increasing the proportion of round coal. It is desirable, though not absolutely essential, that the roof should be good and the inclination not excessive. The roof is often found to improve when the coal is worked by machines, owing to the quicker and more regular advance of the faces. The seam should be fairly free from faults, as a considerable length of

in face is necessary for efficient working.

Advantages of Machine Holing. — The advantages attending the employment of holing machines, under suitable conditions,

. More round coal is made. Under average conditions abotit 10 per cent more round coal is made. This may be a matter of the greatest importance, but, if the slack is of value for coking and other purposes, the advantage may not amount lo much. The increase in round coal amounts to much more ) per cent, in some cases, as, for example, when a seam 18 thin and hard, and holing has to be done in the coal by baod, whilst by machines it can be done in the under-clay, or iliUit band.

The cost of getting the coal is somewhat reduced, e zeductioii in cost, under favourable conditions, averages about bd. per ton, or probably less when consumption of sleanij interest on capital, and depreciation of plant are carefuiJy accounted for. The cost depends upon the nature of the seam, and upon the bargain which can be made with the men. . The output per man employed is increased. In many

J

Coai.M/Ning.

cases the output per man is about doubled, the ptopc increase being greater in thin seams.

4. The length of face required Tor a given output is I lessened. This reduction in pit room leads to a reduction in the cost, as the workings can be concentrated and the length of roads reduced.

Description of Machines. — The machines cut a groove in or under the coal, and at the same time propel themselveB along the face. The cut is made by means of chisels fixed either in a disc, bar, or chain.

Disc Machines. — Machines of this class consist of a faint

mounted on small wheels carrying a pair ot engines ( electric motor. A bracket projects from the machine, ani carries the cutter wheel or disc, which has chisels set in its rim. Bevel teeth are cast in the wheel, and engage with a. small bevel pinion driven by the engine through spur gearing. Fig. 92 shows an end view of a disc machine as it appears when making a cut. Whilst the disc revolves, and the machine cuts, it pulls itself along the face by means of a light steel rope. This rope passes from a drum on the machine round a puliey attached to a prop set in advance, and back to the machine, so that as the rope is wound on the drum the machine is pulled along. Arrangements are always made for varying the

Coal-Cutting By Machinery.

speed of the machine's advance lo suit the material it has to cut. Fig. 93 shows one form of propelling gear, o is a spur wheel, driven from another spur wheel, b. a also serves as a crank with adjustable throw. The crank pin is carried by a slot, along which it can be moved. In the figure the crank pin is at the end of the slot, and has its maximum throw. To reduce the length of the crank, the pin is moved along the slot nearer to the centre of the wheel. The connecting rod e drives the ratchet lever r, and, as the ratchet lever is much longer than the crank, the lever vibrates to and fro, but does not rotate, rf is a ratchet pawl, wh ich drives the ratchet wheel k. As e vibrates it catches the teeth in the ratchet wheel and puUs it round, whilst the check pawl / prevents the ratchet

Fig. 93.— Propelling gear for coal-culter.

wheel from running back. If the throw of the crank is at its maximum, as shown in figure, the paw! catches several teeth and the drum revolves at top speed ; but, if the throw is reduced, the length of stroke of the ratchet is also reduced, so that it does not catch as many teeth in the wheel, and therefore pulls the drum rou.-d more slowly. The drum g is driven by spur gearing on the raithet wheel.

Depth of Cut. — The depth of cut varies from about 3 feet 9 inches up to 7 feet. Deep cuts are of advantage in some seams, as fewer cuts are required for a given output, and* in some cases the number of shots is reduced. It is also claimed that, by having deep cuts, the roof at the face is not broken, as the distance between the breaks is equal to the depth of the

COAL-MfNING.

In some seams, if deep cuts are taken, the coa the floor lifts until the cut is practically closed ; when this is so, the labour involved in breaking the coal up may be almost equal to the labour of getting the coal by hand and the number of shots required to break up the coal increased. The usual depth of the cut is from 4 to g feet

Width of Cut. — The width of the cut varies from inches up to 6 or 8 inches. In coal the width should be small, otherwise a considerable percentage of the seam is ground up into slack. Sometimes the seam has a band of dirt in which the machine can be arranged to hole. When this is so, the width of the cut is modified to suit the width of the band. When there is no such band, and the seam is thin, the holing should, if possible, be done in the underclay. Some machines will hole on the floor level, in which case the cut is made horizontal, but, if the machines are not adapted for holing on the floor level, the machine should be tilted as shown in Fig. 92, otherwise the " bottoms " will have to be got up by hand all along the face.

The following are brief descriptions of some of the principal disc machines : —

The Diamond Maehine.~~¥ig. 94 shows this machine as arranged to be driven by electric motors. Two motors are employed, one being fixed at either end of the machine and the disc carried by a bracket in the centre. About ten are cast into the periphery of the disc, the cutters fit into boxes, in groups of three, and the boxes are secured to the bosses by a pin. This cutter-box arrangement is a speciality of the diamond machine, and has greatly reduced the time required to change the cutters. The weight of a diamond machine is from 25 to 45 ., according to the depthlof the cut it is capable of making. These machines are arranged to work in either direction, that is, along a face and back again. They are made for very deep cuts, and ate very strong and well suited for holing in hard ground. A r shift's work for a machine, when holing to a depth of feet 6 inches in hard ground, is from 50 to 60 yards. Three

COAL-CUTTING BY MACHfNERY.

men are employed to work the machine. When driven by electricity, two motors are employed, one being fixed either end. The disc revolves at about fifteen or twenty revO' lutions per minute.

Rigg-and-McikUjohn. — This naachine is more suitable [ holing in coal than in underclay.

The disc revolves very rapidly (from sixty to eighty revolu- I lion per minute), and is provided with bosses to carry twelve I cutters, but in some cases only six are employed. When so cutters are used, and the speed is so rapid, the effect of

a. H

J. 94. — Diamond ooal-cutting machine.

ters is percussive, that is,, they strike a series of blows, I most machines the action is more like that of b

Machines of this class are driven by compressed air. Each machine has a pair of cylinders about 8 inches in diameter. They are placed side by side at one end of the frame, and the disc is carried by a brackefat the other end. The propelling gear consists of a ribbed drum driven by gearing from the eiig;ine, A g-inch chain is secured to a prop in advance of the machine, and makes three or four turns round the drum.

COAL-MimNG.

The man who holds the chain in his hand can regulate tiie:, speed of advance whilst the speed of the drum remains constant, by slackening the chain and allowing it to slip on the drum.

The bearings in which the wheels run are carried by screws, which can be raised or lowered at will, to enable the disc to adapt itself to any inequalities in the floor. The cut is usually from 2 feet 9 inches to 3 feet 6 inches deep, and the advance is extremely rapid, over 200 yards per shift being holed at some collieries. It is a very simple and strong machine, can run both ways, and for holing in the coal is equal to any machine on the market.

The Gillot-and-Copy Machine. — This machine is arranged to work by compressed air. It has two cylinders fixed side by side at one end of the frame, and the disc is carried by 3 bracket at the other end ; the depth of cut is usually from 3 to 4 feet. The propelling drum is driven by a ratchetwheel ; the rope from the drum is taken round a pulley fixed to a prop set in advance, and back to a bridle fixed to the front of the machine. This bridle carries two pulleys, which run on each side of the outer rail and resist the thrust of the machine. The disc is fitted with about 25 teetli, and makes six or seven revolutions per minute.

These machines weigh about 20 . ; they make the cut above the level of the rail.

The Jeffrey Disc Machine. — This machine is made to be driven either by electricity or compressed air. The engines or motors are at one end of the frame, and the disc at the other. The special features are—

1. It runs on one rail only, the thrust being taken by spragging the rail to the roof with a light screwjack. By having only one rail, more room is available for shovelling away the debris.

2. It cuts on the floor level. (Several other machines are arranged to do this.) '

3. The disc may be adjusted by a hand-wheel.

4. The advance motion can be stopped or started without

Coal-Cutting By Machinrry,

stopping the disc. This is a great advantage, as, when the

disc jams, the feed can be stopped, thus giving the disc a

much better chance of clearing itself.

g. Three rates of cutting are provided, 8, i6, and 25 inches

per nainute.

6. The machine is driven from the front, and will run either

way.

Clarke-atid-Steavenson' s Mathiiie. — This is an electrically driven machine, and is largely used in Yorkshire and elsewhere. A steel frame carries a motor at one end and the disc at the other. The disc is driven through spur and bevel gearing ; the depth of cut is from about 3 feet to about 5 feet. The motor is of the enclosed type, and of 25 30 horse-power, and the weight of the whole machine is about 40 .

Comparative Advantages of Disc Machines. — At the present time disc machines are by far the most popular. The table on page 190 shows that more than So per cent, of the machines of all classes working in Great Britain in 1903 belonged to this type. Notwithstanding the fact that they are used to such an extent, disc machines have considerable disadvantages. The discs take a large amount of driving power, the stuff made by the chisels is dragged round with the disc, greatly increasing the friction; this is especially the case when the machine is holing in a band of coal or dirt which is rather wider than the cut For example, if the cut is 6 inches wide, and the stratum in which the cut is made is 10 inches thick, it is probable that the extra 4 inches will be dislodged, and the additional material greatly impede the rotation of the disc. When the coal is lender, large masses may be shaken by the vibration and fall or "sit " on the disc, causing frequent delays, and even rendering machine cutting impossible. Discs, too, are very heavy and bulky, so that, when the machines have to be "flitted" from one end of the face to the other, the cost and inconvenience is considerable.

Large discs are always made in halves bolted together, so

that they can be removed in two pieces. In some types of

igS COAL-MMING.

disc machines the wear of the pinions and other moving parts ' is very heavy, and may add considerably to the cost of holing. The rails upon which the machines travel along the face hive to be very carefully set and spragged, as there is considerable ,i thrust upon them. Disc machines, as a rule, do not cut Ibdr way into the coal, but require " wheel-holes " to be made at either find of the face to admit the disc at the commencement. These " wheel-holes " usually take the form of headings kept a yard or two in advance of the face.

With the diamond machine there is a special arrangement by which it can cut its way into the coal. The machine is placed on cross rails and set at an angle to the face, the disc is revolved, and the machine gradually pushed up to the fiice by screwjacks placed under the rails. The last yard or two at each end of the face has to be holed by hand, as the ftame projects beyond the disc at either end.

Longwall Bar Machines. — These are similar in general design to the disc machines, except that the disc is replaced by a bar. This bar is studded with small chisels, and revolves i at a high speed. As the machine pulls itself along the &ce the chisels revolve and cut a groove in the coal or underday.

Tlic Hurd Afadiifif.—This machine consists of an electric motor mounted on a frame and wheels, driving a bar, together with the usual propelling gear. The bar is so arranged that it can be drawn out of the cut for examination and to change the chisels ; it can also be turned right over to enable the machine to make its cut higher up in the coal. The bar makes between four and five hundred revolutions per minute ; it has a spiral, groove turned along it to act as a conveyor for bringing the tiib/7s out of the cut. Between thirty and forty chisels are fitted into the bar, which, in addition to the rotary motion, hiS a reciprocating movement of 2 inches in and out of the cut- This prevents the bar from clogging, and helps to clear the cut - The cut is taper, and not parallel, as is the case with disc machines ; it is usually 6 or 7 inches wide at the front, and 3 or 4 inches at the back. The chisels can be either set in the

COAL-CUTTIiVG BY MACHmRRY. 199

lOve or on the spiral, so that the width of the cut can be slightly varied. The speed of the drum can be varied by cam acting on the rachel pawls.

The bar can be swung through a horizontal angle of 180 degrees without throwing it out of gear. Owing to this arrangement the bar can be made to cut its way into the coal at the commencement of the hoUng.

These machines are made in the following sizes : —

I. To cut up to 3i feet in depth, weight about 20 . ; H.P. of

1. To cut up to 4i feet in depth, weight about 30 . ; H.P. of

3. To cut up to 6 feet in depth, weight about 45 . ; H.P. of

The Lee Machine, — In this machine the cutting tool consists of a steel band wound spirally around a taper bar. The band lias forty or fifty teeth cut in it, the advantages claimed being that the band is much more quickly changed than a set of chisels, and forms an efficient conveyor to clear the debris from the cut Another speciality is the manner in which the machine propels itself along the face, neither drum nor rope bemg employed. It runs on two rails, one of which is in the fonn of a rack ; a toothed wheel on the machine engages with this rack and drags the machine along. The rails are kept in position by being spragged from the roof. This machine can cut its way into the coal, and the bar can be raised or lowered within limits, to make the cut in the position best adapted for the seam in which it has to cut.

Comparative Advantas of Bar Machines. — Although bar nudiines are not very greatly used at the present time, they possess several advantages over machines of the disc type, and thrii employment will probably become more general. The bar is light and handy, and no great area is exposed to friction ; iieace bar machines require less power to drive them, and are not subjected to the great variations in load which are found in disc machines. Sprags can be set close up to the edge of Hie cut, and the machines cut their own way into the coal, so

2i8 COAL-MINING.

powers : — That the force applied multiplied by its motion equals force transmitted multiplied by its motion.

By increasing the number of sheaves or pulleys in each set of blocks, the mechanical advantage can be multiplied to any extent

In b. Fig, 103, two sheaves are shown in each block. The rope is fixed to the upper block, and taken round the pulleys as shown ; in this case there are four ropes carrying the load, so that the power applied at the loose rope is multiplied by four, and the space moved through by P is divided by four. In practice the sheaves in each block are placed side by ade on the same spindle to make the arrangement more compact

The mechanical advantage of a set of pulleys equals the number of ropes leading from the bottom blocks. Taking the pull on rope at 150 lbs., in the arraogeinent shown at a (Fig. 103) the weight raised would be 150 X 2 300 lbs, ; in b, 150 X 4 600 lbs.; in each case neglecting friction and the weight of ropes and bottom blocks.

The Inclitied Plane. — The inclined plane is employed for raising bodies from one level to another. It may be inclined at any angle to the horizontal, and the inclination may be expressed either in degrees or by the relative proportions of height and base.

Thus, a plane is said to have a gradient of i in 10 when the rise or fall is i foot vertical for every 10 feet measured horizontally.

The power required to push or pull a body up an inclined plane, when the power is applied in a direction parallel to the plane, bears the same proportion to the weight as the height does to the length of the plane.

For example, find the strain on a hauling rope when pulling a load of 12 tons up an incUne dipping i in 4. The strain on rope bears the same proportion to iz tons as the length of tli

plane bears to the height, so that it will be la x — The

height and base are both given, but the length of the plane (hypotenuse) must be calculated. (For moderate inclinations

Lj

Coal-Cutting By Machinery.

plates, and is driven by the sprocket wheel c, which is driven by the motor, and passes round a wheel at the end of the jib. The jib is free to swing right round the end of the machine, this movement being conlroUed by gearing (not shown in the figure) to enable the machine to cut its way into the coal. The machine does not travel along the face on wheels, but upon a pair of iron plates or sledges. It can be raised or lowered on these sledges by means of the four screwjacks, d, d, which are worked by worm-wheels driven by the motor. In order to keep the machine up to the face, the jib is set at an acute angle to the frame when making a cut, as shown in sketch. The iron fender e prevents the machine from being dragged into the coah This arrangement does away with the trouble of laying rails along the face, and saves a couple of inches of height, but more power is required to pull the midline along. The newer machines are being made with a plough blade to take the outer thrust by cutting a groove in the floor. The propelling gear consists of the vertical drum,/, and guide wheels. The end of the rope is led round the fixed pulley and back to the jib, so that the cutters have a direct pull against the coal. The drum is driven through a friction clutch, and can be thrown out of gear without stopping the chain. The cutters are secured to the chain by set-screws, and are splayed out to make the cut sufficiently wide to admit the jib. The ordinary width of the cut is about 45 inches.

Working Coal by Machines. — There are two general principles upon which the working of coal-cutting machines can be arranged.

1st. By having a considerable length of face along which several machines work, cutting from one end to the other, and being " flitted " or moved back when they reach the end of the face.

snd. By having a short length of face for each machine, dong which it travels backwards and forwards, cutting both ways, the whole length of face being cut every night, and all the coal filled out during the day.

The first of these methods is the more generally adopted, the

igfaidaiAasmatABij'kBgsall, except that the fiKC BMKt be ibanlKc tfiah and good road pionded for "fitnag'dttMxftiDeboiHfMeei Id tiie other, .inordinary cioss-te sores Ike |iptM bat it sboold be laid out with a view to puj ii JiDg a aad taof joamer for the machines. One advantage of Ois ncAod is Aat tbe Was. can be kept a Iitde in adfancc of die liim i, so Aal there need be no on acconnt of tbe coal not being got out of the way of Ac tnaAi*, adnntc is diat tbe cat can be made of any desired dqNfa, and, as two or twice shifts can be spent in getting oat the ooal, die gates can be set ottt a fair distance apoit.

In tbe second, or bact-&ce method, more coal is obtained from a giren Iei;tia of boc, hence die vorkings can be conceniraEed and the &ces advance Teiy quickly ; but the gates must be dose together and the cot not very deep, otherwise It will be fbmid impomibk to get the whole of the coal out during the day shift. The cost of ripping ihe gales is very high by this method. Id practice it is found that the gates must not be more than aboot 15 yards apart, and the holing not more than about 3 feet in depth in a seam 3 feet in thickness. If this system is to succeed, (he discipline must be veiy good, and arrangements most be made for both fillers and machine men to stop at their work until all the coal is got out on the one shift and all the face cut on the other.

Timhering. — Machines require a width of about 4 feet from the face clear of props.

If the roof is good, props are set in rows, the first rowbeing about 4 feet from the face. Eich prop is provided with a long lid or plank to reduce the width of unsupported roof. If the roof requires the support of bars, one end of the bar rests on props, and the other is let into the coal, as shown in Fig. 92. When the coal is cot sufficiently strong to carry one end of the bars, longitudinal bearing bars are set against the face to carry the ends of the short bats instead of the coal. The props which carry these bearing bars are removed immediately in of the machine and reset behind it.

COAL-CUTTLVG Br MACHINERY. zoj

Cutting the Coal. — From two to four men are reiiuired to work a machine, three being the usual number.

The work of the machine men is to start and stop the tnichiae when required, see thai it is properly lubricated, and not subjected to undue strain, change the cutting tools when ihey become blunt, lay the rails and sprag them properly into position, set the timber at the face and clean out the cut, arrange the haulage rope, look after the hose-pipe or cable and make the connections when required, and attend to the many small details upon which the success of machine- cutting so much depends.

Three or four lengths of rails are required, the back length being taken up, handed over the machine, and relaid in front. As there is considerable outward thrust on disc machines, the tails should be of strong section, and securely stayed in position. The simplest form of rails are steel bars to ij inches square ; holes are bored tlirough each end, and are dropped on to pins fixed on the flat steel sleepers. Flat-bottomed rails weighing from 20 to 36 lbs, per yard are commonly employed ; they are carried by sleepers made of dished steel fitted with projections to hold the bottom of the rails.

Motive Power. — Coal-cutting machines are driven either by electricity or by compressed air ; at the present time compressed air is the more common motive power, but electricity is rapidly gaining ground. The advantages of electricity are that it is the more efficient, and therefore the more economical in steam ; and that the cables along which it is conducted are more convenient than air-pipes. On the Other hand, compressed air has advantages which go a long way towards making up for its lower efficiency, and more inconvenient conductors. It is absolutely safe in an explosive atmosphere — which electricity is not. The engine is cheaper, lighter, and simpler than the motor ; moreover, it will stand rough usage better, and is more readily repaired by the men and with the appliances usually found at collieries.

Cost of Machine Holing. — The cost of the machines v frora about to about each, including accessories,

Coal-Mining.

machines driven by compressed air being the cheapest. The cost of cutting is between and (>d. per ton ; in some places the cutting is let by contract, and at others the machine men are paid by the shift. The cost of steam, interest on capital, depredation and repairs, amounts to about 6jf. per ton on the

Heading Machines.— The only machine now used exclusively for heading is the Stanley heading machine. It consists of a narrow frame carrying a pair of vertical engines which drive a central shaft through suitable spur gearing. The shaft carries a heavy casting upon which a pair of arras arc bolted, cutlers are attached to the arms, and, as the shaft is revolved by the engines, an annular space is cut around a central core, making a perfectly circular road. The core is wedged down and removed by hand in some of the machines, but in others it is cut up by the machine, and the pieces are elevated and deposited in the pit tubs by a conveyor. The central shaft, which carries the arms and cutters, has a thread cut upon it, so that it is slightly advanced at every revolution. The machine is held up to its work by screws which are forced into the roof, and, for ease in moving back, it is carried on wheels. In thin seams duplex machines may be employed, which cut out two circles side by side ; or a single machine may cut out one circle, and another follow it up and cut out another circular road alongside the first, the triangular pieces next roof and floor being subsequently removed by hand.

These machines will drive a heading at the rate of about I yard per hour, but for regular work the rate of progress is about 4 to 6 yards per shift

Machines for Use either for Headings or Banks.

— Machines of this class are largely used in America, where the pillar-and- stall melliod of work is almost universal. They are also used to a limited extent in England for driving headings, and in a few places for getting the coal in pillar-andstall workings, or in longwall faces.

Coal-Cutting By Machinery.

Sos

The Jeffrey Chain Machine. — This is a breast machine, making its cut straight in front, and being moved along by hand after each cut. An outline of the machine is shown in Fig. 96. The bed frame a is stationary, and is held in position close up to the face by the screw b. The sliding chain cutter frame c works between the side girders of the bed france, and is racked forward as the cut advances, d is the electric motor (air-engines may also be employed) which is attached to the sliding frame, and moves with it upon the bedframe. The cut is made by chisels fixed to the endless chain. When the machine is making a cut, the sliding frame is gradually racked forward, and at the same time the endless chain which carries the chisels is driven round and round the

Fig. 96.— Jeffrey chain machine.

sliding frame, and so cuts its way into the coal. After the sliding ftatne has advanced its full length, it is run back by the engine, and the whole machine is moved along the face, and secured by screws ready for the next cut. The drawbacks to the employment of this machine for longwall work are its great length, making the timbering of the stalls very awkward ; and the labour involved in sliding it along by hand. This litter is lessened by allowing the back of the machine to rest upon a rail or skid-board. For coaveyance from one place to another, when used in headings or short banks, the machines may either be placed on trolleys, or mounted on wheels. Self-propelling trolleys are made, the wheels being actuated by 'the motor through chains. These machines are made lo cut 5, 6, or 7 feet in depth, the width of each cut being

Coal-Mining.

44 inches, and the height takea out by the cut about 4

inches.

Percussive Machines. — These machines are of American origin, the three types principally used being the Harrison, Ingersoll — Sergeant, and Yoch. They have been tried at several collieries in Great Britain, but have not met with any great success. It has been found difficult to get men to work them ; men new to the work suffer from the great vibration, but they are said to get over this with a little practice.

Fig. 97 shows a machine of this class as it appears when at work. It consists of an air-cylinder, a, from 4 Co G inches in diameter, mounted on vrheels, and provided with a pair of handles, b. The chisel c is attached to the piston-rod of the aircylinder, and is driven rapidly backwards and forwards, striking a heavy blow forwards, and being forced lightly backwards against an air - cushion. The machines are really rock-drills mounted on wheels. When at work they are placed on sloping timber platforms (d in figure). They are steered by the operator, who sits on the platform and directs the blows of the chisel with hards and feet. The recoil is taken by the slope of the platform, and, in some of the larger machines, by an automatic brake. The average amount undercut is about 50 square yards per shift. For making vertical cuttings a similar machine is employed, but it is mounted on larger wheels. The great advantage of these machines is in their portability, as they can very readily be moved from place to place. They weigh from 7 . to 10 ., and cost about ,;ioo each.

The Champion Coal-cutter. — This machine is very similar

Fig. 97. — Ingersoll machine.

Cutting By Machinery.

to the percussive machines already described, except that it does not run on wheels, but is mounted upon a supporting column. It can be used either for shearing, holing, or drilling shot-holes, and, being light and portable, is suited for driving headings. Fig. 98 shows a plan of this machine as arranged for holing, a is the vertical supporting column, which is screwed tightly between roof and floor ; it carries the machine by means of a sleeve, which can be fixed at any height upon the column. The toothed segment b is carried by a bearing on the sleeve, and is so arranged that it can be turned horizontally, as shown in Fig. 98, when holing is to be done.

Fig. 9B.— Champion coal-culling machine,

or vertically when a shearing is to be made. Tbe machine can be swung through the arc of a circle by turning the handle f, which acts on the segment b. The bit strikes about 350 blows per minute, and is advanced into the coal or stone by tuning the handle d, which moves the whole machine forward on the column. After the machine is set up, compressed air is admitted into the cylinder, and tbe bit commences to strike the coal ; as it does so, the handle e is slowly turned, causing the machine to gradually move round, so that instead of drilling a hole, it cuts a groove. After the machine has been swung through the width of the cut (/ to g in figure), the feed-screw is advanced, and it is swung back again by reversing the handle c Each cut is in the form of the segment of a

2o8 COAL-MINING.

circle, as shown in figure. When the feed has reached its limit, the machine is run back, and an extension rod added between the piston rod and the bit The width of the cut is about 3 or 4 inches, and die depth may be as much as 9 feet ; machine and supporting column weigh about 5 or 6 ., and cost about;£'ioo.

Work is said to be done when a force acts tlirougli a space overcoming resistance.

The British unit of weight is the pound, and of length the foot, and the unit of work is the foot-mind, which is the amount of work required to raise a weight, or maintain a pressure of i lb., through a space of i foot, so that —

Foot-pounds force exerted in pounds multiplied by space in feet through which the force is exerted.

Example, — How many foot-pounds of work are done in raising a ton of coal up a shaft 400 yards deep ?

Force weight raised 2240 lbs, and space through which it is raised 1 200 feet Then foot-pounds 2240 x laoo 2,688,000

The power exerted in raising the above cannot be estimated unless the time occupied is known. Obviously, it would take ivoy much more powerful engine to raise the coal in i minute diM in 10, hence power is the measure of the rate at which iiiwi u done. The measure of power is the number of footpounds per minute.

If the coal in the example given above were raised in of a minute, the power exerted in foot-pounds per minute would Ik 1,638,000 3,584,000,

In order to facilitate the expression of power without the "K of such large figures as foot-pounds per minute, Watt

2Io Coal-Mining,

adopted a unit of power which he called the " horse-power, and this is now generally employed by engineers.

One horse-power is the power necessary to perform 33,000 foot-pounds of work in one minute, or —

Foot-pounds per minute

Hence the H.P, in the example given above is—

J =184000

The horse-power of a steam-engine is obtained by the following formula; —

where P effective pressure in lbs. per square iach on piston. L length of stroke in feet, A area of piston in square inches. N number of strokes per minute.

The following example shows the manner in which this formula is arrived at : —

Find the horse-power exerted by an engine having a cylinder 18 inches in diameter by 3 feet stroke, when making loo strokes per minute and having an average pressure on the piston of 45 lbs. per square inch,

The area of the piston is found by squaring the diameter and multiplying by 07854; thus the area is —

18 X 18 X o'7854 254"47 sq. inches

As the pressure per square inch is 45 lbs., the total pressure on piston is 254"47 X 45 Iii45'i5 's.

The length of stroke is 3 feet, and the number of strokes per minute is 100, so that the distance the piston moves per minute is 3 X 100 300 feet.

Mechanics.

IVz. foot-poimds exerted per minute are 11,451 '15 X 300 3,435,345, because the piston is subjected to a pressure of "i4S''iS travels under that pressure through a space of 300 feet As 33,000 foot-pounds per minute make i horse-

Condensing the above, we get —

45 X 3 X 354-47 X ]

I04-I

The energy transmitted by any machine is partly spent in doing useful work, and partly in overcoming frictional and other resistances.

The modulus, useful effect or efficiency of a machine is the

proportion of the energy expended which is converted into

r , , , , useful work done . ,

useful work and equals . , Efficiency may be

expressed as a fraction, or, as is more usual, as a percentage. ICfor example, an engine exerted 270 horse-power, and accomplished useful work to the extent of 180 horse-power, the efficiency would be 57 5, or, expressed as a percentage,

iSo X 100 ,,,

—- 665 per cent.

The horse-power developed in the cylinder of an engine is bown as "indicated horse-power" (written I.H.P,), because the average steam pressure from which it is calculated is obtained by the aid of an indicator (see Chapter XVIII.). The actual horse-power available is known as the " brake horse-power" (written B.H.P,), and is arrived at by means of a dynamometer, or brake, arranged to absorb the power given off from a pulley.

The Mechanical Powers. — There are several mechanitil appliances by which either force applied through a given (distance is altered to a greater force moving through a correspondingly smaller distance, or they may operate in such a

Coal-Mjning.

machines driven by compressed air being the cheapest. The cost of cutting is between and (>d. per ton ; in some places the cutting is let by contract, and at others the machine men are paid by the shift. The cost of steam, interest on capital, depreciation and repairs, amounts to about dd. per ton on the coal cut.

Heading Machines. — The only machine now used exclusively for heading is the Stanley heading machine. It consists of a narrow frame carrying a pair of vertical engines which drive a central shaft through suitable spur gearing. The shaft carries a heavy casting upon which a pair of arms are bolted, cutters are attached to the arms, and, as the shaft is revolved by the engines, an annular space is cut around a central core, making a perfectly circular road. The core is wedged down and removed by hand in some of the machines, but in others it is cut up by the machine, and the pieces are elevated and deposited in the pit tubs by a conveyor. The central shaft, which carries the arms and cutters, has a thread cut upon it, so that it is slightly advanced at every revolution. The machine is held up to its work by screws which are forced into the roof, and, for ease in moving back, it is carried on wheels. In thin seams duplex machines may be employed, which cut out two circles side by side; or a single machine may cut out one circle, and another follow it up and cut out another circular road alongside the first, the triangular pieces next roof and floor being subsequently removed by hand.

These machines will drive a heading at the rate of about I yard per hour, but for regular work the rate of progress is about 4 to 6 yards per shift.

Machines for Use either for Headings or Banks.

— Machines of this class are largely used in America, where the polar-and-stall method of work is almost universal. They are also used to a limited extent in England for drive headings, and in a few places for getting the coal in pilla&tj stall workings, or in loDgwall faces.

Machinery,

The Jeffrey Chain Machine. — This is a breast machine, making its cut straight in front, and being moved along by hand after each cut An outline of the machine is shown in Fig. 96. The bed frame a is stationary, and is held in position close up to the face by the screw b. The sliding chain cutter frame c works between the side girders of the bed frame, and is racked forward as the cut advances, d is the electric motor (air-engines may also be employed) which is attached to the sliding frame, and moves with it upon the bedframe. The cut is made by chisels fixed to the endless chain. When the machine is making a cut, the sliding frame is gradually racked forward, and at the same time the endless chain which carries the chisels is driven round and round the

d

xn

1 (0) 1

;

a.

Fig. 96. — Jeffrey chain mncbine.

sliding frame, and so cuts its way into the coal. ARer the sliding has advanced its full length, it is run back by the engine, and the whole machine is moved along the face, and secured by screws ready for the next cut. The drawbacks to the employment of this machine for longwall work are its great length, making the timbering of the stalls very awkward ; aod the labour involved in sliding it along by hand. This latter is lessened by allowing the back of the machine to rest upon a rail or skid-board. For conveyance from one place to mother, when used in headings or short banks, the machines niay either be placed on trolleys, or mounted on wheels. Sdf-propelling trolleys are made, the wheels being actuated liy'llie motor through chains. These machines are made to cut 5, 6, or 7 feet in depth, the width of each cut being

COAL-MTNING. 44 inches, and ihe height taken out by the cut about 4

' Peraissive Mac/urns. — These machines are of American

origin, the three types principally used being the Harrison, Ingersoll — Sergeant, and Yoch. They have been tried at several collieries in Great Britain, but have not met with any great success. It has been found difficult to get men to work them ; men new to the work suffer from the great vibration, but they are said to get over this with a little practice.

Fig. 97 shows a machine of this class as it appears when

at work. It consists of an air-cylinder, a, from 4 to 6 inches

I in diameter, mounted on wheels, and provided with a pair of

L handles, b. The chisel

I c is attached to the

I piston-rod of the air-

SgK w backwards against an

Fig. 97,— Ingersoll machine. rock-drills mounted on

wheels. When at work

they are placed on sloping timber platforms (d in figure).

They are steered by the operator, who sits on the platform and

directs the blows of the chisel with hands and feet. The recoH

is taken by the slope of the platform, and, in some of the

larger machines, by an automatic brake. The average amount

undercut is about 50 square yards per shift. For making

vertical cuttings a similar machine is employed, but it is

mounted on larger wheels. The great advantage of these

machines is in their portability, as they can very readily be

moved from place to place, They weigh from 7 . to 10

., and cost about ;£ioo each.

T/ie Champion Coal-cutter. — This machine is very similar

not increaEed by the application of further heat, but the water conliDues to boil, and becomes steam at the same temperature as the water. The heat required to change water at z 1 2 degrees 1 Fahr. to steam at the same temperature is known as latent heat, ; because its application does not result in an increase of temperature. The latent heat of a body is the quantity of beat which must be applied to it in order to change its form without raising its temperature. The latent heat of water is gSS, so that i lb. of water at boiling-point requires the applicalioD of 966 units of heat to change it into steam, arid i lb, of steam at 212 degrees Fahr. must be denuded of 966 units of lieat to condense it into water at the same temperature.

Transfer of Heat. — Heat is trans/erred from one body to another by Radiation, Conduction, and Convection.

Radiation. — The transfer of heat in the form of rays is knoffo as radiation ; as, for example, the heating of the arch of a faraace by heat rays from the fire below it.

Conduction. — When one part of a body is heated, the heat dually extends throughout the body by means of conduction ;

that conduction is the passage of heat from one part of a dy to another, or from one body to another body which is in contact with it. The heat from a boiler furnace passes through the plates to the water by conduction.

Some bodies conduct heat much more readily than others. Bodies that conduct heat freely are called conductors ; those which conduct heat with difficulty are known as non-conductors. The metals are all good conductors ; liquids, gases, and fibrous materials bad conductors.

Convection. — The passage of heat through liquids and gases liy means of currents is known as convection. This is the most important manner in which liquids are heated. Convection currents always ascend, because the heated particles become less dense, and consequently rise. For this reason liquids nist be heated from below : as the lower particles are heated iey rise, and other cold particles take their place ; these in keir turn are heated, and rise, so that the whole of the liquid exposed to the heat ; whereas, if heated from near the top,

2o8 COAL-MINING.

circle, as shown in figure. When the feed has reached itslimit, the machine is run back, and an extension rod added between the piston rod and the bit The width of the cut U about 3 or 4 inches, and the depth may be as much as 9 feetmachine and supporting column weigh about 5 or 6 ., an . cost about 1 00.

Steam.

By this arrangement the expansion of the steam takes place in two cylinders, the second much larger than the first, so that a much greater range of expansion can be obtained ; moreover, the pressure on the cranks is kept fairly uniform, and high ranges of pressure, and therefore of temperature, in one cylinder are avoided.

In Fig. 1 10 the steam enters the high-pressure cylinder at c and c', and is expanded three or four times ; it then exhausts into the low-pressure cylinder through the ports d and d', where it is further expanded, and finally escapes into the atmosphere or into a condenser, through the exhaust ports e and .

When very high steam pressures are employed, three or four cylinders may be necessary.

Condensing Engines. — The pressure ' of the atmosphere averages nearly r5 lbs. per square inch, and as engines have to exhaust against this pressure, a considerable proportion of the steam pressure is wasted. By the use of condensers the effects of atmospheric pressure are removed from the back of the piston, and a greater rate of expansion is permissible. There are two kinds of condensers in general use— jet condensers and surface condensers.

Jet Condensers. — In condensers of this class the Steam is condensed by actual contact with cold water.

Fig. Ill shows the form of condenser which is ordinarily employed in Cornish pumping engines ; it is also employed in conjunction with other engines of both old and modern design.

a is the condenser into which the exhaust steam is admitted through the pipe b. This condenser is a cast-iron vessel, and is fitted with the injection nozzle c. d is the air-pump and e

A

a.

H

M

r

-Jet e(

Foot-pounds per minute

Coal-Mining.

Ldopted a unit of power which he called the " horse-power,

and this is now generally employed by engineers.

I One horse-power is the power necessary to perform 33,( bot-pounds of work in one minute,

H.P.

Hence the H.P. in the example given above is— 3584000

Tlie horse-power of a steam-engine is obtained by the fol- 1 lowing formula ; —

P. L.A.N

H.P.

h

:UeKU- I nt5lon. '

where P effective pressure in lbs. per square inch 00 piston. L length of stroke in feet. A area of piston in square inches. N number of strokes per minute.

The following example shows the manner in which this formula is anived at ; —

Find the horse-power exerted by an engine having a cylinder 18 inches in diameter by 3 feet stroke, when making 100 strokes per minute and having a,n average pressure on the piston of 45 lbs. per square inch.

The area of the piston is found by squaring the diameter and multiplying by 07854; thus the area is —

18 X 18 X 0-7854 254'47 sq. inches

As the pressure per square inch is 45 lbs,, the total pressutC

The length of stroke is 3 feet, and the number of strokes per minute is 100, so that the distance the piston moves per kwinute is 3 X 100 300 feet.

Mechanics.

"he /aai-pouruis. exerted per minute are 11,451-15 X 300 because the piston is subjected to a. pressure of "i+Si'iS lbs,, and travels uaderthat pressure tlirough a space oEjoofeet. As 33,000 foot-pounds per minute make i horse-

pon,the H.P. exerted is ?-13S34_5 j-i. 330D0

Condensing the above, we get —

45 X3 X 354-47 X '°°

Tlie energy transmitted by any machine is partly spent in "Joing useful work, and partly in overcoming frictional and other 'fsistances.

The modulus, useful effect, or efficiency of a machine is the proportion of the energy expended which is converted into useful woric done total work applied' expressed as a fraction, or, as is more usual, as a percentage. for example, an engine exerted 270 horse-power, and accomplished useful work to the extent of 180 horse-power, the efficiency would be yj or, expressed as a percentage, '80 Y. 100 „„ — ; 66f per cent.

The horse-power developed in the cylinder of an engine is Inown as "indicated horse-power" (written I.H.P.), because ihe average steam pressure from which it is calculated is obtained by the aid of an indicator (see Chapter XVIIL). The actual horse-power available is known as the "brake tenfrpower" (written B.H.P.), and is arrived at by means of tfynamometer, or brake, arranged to absorb the power given off from a pulley.

The Mechanical Powers. — There are several mechaniul appliances by which cither force applied through a given fetance is altered to a greater force moving through a correspondiugly smaller distance, or they may operate in such a

Coal-Mining.

manner as to alter the force transmitted into a smaller force acting through a proportionately greater distance.

la every case where W force applied, D distance through which the applied force moves, it force transmitted, and d distance through which the transmitted force moves —

W X D

'X d

¥--

.:.Ji

In other words, neglecting frictional losses, the force applied, multiplied by the distance through which this force is exerted, equals the force transmitted multiplied by the space through which the transmitted force moves.

The simple mechanical powers are : TAe lever, the whedm axle, pulleys, toothed wheels, etc., the inclined plane, the si Levers. — A lever is a rigid bar supported at one called Qia fulcrum. The weight is placed at a certain d from the fulcrum, and the power is applied at another J along the bar. Levers are of three kinds, and are shown al 2, and 3, Fig. 99.

In the first kind, fulcrum F is between power P and

weight W; in the second kind, weight is between fulcrum antJ

power ; in the third kind, power is between fulcrum and weight.

three cases, where a length of power arm, b length

it arm, P X ff X i, because a is proportional

re

Mechanics.

Itie distance moved by P, and b is proportional to the distance moved by W.

The beam of an ordinary pumping engine is an example of a lever of the first kind. The power is applied by means of the pressure of steam on the piston, the axle of the beam is the fulcrum, and the weight is the weight of the pump-rods and *ater. The mechanical advantage gained by having one end "Jl the beam longer than the other is found as follows : If the local pressure of steam on the piston is 8i tons, and the portion of the beam to which the piston is attached is i z feet 9 inches long, and the other portion being 10 feet 6 inches long, what I eight will the engine hft?

P Xrt w

\2% weight lifted X 10

It will be noticed that the weight lifted bears the same Proportion to the pressure applied as the length of the arm "irough which the pressure is applied bears to the length of the r-m carrying the weight.

The most familiar example of a lever of the third class is Ound in the ordinary lever safety valve, in which the fulcrum the fixed end, and the power is the pressure of the steam on *he valve. The total pressure bearing down on the valve is ue to the weight of the valve itself, and the weight of the lever and of the weight upon it. Fig. 100 shows an ordinary lever Safety valve, all dimensions being given. The weight of the Valve is z lbs., of the weight 60 lbs., and of the lever 10 lbs. Before calculating the effect on the valve of the weight of the lever, the centre of gravity of the lever must be determined. The centre of gravity of a body is a point within it upon which, if supported, the body will rest, or be balanced in any position ; and the total weight of the body may be taken as acting at iliM point.

So that if the centre of gravity of the lever is 9 inches from the folcmm, as shown in figure, the effect is the same as if its

204 Coal-Mining.

machines driven by compressed air being the cheapest. The cost of cutting is between and dd. per ton ; in some places the cutting is let by contract, and at others the machine men are paid by the shift. The cost of steam, interest on capital, depreciation and repairs, amounts to about (id. per ton on the coal cut.

Heading Machines. — The only machine now used exclusively for heading is the Stanley heading machine. It consists of a narrow frame carrying a pair of vertical engines which drive a central shaft through suitable spur gearing. The shaft carries a heavy casting upon which a pair of arms are bolted, cutters are attached to the arms, and, as the shaft is revolved by the engines, an annular space is cut around a central core, making a perfectly circular road. The core is wedged down and removed by hand in some of the machines, but in others it is cut up by the machine, and the pieces are elevated and deposited in the pit tubs by a conveyor. The central shaft, which carries the arms and cutters, has a thread cut upon it, so that it is slightly advanced at every revolution. The machine is held up to its work by screws which are forced into the roof, and, for ease in moving back, it is carried on wheels. In thin seams duplex machines may be employed, which cut out two circles side by side ; or a single machine may cut out one circle, and another follow it up and cut out another circular road alongside the first, the triangular pieces next roof and floor being subsequently removed by hand.

Tliese machines will drive a heading at the rate of about I yard per hour, but for regular work the rate of progress is about 4 to 6 yards per shift.

Machines for Use either for Headings or Banks.

— Machines of this class are largely used in America, where the pillar-and-stall method of work is almost universal. They are also used to a limited extent in England for di headings, and in a few places for getting the coal in pillarstall workings, or in longwall faces.

Coal-Cutting By Machinery.

The Jeffrey Chain Machine. — This is a breast machine, making its cut straight in front, and being moved along by hand after each cut. An outline of the machine is shown in Fig. 96. The bed frame a is stationary, and is held in position close up to the face by the screw b. The sliding chain cutter frame c works between the side girders of the bed frame, and is racked forward as the cut advances, d is the electric motor (air-engines may also be employed) which is attached to the sliding frame, and moves with it upon the bedframe. The cut is made by chisels fixed to the endless chain. When the machine is making a cut, the sliding frame is gradually racked forward, and at the same time the endless chain which carries the chisels is driven round and round the

Fig. g6. — Jeffrey chain machine.

sliding frame, and so cuts its way into the coat. After the sliding frame has advanced its full length, it is run back by the engine, and the whole machine is moved along the face, and secured by screws ready for the next cut. The drawbacks to the employment of this machine for longwall work are its great length, making the timbering of the stalls very awkward ; aDd the labour involved in sliding it along by hand. This latter is lessened by allowing the back of the machine to rest apOB a rail or skid-board. For conveyance from one place to another, when used in headings or short banks, the machines miy either be placed on trolleys, or mounted on wheels. Self-propelling trolleys are made, the wheels being actuated liy'llie motor through chains. These machines are made lo cut 5, 6, or 7 feet in depth, the width of each cut being

lated being

Coal-Mining.

44 inches, and the height taken out by the cut about 4 inches.

Peraissive Machims. — These machines are of American origin, the three types principally used being the Harrison, Ingersoll — Sergeant, and Yoch. They have been tried at several collieries in Great Britain, but have not met with any great success. It has been found difficult to get men to work them ; men new to the work suffer from the great vibration, but they are said lo get over this with a little practice.

Fig. 97 shows a machine of this class as it appears when at work, ll consists of an air-cylinder, a, from 4 to G inches in diameter, mounted on wheels, and provided with a pair of handles, b. The chisel e is attached to the piston-rod of the aircylinder, and is driven rapidly backwards and forwards, striking a heavy blow forwards and being forced light}— backwards against ar~K air - cushion. T h machines are really rock-drills mounted on I wheels. UTien at wori J (hey pUced on doping timbei pladbnns in figure). 1 They steered by the operator, who sits on the platfonn and j directs the blows of the child with bands and feet. The recoil is taken by the dope of the , and, in some of tbe raacWncs, by an autOBiatic . Tbe average amount uiuleicut is about 50 square yards pet shift. For making vtltkal cuttings a siinitai nndune is employed, but it is uonnted on vheejs. Tbe great advantage of these QlMhiaM is in their poitaMtty. as they can very readltr be ptM to phoe. Tbey web from 7 . to

I CMoMBr.— Tlib uadiuie b very

FlQ, 97.— IngersoU Duchine.

Steam.

cold surface. The condensed steam is drawn off by an airpump, filtered, and forced back into the boilers ; and the water used for condensation is cooled in towers or in a pond, used again when cool.

Some collieries have large central condensers, taking steam ffom all the engines ; this is an advantage where engines work intermittently, as the supply of exhaust steam is regulated,

Boilers. — The pressure of the steam used at collieries has greatly increased during the last few years ; at new collieries boilers are now seldom put down to work at less than from loo to I20 lbs. per square inch, and in some cases these pressures have been greatly exceeded.

The Lancashire Boiler. — This type of boiler is almost universal at collieries. It is suitable for pressures up to about 1 60 lbs. per square inch, and qualified to work with bad water which is frefound at collieries, good Lancashire boiler should evaporate

from 7 to 9 lbs. of water per pound of coal which is consumed, and should consume about 20 lbs. of coal per square foot of firegrate area per hour. The Lancashire boiler consists of a plan cylindrical shell, with flat ends and two internal flues running the whole of its length. The usual size for heavy Work is S feet in diameter by 30 feet in length. The ends ate secured to the shell by being riveted to steel angles, and by gusset plates, and when the pressure is high, by tie bolts lunning right through the boiler- Fig, 1 13 shows' a cross-section through a Lancashire boiler and its seating, and Fig. 114 a longitudinal section. The

J

2o8 COAL-MINING.

circle, as shown in figure. When the feed has reache limit, the machine is run back, and an extension rod a between the piston rod and the bit. The width of the c about 3 or 4 inches, and the depth may be as much as 9 machine and supporting column weigh about 5 or 6 ., cost about 1 00.

Chapter Xvil

Mechanics.

Wore is said to be done when a force acts through a space overcoming resistance.

The British unit of weight is the pound, and of length the foot, and the unit of work is the foot-pomd, which is the amount of work required to raise a weight, or maintain a pressure of i lb., through a space of i foot, so that —

Foot-pounds force exerted in pounds multiplied by space in feet through which the force is exerted.

Exampk. — How many foot-pounds of work are done in raising a ton of coal up a shaft 400 yards deep ?

Force weight raised 2240 lbs. and space through which it is raised 1200 feet Then foot-pounds 2240 x laoo z, 688, 000

The power exerted in raising the above cannot be estimated unless the lime occupied is known. Obviously, it would take a very much more powerful engine to raise the coal in i minute Itian in 10, hence power is the measure of the rate ai which Mrkisdoiie. The measure of power is the number of footpounds per minute.

If the coal in the example given above were raised in J of 2 minute, the power exerted in foot-pounds per minute would be J,fi88,ooo X% 3,584,000.

In order to faciiitale the expression of power without the use of such large figures as foot-pounds per minute. Watt

24° Coal-Mining.

Fig. 115 is a section through a Stirling boiler. There are three top drums, a, h, and f, connected by tubes lo the bottom drums d and i? ; the drums are from 3 feet to feet in diameter, and the outside diameter of the tubes is 3 J inches. About of the capacity of the top drums is occupied by water and the remainder by steam ; the lower drums as well as the whole of the tubes are, of course filled with water. Owing to the large surface area of the tubes, the heating surface is very great, and as the water circulates freely, a large quantity can be evaporated.

I"[G. 115. — Secllon through Slirling boiler.

The tubes are all nearly vertical, so that sediment does not I settle in them, but falls into the two lower drums, from which il can be cleared periodically liy blow-off taps. The length ofth* I drums varies from 4 feet 8 mches in the smallest size up to 18 feet in the largest.

Economizers.— The gases from the boiler furnaces enter the main flue at a high temperature, and, if they are allowed 10 escape directly into the chimney, a considerable amount ol heat is wasted,

This waste heat may te utilized by " fuel economizers."

Mechanics.

t foot-poiinds. kxGiKd. per minute are 11,451 '15 X 300

|6Si345> because the piston is subjected to a pressure of

i"i5 lbs., and travels under that pressure through a space

I of joo feet. As 33,000 foot-pounds per minute make i horse-

I pomr.the RP. exerted is 104-1.

Condensing the above, we get —

45 X 3 X a54'47 X 100

33000

The energy transmitted by any machine is partly spent in going useful work, and partly in overcoming frictional and other

The modulus, tisefid effta, or efficiency of a machine is the

proportion of the energy expended which is converted into

„. , . , , useful work done „„ . .

nsefiil work and equals - ,- , — ,-i j. Efficiency may be total work applied ' '

pressed as a fraction, or, as is more usual, as a percentage. lUor example, an engine exerted 270 horse-power, and accompUshed useful work to the extent of 180 horse-power, the efficiency would be §, or, expressed as a percentage, i3o X 100 ,,„ 66 per cent.

The horse-power developed in the cylinder of an engine is linown as "indicated horse-power" (written I.H.P.), because ibe average steam pressure from which it is calculated is obtained by the aid of an indicator (see Chapter XVIII.). The actual horse-power available is known as the "brake iorse-power" (written B.H.P.), and is arrived at by means of a dynamometer, or brake, arranged to absorb the power given off from a pulley.

The Mechanical Powers. — There are several mechanics appliances by which either force applied through a given dj'stance is altered to a greater force moving through a correspondingly smaller distance, or they may operate in sucli a

jS

Coal-Mining.

The part of the curve ab shows the pressure in the lowpressure cylinder ; the effect of the inter-cooler is shown bj the decreased volume at bc: the upper part of the diagram, cd, is the line of pressure in the high-pressure cylinder. The shaded portion represents waste work, owing to the irapossi' bility of keeping the temperature constant by the water-jittets. If the air had been compressed in one cylinder, the pressure curve would have been about that of ihe line ahe, so ihe saving effected by compressing by stages is represented by ihe spaces e, b, c, d.

Air Mains. — For efficient working, the velocity of the aii through the mains should not exceed 50 feet per second, and large receivers should be employed, placed as near to the airmotors as possible.

Compressed air is very safe and convenient, but it usually gives a very low efficiency. This is not so much due to the system itself as to the manner in which it is employed, the machinery being generally of an uneconomical type. Tbe efficiency of compressed-air plants may be improved by the me of reheaters, in which the compressed air is heated before it enters the cylinders of the engines in which it is to be usei

In order to combine the economy of transmission of poer by electricity with the convenience and safety of compressed air, electrically driven air-compressors have been designed.

By fixing these in the intakes the risk of firing gas is reduced to a minimum, and long air mains are avoided.

Steam.

compressor. In Fig, 1 16, a is the piston-rod, b the piston, f the air inlet valves opening inwards, and d the outlet or delivery valves opening outwards, and communicating with the air-receiver. The cylinder is surrounded by a water jacket, or box through which water constantly circulates. As 'the piston moves in the direction of the arrow, air at atmo- 'Pheric pressure is drawn into the cylinder behind It, through the inlet valves ; at the same time the air in front of the piston is being compressed, and is forced through the outlet valve as Isoon as its pressure exceeds that of the air in the receiver. JiX the retiun stroke, air is drawn into the cylinder through the inlet valves at the other end, whilst the air drawn in at the previous stroke is being compressed.

The behaviour of air during compression will be understood by an examination of the diagram given in Fig. 1 1 7,

ab is the air-cylinder fitted with valves and piston, as shown in Fig. 116. Taking the piston to be at the end of the cylinder marked and travelling slowly in the direction of the arrow, the whole space in front of the piston is occupied air at atmospheric pressure, or, say, 147 lbs. per square inch absolute. By the time that the piston has moved througli ' In of the length of the cylinder, the volume of air is reduced to of its original bulk, and, according to Boyle's Law, its pressure is increased in inverse proportion, and has become of 147 lbs., that is i6"33 lbs.

Similarly, when the piston has moved through of the stroke, the volume is reduced to and the pressure increased to so that the pressure at that point is 147 x' i8'37 lbs. In like manner, the pressure of the air at any point in Ihe stroke can be determined. The line marked "isothermal curve" in the diagram shows the pressures generated during compression plotted to a scale.

The pressure in the cylinder continues to rise until it is Equal to the pressure in the receiver. As soon as this point is reached, the piston forces the compressed air through the 'flntlet valve. For example, if the pressure in the receiver ;irere 4 atmospheres, or SS lbs. absolute, air would be

r

150 COAL-MimNG.

A compound or mixture is composed of elements ; elemeatB are made up of molecides, and raoiecuies of atoms.

An atom is the smallest particle of matter capable of entering into a chemical combination.

A mokcnk is the smallest particle of matter which can exist in a free state.

The weight of an atom is not known, but the relative weights of atoms are known.

The atomic weight of an element is the weight of an atom of that element as compared with an atom of hydrogen. The atomic weights represent the proportions by weight in whidi the various elements combine with each other, and no element ever combines with another element except in proportion toils atomic weight or to some multiple of its atomic weight.

The Atmosphere. — The atmosphere, or air, is a mechamral mixture of nitrogen and oxygen ; it also contains small and variable quantities of carbonic acid, aqueous vapour, and ammonia. The composition of air, when pure, is as follows;—

Oxygen. — Chemical symbol, O, Specific gravity (air being i), 1T05. Oxygen is the support of animal life. AU animals must breathe it ia its uncombined state, or die from oxygen starvation. Oxygen combines readily with many substances, and when the combination is rapid, and is accompanied by heat and Same, it is known as combustion. All substances which burn in air bum more freely in pure oxygen ; and many substances which will not burn in air burn quite readily when immersed in oxygen. Oxygen is used to revive men who have been partially suffocated by poisonous gas, or when, owing to illness, vitality becomes very low ; but, if breathed for long in its pure state, it would cause death, owing to the too action of the heart and other functions.

Steam.

tlie two curves being the result of the heating of the air during CompressioD.

The adiabatic curve is of course always the higher ; thus at 0-5 of [he stroke the pressure due to isothermal compression is 3 atmospheres, or 394 lbs., whilst with adiabatic compression the pressure is 39 lbs. ; at 07 of the stroke the pressures are 49 and 81 lbs. respectively.

As the curves represent the pressure of the air behind the vision, they must also represent the pressure required to drive the piston along, so that they show that much more pressure, and therefore more power, is required with adiabatic than with isothermal compression.

This excess of power is caused by the heating of the air ; and as the air cools before it is used, it follows that this extra power is wasted. For example : whilst compressing air, 2 cubic feet may expand by the heat to 3 cubic feet, and sufficient power has to he used to compress those 3 cubic feet, tut when the air comes to be used, it has cooled and shrunk again to a cubic feet, and of the power is wasted.

In order to avoid this loss, the air-cylinder is kept as cool as possible by a water-jacket, and in some cases water is injected into the cylinders during compression.

The curve obtained in practice is always between the

adiabatic and isothermal curves. The more perfect the

cooling arrangements, the more nearly it approaches the latter.

The temperatures generated by compressing air are shown

in the following table : —

Pound, per wuar=

,

6o'o

I7S'8

3"7"4

369'4

Ss-2

346 Coal-Mining.

These high temperatures act adversely in other directions they render proper lubrication of the cylinders very difficult and when the atmospheric air is drawn into a hot cylinder j

expands, so that the weight of air which is actually taken ' the cylinder at each stroke is diminished.

The quantity of air delivered by a compressor at a gi" ' pressure may be calculated as follows : —

How many cubic feet of air at 60 lbs. pressure will an aSr compressor, having an air-cylinder 30 inches in diameter by 5 feet stroke, deliver when making 40 revolutions per minut=? The pressure on the gauge being 60 lbs., the absolute pressiL -re is 75 lbs. (Atmospheric pressure is usually taken at 15 lbs, p- er square inch in practice.)

Area of cylinder 2'5' x 07854 4'9i sq. feet, Feet per minute travelled by piston 40 x 5 X a - 400 feeL

Volume of free air taken into cylinder per , , ,

nimute 4*91 x 400 J

Pressure of free air 15 lbs. Pressure of compressed air 75 lbs.

Ratio of pressure 15 to 75 lbs- „ volumes 75 to 15 lbs.

Actual volume — sgJS cub. fe'-

This rule may be stated as follows :—

Add 15 to the pressure on gauge, and divide the sum fc? 15, which gives the number of atmospheres ; divide the ciilw feet of free air by this, and the quotient is the cubic feet compressed air.

The volume of air found in this manner is the theoreti*' quantity delivered by isothermal compression, A deduct*" of about 25 per cent, should be made for the losses by healing, clearance, and leakage through valve and pistons, etc,

T!ie pressure on the steam piston is greatest during commencement of the stroke, and after the steam is cut oS the pressure rapidly decreases; whereas the pressure in the aircylinder is zero at the commencement of the stroke, and rapid'/

'increases until it reaches the maximum, and air is forced through the dehvery valve. From this it follows that when both steam and air pistons are attached to one rod, the pressure of steam is at its minimum when the pressure of air is at its miKimum, and vice versA. This difficulty is overcome by constructing air- com pressors in pairs, with cranks coupled at right angles ; and by the provision of a heavy fly-wheel. The excess of power is absorbed by the fly-wheel during the earlier part of eidi stroke, and given out during the latter part, I Air-compressors work most efficiently when the pressure is I W, but the engines they drive are more efficient with high I measures.

loe most economical method of transmitting power by Twaipressed air is to use a high pressure, and compress the air r 10 stages. Two air-cylinders are employed, the low pressure p*"! high pressure, the former being the larger of the two. I Atmospheric air is taken into the low-pressure cylinder and jwmpressed to about 30 to 40 lbs. ; it then passes through an poter-cooler, where it is cooled by coming in contact with the SUiface of pipes through which cold water is forced. From le inter-cooler the compressed air passes into the high-pressure blinder, and its pressure is raised by further compression to JO lbs. Fig. 118 shows the effects of compressing air in stages.

ir-comprcsaing in slag=.

in die lo-

is sboim by

of the dtagra

e7lmder. The

to the impossi-

bf the water-jackets.

CfiiBder, the pressmxie

t tlM of fate so tlK i

ives k iqfKesented bp tie

tie Tdodtf of the aii 50 feet per secotid, and pboed as Dear to the aitnsHan si posBble.

Con pi esBeJ ar k ny ssfe and csmcniaiL bat it usamXf gires a ray lov ll ii M.Mfj. is not so ranch due to ti sjrsten itstf as to the t iwii 1 is wUch it is employed, dK urtiM.i) beb geacrafly of lecoDomical type. Tbe efficieiK7 of co Mtp cc Me d-air plants bk be unprored by the me of icheateis, io which the cranpressed air is heated before it enters the cylinders of the ettes in which it is to be used.

In OT&a to combine the eaHHny of transmission of power by electiicity with the convenience and safety of compressed air, electrically driven air-compressors have been designed.

By fixing these in the intakes the risk of firing gas is reduced to a mioimuiD, and long £ur mains are avoided.

GASES. ass

poisonous gas ; o'l per cent, is said to cause death if breathed for any length of time. This gas ts readily recognized by its unpleasant smell.

After-damp. — The mixture of gases which results from an explosion of gas, or of gas and coal-dust, is known as afterdamp.

The composition of after-damp depends upon the pro-

of ni

and coal-dust which take part in the ex- 1, At one time it was thought that the atmosphere of !, after an explosion had taken place, consisted at first .trogeo, carbonic acid gas, and steam, and, after the steam had condensed, of nitrogen and carbonic acid gas. That this is not so is proved by the fact that fires caused by the explosion, and even men's lamps, have continued to burn in places in which all the men have been killed.

According to Dr. Haldane, the chief cause of death in [Colhery explosions is the presence of carbon monoxide. He ' found that in three large explosions 77 per cent, of the men I killed were not killed by the force of the blast, but by the afterdamp, and their bodies showed every symptom of death by carbon monoxide poisoning.

2So

Coal-Mining.

A compound or mixture is composed of elements ; elemeoti I are made up of mokcuks, and molecules of atoms.

An atom is the smallest particle of matter capable of entering into a chemical combination.

A molecule is the smallest particle of matter which can eiist in a free state.

The weight of an atom is not known, but the relative weights of atoms are known.

The atomic weight of an element is the weight of an atom of that element as compared with an atom of hydrogen. The atomic weights represent the proportions by weight in wliicli the various elements combine with each other, and no element ever combines with another element e.fcepC in proportion toiB atomic weight or to some multiple of its atomic weight.

The Atmosphere. — The atmosphere, or air, is a mechanical mixture of nitrogen and oxygen ; it also contains small and variable quantities of carbonic acid, aqueous vapour, and ammonia. The composition of air, when pure, is as follows :—

I By ncighl. By volume.

Oxygen. — Chemical symbol, O. Specific gravity (air being t), i'to5. Oxygen is the support of animal life. All animals must breathe it in its uncombined state, or die from oxygen starvation. Oxygen combines readily with many substances, and when the combination is rapid, and is accompanied by heat and flame, it is known as combustion. All substances which burn in air burn more freely in pure oxygen ; and rosuiy substances which will not burn in air burn quite readily when immersed in oxygen. Oxygen is used to revive men who have been partially suffocated by poisonous gas, or when, owing to illness, vitality becomes very low ; but, if breathed for long its pure state, it would cause death, owing to the too rapid action of the heart and other functions.

Gases.

' NUrogen. — N. Sp. gr. o'97i. Nitrogen will not supportlifeor ombustion, but it serves to dilute oxygen and render it fit to be reached. It is not poisonous, but, as it will not support life, any oe breathing it in its pure state would die for want of oxygen.

When a man or other animal breathes, he inhales pure air, at exhales a mixture of unchanged air, free nitrogen and ironic acid gas. Plants, on the Other hand, absorb carbonic dd gas and give out oxygen, but retain the carbon. When trest, a man inhales about 55° cubic inches of air per minute, nd the mixture exhaled contains about 4 per cent, of carbonic cid gas, so that each man produces about 22 cubic inches of atbonic acid gas per minute. When a man is at work he BMthes much more rapidly, and consequently produces much oore carbonic acid gas.

The air in mines is vitiated by the following causes : —

1. Presence of noxious gases given off by the strata.

a. The breathing of men and horses.

J. The burning of lights, and

4. The firing of explosives,

5. The admixture of coal and other dust fi. The absorption of oxygen by coal. 7. In some cases the presence of gob-fires. The first is by far the most important cause of vitiadon,

md, in some mines, much air may be required to dilute tlie fumes given off" from the firing of explosives.

Gases found in Mines. — The following "noxious" gases found in mines : —

the

Carbnietted hydrogen, methyl hydride, I nuish gas, fire-damp, or "gas " ... Cubon dioxide, carbonic ncid gas,

t black damp, or "damp"

Carbon monoKide, or carbonic oxide,

j. 01 " white damp "

rf- Bulphnietfed hydrogen, or hydrogen I rolpMde

COAL-AfimNG.

Carburdted Hydrogen Gas. — This gas is given offnahiraliy in most coal mines, though there are some mines, and even whole coal-fields, in which it is never met with. It results from the decay of vegetable matter, and may exist in the strata at extremely high pressures. The pressure has been ascertained in several collieries by boring holes into the coal and plugging them tightly up, leaving a tube through the plug, to which 1 pressure gauge could be attached. In some cases a pressure of over 400 lbs. per square inch was registered, although the volume of gas given off was inconsiderable.

Gas may be given off from the coal face in the form of mmute sprays, which escape from the pores of the coal ; or it may be given off from blowers, which may continue W produce large volumes of gas for years. Some seams we liable to sudden outbursts of gas, in which a huge volume of gas is given off, but gradually decreases and dies away in a few days. Gas is not necessarily given off from the coal itself, but often from the adjacent strata ; a thin seam of coal, abore or below the one being worked, is often productive of mneh gas. Goaves often contain a large quantity of gas, some of which escapes into the roadways and workings when fte pressure upon it is reduced.

Carburetted hydrogen alone cannot be breathed, but, wlien mixed with air, has no effect on man until it forms about 50 per cent of the mixture. Fatal accidents occasionally occur through men going into an accumulation of almost pu' gas ; they are apt to devote the whole of their attention to iB explosive properties and forget that it cannot be breathed,

Carburetted hydrogen alone is not explosive, but only when mixed with ait in certain proportions. When miie*' with about five times its bulk of air it explodes feebly. The raost explosive mixture is reached when mixed with eight W ten times its bulk of air, and when mixed with more ihao fifteen volumes of air it ceases to be e.xplosive.

Many experiments have been made to ascertain the cart proportions of air and fire-damp which are explosive ; all difltf slightly. This is probably because the composition of the gas

Gases.

Kd in the various experiments was not the same. Gas as {iven off in mines usually uonlains impurities.

Carburetled hydrogen, being so much lighter than air, is Ways found near the roof and in the higliest places in the aine. For this reason dip roads are always more easily ventiited than roads driven to the rise. Owing to that property Jiown as diffusion, which all gases possess, carburetted hydrogen tid air, when in contact, do not form distinct layers — as, for Kample, is the case of oil and water — but gradually mingle (ith each other, and pass imperceplibly from pure CH. at the dghest points to pure air at the lowest.

The presence of this gas is detected by noting the beaviour of the flime of a safety-lamp. When about 2i per ent. of gas is present, the flame flickers, and is slightly 'drawn;" as the percentage of gas increases, a slight blue is formed, which becomes more marked until about 6 per ant, of gas is present, when the gas burns in the lamp.

Carbomc Aeid Caj,— This gas is given off naturally from he strata in some mines, and is also produced by the iteathing of men and animals, and by the burning of lights ind explosives. It is usually much more prevalent in shallow han in deep mines, and, being rnuch heavier ihan air, it iccumulates near the floor and at the bottom of sumps or . Carbonic acid gas results from the combustion of carbon in a plentiful supply of oxygen. When 15 per cent. pf this gas is present in air, lights are extinguished, and the nixture becomes fatal to life when 25 per cent, is present. He "black damp," or "choke damp," found in mines or lls, is often a mixture of nitrogen and carbonic acid gas, ffhen the barometer rises, it is a sign that the pressure of the taiosphere is increased (Chapter XXL), and air is forced into w strata, undergoing a process of oxidation whereby the oxygen I absorbed, leaving only nitrogen ; when the pressure is de- ITeased, this nitrogen issues from the strata, carrying with it |lniall percentage of carbonic acid gas. Dr. Haldane has clearly mwn that the choke damp found in wells is poisonous, not so pich from the amount of CO, that is present, but from the

J

Coal'Mining.

roadways of a mine it rubs against the roof, Hoor, and sides, and this gives rise to friction.

The laws governing the friction of air in mines are as follows : —

The pressure required to overcome the resistance caused by friction varies — ' (<i) Directly as the rubbing surface ; V Inversely as the area of the airway ; B Directly as the square of the velocity ;

(rf) According to the nature of the rubbing surface, bein| greater with rough than smooth surfaces.

The Rubbing that the friction is caused solely by the air coming in contact with the " rubbing surfice," it follows that the greater the rubbing surface the greater the friction, other things being equal. The rubbing surface is the total area exposed to the air, and is obtained by multiplying the perimeter of the airway by its length. The perimeter ofj road is obtained by measuring around its section, and in lli5 case of a rectangular road is the combined length of roof, floor, and sides. Thus, a road 7 feet high and feet wide has J peijmeter of; + 7 +95+95 33 feet; and its rubbing surface in square feet, if one mile in length, is 33 x 1760 X 3 174,240 sq. feet.

Area, — The area of a rectangular rpad is obtained by rouluplying the width by the height. Thus a road 6 feet 3 inches high by 7 feet 9 inches wide has an area of 48-4375 sq. feet.

The total pressure on an airway is the pressure per square foot multiplied by the area. If the WG were 1 -3 inch, the total pressure on the above road would be I'jXS'sX 48'4375 327"437S lbs.

Now, if the airway were only half the area, the pressure pet square foot necessary to obtain the same iolal pressure must be doubled ; hence it follows that (other conditions being equal) the pressure per square foot necessary to overcome the friction varies inversely as the area.

These first two rules show that the best form for an airway, as regards friction, is the one which has the smallest rubbing

Gases. 255

poisonous gas ; 0*1 per cent is said to cause death if breathed for any length of time. This gas is readily recognized by its unpleasant smell

After-damp. — The mixture of gases which results from an explosion of gas, or of gas and coal-dust, is known as afterdamp.

The composition of after-damp depends upon the proportions of gas, air, and coal-dust which take part in the explosion. At one time it was thought that the atmosphere of a mine, after an explosion had taken place, consisted at first of nitrogen, carbonic acid gas, and steam, and, after the steam had condensed, of nitrogen and carbonic acid gas. That this b not so is proved by the fact that fires caused by the explosion, and even men's lamps, have continued to burn in places in which all the men have been killed.

According to Dr. Haldane, the chief cause of death in colliery explosions is the presence of carbon monoxide. He found that in three large explosions 77 per cent of the men killed were not killed by the force of the blast, but by the afterdamp, and their bodies showed every symptom of death by carbon monoxide poisoning.

In common witli other gases, air has the following ptOpeitiSi' It is elastic; it has weight; and it has the property of inertia, which means that it never moves without the application of force, and, if once set in motion, never stops unless exposed in some resistance — the resistance usually being friction.

In order to produce the currents of air for the ventilatJM of mines, advantage is taken of the facts which are expressed in what are known as Charles' and Boyle's Laws,

Charles's Lam. — This law states that the volume of a pi varies directly as the absolute temperature, when the pressure is constant.

The "absolute zero" is —459 degrees Fahr., or -JJJi degrees Cent., and is supposed to be Che lowest temperatnK which is attainable. The absolute temperature, using FahraP heit's scale, is the temperature given by the thermometer +459. Thus the absolute temperature of a gas at 50 di Fahr, is 50 + 459 509 degrees; and of a gas at loodegreS Fahr., too + 459 559 degrees. Thus, if 100 cub, feet of air at 50 degrees Fahr. were heated to 100 degrees, therelallW volumes would be in the proportions of 509 to 559, andll*

. „ . , , I'iii X 100

actual volume after the increase m temperature

io9'32 cub, feet.

The /iJ/a/ weight of air would of course remain unchaag* so that the weight per cubic foot would be decreased by

e-eleventh. Hence it follows from this law that the wei per cubic foot of air decreases when the air is heated.

Ventilation.

Boylis Law. — This law states that the volume of a gas varies inversely as the pressure, if the temperature remains conslanL Thus if the pressure on a body of gas is doubled its volume is halved. Although the air is compressed to half its former bulk, the total weight of air is unchanged, so that the weight per cubic foot is doubled ; from this it follows that tbe weight per cubic foot of a gas varies directly as the pressure upon it. The pressure upon free air is that due to the weight of the atmosphere, and is usually expressed in inches of mercury (see Chapter XXI.). The alteration in volume due to the alteration in pressure is calculated as follows : Find the alteration in volume of 50 cub. feet of air if the barometer rlills from 30'74 to z8'i6. ' As zS-i6 : 3074 : : 50 to altered bulk,

So that the altered bulk is ''"— S4'S8 cub. feet.

These two laws show that the weight of a given volume of air depends upon the temperature and pressure, and as these *aty constantly, the weight of air also varies from time to time, t has been calculated that 459 cub. feet of air weigh '3153 lbs. when the temperature is o degrees Fahr., and the pressure is equal to i mch of mercury. The weight of i cub. 3-_3j [fjg_ weight

any pressure is-- — -— , where B is height of barometer

ii inches, and, as the weight varies inversely as the absolute emperaturc, the weight at any pressure and temperature i

Hind by the formula W — 7-7-. For example,

nd the weight of a cubic foot of air when the barometer ads 30-6 inches and the thermometer 65 degrees.

W 30-6 X 1-3.53 , It,.

Pressure producitig Ventilation. — Mines are ventilated entirely gravity ; for in order to produce a current of air there n

Coal-Mining.

I be two columns of air of different densities, that is, the weigh: I per cubic foot of air in the one column must be different tc I the weight per cubic foot m the other. The two columns are ) those found in the upcast and downcast shafts, or their I equivalents ; the difference in density is caused either by a 1 furnace, which heats the air in the upcast and so reduces its I density (Charles's Law) ; or by a fan, which reduces the pressare I below that of the atmosphere (Boyle's Law).

:r9 illustrates the manner in which the pressure

giving rise to a ventilating current is calculated, a and h are

two shafts, each looo feet in depth: the air

in a weighs o'oS lb. per cubic foot, and in h

o'o6 lb. per cubic foot. This difference in

weight may have been brought about either

. by a faa or furnace, as explained abow.

If the communication between the bottoms

of the two shafts is closed by a stopping,

the pressure per square foot on either side

of it is equal to the weight of a column of

air I sq. foot in area in and above eadi tf

the shafts; but the columns of air above

the tops of the two shafts are of the same

density, so that they exactly balance eadl

other, and can be omitted from the calculation. Ignoring ibe

I columns of air above the shaft tops, the pressure per squirt

I foot on the side of the stopping communicating with a is equal

J to the weight of i cub. foot of air multiplied by the height of

' the column, which is o'o8 X looo So lbs., and the pressure

per square foot on the other side is o-o6 X looo 60 lbs.

The difference in pressure is 20 lbs. per square foot, whidi

is the pressure producing ventilation. If a waler-gaugE

(Chapter XXI.) is placed on the door, the water in the lcoc

municating with a will be depressed, and as 5*2 lbs. pressaw

per square foot balances i inch of water, the depression

5 inches. As the le downcast and b

pressure is f the upcast s

Ventilation.

'59

Motive Column. — It will be seen from the above that the pressure producing ventilation may be expressed either in pounds per square foot or in inches of water-gauge; but it may also be expressed in feet of motive column. The motive toluQin is a column of air i sq. foot in area, and of the same weight per cubic foot as the air in the downcast shaft, itid of such a height that its weight is equal to the ventilating pressure. In the example given above, the ventilating pressure is 20 lbs. per square fool, and the weight of air in the downcast shaft is o'oS lb. per cubic foot : hence the length of the

motive column is —5 250 feet Looking at the question in a slightly different light, we see that the weight of the air column in b is 15 lbs. for every 250 feet, and in a it is zolbs. far every 250 feet, so that a column in it 750 feet long balances column in b 1000 feet long. This leaves a column of a in a 250 feet long, which is unbalanced and free to give rise to tlie motion of the air ; this is known as the motive column. The velocity at which the air would circulate if the stopping were removed, and no friction existed, would be equal to the velocity that a body would acquire in falling through a height equal to the length of the motive column. In practice, however, most of the ventilating pressure is required to 01 Kction, only a very small proportion being spent in giving rise to velocity.

The relation between pressure, water-gauge, and motive WJiumn is expressed in the following formulte, Vhere P pressure in pounds per square foot, I WG water-gauge in inches, 1 M motive column in feet : —

average weight of a cubic foot of air in downcast M X average weight of a cubic foot of air in downcast

The Friction of Air in Mines. — As the air traverses the

roadwsya of a mine it rubs against the loof floor, and ndes, and thU gives rise to friction.

The laws governing the fiictioQ of air in mines aie as roQows : —

The jwessore required to overcome the resistance . caase<) by friction varies—

(a) Directly as the rubbing surface ;

(b) iDveisely as the area of the airway ; Directly as the sqnarc of the velocity ;

[d) According to the nature of the rubbing surface, bong

greater with rough than smooth surfaces, Thi Rvhbing Surfau. — Seeing that the friction is caused solely by the air coming in contact with the " rubbing surface," it follows that the greater the rubbing surface the greater the friction, other things being equal The rubbing surface is ik total area exposed to the air, and is obtained by multiplying the perimeter of the airway by its length. The perimeter of a road is obtiuned by measuring around its section, and in ths case of a tectaugnlar road is the combined length of roof, floor, and sides. Thus, a road 7 feet high and feet wide has a perimeter of 7 + 7 + 9a +92 33 feet; andits rubbingsuriace in square feet, if one mile in length, is 33 x 1760 X 3 174,240 sq. feet.

Area. — The area of a recUngular road is obtained by multiplying the width by the height. Thus a road 6 feet 3 inches high by 7 feet 9 inches wide has an area of 4S'4375 sq. feet.

The total pressure on an airway is the pressure per square foot multiplied by the area. If the WG were i -j inch, the tutal pressure on the above road would be i'3XS"aX 48-4375 V-TMIi lbs.

Now, if the airway were only half the area, the pressure pet stjuare foot necessary to obtain the same Mai pressure must be doubled ; hence it follows that (other conditions being equJ) the pressure per square foot necessary to overcome the friction varies inversely as the area.

e first two rules show that the best form for an airway, s friction, is the one which has the smallest rubbing

VENT/LATfON.

surface in proportion to its area. For example, a road S feet square has an area of 64 sq, feet and a perimeter of 32 feet, whilst a road 16 feet by 4 feet has the same area, but has 1 perimeter of 40 feet. Hence the latter road would offer more resistance to the air than the former in the proportion of 40 to 32, The best form of airway as regards friction is the circular, but usually the shape of the road is governed by practical considerations, such as thickness of seam and character of roof and floor.

Velocity. — The quantity of air passing through a road of given area varies directly as the velocity. If the velocity is doubled, the quantity is also doubled ; and therefore double the quantity of air comes in contact with the sides of the airway at double the velocity ; this results in four times the friction. If the velocity of the air is increased fourfold, four times as much air comes in contact with the rubbing surface at four times the velocity, so that the increase in friction is 4 X 4 16. From this we get the rule that the resistance due to friction increases as the square of the velocity. This rule shows the great necessity that exists for keeping down the velocity by the provision of large airways, and by splitting the air.

The Coefficient of Friction. — This is the pressure required to overcome the resistance due to friction for each square foot of nibbing surface exposed to the air when it is travelling at a velocity of 1000 feet per rainute. This will be understood by the following example ; The pressure required to force air along a road 6 feet by 5 feet and laoo yards long, at a velocity of 1000 feet per minute, is 15 lbs. per square foot. Find the coefficient of friction.

The total rubbing surface is (6 + 6 + 5 + 5) x ' 200 X 3 79t2oo sq. feet. And as the pressure is 15 lbs. per square foot, the total pressure is 15 X 30 450 lbs. {30 being the area of the road, in square feet). So that a pressure of 450 lbs. IS required to overcome the resistance offered by 79,200 sq. feet of surface, when the air moves at a velocity of 1000 feet per niiaute. Each square foot offers a resistance of 00056S Ih., which is the coefficient of friction.

COAL-MrNING.

In the example given above, the coefficient of friction f s expressed in pounds per square fool, but it may also be repressed in inches of water-gauge, or in feet of motive column.

As stated on p. 260, the pressure required to overcome friction varies with the nature of the rubbing surface. The following arc coefficients of friction given by various autho ri- ]

Pound. pr.>ur, per sqimre fool.

Murgue— Arched roads Unlined roads Timbered roads ...

o'oiooSS

0'004I7

O-00194

The coefficients given by Murgue are averages, and aho* the influence of the nature of the lining upon the friction. From these rules the following formula has been arrii

pa

where / pressure in pounds pec square foot, a area of road in square feet, s rubbing surface in square feet, k coefficient of friction in pounds per square foot, V the velocity in thousands of feet per minute, Both p and k may be expressed in inches of water-gauge or feet of motive column ; but care must be taken to employ the same for both.

If the truth of the foregoing rules is accepted, this rule of

ventilation is evident ; for if/ varies as j, and as -, and as then it is evident that if we know p, unit rubbing surface, anJ unit velocity, the pressure in any case is the produc

pressure or coefficient of friction and

Vbntila Tion.

From the formula given above, we have the following ; — ksv" ksv .pa. pa , , Pa

The following examples show the application of these formulge : —

(i) Find the water-gauge necessary to force 30,000 cub. feet of air per minute along a road i8oo yards long and 6 feet , high by 8 feet wide, taking the coefficient of friction at O'oo5

lb. per square foot. By the formula / — ,

J s8 X rSoo X 3 151,20

o 6 X 8 48

v'= 0-39

To find the numerical value of r', the velocity of the air is first found by dividing the quantity passing by the area, 625 ; but this is the velocity in feet per minute, whereas " itt the formula represents thousands of feet per minute, therefore v o'625, and o'fizS" o'39o625, which is iJie numerical value of v.

Then p

1 X 0-390625 .

This gives the pressure required in pounds per square foot, 3nd must be divided by 5'2 to get the inches of water-gauge —

5'2

183 inch W.G.

(2) Find the quantity of air which would circulate the roads in No. i example under a pressure of 12*30468 lbs. per square foot.

By the formula, T' substituting the numerical "alues in example No. 1 —

0-005 X 151200 '

and V V78122 o'8339 883-9feet per minute

26a

Coal-Minjng.

The quantity of air is obtained by multiplying this velocity by the area; 883-9 X 48 42427 cub. feet per minute. Thus by doubling the pressure the quantity is raised from 30,000 10 42,427 cub. feet per minute.

It will be noticed that the increase is not in proportion to the pressure but to the square root of the pressure, and ftom this we get this important rule : —

The pressure varies as the square of the quantity; andi conversely, the quantity varies as the square root of the pressure. Thus to double the quantity four times the pressure is required, and by doubling the pressure the quantity is increased in the ratio of V'l : J'-. tliat is as i is to 1-4142.

Horse-power to prodme Ventilation.— foot-pounds of work done in ventilation equals weight of air moved multiplied by length of motive column through which it is lifted. That is, foot-pounds weight of a cubic foot of air X length of motive column x quantity of air in cubic feet

But the pressure weight of a cubic foot x length of motive column ;

.'. foot-pounds pressure X quantity and liorsP- quantity per minute X pressure I

In the first example given, H. P. :

In the second example, H.P.

33°'

15-819

These figures show that whilst to produce 30,000 cub. feet of air requires only 5-59 H.P., is'82 H.P. are required to produce 42,427, the airways being the same, 30,000 bears the same proportion to 42,437 as Vs bears to \'i5-S, which proves that the quantity varies as the cube root of the power; thus, by doubling the power the quantity is increased in the proportions of V7 to V2 ; that is, as i is to I'zgg.

Conversely the power varies as the cube of the quantity ; us to double the quantity z'' or 8 times the power is required.

Ventilation.

Furnace. Furnaces are now rarely built to ventilate t collieries, fans being usually preferred. There are, many old but large collieries in the Nortii of England here which are very efficiently ventilated by furnaces, of the old collieries steam is generated underground, waste heat from the contributes largely ventiladon of the

ntilating furnace in ion with underboilers is probably apes method of ig a deep pit, but antages are more anced by the great ience, and by the of danger that is ;d by having fires

ISO shows the ordi- :m of ventilating in elevation and The arch over the lid have an indefirebrick hning n be replaced when lut. A cooling drift e provided on either lugh which air can , to prevent the heat from the fire igniting the strata, maces have fireholes at either side of the firebars as

1 the mine is gaseous, the return air should not pass furnace, but should enter the upcast shaft by a dumb lich is a road driven into the shaft some ao or 30 ore the furnace, as shown at A, Fig. 121, or the furnace

ing furnace.

Coal-Mining.

drift may enter the shaft at a point some distance above the return airway, as shown at B, Fig, i2i. When a dumb drift is employed, the furnace must be supplied with the air necessary for combustion by a separate split ; and when this is the case, the front of the furnace is closed by brickwork and dooi in order to force the air through the fire, and prevent iti being wasted by passing right over the fire.

The pressure- or water-gauge produced by a furnace is calculated as follows : —

A pair of shafts are 1400 feet deep; the temperature in t!ie downcast is 56 degrees Fahr., and in the upcast ifii

degrees. What is the water-gauge? First, find the of a cubic foot of air in each shaft by the rule given on p. 257 ; assume the barometer to stand at 30 inches.

In downcast, W

3 cj-oyj2 lb, per cubic foot

459 + 56 1°-— 3-53 o.o5_, lb, per cubic fool

The difference in weight of a cubic foot of air in eicli shaft is 0-0772 - 0-0641 0-0131 lb. The depth is 140* feet, so that the total difference in weight between columns of air 1 sq. foot in area in each shaft is 1400 X o'oij' 18'34 lbs. This, then, is the ventilating pressure in poumJ"

Ventilation. 273

kt will be noticed that its width decreases from the centre to klie circumference, so that the air passes through the fan at a uniform velocity ; the blades are curved back into the circumlierence. The fan is hung at the end of the shaft, and is carried by bearings on the engine-bed only ; this arrangement Jcaves the inlet perfectly open and unrestricted.

A 21-feet Waddle fan gave the following results : —

136 revs, per min. 88,700 cub. ft. per min. 5'2 in. W.G. 168 „ „ 110,200 „ „ 7-4

The Capell Fan. — These fans are made of very varying widths and diameters ; they have both single and double inlets, .and are sometimes driven direct, but more often by belts, As shown in Fig. iz6, they consist of an inner cylinder FiEtted with curved blades, which discharge the air into an

Fig. 126.— Capell fan.

outer cylinder, also fitted with curved blades, from whence 1 it is driven into the expanding chimney.

I The air which passes through the fan is acted on, first by

1 the inner and then by the outer blades. The newer fans are

provided with scoops in their inlets in addition to the two sets

of blades. These fans are at work at many places, and can

:68

Coal-Mining.

conditions will be reversed, and the air in AB will be the cooler and heavier, which will result in AB being the downcast. When the temperatures of atmosphere and mine are , equal, the two columns of air will balance, and no ventilation will take place. Natural ventilation is often employed in metal mines, but is never relied on for collieries, except when they are on the smallest scale. The ventilation of a deep mine is, however, always assisted by natural ventilation, bC' cause the mine temperature is higher than the temperature of the atmosphere; as the outside temperature rises the natural ventilation slackens, so that in summer increased ventilation is required.

Steam Jeis. — For temporary purposes steam jets may be employed to heat the air in the upcast shaft, and so produce ventilation. A steam- pipe is taken part way down the sbaft; horizontal pipes branch out at the bottom, and the steam issues from perforations bored in their upper surface.

Ventilating Fans.— Fans may either force fresh ait down the downcast shaft, or draw the return air from upcast ; the latter is by far the more common, as it is inconvenient to close the top of the downcast shaft, and therefore exhaust fans are almost universal. The fan is conneciei! to the upcast shaft by a drift, and the top of the shaft is kept closed, so that all the air coming to the fan has to pass through the mine.

Ventilating fans depend for their action upon centrifuge force. If a stone is whirled round in a circle at the end o. a string, tension is put upon the string, and if it is cut, the stone flies off at a tangent. Similarly, if air is whirled round in a circular box in which vanes revolve, it tends to fly off a' the circumference, and is only prevented from doing so by the box. This tendency to fly off at a tangent, which is known as centrifugal force, puts pressure on to the air nwT the circumference of the box, and reduces the pressure of th* ! air at its centre j so that if an opening is cut in the drcuiO' ference of the box, the air will rush out, owing to the increase

Ventilatton.

pressure at that point, and if another aperture is cut in the centre, air rushes in, owing to the reduced pressure at that point; this results in a constant flow of air through the fan. What a fan really does is to drive the air from its centre to itJ circumference ; the air in the fan body and in the roads eonnected to it is thereby rarefied and made lighter than the sir in the downcast shaft, thus giving rise to a motive column. The theoretical motive column, or water-gauge, produced by a fan depends upon the velocity of the blade tips, and is calculated by the following formula : —

nheie h air column in feet,

V velocity of blade tips in feet per second,

g force of gravity 3a"2. Example. — What water-gauge should be produced by a 30 feet in diameter when making 60 revolutions per minute?

Circumference of fan — 94*24 feet

R l and jr 8881-2

H Then h ??fi 275-8 feet

e weight of a cubic foot of air in the upcast must next w calculated by the rule already given. Suppose this works W at o"07 lb., then the total weight of the air column,

i sq, foot in area, is 37S"8 X o"o7 i<)-$ lbs., and — —

37 inches of water-gauge.

No fans actually produce their theoretical water-gauge ; 'fte ratio of actual water-gauge produced to the theoretical .Wler-gauge is known as manometric efficiency. If, for example, ttie above fan actually produced a water-gauge of 2"6 inches, its

'"anometric efficiency would be 70-27 per cent.

Coaimtnjng.

Types of Fans. — Fans may be either open running or eik dosed. In the former the vanes and casing revolve together, and the casing is open at the circumference; in the lattcj the casing is stationary, and provided with an opening for the escape of the air. Fans may also have single or double inlets. Single-inlet fans take the air in on one side only, whilst I double-inlet fans communicate with drifts at either side. The I drifts for a double-inlet fan are shown in Fig. 133. Fans of this type arc usually divided by a plate or diaphragm

123. — Dokibtc-inlcl

shown, so that the air from the two drifts does Dotf| in the fan and set up cross-currents.

Fans may be either of large diameter and run slonq of small diameter and run quickly; the tendency is t wards the latter type. Quick-running fans may be t driven direct by high-speed engines, or by belts or rtq low-speed engines; the latter being the more Usually duplicate engines are provided in case on requires repairs or breaks down.

The Schidt Fan. — These fans have double inlets, t made of small diameter to run at a high speed. in Fig. 124, they have wings, curved backwards and q

I central disc or diaphragm. The fan is placed llically in a spiral casing, so that the velocity of the'J

Ventilation.

gradually reduced from the time it leaves the blades to when

is discharged into the atmosphere. Almost all fans have

expanding chimney, for if the air from the fan is discharged

a high velocity into the

atmosphere, an unnecessary (moiint of power has to be Kpended.

The blades taper in width towards the circumference, that the air passes through

fan .at a uniform velocity ; if the air leaves the fan blades too slowly, it may reihe fan instead of being swept clear away. These fens are generally driven by or cotton ropes from the fan engine.

Schiele fans are made up to about i5 feet in diameter; i+-feet fan will produce about 250,000 cub. feet of air at

or 7-inch water-gauge.

The Guibal Fan. — This is one of the oldest types of Mntrifugal ventilators. It is a single-inlet fan, and is made

lo about 50 feet in diameter by about 12 feet in width. The blades, which are eight or ten in number, are of timber, Wid bolted to an angle-iron framework; this is bolted to a of two or three cast-iron centres which are keyed on to De fan shaft. The blades are straight, but are set back, not ioed radially. The casing and evasee chimney are of briclcthe casing fits closely to the fan for about three parts rf its circumference, the air being discharged into the ease ctiimney through an adjustable wooden shutter. There are fflany of these fans now at work, but no new ones are built "pon this principle, as they require very costly foundations id buildings, and are of somewhat weak construction on iKoimt of the many bolts which are apt to work loose.

Walker's Guibal. — This is a modified Guibal fan ; it is Irilt entirely of iron and steel, has a double inlet and blades

278 Coal-Mining.

A fair velocity fcx- the air to travel at

In shafts, up to about looo feet per minute.

In main airways, up to from 800 to 1000 feet per minute.

In working places, from about 150 to 300 feet per minute.

The quantity of air per man per minute varies very greatly in different mines, and may be anything from about 100 to about 500 cub. feet

Ventilation.

ft ifil! he noticed that its width decreases from the centre to the circumference, so that the air passes through the fan at a Inniform velocity; the blades are curved hack into the circum- 'ference. The fan is hung at the end of the shaft, and is ;canied by bearings on the engine-bed only ; this arrangement leaves the inlet perfectly open and unrestricted.

i-fcet Waddle fan gave the following results : —

i3fin

i. per ;

8,700 cub. ft, per n

. 5'z

L. W.G.

The Capell Fan, — These fans are made of very varying sidtiia and diameters ; they have both single and double inlets, and are sometimes driven direct, but more often by belts.

As shown in Fig. 136, they consist of an inner cylinder fitted with curved blades, which discharge the air into an

Capall fnn.

Alter cylinder, also fitted with curved blades, from whence il is driven into the expanding chimney.

The air which passes through the fan is acted on, first by Hie inner and then by the outer blades. The newer fans are (Tovided with scoops in their inlets in addition to the two sets ' blades. These fans are at work at many places, and can

28o COAIMINING.

The barometer is also used to indicate differences in kvd As we descend a pit the column of air above us becomes longer, and consequently heavier, and if a mountain is ascended, part of the atmosphere is left below, so that the column above is shorter and lighter. It follows, therefore, that the barometer rises with descent, and falls with ascent

hH

This variation amounts to about : inch for every goo feet o( rise or fall; so that a barometer at the bottom of a shaft 600 yards deep would read about a inches higher than s similar instrument placed on the pit top.

The height of the barometer varies at sea-level betwetu about a8| and 30 inches.

Ventilation,

the corves on the cages are to be changed, the inner doors are opened and the outer doors closed.

Ventilating the Workings.— The air is conducted round the workings by means of stoppings, doors, overcasts,

Fig. 127. — Upcast pit top, closed with double doors.

brattice, and air-pipes. Fig. 128 shows the manner in which these are employed.

The roads closed by the stoppings are permanently closed ; doors are employed in roads which have to be closed to the

Fig. 128. — Distributing the air-current.

air, but open for traffic ; overcasts are used when one current of air has to cross another without mixing with it.

The dead-ends are ventilated by brattice or air-pipes. Stoppings. — These usually consist of brick walls 9 inches in thickness ; sometimes two walls are built a few feet apart, . and the space between is filled in tightly with dirt.

Do&rs. — Ventilating doors should be set in pairs, the space

r

282 Coal-Mining.

exhausted of air. The atmospheric pressure upon the upper surface of the box tends to push it down, whilst the spring of the box tends to push it up. When the atmospheric pressure increases the box top is depressed, and when it decreases it is raised by the spring.

One end of the pointer b is connected to the box top by the Hnk c; b is pivoted at d, and carries a pencil, e, at the end. The pencil-point presses lightly against a paper wrapped round the slowly revolving drum/.

When the atmospheric pressure increases the bos top is depressed and the pencil is raised; the combined vertical movement of the pencil and horizontal movement of the drain

result in a slanting line being drawn upon the paper. In lUs way a chart is made which shows continuously the variations in atmospheric pressure, the quicker the variations in pressure the more the lines on the chart approach the vertical

Titer mometers. — Moderate temperatures are measured by thermometers, but when the temperatures are very bigti, are employed. Thermometers depend for then action upon the fact that certain substances vary greatly and uniformly in bulk with the temperature. The ordinary thermometer consists of a thick glass tube of small but uniform bore, sealed at one end and terminating in a bulb at the

Ventilation.

employed, and, for the more important roads, such as stone drifts, which may have to be driven great distances without communications, a brick wall is built from roof to floor. The brattice is not put down the centre of the road, but a.tout a couple of feet from one side, the narrow side being i-xsed as an intake and the wider side as a return, and for tlie traffic.

Air-pipes of wood or iron are frequently used instead of ; they are cheaper, and take up less room, and can be easily fixed or taken down.

Splitting tite Air. — At one time the whole of the ventilation was taken round the whole of the workings in a single z;iirrent ; this had many serious disadvantages, indeed it would lae quite impossible to ventilate a modern colliery in this xnanner. The air is now always split, each split serving a Separate district. There are usually several main roads leadiiag from the downcast shaft, and part of the air is led along sch. These form the main splits; each main split is then *3.ivided into sub-splits, each of which ventilate one district, more than from eighty to a hundred men should work one split.

The advantages of splitting the air are —

(i) Each district is ventilated by fresh air.

(a) A fall of roof only affects the district in which it occurs.

(3) The smoke from a lire, or after-damp from a smaU aplosion, would not be carried through the whole of the "-orktngs,

(4) The total quantity of air is increased.

(s) The current velocity is kept within reasonable limits.

If splitting is carried too far, the velocity of the air in each *iistrict may be reduced until the current is not brisk enough sweep away any gas which may be made. The current v-elocity should not be too great, as that would add to the <3.anger of a coal-dust explosion, and increase the risk of a *defective lamp firing an explosive mixture ; moreover, an Extremely high velocity is unpleasant, and adds greatly to the friction.

r

; Coal-Mining.

A fair velocity for the air to travel at is —

In shafts, up to about looo feet per minute.

In main airways, up to from 8od to looo feet per minute.

In working places, from about 150 to 300 feet per minute.

The quantity of air per man per minute varies very greatly . in different mines, and may be anything from about roo about 500 cub. feet.

Barometer.— This is an instniment for measuring the Pressure of the atmosphere. In the ordinary mercurial barometer the pressure of the atmosphere is balanced against the f*ressure due to a column of mercury. In Fig. 1 30 an ordinary option barometer is shown. The tube n is about 36 inches fong; it is closed at the top, and the bottom end is turned up *nd terminates in a small vessel, as shown. If this tube is Blled with mercury and raised to a perpendicular position, ttle mercury will fall in the tube until its weight is exactly Balanced by the atmosphere. If the atmosphere had no height, the mercury would fall in the tube and run out over iie top of the vessel; but it is prevented from doing this by the atmosphere pressing upon the mercury in the vessel. The atmospheric pressure per square inch must be exactly the same (Fig- 130) 3.S the mercurial pressure at i" (the mercury below ii£ balances itself), so that if we know the pressure at " we also know the pressure of the atmosphere.

When the atmospheric pressure decreases the mercury falls the tube, because the lessened atmospheric pressure is Unable to balance so great a pressure of mercury.

One cubic inch of mercury weighs o'49o8 lb. Hence, height of barometer in inches multiplied by 4908 gives atmopheric pressure in pounds per square inch.

Example. — Find atmospheric pressure when the barometer Stands at 29*15 inches.

X o'4go8 i4'3o8 lbs, per square inch

Coal-Mining.

The barometer is also used to indicate differences in le As we descend a pit the column of air above us becoi longer, and consequently heavier, and if a mountain is cended, part of the atmosphere is left below, so that column above is shorter and lighter. It follows, theref that the barometer rises with descent, and falls with mo

TTiis variation amounts to about i inch for every 90 rise or fall; so that a barometer at the bottom ( 600 yards deep would read about 2 inches higher similar instrument placed on the pit top.

The height of the barometer varies at s about 28 and 30 inches.

Instruments.

The height at which the mercury stands is read off by

nieans of a fixed scale and siding vernier. The scale is

divided into inches and tenths, and the tenths are subdivided

into hundredths by the vernier. Fig. 131 represents a portion

of the face of a barometer, and shows the fixed scale and

Vernier in position. The vernier is r-j inch long, and is

divided into ten equal parts, and the fixed scale is divided

into inches and tenths, so that each division on the vernier

equals division on the fixed scale. The fixed scale is

rnarked upwards and the vernier downwards. To read the

leight of the mercury the top of the vernier is set exactly

lvel with the top of the mercury. Supposing the mercury

caches exactly of the distance between two of the divisions

the scale, the line marked 4 on the vernier will exactly

:coincide with one of the division lines on the scale. The line

ixarked o on the vernier, being level with the mercury, is

Exactly above one of the division lines on the scale ; line i

vernier is above the next line on scale, because the

*3visions on the vernier are longer by than the divisions on

the scale; line 2 on vernier above; line 3, above; and

line 4 exactly level with a division line on scale. From this

"eget the rule to read the vernier and scale, which is —

First read the inches and tenths from the fixed scale reading upwards), then notice which division line on the "v-emier exactly coincides with a mark on the fixed scale ; read *liat off from the vernier as hundredths.

In the figure the inches and tenths are 29'4, and the

1 on the vernier exactly coincides with a line on the scale so

thit the hundredths are 7, hence the reading is 29'47 inches.

It is important to understand the principle upon which

I verniers are constructed, as they are largely employed in

jesl mathematical and surveying instruments.

J il Aneroid Barometers. — No mercury is employed in aneroid

barometers. They can be made very sensitive, and are much

I more portable than mercurial barometers, but more liable to

liisarraDgements. Fig. 132 shows a simple arrangement of a

I selfHrecording aneroid, a is a corrugated steel box partly

z8z COAL-MimNG.

exhausted of air. The atmospheric pressure upon the upper surface of the box tends to push it down, whilst the spring of the box tends to push it up. When the atmospheric pressure increases the box top is depressed, and when it decreases it is raised by the spring.

One end of the pointer b is connected to the box top by the link c; b is pivoted at d, and carries a pencil, e, at the end. The pencil-point presses lightly against a paper wrapped round the slowly revolving drum/.

When the atmospheric pressure increases the box top is. depressed and the pencil is raised ; the combined vertical movement of the pencil and horizontal movement of the drui

result in a slanting line being drawn upon the paper, way a chart is made which shows continuously the variation in atmospheric pressure, the quicker the variations in pressuthe more the lines on the chart approach the vertical.

Thermometers.— WqAtsXis. temperatures are measured ti thermometers, but when the temperatures are very higi pyrometers are employed. Thermometers depend for tha action upon the fact that certain substances vary grea and uniformly in bulk with the temperature. The ordin-iy thermometer consists of a thick glass tube of small but ua form bore, sealed at one end and terminating in a bulb at C other.

Instruments.

TMs bulb contains alcohol or mercury, wbich also extends a short distance up tlie tube.

As the temperature increases the mercury expands in the buib and rises in the tube, and when the temperature decreases converse is the case.

The two fixed points of temperature are the freezing -nd boiling points. Freezing-point is the temperature of rnelting ice, and the boiling-point is the temperature of steam from water boiling under the normal atmospheric pressure. (The temperature at which water boils varies with the pressure, being less when the pressure is low.)

Thermometers are marked on three different scales, namely, ' Centigrade, Fahrenheit, and Reaumur. The gradations on

Fahrenheit, freezing-point 32°, boiling-point 212° Centigrade, ,, „ 0°, „ „ n

Reaumur, „ „ 0°, „ „ I

From this it follows thai —

1° Fahr. jj Cent, and Reaumur 1° Cent. f Fahr, and Reaumur 1° Reaumur f Fahr. and Cent Fahrenheit's scale is popularly employed in Great Britain, for scientific work the Centigrade scale is almost universaL To convert degrees Cent, to degrees Fahr multiply by B: and add 32.

Example. — Convert 60 degrees Cent, to degrees Fahr. I

60" Cent. — 108° Fahr.

I So that the temperature is 108 degrees above freezing-

Point on Fahrenheit's scale, and as the freezing-point is 32 degrees, the reading will be loS -f 32 UO degrees. Convert i6a degrees Fahr. to degrees Cent. 162 degrees Fahr. 162 degrees — 32 degrees degrees above freezing-point, and 130 X 73'2 degree Cent.

Coal-Mtning.

Examples similar to the above may be worked by lie following formulae : —

Cx9 ., Rx9,

F — - ' ami + 3! 32

The Water-gauge— Small differences in iiuid pressure C measured by a " water-gauge." Tliis, in its simplest form, " consists of a glass tube bent into the shape of the letter U, and provided with a sliding scale of inches and decimals- Water is poured into the tube, filling the bend and reaching a little way up each leg. The top of one leg is open to ik Kimosphere and the other communicates by a pipe with lie ir, the relali\-e pressure of which it is desired to measure,

The water-gauge is used in mines to measure the pressure which produces ventilation. As explained in Chapter XX., mines arc ventilated by a difference in pressure betwewi columns of air in the upcast and downcast shafts, the pressure in the downcast shaft being always the greater. If a watergauge is placed in the intake and the pipe from the closed end ia led into the return, one column of water is subjected to the pressure of the intake and the other of the return air. But uf the pressure of the intake is the greater, it will press down the water in the with which it communicates, raising it i" the other leg, and the difference in pressure per square fool is equal to a column of water i square foot in area, and of hei(:ht etjual to the difference in level between the water in the two legs of the water-gauge.

A culiic inch of water weighs 0*036 lb., so that a column of water i square foot in area and i inch high weighs

1 gives the rule that : Inches of water-gauge x 5" i.% pressure per square foot.

Lighting.

lamps are unsafe when exposed to high velocities ; the modern lamps are provided with shields or bonnets, and have their inlets and outlets so arranged as to prevent a rapid current of air passing through the lamp even when It is exposed to a very high velocity.

3. By the gauze being allowed to become red hot, and so lose its cooling action. This may occur where lamps are left in an explosive mixture, nhich continues to bum in them. A good safety-lamp should become extinguished if left in an explosive mixture, the products of combustion should not be able to pass freely away ; hence the lamp becomes filled with incombustible gases, and the flame dies out.

The Davy Lamp. — This lamp is shown in Fig. 136. It consists of a brass oil-vessel, surrounded by a wire gauze about 7 inches long and inch in diameter. The vessel is screwed on to a brass ring, which is connected to the lamp top by four bars or standards. The course of the air to and from the lamp is indicated by arrows in the figure. The Davy lamp is now quite obsolete. It gives a poor light, owing to the flame being surrounded by gauze, and is unsafe in a current which has a velocity of more than from 3 to 5 feet per second.

When placed in a tin case with a glass front, it is known as a " Tin can Davy," and in this form is still employed by the officials in some of the North of England pits on account of its alleged virtues as a gas-tester.

The Clanny. — In this lamp (Fig. 137) the flame is surrounded by a short thick glass cylinder surmounted by a gauze. The fresh air enters above the glass, and the products of combustion pass out at the top. Owing to the absence of gauze around the flame, the Clanny gives a superior light to the Davy ; but it is not now used, being unsafe at a Velocity of about 8 or 10 feet per second.

The Strpheiisoii.—'Y\\\% lamp (Fig. 138) has a gauze rather larger in diameter than that of the Davy ; the gauze surrounds a glass cylinder provided with a perforated copper cap. The air to support the flame enters through holes in the base of Ihe lamp, and the products of combustion pass out through

Coal-Mining.

The Hygrometer. — Tbe humidity of the air is measure

I by an iDstrument known as the hygrometer.

Air can only hold a certain amount of moisture in suspen sion, and this amount varies with the temperature, the highe/ the temperature of the air, the more moisture it will cany. When air contains its maximum amount of moisture it is said to be saturated. If saturated air is cooled, its capacity iot moisture is decreased, and part of the moisture it contaios ii deposited in the form of dew. On the other hand, if the temperature of air is increased, its capacity for moisture is also increased, and it dries up any moisture it comes in contact with. Thus cool air goes down a pit, and becoma heated as it passes along the roads ; this increases its capaol)' for moisture, and causes it to absorb any there may be present. This drying action has a very important bearing upon the danger of explosions from coal-dust.

The most common form of hygrometer is that known u

Mason's, which depends upon the fact that the action of

evaporation is accompanied by a lowering of the temperature.

This hygrometer consists of two thermometers placed side

by side. The bulb of one of these is kept moist by bang

wrapped round with a piece of muslin. One end of this muslin

is dipped in a small vessel of water, and draws the water up

k to the bulb by capillary attraction. If the atmosphere is di/i

' moisture is evaporated from the muslin round the bulb, causing

the temperature to be lowered, so that the reading of the t"0

thermometers is different. If the air is saturated with moisture

no evaporation can take place, so that the reading of the tW

thermometers is the same.

Anemometers,— The velocity at which air travels measured by an anemometer. A Davis anemometer is shown in Fig. 134-

It consists of a small fan, the vanes of which, being set at an angle, are revolved by the air. These vanes are conneeW . by gearing to dials, which show the number of lineal feel of ir which pass the instrument.

Instruments.

To read an anemometer similar to the one shown in [Jig. 134, the position of the small finger is first noted, this

t read off from

gives the hundreds ; tho tens and units a

the larger dial. The reading of the

instrument shown in the figure is 67B, I To use the anemometer, it is held tin an airway for exactly one minute, I the dials are read off before and after jthe trial, and the former reading sub- ;tracted from the latter gives the number of lineal feet of air which liave passed the instrument during she minute, or, in other words, the velocity of the current in feet per Bninute. The velocity in feel per '"'- '.1+—

minute multiplied by the area of the gives the quantity passing in cubic feet per minute. I Example.— K road is feet wide by 7 feet high ; the

velocity is 550 feet per minute. What is the quantity ?

Area of road, 8-5x7= 59"5 sq. feet Quantity passing, 59*5 x S5° 32725 cub. feet per minute

If the quantity of air passing along a road is known, the Telocity can be determined by dividing the quantity by the rea of the road.

Example. — The quantity of air passing along a road of the fcmi and dimensions given in Fig, 135 is 35,000 cub. feet per minute. \Vhat is the velocity ?

The area of the road must first be determined. It will be noticed that a section of the road consists of a semicircle and a rectangle ; the areas of each must be found separately, and added together.

area of the semicircular portion is equal to half the area of a circle feet in diameter. The rectangular portion

feet wide, and its height is the total height of the road limbs the radius of a circle feet in diameter, that 4 feet.

J

Coal-Mining.

Area of semicircular portion

J, rectangular portion Total area quantity

Velocity

The velocity of an air-current varies greatly in differerparts of the same section of a road ; it is always higher in tta, centre of the road, and lower near the roof floor, and sides

In some cases it has been found that the velocity in the COUr; is more than double what it is at the sides. This is due the air which rubs against the sides being retarded by ibe friction against them. If the anemometer is held in one position during the whole of the trial, erroneous results arc obtained. To obtain the average velocity, it should be slow'y moved in the manner indicated by the dotted lines and arrow in Fig. 135. In making very important observations, tbe road should be divided by vertical and horizontal strings, an the velocity obtained in each of the divisions thus made.

Care must be taken to keep the anemometer squaicl]' facing the current ; and the section of the toad in which i' is held should be as regular as possible, because ledges projections produce eddies, and increase the variations i" velocity.

Chapter Xxii.

Lighting.

Vhere naked lights are permitted they genetally take the Vmd of tallow candles or small tin oil lamps ; the former are *lie more generally used, being stuck into lumps of clay, by hich they can be fixed to the props or to the coal face. Oil are chiefly used in Scotland ; they consist of small conical-shaped tin vessels, having a spout through which the "Vvick passes and a hook on the top, by which they can be Secured to the timbers, or carried on the workman's cap. The Employment of naked lights is becoming rarer as collieries are increasing in size and depth; in some districts naked lights commonly used, whereas in others safety-lamps are almost laniversal.

Naked lights give a better light than the best safety-lamps, lictice where they can be used the danger from falls of roof is somewhat reduced, and the output of coal per i Klightly increased.

The downcast pit bottom and sidings are illuminated either

Twith large paraffin lamps, gas, or electric light ; the latter is now

the most common at large collieries, as it is safe in an explosive

mixture, except in the case of accident A further advantage

of electric light at pit bottoms is that open lights of any sort

can be altogether prohibited down the pit, and this lessens the

chance of their being inadvertently taken into the workings.

Safety- ia flips. — A safety-lamp should be absolutely in-

jL capable of firing an explosive mixture under any possible

)Jk combination of circumstances which could occur underground ;

r

396 Coal-Mining.

being cut. Additional security is attained by stamping some device upon the rivets, by changeable dies fitted on to the press.

Some lamps are locked by means of bolts closed with springs and withdrawn by magnets, by compressed air, or by a partial vacuum ; this type of lock is very secure when in good order, but in some forms can be opened after the has been subjected to the rough usage often met with in minei Lamps of the Protector type are so arranged that the action of unscrewing the oil-vessel draws a sleeve over the flame and extinguishes it when the lamp is opened.

Relighting Lamps. — Tn many collieries no naked lights are allowed in the mine, and all lamps must be sent out to be relighted when tliey Jiave become accidentally extinguished, This is a very serious inconvenience, as when a man, working in a remote district, loses his light, a couple of hours or more may elapse before be can get it back relighted.

Lamps are now made that can be lighted whilst locked; this is accomplished either by means of matches carried inside the lamps, or by the aid of electricity. The Wolff lamp is an example of the former class; the matches are arranged in a waxed tape, wliich is coiled spirally in a box within the lamp. These matches can be struck one at a time just over the wick tube by manipulating a lever. Tliese lamps are very convenient for the use of officials who have to travel the workings and airways alone, but can hardly be recommended for the workmen, as the accident which extinguished the light may have damaged the lamp, and it should not be relighted until it has been carefully examined.

Lamps may be lit by electricity either by heating a platinum wire placed just over the wick tube by means of a fow-tension current, or by a spark produced by a current of high tension. The former method is employed with lamps which bora the vapour given off from light oils, and the latter with the ordinary oils burned at wicks. The electric current is usually furnished by an accumulator, and the wire is heated or spark produced when a connection is made between the two terminals of the

lamps are unsafe when exposed to high velocities ; the modern lamps are provided with shields or bonnets, and have their inlets and outlets so arranged as to prevent a rapid current of air passing through the lamp even, when it is exposed to a very high velocity.

3. By the gauze being allowed to become red hot, and so lose its cooling action. This ma-y occur where lamps are left in an explosive mixture, which continues to bum in ihem, A good safety-lamp should become extinguished if left in an explosive mixture, the products of combustion should not bo able £0 pass freely away ; hence the lamp becomes filled with incombustible gases, and the flame dies out.

The Dary Lamp. — This lamp is shown in Fig, 136, It consists of a brass oil- vessel, surrounded by a wire gauze about 7 inches long and ij inch in diameter. The vessel is screwed an to a brass ring, which is connected to the lamp top by four bars or standards. The course of the air to and from the lamp is indicated by arrows in the figure. The Davy lamp is now quite obsolete. It gives a poor light, owing to the flame Ijemg surrounded by gauze, and is unsafe in a current which has a velocity of more than from 3 to 3 feet per second.

When placed in a tin case with a glass front, it is known as a " Tin can Davy," and in this form is still employed by the officials in some of the North of England pits on account of its alleged virtues as a gas-tester.

T/ie Claniiy. — In this lamp (Fig. 137) the

Burrounded by a short thick glass cylinder surmounted by

a gauze. The fresh air enters above the glass, and the

products of combustion pass out at the top. Owing to the

absence of gauze around the flame, the Clanny gives a superior

light to the Davy ; but it is not now used, being unsafe i

velocity of about 8 or 10 feet per second.

J Tlic Stephenson.— lamp (Fig. 138) has a gauze rather

iffk larger in diameter than that of the Davy ; the gauze surrounds

, E a glass cylinder provided with a perforated copper cap. The

hH ai[ to support the flame enters through holes in the base of

pB the lamp, and the products of combustion pass out through

a g8 C OAL-MINING.

The advantages claimed for electric lamps are —

1. Absolute safety (unless the glass breaks),

2. They keep quite cool in any atmosphere, and do not go out if overturned.

3. They can be held at any angle in order to facihtate the examination of the roof.

4. They can be turned on or off at will, so that, in case a set of men should become imprisoned, a light could be maintained for a long time by using one lamp at once.

A few electric lamps should be kept at every colliery, as they are of great value to parties exploring a mine after an explosion has occurred, or for any similar work. They should, however, be used in conjunction with ordinary safety-lamps, so that the presence of poisonous or explosive gas may be detected.

Fire-damp Indicators. — The presence of gas (CHJ in the atmosphere of a mine is detected by the behaviour of the flame of the safety-lamp.

To test for gas the lamp flame is drawn down very low, so that it may not daz/le the eyes of the observer ; the lamp is then raised slowly and carefully into the place in which gas is expected and the appearance of the flame noted. When about 2; per cent, of gas is present the flame is slighdj drawn, flickers a little, and shows a very faint blue cap; as the percentage of gas increases these eflfects become more and more marked. If less than per cent, of gas is present, no visible effect is produced on the lamp flame, so that other means have to be adopted for measuring the percentage of gas present when it forms a proportion of less than about of the atmosphere.

It is desirable to measure very small proportions of gas, because the presence of a very small percentage greatly adds to the explosive properties of coal-dust ; and by knowing what proportion of gas is present in the return airways nnder normal conditions, the effect of a reduction in the quantity of the air can be ascertained.

Lighting.

ilarsaut in its ordinary form. It is similar in construction to the Clanny, except that it is provided with a shield or bonnet, JHnd is fitted with two, and in some cases three gauzes. The Miuzes are slightly conical in shape, as shown in the figure, irrhe course of the air-current to and from the lamp is indicated Ijy the arrows ; there is no distinct division between the intake ead return air, which is detrimental, as the fresh air is apt to lingle with the spent air, causing the light to burn dimly.

A lamp such as the one shown in Fig. 139, can withstand M explosive mixture travelling at a velocity of from 30 to 40 feet per second.

The chief feature of this lamp (Fig. 140) is Ihe metal chimney a in the figure, which is secured in position b/ the gauze diaphragm. The chimney separates the intake air from the return and induces a brisk current through the lamp, these lamps are extinguished if tilted, because the spent air,

Coal-Mining.

[instead of going up the chimney, passes away on oiie"siae c r the lamp, and, meeting the fresh air on its way to the Aame, : I carried back and puts out the light. Mueseler lamps may

either unbonoeted, or they may be bonneted, in which ra e

Ihey are able to resist a high velocity.

He/'Plewkite-Gray. — This lamp (Fig. 141) is much used ty officials. The feed air enters the lamp at the top, through tubes a, and passes to the flame through the gauze ring b ; tl -e products of combustion pass away through the upper gauze ("i and out at the top of" the lamp ; the outlet is restricted at ''

in order to keep the upper portion of the lamp filled with tl

products of combustion. The lamp can be extinguished means of a "shut-off," which is a contrivance for closing tt inlets and so causing the lamp to be extinguished by cutticrrS off the supply of air. The shut-off consists of a flat brass riti— "R placed over the tops of the tubes (shown in section at

Fig. 141). The ring is pierced with holes so arranged ihsthey come exactly over the tops of the tubes and offer obstruction. To extinguish the light, the ring is turned unt -'"' the holes in it no longer coincide with the tops of the tube which are then covered with the solid portions of the rin S- Shut-off arrangements can be apphed to any bonneted lampcrs, but are more commonly arranged to close the outlet holes the top of the bonnet.

The advantage gained by having the air inlet at top of the lamp is that a very thin layer of gas can 1— detected. This lamp has a conical glass, which enables tlroof to be inspected more easily, as the light is not obstruct**d by projecting bonnet and flange, as is the case in mo lamps.

The Thorncbitiry. — This lamp is provided with two co "dicentric glasses having a space between them ; a metal chimn"/ extends from the top of the inner glass, and is surrounded a gauze and bonnet. The feed air enters through holes in base of the bonnet, passes through a gauze and down the between the glasses ; it then goes through another gauze to tfc' flame. The products of combustion pass up the metal chimneJl

Lighting. 295

tlraugh the large gauze, and away through holes in the upper part of the bonnet.

Thorneburry lamps are rather heavy, but are safe and give a very good light. They are made in large sizes, to Be hung in pass-byes and at other busy places,

lUuininanis. — The oil burned in a safety-lamp may be either vegetable, animal, or mineral ; frequently a mixture is employed.

Mineral oils give a good light, and do not require as much attention as the other varieties, being less liable to form crusts on the wick ; they are, however, rather more dangerous to use, and none should be employed which have a flashing point of under 73 degrees Fahr, The wick tube should be flat, about inch in width, and the lop of the tube should stand about inch above the bottom of the glass.

The wick should be short, and fit loosely in the tube, to allow the oil to circulate freely, to which end some wick tubes are made with a corrugation in one side. The height of the wick is regulated by a " pricker," which consists of a wire passing in a small tube through the oil-vessel, and bent at the end in such a manner as to enable it to catch the wick through a slot in the tube provided for the purpose. The light given by 1 safety-lamp under ordinary conditions varies between and candle power, though towards the end of the shift, and in a dusty or impute atmosphere, the light frequently falls below the former figure.

The cost for oil should not reach per lamp per shift, and the total cost, including cleaning, repairs, and renewals, should lot exceed \d. per lamp per shift.

Locks. — AH safety-lamps must be securely locked before being taken into workings in which naked lights are prohibited.

The simplest form of a really efficient lock is the lead rivet ; this consists of a hasp secured to the lamp frame and passed Over a brass staple fixed to the lamp bottom. The hasp is secured by means of a small lead pin, which is pushed through the staple and firmly riveted, by means of a press, in such a tQaimer that the hasp cannot be lifted without the lead pin

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296 COAL-MmmG.

being cut. Additional security is attained by stamping some device upon the rivets, by changeable dies fitted on to Ibe

Some lamps are locked by means of bolts closed with springs and withdrawn by magnets, by compressed air, or bj a partial vacuum ; this type of lock is very secure when in good order, but in some forms can be opened after the limp lias been subjected to the rough usage often met with in mines. Lamps of the Protector type are so arranged thit the action of unscrewing the oil-vessel draws a sleeve over the flame and extinguishes it when the lamp is opened.

Relighting Lamps. — In many collieries no naked lights are allowed in the mine, and all lamps must be sent oat to be relighted when they have become accidentally extinguished. This is a very serious inconvenience, as when a man, working in a remote district, loses his light, a couple of hours or mote may elapse before he can get it back relighted.

Lamps are now made that can be lighted whilst locked; this is accomplished either by means of matches carried inside the lamps, or by the aid of electricity, The Wolff lamp is an example of the former class ; the matches are arranged in a waxed tape, which is coiled spirally in a box within the lamp. These matches can be struck one at a time just over the wick tube by manipulating a lever. These lamps are very convenient for the use of officials who have to travel the workings wid airways alone, but can hardly be recommended for the wortmen, as the accident which extingiiished the light may have damaged the lamp, and it should not be relighted until it has been carefully examined.

Lamps may be ht by electricity either by heating a platinum wire placed just over the wick tube by means of a low-tension current, or by a spark produced by a current of high tension. The former method is employed with lamps which bum llw vapour given off from light oils, and the latter with the ordinaij oils burned at wicks. The electric current is usually furnished by an accumulator, and the wire is heated or spark produced when a connection is made between the two terminals of

' baHery and those on the lamp ; the lamp itself usually forms one lenninal, and an insulated wire passing through the lamp toltom serves as the other.

To light a lamp, it is placed on a stand which is connected to the battery and has two terminals, one of which presses gainst the insulated wire and the other against the lamp bottom. The current then passes through the circuit in the lamp, and either heats the wire or produces a spark, as the case may be. The relighting batteries should be locked, and placed in charge of a responsible person, who should examine every lamp before lighting it.

Electric Lamps.— Portable electric lamps have been Introduced for use in mines, but their employment has not as fet become at all general.

They are more costly than ordinary safely-lamps, and, cough they give more light, it is not so well diffused. So long B the glass remains intact, electric lamps cannot cause an explosion, but should the glass become broken, an explosive mixture might be ignited ; in this they are only on an equality tith the ordinary oil lamps.

The chief drawback to the use of electric lamps is that bey give no indications of the presence of gas or " damp," ltd as the workman is almost entirely dependent upon the lehaviour of his lamp as a guide to the state of the air, this is ( rather serious matter.

One of the best-known electric lamps is the Sussraan, fitch consists of a small incandescent lamp mounted on the bp of a storage battery.

1 The lamp and battery measure aj by by S inches, and thigh from to 4 lbs,, which is about the weight of an dinary oil lamp.

The battery is of tlie Faure or pasted type, and contains liquid that can spill if overturned ; two cells are employed, ich having an E.M.F. of 2 volts. The ceils are charged by I dynamo, the operation taking 12 or 13 hours; and when Blj' charged the light is maintained for 8 O' 9 hours.

398 Coal-Mining.

The advantages claimed for electric lamps are —

1. Absolute safety {utiless the glass breaks),

2. They keep quite cool in any atmosphere, and do not go out if overturned.

3. They can be held at any angle in order to fadliUte tlie examination of tlie roof.

4. They can be turned on or off at will, so that, in ase a set of men should become imprisoned, a light could be maintained for a long time by using one lamp at once.

A few electric lamps should be kept at every colhety, M they are of great value to parties exploring a mine after aa explosion has occurred, or for any similar work. They should, however, be used in conjunction with ordinary safety-lamps, so that the presence of poisonous or explosive gas nuy be detected.

Fire-damp Indicators.— The presence of gas (CHJ in the atmosphere of a mine is detected by the behaviour of the flame of the safety-lamp,

To test for gas the lamp flame is drawn down very low, so that it may not dazzle the eyes of the observer ; the lamp is then raised slowly and carefully into the place in which gu is expected and the appearance of the flame noted. When about per cent, of gas is present the flame is slightly drawn, flickers a little, and shows a very faint blue cap; the percentage of gas increases these effects become more and more marked. If less than 2j per cent, of gas is present, no visible effect is produced on the lamp flame, rt that other means have to be adopted for measuring the percentage of gas present when it forms a proportion of lesi than about of the atmosphere.

It is desirable to measure very small proportions of gSJi because the presence of a very small percentage greatly adds to the explosive properties of coal-dust ; and by knowing what proportion of gas is present in the return airways ondet normal conditions, the effect of a reduction in the quantity of

air can be ascertained.

Lighting. 299

Instruments for measuring minute percentages of fire-damp e known as fire-damp indicators. Many different types ive been introduced, depending for their action upon the Ho wing priociplcs : —

I, The behaviour of certain classes of llame when burning an atmosphere in which gas is present,

1. The contraction 'of the volume of a mixture of air and IB when in contact with a heated platinum wire, owing to e burning of the gas,

3. The greater amount of heat or light given off from a ated wire when the mixture exposed to the wire contains gas.

4. The difference in the rate of diffusion of gas and air,

5. The difference in the specific gravity of gas and air.

6. The difference in sound given off by a tuning-fork if .s is present.

Those designed upon the first of these principles are the ost practical and successful.

The oldest of these is the Fteltr, which consists of a large Dip burning pure alcohol. In construction the lamp is mewhat similar to a large Davy, but the wick is of the grand type, that is, it is wrapped around a tube through lich air passes to the Hame. When per cent, of gas is esent a cap of inch in height is produced, and when E atmosphere contains 2 per cent, of gas the cap extends |iit to the top of the lamp.

In its original form this lamp is highly dangerous, even in nirrent of very moderate velocit)'.

Clowes' Hydrogen Fin-damp Detector. — This appliance is own in Fig, 142. It consists of a detachable steel cylinder,

fitted to an ordinary Hepplewhitc-Gray lamp. This linder is about 5 inches long and i inch in diameter; it Btains hydrogen at a pressure of about 100 atmospheres, and attached to the lamp by means of a dip and by the screw b. nall tube, c, runs from the cylinder through the oil-vessel, id extends a little above the lamp-wick, the flow of the 'dtogen being regulated by means of the screw d. A test first made with the oi! flame in the usual way, the hydrogen

Coal-Minwg.

being shut off. If 3 per cent, or more gas is present, i detected by a cap on the oil flame, but if no cap is shown, hydrogen is turned on and lights at the oil flame ; this latt then extinguished by drawing down the wick, and the made again with the hydrogen flame. As this flarot extremely hot and non-luminous, a cap is shown when a small percentage of gas is present ; per cent, is said to j

a cap about inch in height, and i per cent, gives a C3 about inch.

After the test has been made, the wick is pushed up lit at the hydrogen flame ; the hydrogen is turned off" anc cylinder detached.

Siokes' Fire-damp Indicaloi: — This arrangement is some

similar in principle and application to Dr. Clowes' appar

' except that pure alcohol is employed instead of hydrogen.

The alcohol is contained in a small vessel fitted wi

Lighting, 301

long tube, and is used in conjunction with a safety-lamp which has a small pipe running vertically through the oil-vessel and closed with a spring cap. To make a test with the alcohol flame, the tube of the alcohol vessel is pushed through the pipe; the alcohol is then lit at the lamp flame, which is drawn dotrn and extinguished.

The Beard'Mackie Gas Indicator. — This apparatus can be fitted to an ordinary safety-lamp ; the principle upon which it depends is the absorption of gas by platinum wire, causing incandescence. It consists of a small frame of brass and platinum wires fixed vertically over the lamp flame. This frame is arranged like a ladder, the brass wires forming the supports, and the platinum wire, 6 staves. The height of the flame is regulated by a thin iron wire placed below the lowest platinum strand. The presence of gas causes the platinum wires to glow, and the number of wires affected indicates the percentage of gas present If the lowest strand only glows, per cent, of gas is present 3 if the two lowest, i per cent. ; and if all, 3 per cent.

3o8

COAL-MINfNG.

between the cage corners and shaft sides. There is usuiUy considerable oscillation at the meeting of the cages, owing to the restriction of the area for the passage of the air.

Ropes and Chains. — WncBng ropes are now always made of steel. They may be either roOnd or flat. Flat ropes are never employed at new collieries, owing to their greater weight and cosl. Round ropes are made up of strands twisted together, each strand being composed of thin wires ; usually the strands are coiled round a. central core of hemp. Flat ropes are made up of several thin round ropes placed side by side and stitched together with wire. Sereral qualities of steel are used in the manufacture of colliery rope. Plough steel has the highest tensile strength, no to iso tons per square inch, and Bessemer or mild steel the lowest, 40 to 45 tons per square inch. Round winding or hauHng ropes may be either of Ordinary Lay, Lang's Lay, or Locked CoU.

In ropes of ordinary lay the wires in each strand me twisted in the opposite direction to the strands in the rope, as

shown in Fig. 147. This method of twisting the rope results in the crowns of the strands being exposed to the greatest amount of wear, and leads to the wires breaking at those points.

Fig, 148 shows a rope constructed on 's lay principle;

Winding.

s possible, consistent with strength and durability, as, if heavy, the pulleys may spin after the cage is at bank le rope is stationary. Pulleys should run quite truly, ise much extra wear is put upon both ropes and pulleys, ure usually made in one piece, but to facilitate carriage re sometimes made in halves or quarters and bolted er.

Fig, 143. — Steel head gear.

iges. — The tubs are conveyed up and down the shaft in These cages carry from one to twelve tubs, and have >ne to six decks, varying according to the size of the ind tubs and the power of the engines. The weight of He is usually about 50 per cent of the total weight of and coal.

iere are usually two cages in each shaft, one of which ids whilst the other ascends, and as the ropes from both

3IO COAL-MmiNG.

upon the circumstances under which it will have lo woili. K a rope has to pass round a small pulley or sharp bends, the wires must be of small diameter, and their number increased in order to give the necessary flexibility.

The approximate weight of round ropes may be calculated by the following formula : —

C circumference in inches ; W weight in lbs. perjrud

Hemp ropes, W -5-

Iron or steel ropes, W --

For example, a steel rope 5 inches in circumference and 500 yards long would weighs

5X5x5°':

: 6250 lbs. 55-8 .

The following are the formulas for determining the appioiimate breaking strains of round ropes : —

B breaking strain in tons ; C circumference of rope is inches.

Hemp

B

and C

Iron

B

X i-s

V?,

Mild steel

B

C X 2,

„ c

V?

Plough steel

B

C" X 4,

„ c

v/f

The factor of safety for winding ropes is usually taken it 10. This means that the working load of a winding rope should be only J5 of the breaking strain.

The reasons for employing so high a factor of safety are— I. If the chains are allowed to become slack, the strain on the rope may greatly exceed the normal load.

WINDING. 30s

hangers b, h. The decks are provided with rails upon which the corves stand, the latter being kept in position by the bars d, which are raised when they are changed. A sheet-iron bonnet, f, is provided to protect the men travelling in the cage from anything which might fall down the shaft. The cage chains ate secured to wrought-iron plates riveted to the tops of the hangers. Each pair of chains is connected at the top by a ring, and each of the three rings is connected to a plate as shown in the figure.

Id a few instances no cage chains are used, their place being talcen by a strong bar, which passes through the bonnet

secured to the cage frame

j' the centre of the cage, and i ough a coach-spring.

Cages should be as light and rigid as possible, and for this

ason they are usually constructed of angle, tee, and channel teel ; the joints between the vertical hangers and horizontal logs are often made by means of an intermediate plate,

hich gives a larger area for the rivets and stiffens the whole

tame.

Propi or A'j.— When the cage reaches the surface, the lidl corves are pushed off, and empty corves pushed on in their place. Whilst this is being done, the cage rests on props keps, a set of which is shown in Fig, 145. As the cage is

J

$12

Coal-Mining.

section at B and outside elevation at C (Fig. 150). The end of the socket is then hammered firmly into position, and the three hoops, which have previously been slipped up the rope, are driven down on to the socket.

I'll;, 15a,— Socket for round ropes.

Locked-coil ropes require a special form of socket. The examples shown in Fig. 151 are supplied by Messrs. Geoi Elliott & Co.

These cappings consist of an open-ended conical socket, furnished with a bolt to carry the cage chains. To fix this, it is first slipped down the rope, and the rope end enlarged and made wedge-shaped, either by driving into the rope copper or soft iron conical plug, as at A ; or by means oT half-round wedges, as at B (Fig. 151). The socket is then drawn down over the wedge-shaped end, and the bolt which has to carry the link inserted.

wmoiNG. 307I

taken by short guides or off-lake rods, which are placed on either side of the cage and not at the ends.

Rail guides are usually employed in deep shafts of limited area, where there is not sufficient clearance between cages and sides to admit of the use of rope guides. Flat-boitomed steel rails, weighing 50 or 60 lbs. per yard, are usually employed; they are bolted to buntons qr girders placed about 10 feet part, the general arrangement being similar to that adopted "with timber guides. Rail guides are very durable and efficient, tiut are expensive in first cost, and are somewhat noisy in use. Wire-rope guides are largely used, and are preferable to ny form of rigid conductors under ordinary conditions. The -opes are suspended from the bead-gear, and hang down the haft to the sump, where they are weighted with cast-iron weights to keep them taut.

The ropes themselves are similar in construction to ordinary -ound wire ropes, except that each strand consists of one solid vire of large diameter, instead of being built up of thin wires. "This is to enable the ropes to stand great wear without the "vvires breaking. Each rope is hung from the head gear by xneans of several pairs of strong clamps. By this arrangement length of spare rope can be provided, which is desirable, "because the end of the rope which is in the sump is apt to ciiorrode. Each rope is weighted in the sump by cast-iron "Vveights, about i ton being allowed for every 200 yards in length 3f rope. The ropes are passed through staples fixed to timbers in the sump to hmit the oscillation.

Four guides are usually provided for each cage, the cages teing fitted with small cast-iron thimbles, which embrace the guides. Loose guides are often hung down the shafts between the cages in addition to the other guides, or somedmes instead of the inner ones.

Fig. 146 is the plan of a shaft fitted with these loose or "rubber" guides. The cages are brought close together and kept from contact by the loose guides a, a, which are not in any way attached to the cages. By using these loose guides and bringing the cages close together, more room is left

Coal-Mining,

Winding Ennes. — The work that winding engines kve to perform is very different from that required of most engines. They are continually stopping and starting, and both load and speed vary at almost every stroke. For these reasons, winding engines are usually built with a view to strength, simpliciljf, and handiness, rather than to economy. The great majotily of winding engines are simple, non-condensing engines, and many work with but lite expansion. The tendency now is for collieries to use steam at much higher pressure than formerly, and winding engines are being built to take advantage of this by working compound. The steam from winding engines is condensed at a few places by independent condensers.

Nearly all the large winding engines which are now built are fitted with some form of automatic cut-ofF gear, which comes into action as soon as the engines have attained thcit maximum speed, and cuts off the steam as early in each stroke as is necessary to maintain that speed.

Winding engines may be either vertical or horizontal, but the latter are by far the more common. Except for very small places, winding engines are direct-acting, that is, the connecting rods are coupled direct to cranks on the dniu shaft without the intervention of gearing. A pair of couplrf engines should be employed, their cranks being at right angles to each other ; this ensures smooth running, and one engine s exerting its maximum power whilst the other is on its deadcentre. Double-beat equilibrium valves are usually employed, being much more easy for the engine-man to handle than the ordinary slide-valve. Fig. 153 shows a large pair of winding engines bulk by Messrs, Thornewell & Warham, of Burton-on- Trent.

Egnalising the Load on Winding Engines. — The load upo" a \s'inding engine is made up of the weight of unbalanced rope plus the weight of the coal : the weight of the ascending cage and corves being balanced by that of the descending ones. The length of rope which has to be raised becoins shorter as the cage ascends, and part of it is balanced by the

this case the wires which form the strands are twisted in ! same direction as the strands themselves. By this arrange- !iit a much larger surface is exposed to friction, which results

— Sleel ropE— 's lay.

being more uniform, hence the ropes have a. longer

Fig. 49 shows a locked-coil rope, as constructed by [essrs. George Elliott S: Co., of London and Cardiff. The mer strand is composed of ordinary round wires, but the nter coils are of wires of special section, coiled spirally in ach a manner as to interlock and form a perfectly smooth liking surface.

iflvantages of locked-coil ropes are — . They do not twist in working; this is frequently of importance, especially in sinking.

J. They are very flexible, and wiU therefore work round tmall drums and pulleys.

3. They possess a large and uniform working surface.

4. They are of less weight and size, strength for strength, tlian ropes of ordinary construction.

The number of wires of which a rope is composed depends

3'6

Coal-Mining.

descending rope. Vhen the cages meet in the centre of the shaft, the descending ropes equal in length to the asceodiDg rope, so that the weight of the ropes is balanced and has qd influence on the engines. When the full cage is at the pit-top, the whole weight of rope is on the empty side and is assisting the engines, so thai if the weight of the rope were just equal lo the weight of the coal, there would be no strain on the engine at all. If the rope were heavier dun the coal, the descending would overbalance the ascending load, giving rise to what is known as a negative load.

For example, if the coal raised per wind weighed 3000 lbs,, and the weights of therops were 5000 lbs, each, at the commencement of the wind there would be 5000 -f- 3000 8000 lbs. against the engines ; in the middle the load would be 3000 lbs. only, as the ropes wouid be balanced ; and at the end of the wind the load would be 3000 — 5000 —2000, that is, a native load of ;ooo lbs.

So that, although the average load is 30QO lbs, the engines have to raise 8000 lbs, at the benning of the wind, and hold back aooo Ibs.atibc end. This is, of course, very detrimental, M power has to be provided for raising nearly three times the average load, and engines woik' ing under such conditions cannot well be economical.

Balance AVj.— The simplest method of

equalizing the weight upon a winding engine Is by means of a balance or tail rope. The general arrangement of a balance rope is shown in Fig. 153. A rope, equal in weight to each of the winding ropes, is hung from the bottom of one cage to the bottom of the other ; it makes a turn m the sump, where It may either pass round a pulley, as shown in the figure, or simply hang in a loop. With this airangemeiit the weight of balance rope plus weight of winding rope is

Winding.

2. The apple is rarely as strong as the rope.

3. The fires harden with use and the strength of the rope I decreases.

Examples. — (i; Find the safe working load of a plough- I steel rope inches in circumference.

B 4'S X 4'5 X 4 81 tons; taking 10 as the factor of ] Safety, the safe load is 8'i tons.

{2) What size mild-steel rope would be required for a I working load of 4 tons ?

The rope must have a breaking strain of 4 X 10 40 tons, J

a.nd the circumference is C

4'47 inches.

In estimating the load upon a winding rope the weight of Xlie rope itself must be taken into account. In deep pits the -weight of the rope forms a very considerable proportion of the load.

Example. — Find size of plough-steel rope to lift a load of .4 tons from a depth of 500 yards.

Using the formulae given above, and taking the factor of safety as 10 —

4C 8960=

40 + m'

2960 -|-25oC*

8960

14, and C 37

inches.

Ropi Cappings. — Rope ends are fitted with cappings or ckets. Fig. 150 shows three views of a socket for a round 'sinding rope.

To fit a socket of this description, the rope, where it Comes into it, is wrapped round with copper wire, the wrapping Extending to within a foot or two of the rope end. A hollow Cone is then slipped over the wrapping, and the loose wires \'hich extend beyond are bent back over it, as shown io

Coal-Mining.

section at B and outside elevatioa at C (Fig. 150). The end of the socket is then hammered firmly into position, and the three hoops, which have previously been shipped up the rope, are driven down on to the socket

Loclced-coil ropes require a special form 0/ socket. The examples shown in Fig. 151 are supplied by Messrs. George EUiott & Co,

These cappings consist of an open-ended conical socket, furnished with a bolt to carry the cage chains. To fix this, . it is first slipped down the rope, and the rope end enlarged J and made wedge-shaped, either by driving into the rope a — copper or soft iron conical plug, as at A ; or by means oF half-round wedges, as at B {Fig. 151). The socket is then J drawn down over the wedge-shaped end, and the bolt which has to cany the link inserted.

BB Ciaim. — The approximate safe working load of chains may ' Is calculated by the following formula ;-

S working. load in tons ; D diameter in eighths of an I inch,

J', and D v'S ,X i

Fk;. 151. — Sockets for locked-coil ropes."

Examples. — (i) Find the safe working load of a chain vnade of -inch iron.

S 3'6 tons

Id be required for a working load

o inch It inch

314 Coal-Mining.

Winding Engines. — The work that winding engines I to perform is very different from that required of most engi They are continually stopping and starting, and both load a speed vary at almost every stroke. For these reasons, winding engines are built with a view to strength, simplicity and handiness, rather 'than to economy. The great majority '

of winding engines are simple, non-condensing engines, and

many work with but little expansion. The tendency now is

for collieries to use steam at much higher pressure than__ formerly, and winding engines are being built to take oAvaa — tage of this by working compound. The steam from windinT engines is condensed at a few places by independeoc condensers.

Nearly all the large winding engines which are now are fitted with some form of automatic cut-off gear, whiclt comes into action as soon as the engines have attained maximum speed, and cuts off the steam as early in each stroke3 as is necessary to maintain that speed.

Winding engines may be either vertical or horizontal, bu*" the latter are by far the more common. Except for verv small places, winding engines are direct-acting, that is, - connecting rods are coupled direct to cranks on the drun — ro. shaft without the intervention of gearing. A pair of engines should be employed, their cranks being at right angler to each other ; this ensures smooth running, and one engine s exerting its maximum power whilst the other is on its centre. Double-beat etjuilibrinra valves are usually employee3, being much more easy for the engine-man to handle than th e ordinary slide-valve. Fig. 152 shows a large pair of winding engines built by Messrs. Thornewell & Warham, of Burton-Oc:3- Trent.

Equalizing lite Load on Winding Engines. — The load upo B" a winding engine is made up of the weight of unbalanc fc rope plus the weight of the coal : the weight of the ascendiit cage and corves being balanced by that of the descendio £ ones. The length of rope which has to be raised become* shorter as the cage ascends, and part of it is balanced by th.

322 Coal-Mining.

plates are kept in position during the winding by means of the soft-iron rivet gy which passes through all four plates, and is sheared when the hook is pulled into the ring.

Winding from Two I.eveis.—\N\\GU two seams have to be wound from one shaft, they should, if possible, be connected by a drift, and both wound from one level. If this cannot be arranged, the winding engine is fitted with a drum having two diameters, the larger diameter serving the deeper sara. This arrangement is objectionable for several reasons ; the output from each seam is liinited, and if more coal is turned from one seam than from the other, one cage has to travel the shaft empty, and the cost of handling the coal is increased.

When winding from two levels, the relative diamelere of the drum vary with the depth of the two seams. Thus, if the depths to the seams were 360 and 410 yards respectively, and the smaller diameter of the drum were 12 feet, the larger

Calculating the Size of Winding Mngiries. — The work done by a winding engine is spent on raising the load and oa imparting velocity to it. The simplest method of finding the approximate size of winding engines for a given amount of work is to calculate the size of engine necessary to raise the load plus 35 per cent, for friction, and take this as one of 1 pair. Although this rule is largely employed and gives fairly accurate results, it is not scientifically correct, as the power spent in the acceleration of the moving mass is not taken into consideration.

In making calculations of this description, there are always several factors to assume, and to do this correcdy requires a certain amount of judgment.

The piston speed of winding engines is usually from 400 to 600 feet per minute, and the cage speed from 25 to 50 feel per second ; the larger the engines, the higher the piston and cage speed. The stroke is usually about twice the diameter of the cylinder, and the diameter of the drum about three or four times the length of stroke.

Winding. 323 I

Exampk. — Find the size of a pair of winding engines to pull 1500 tons in 10 hours from a depth of 500 yards, the weight of the ropes being balanced, and the average pressure of steam on the piston 45 lbs. per square inch.

Tons in to hours, rsoo ; tons per hour, -5°? 150, Taking the cage speed at 3s feet per second, the number

of seconds spent in a journey are S°° 43 nearly,

Allowing rz seconds for changing corves, the time spent per wind is 43 4- 12 55 seconds.

Number of winds per hour — - — ? 6s'g.

Making an allowance of about 10 per cent, for minor delays, the number of journeys per hour -may be taken at 60.

Tons per journey 2i 5600 lbs.

If the diameter of the drum is four times the length of stroke,

the leverage is --- to i 6-382 to i ; that is, the

load moves through 6'2Sz feet for every foot moved through by the piston upon which the pressure is applied ; hence the pressure must be 6'282 times the load. The total pressure on piston, then, is 5600 X 6-282, but 25 per cent, must be allowed for frictional resistances, so that the total pressure

must be Taking the average steam

pressure on piston at 45 lbs. per square inch, the area is

5 600x6 -283'

ind the diameter

/5600 X 6 V 45 Xo-,

45 X 100 ' V 45 X o'7854 X 100

A pair of engines would be required having 36-inch cylinders by 6-feet stroke, the drum being 34 feet in diameter.

If the weight of the rope were unbalanced, it would have to be added to the weight of the coal, and would necessitate laiger engines.

Chapter Xxiv.

Haulage.

The conveyance of the coal from the workings to the shaft is usually performed in at least two operations. First, the coal has to be collected from the various working places, and taken to the pass-byes or sidings, from whence it is conveyed by the main haulage to the shafts. The pass-byes should be kept as near to the workings as possible, in order to reduce the length of the secondary haulage, which is much more costly than the main haulage.

Corves. — The vehicles in which the coal is carried are variously known as "corves," "tubs," "boxes," "trams," etc They vary in capacity from about . to about 50 . The average weight carried in the Midlands is from 9 to iz , ; in Wales very much larger weights are commonly dealt with, even in thin seams.

Corves may be constructed either of wood or of iron ; a wooden corf of ordinary construction, suitable for a load of 10 to 12 ,, is shown in Fig, 158.

The body is rectangular in siiape, and built of elm or larch boards inch in thickness; the comers may be protected by external plates of g-inch sheet iron. The framework upon which the body is carried consists of two oak legs, a, a, each 6 by 3 inches, held in position by cross-pieces or spendrils. The body is secured to the framework by bolts, and by the bars i, which are made of 2 by inch flit wrought iron. These bars extend along the sides and across the body of the corf, stiffening it and bracing the whole

Hi

Winding.

tanner the weight of the chains assists the engine at the c rnencement of the wind when the load is greatest, and retards J it at the end when the load is lightest.

Cogs Indicators. — Every winding engine must be provided with an indicator to enable the engine-man to know the exact of the cages in the shaft. The simplest form of in- <locator consists of a small drum driven from the main shaft of tile engine, upon which is coiled a light chain. The chain is Carried over a small pulley, and to it is attached a weight which slides in a vertical frame. As the Cage is raised, the weight descends, and reaches the bottom of its run vhen the cages meet ; the chain then Coils on to the drum in the reverse direction, and raises the weight to the top of the frame as the cage reaches the top of the shaft. When the cage is Hearing the surface the indicator is arranged to ring a bell which is

attaclied to its frame.

Fig. 15s shows a more modem

and superior form of cage indicator.

The bevel wheel a is driven by a light

crank from the engine crank-pin,

and drives the wheel c through the

small wheels a and shaft c. c carries

a pointer, which revolves round a

dlj and shows the position of the

Cages. The pointer moves backwards

and forwards round the dial, making a complete revolution for each wind. Some indicators have two pointers, one making a complete revolution per stroke.

Brakes. — Every winding engine must be provided with a lirake, which should be of sufficient power to hold the load if the engines should be disabled. Brakes depend upon friction

for their action, and consist of a block or strap which is pressed

ainst a brake ring or the drum. Brakes may be worked

(G. 155. -Cage

r

3'6

Coal-Mining.

The Road. — The corves run on rails. These are usually flat-bottomed, weighing from 15 to 30 lbs. per yard, and made in lengths of from 6 to 1 2 feet. They are spiked on to sleepers placed transversely, from 3 to 6 feet apart.

In the main roads, rails of heavy section are employed; Ihey should be in long lengths, and the ends connected by fish-plates.

The rails in the working places are of lighter section and shorter lengths ; they are spiked to sleepers, but no fisliplates are employed. Junctions are made either with short points, or, in the case of unimportant roads, with metal plates or hard-wood boards, the latter being preferred in steep seams.

When main roads change their direction, the curve eoanecting the straight lengths should be the arc of a circle tangential to both straight roads. The radius of the curve should be as large as possible, especially where the haulage is rapid, The proper method of laying out a curve is shown in Fig. iSJ BA and CA are the straight roads which it is desired to connect by a tangential arc. Bisect the angle BAC by the line DA, draw GF parallel to CA at a distance from it equal to the radius of the required arc, cutting the line DA at G. G is then the centre from which the tangential arc must be struck.

Vhen corves run round a curve by gravity, they have 1 tendency to jump the outer rail, but when they are pulled round with a rope, they are liable to be pulled into the side, over the inner rail. To guard against the former contingencji the outer may be raised above the inner rail ; and to prevent the latter, rubbing boards may be set at the inner side of fiie bend, against which the corves rub, and by which they are prevented from being pulled into the side.

— Method of selling 01

Winding.

sTe designed to save the ascending cage horn the effects of an . overwind by liberating the rope and suspending (he cage in the I bead-gear.

Fig. igy shows King's detaching hook as seen when suspending a cage. It consists of four wrought-iron plates. The cage is hung from the outer plates a in the figure, and the rope "s held by jaws on the inner plates b. The inner plates are pivoted on the central pin c. When the hook is carrying the load in the shaft, the wings d, d on the inner plates project beyond

FlO. 157.— King's detaching hook.

I tile outer plates, but that portion of the plates shown shaded in I 'he figure is flush, ? is a strong iron plate bolted on to the head- r, and through which the winding rope passes on the way I ftom the pulley to the cage. If an overwind occurs, the hook is I pulled into this plate, and the projecting wings d, d are knocked I into the position shown in the figure. As the wings are forced I inwards, the projections // are forced outwards, and hold J the hook securely as in the figure ; at the same time the jaws b, b f are forced open and the winding rope liberated. The inner

Coal-Mining.

plates are kept in position during the winding by means the soft-iron rivet g, which passes through all four plates, ar is sheared when the hook is pulled into the ring.

Winding from Two Levels. — When two seams have to I wound from one shaft, they should, if possible, be connect* by a drift, :uid both wound from one level. If this cannot 1 arranged, the winding engine is fitted with a drum having tw diameters, the larger diameter serving the deeper seam. Th arrangement is objectionable for several reasons : the outp from each seam is limited, and if more coal is turned from oi Beam than from the other, one cage has to travel the sha empty, and the cost of handling the coa! is increased.

When winding from two levels, the relative diameters i the drum vary with the depth of the two seams. Thus, if th depths to the seams were 360 and 410 yards respectively, ani the smaller diameter of the drum were 12 feet, the large

diameter would be -- --, — 13 feet 8 inches.

Calculating the Size of Winding Engines. — The work done by a winding engine is spent on raising the load and on imparting velocity to it The simplest method of finding the approximate size of winding engines for a given amount of work is to calculate the size of engine necessary to raise tlw load plus 25 per cent, for friction, and take this as one of a pair. Although this rule is largely employed and gives &irly accurate results, it is not scientifically correct, as the power spent in the acceleration of the moving mass is not taken into consideration.

In making calculations of this description, there always several factors to assume, and to do this correctly requires a certain amount of judgment

The piston speed of winding engines is usually from +00 to 600 feet per minute, and the cage speed from 25 to sofcS per second ; tlie larger the engines, the higlier the piston md cage speed. The stroke is usually about twice the diametei of the cylinder, and the diameter of the drum about three times the length of stroke.

Winding.

Find the size of a pair of winding engines to pull 1500 tons in to hours from a depth of 500 yards, the weight of the ropes being balanced, and the average pressure of steam on the piston 45 lbs. per square inch.

Tons in 10 hours, igoo; tons per hour, "°— 150.

Taking the cage speed at 35 feet per second, the number of seconds spent in a journey are '°° - 43 nearly.

Allowing 12 seconds for changing corves, the time spent per wind is 43 + 12 55 seconds.

Number of winds per hour — - — -° 65'5.

Making an allowance of about 10 per cent, for minor delays, the number of journeys per hour-may be taken at 60,

Tons per journey 5600 lbs.

If the diameter of the drum is four times the length of stroke,

the leverage is -— to i 6-282 to i ; that is, the

load moves through 6-282 feet for every foot moved through by the piston upon which the pressure is applied ; hence the pressure must be fi'zSa times the load. The total pressure on piston, then, is 5600 x 6'282, but 25 per cent, must be allowed for frictional resistances, so that the total pressure

, g6oo X 6'282 X IS"; „ , . must be -. Taking the average steam

pressure on piston at 45 lbs. per squa re inch, t h e area is

5600x6-282x125 J .u J' . /5600 y. 6-282 X 135

— --, and the diameter . /

45 X too ' V 45 X 0-7854 X roo

35j inches.

A pair of engines would be required having 36-inch cylinders by 6-feet stroke, the drum being 24 feet in diameter.

If the weight of the rope were unbalanced, it would have to be added to the weight of the coal, and would necessitate larger engines.

330 Coal-Mining.

electricity or compressed air are now being ii some collieries to do the work formerly done by horses.

Self-acting: Inclines. — Coal is usually conveyed ftomi higher to a lower level by means of self-acting inclines, or "jinneys." Awheel or drum is fixd at the top of the incline, round which a rope passes. To one end of this rope the full ran is attached, and to the other end the empty nio. As the full run descends the incline, it pulls the empty run up by means of the rope.

Fig, i5o shows a common arrangement of roads on a self-acting incline. There are pwsbyes at top, bottom, and centre. The lower length is laid with two rails, and the upper with three.

A common form of jinney wheel is shofB in Fig. 161, In order to prevent the rope from slipping when the brake is applied, two wheels are employed, the rope being passed round both ; the upper and smaller of the two is provided with one groove, and the lower with two. The lower wheel is fitted with a powerful brake. The wheels and frame arc set vertically beiweeo the two roads at the top of the incline, A sdfacting incline should be steep at the top ami flat at the bottom, to enable the load to start quickly and be easily stopped.

The motive power of a jinney consists of the gravity of the full run ; the resistance is made up of the gravity of the empty run and of the rope, plus the friction of rope and full and empty

Fig. 160. — runs. Thus the power of a jinney may be Self - acting increased by putting additional corves on to the runs, and the resistance may be decreased by

shortening its length and so reducing both friction and gravity

of the rope.

Ha Ulage.

3'S

gether. The legs are a few inches longer than the body, to rm buffers, and are protected by a hoop-iron ring.

The draw-bar is made of 3 by 3 'iich best wrought iron, arious forms of couplings are employed. They may be ther loose — in which case a hole is pierced in either end of e draw-bar, and the coupling provided with a couple of hooks — ' one end of the draw-bar may be fitted with a link, and the her end with a hook, In the figure both link and hook are ted at each end ; this makes a secure coupling, and both ends the corf are similar. The wheels and axles are of cast steel, e wheels being 12 inches and the axles inch in ameter the gauge of the road is 34 inches. Wheels may

Fio. 158.— Tiral

e either fast on the axle and revolving with it, or loose j in tie latter case, both wheels and axles are free to revolve, eels are now generally made fast on the axles, as they can le more efficiently lubricated, and are less liable to get out of imder. Loose wheels are better adapted for running round rery sharp curves, because the outer rail of a curve is longer ihan the inner rail, consequently, if both wheels are fast on ie axle, one has to skid through a short distance. The "beel base is the distance between the centres of the axles ; Shea the wheel base is short, the corves can be more easily landed and lifted on the road if they become derailed. A Aort wheel base causes the corf to be unstable and more Kisily upset when travelling steep roads.

r

328 Coal-Mining.

Hence the tractive force necessary to move the level road is of the weight.

If the plane along which the corf has to he moved inclined, the force of gravity must be taken into account well as the resistance due to friction.

Example. — A road dips at the rate of i in 3 ; find tractifc.e force necessary to draw up a train of corves weighing 10 toiB&

The dip is 1 vertical to 3 horizontal, hence the lengt b, measured along the slope for every foot of vertical rise or fa 1— U, is /iM' /lo 3'i6z-

Resistance due to gravity —r~tr 70S4 lbs.

Total resistance ,., (See also Chapter XVII.)

The useful H.P. developed, if the speed is 8 miles [ hour, is found as follows : —

S miles per hour foot-lbs. per minute 704 x 7484

ji 1 704 X 7484 ,

and horse-power iSQ'o

Tramming. — When the distances are very short, or t.

road too low to admit ponies, the corves may be pushed -*y hand. The "trammer" or "putter" holds the corf with bt''' hands, and pushes it along with the assistance of his Tramming is very costly, and every care should be taken '" keep down the length of the roads along which corves must trammed. In some methods of working thin seams, no ponare employed, all the coal being trammed from the faces lo l'we ropes, the extra expense of the tramming being compensat by the lessened cost of making the roadways.

The cost of tramming is enormously increased if the lo"

Haulage.

bas to be pushed up an incline, so that tramming should never be allowed except on favourable gradients.

If the road is perfectly level, more force is necessary to move the full than the empty corves. For example, if the full corf weighs lo . and empty corf 3 ., the coefficient of friction being the force necessary to move a full corf on a

level road is — -Hi 20 lbs., whilst the empty corf would

only require a force of 6 lbs. From this it follows

that, in order to get the load exactly equal in both directions, the road must have a slight dip in favour of the full load.

The most favourable gradient may be found by the following formula : —

H height of plane; L length of plane ; F weight of full corf; E weight of empty corf; K coefficient of friction.

(F -

Example. — Full corf weighs 15 ., and empty cort 5 ., and the coefficient of friction is : find the gradient upon which the load is equal both ways.

L iS + 5 "

Hence the desired gradient

3 in favour of the load.

Horse Haulage. — Horses are employed to collect the from the various workings and haul it to the sidings. "VVhere gradients are favourable, and distances not great, horse liiulage is economical, but horses should not be employed on steep or long roads. Horses are attached to the corves either fcy chains or by some form of shafts, the latter being the better except on level roads. The cost of feeding a pit horse "Varies between gf. and 13J. per week, according to the selection and market price of the food. Small engines driven by

feet : find the horse-power necessary to haul lo tons of coal up it in 4i minutes, the hauling rope being inches in circumference.

The weight of the corves is usually about one-half the

weight of coal carried, so the total weight of coal ibi. and corves will be 15 tons 3316M

The weight per yard of a rope 25 inches in circumference is - -- — 3125 lbs. (see p. 310)

The total length of rope is goo yards, but the average Imgth i, "."mum length_+

450 yards, and the average weight is 450 X 3'rz5

Average moving weight 35,006

The length of the plane is 900 yards, and the height 50 yards, so that the resistance due to gravity is u weight.

Gravity of qoal, corves, and rope MMR igg lbs,

Friction of corves 600 „

Friction of rope 50 „

Total resistance 2595 „

The speed at which the load moves is 635 feet per minute, so that the

The maximum horse-power is rather more than this, sod the minimum rather less, on account of the varying weight the rope. Taking the useful effect of the engines at $0 cent, the necessary indicated horse-power is about roo.

This method of haulage is sometimes modified by havii two drums and hauling one train of corves up whilst another rims down.

Haulage.

Very long roads are usually divided into a series of jianeys, in order to proportionately reduce the weight of the rope.

The least inclination at which a jinney will work nnder given conditions can be calculated as follows : —

Find least inclination at which a jinney Soo yards long will

Fig. 161.— Jinney wheels and frame.

Work, when the corves weigh 4 . and carry i o ., 1 5 corves

to constitute a set, and rope to be inches in drcumference.

Weight of rope — x 800

-- 2Z120

„ empty set 15 x 4 X i „ full set 15 X 14 X II

„ full and empty sets 22 540 The force of gravity of the full corves must overcome the pavity of the empty set pins the frictional resistance of rope, full and empty sets. So that

M£H — + 635 (friction resistances)

625=

g

639

g

22-7

So that the least gradient at which the jinney would work 1

under the conditions given, is 1 in 33'7.

Jinmyingfram Two or More £ds.—\t

t often happensthataself-actinginclinehaa

a t— several intermediate landings to and lion

r which corves have to be conveyed. Fig. 162 illustrates the two most common methods of arranging this. A (Fig. 156)

shows the rope or chain divided into two

sections. A small sheave is fixed at each landing in such a manner that it can be moved clear of the roads when not re-

,"jr

quired. When serving the lower landing,

the top portion of the rope is uncoupled,

and lies idle, whilst the lower portion is

a in use. When the upper landing has lo

be served, the rope or chain is coupled at

1 rt and by means of a D link, and the

r sheave e is moved out of the way.

In the method shown at B, one chain extends the whole length of the incline.

and short lengths a and i extend from

,ni!i.

level to level, and can be uncoupled

i:and d. The figure shows ropes in poadon

to serve the second landing, the length

being uncoupled and lying idle.

Balance Inclines.— These are some-

times employed for conveying coal from

a higher to a lower level. They are used

chiefly in very steep seams on inclines

iln

F having several landings, and also to assis' f trammers on steep roads. The road is

Fig. 162. -

\arrange- laid with two pairs of rails, placed either

menls for from ievera

side by side or one inside the other. Tk

balance carriage travels on the one pair and

the corves

n the other. A rope passes round a pulley at the lop

Haulage.

. 'the incline, and has a balance carriage attached to one of its [ods ; this balance carriage is heavier than the empty and lighter Itan the full corf. When an empty corf has to be raised to (ly of the levels which communicate with the incline, the (tight of the balance carriage, as it descends the hill, pulls up le empty corf which is attached to the other end of the rope. lie empty corf is then changed for a full one whose weight is fficient to pull the balance weight back again to the top of : incline.

Single-rope Haulage. — This method of haulage is only )plicable when the dip of the road is sufficiently steep to lable the empty corves to run to the bottom of the hill and

g the rope after them by gravity.

The hauling engines may be placed either on the surface or kierground. They should have a drum provided with an icient brake, and capable of being thrown out of gear with

engine. To lower the empty corves, the engine is stationary d the drum thrown out of gear ; the corves run down the by gravity and take the rope with them, the speed being ntrolled by the brake. When they reach the bottom, the is changed from the empty to the full run, the drum [own in gear, and the engines started. The engines are nilar to winding engines, except that the drum is driven Wugh gearing in order to reduce the speed of the rope to tout 10 miles per hour.

The rope is carried on light steel rollers, about 6 inches in

The resistance the engine has to overcome is made up of —

ivity of coal and corves ) total wt. X vertical ht. of incline gravity of rope J

iiction of coal and corves

length of incline weight of coal and corves

Friction of rope "ght of rope Example. — The total rise in a road 900 yar

the tail rope. Either of these drums can be put in gear with the engine, or can run free, and each is provided with a brake. The tail rope is twice the length of the engine plane. It passes from the drum to the end of the plane, where it is taken round a return wheel and hack to the pit-bottom. The return wheel may be either horizontal or vertical In the former case it is set under the rails, and in the latter either at the road-side or between the roads in the pass-bye. The tail rope is carried from drum to return wheel on sheaves ; these may be carried on roof, floor, or side.

In the figure the empty corves are being hauled to the far end of the engine plane. To do this the main drum a is thrown out of gear, and runs loose; the tail rope-drum /' is iri gear, and as the rope is wound upon it by the engine the corves are hauled along. The main rope is attached to the end corf in the train, so that it is dragged to the end of the plane, behind the run.

When the pass-bye is reached, both ropes are changed on to the full train"; the main-rope drum is thrown in gear, and the tail-rope drum allowed to run loose; so that when the engines are started the load is hauled to the pitbottom by the main rope, and the tail rope dragged behind it in readiness for the next train of empties. Branches. — There are several methods by which branches can be worked. Fig. 164 shows one method which is frequently adopted. The branch road is provided with a separate tail rope double its length, and working round a return wheel io the usual manner. The principal tail rope has in it two shackles, c, c, by means of which that part of the rope marked b b can be disconnected ; these shackles are made very small and neat, to enable them to run round the return wheel.

The ends of the branch Uil rope a, a are also fitted with

Fig. 164. — Main an lail rope haulage - briuich.

Haulage.

shackles, When the train is in the pit bottom, the shackles in the principal tail rope come just opposite those in the ends of the branch tail rope. If the train has to run into the branch, the shackles c, c are disconnected and connected to the shackles at the ends of the branch rope a, so that when the engine starts the rope a moves, whilst b lies idle.

The main and tail rope method of haulage can be applied to roads having varying gradients and many bends ; it also possesses the great advantage of only requiring a single road, and for roads of great length there is no method by which a moderate quantity can be hauled so cheaply.

A very large output cannot be dealt with from a single road by the main and tail rope method, and chiefly for this reason it is seldom put down at new collieries, at any rate in the Midlands.

''i"P,

P :

Haulage by Endless Rope.— In this method of haulage a double road is required, and an endless rope extends from one end of the road to the other, and travels slowly along it. The general arrangement is shown in Fig. 165. The rope is taken down the shaft from engines on the surface, under the pulley a to the tightening wheel b, where the slack rope is taken up ; from b it is led down the engine plane, round the return wheel f, and back to the pit bottom, where it passes under the pulley d and up the shaft to the engine. The corves are hung on to the rope either singly or in sets, and the rope may travel either above or below them.

Engines, — The engines may be placed

r

Coaz-Mining.

either on the surface or underground. If the shaft is of moderate deptli, it is usual to fix the engines on the sur&ce, and drive the haulage by means of a belt rope ; but if Ihe shaft is very deep, the haulage is best driven either by electric motors or by engines driven by compressed air, placed underground.

The gearing of the engines is required to give the rope a speed of from 2 to miles per hour. For example, if an engine makes 70 revolutions per minute, and the rope wheel is 7i feet in diameter, what must the ratio of gearing be to give the rope a speed of ai miles per hour?

220 feet per mifl.

, ., , 1760 X 3 X 2i

2i miles per hour -r-- —-

Circumference of rope wheel 7J X 3T41 Revs, of rope wheel per min. — —-

Ratio of gearing 7 '49 to i

As the engines run in one direction only and at a unifonD "velocity, neither brake nor reversing gear is necessary, but a set of good governors should be provided.

Jfeipc Wheel. — Many patent clip pulleys have been designed,

but an ordinary taper pulley around which the

rope makes four or five turns is generally

adopted. An example of this class of pulley is

shown in Fig. 166, which is a section through

the rim. The pulley is made of cast iron, but

is fitted with a steel liner, a, which can be taken

out and renewed when worn. The rope goes

''wlf'd'*'''' on to the pulley at the larger and comes off at

the smaller diameter, so that each coil has to

slip down the pulley, and to enable this to be done smoothly

the pulley is tapered.

The steel liners are made of many different shapes ani) tapers ; the one in the hgure has a straight taper of i in la.

Haulage.

Thtming Pulleys. — Arrangements should be made for [Utiog up the slack in each rope. One form of tightening gear is shown in Fig. 167. The horizontal pulley a is mounted on the carriage which runs on a short length of rails. The rope passes round the pulley and strain is put upon it by means of the heavy weight c. Screws are sometimes employed instead of weights, but the latter are preferable, as they adapt themselves automatically to the varying stresses which are put upon the ropes. The tension carriages

are sometimes placed at the far end of the haulage road, but

more often close to the driving pulley.

Junctions. — The haulage on each road should be worked

bj an independent rope, so that one road may stand whilst the

Q

I Fig. 167.— Endless-rope haulage— tigh (an in g piille)'.

iWhers work, and any accident only alTects the road upon Wich it occurs.

The arrangements at an important junction are shown in Jig. 16S. a is a vertical shaft, having keyed on to it the rope Ifhee! b. Loose on the same shaft are the two rope pulleys c and p; each of these latter is provided with a friction clutch, by means of which it can be put into gear with the shaft a. The lift continually revolves, as it is driven by the engine through &e band rope, which passes four times round the fixed pulley The band rope does no actual hauling, but only serves 3 transmit the power from the engine to the shaft, and may e dispensed with if power is transmitted by electricity or Wnpressed air.

The pulleys c and d each serve a different road, and can

J

COAL-MmiNG.

Pbe started or stopped at will by means of friction clutch

' The arrangement shown in the figure is suitable for fixing ni 1 pit bottom which has two main roads; a similar arrangemt is placed at each branch road.

Fig, 168.— Endless-rope hiulaEe— arrangements

Friction ClutcJm.--ln Fig. 168, the shaft a contiM revolves, but the pulleys c and d must be arranged eithei revolve with the shaft or to run loose upon it. This is doD will by means of friction clutches. The principle upon id friction clutches act will be understood from Fig. 169.

Haulage.

le shaft upon which the pulley b runs loose ; is a. cast-iron boss, thich is keyed to the shaft a, and therefore revolves with it.

The pulley i is fitted with a flange, d, placed inside which is the casing e. This casing is connected to the boss c, and therefore revolves with the shaft. If the casing fits the flange loosely, it will revolve inside it, but by moving the sleeve / inwards, the casing is forced against the flange by the connecting rods g; the flange is thus held tightly to the casing and Is pulled round with it. The sleeve is actuated by means of a id-wheel and levers, and the pulley can be gradually thrown

Bi or out of gear without stopping the shaft.

Fig. 169.— Friolion clutch.

' Atfackmeiil of Corves to Mope. — The corves may be attached to the rope either singly or in sets. When the rope is Carried above the corves, the attachment is frequently made tij means of a lashing chain about 10 feet long, made of iron *bout inch in diameter. Each end of the lashing chain Cries a hook, one of which is hung on to the corf; the other tad of the chain is twisted three or four times round the rope tad brought through the hook. Clips are also used for over- Itead haulage, but chains have the advantage of requiring Rter binding pulleys, as the lopes need not be kept exactly in bW centre of the road.

When the rope is carried under the corves, some form of Wp must be used. For light gradients Fisher's chp, which is Pown in Fig, 170, gives excellent results. The hook a is hung Ip the coif, and the hauling rope is passed through the jaws 6.

r

The height of the plane is 660 feet, and the len| 5 280 feet, so effect of gravity is 5 of load.

Resistance due to gravity of coal, — — 12,432

„ „ friction of coal and corves, '"g" j.jjS

Total resistance ... ... i6.374

The speed of rope is miles per hour ; that is, 2I X 3S 220 feet per minute.

So that a resistance of 16,376 lbs. is being moved through a space of 220 feet per minute. Hence foot-lbs. of work done per minute are 16,376 x 220.

If the efficiency of the plant is 70 per cent., and a pair of engines are employed working at a piston speed of 360 ft per minute and having an average steam-pressure in ttit cylinder of half the pressure on the boiler, the diameter of their cylinders should be —

v/;

40 X 360 X 2 X 0-7854 X 70

155 inches

Wherever mechanical haulage is employed, means of cotnmunication with the engine-man must be provided. Tills is now universally accomplished by the use of electric signals. The current is carried by bare wires fastened upon insulatoni which are secured to props fixed alongside the road. By bringing these wires into contact with each other, or by connecting them by a metal conductor, a bell is rung in the enginehouse. Signal wires can also be made to cany telephonic messages by connecting them to small portable telephones.

Haulage, 343

corves have to pass across the road along which the full corves travel. If the ropes are carried overhead, they are raised at the branches to allow the corves to pass beneath them ; but if the ropes are under the corves, the rails are cut at and the rope is carried a little below rail-level.

To avoid the trouble caused by taking the corves across

one of the roads, subways are sometimes employed at busy

branches. When this is done the full corves, instead of

crossing one road, run underneath both, and are switched back

wtien they reach the other side.

The size of engines necessary for an endless-rope haulage ixiay be calculated as in the following example : —

Find the size of hauling engines necessary to haul looo tons in 9 hours up a road one mile long, having a total fall of feet, taking the corves to weigh 4icwts. and carry 10 ., tl€ rope to be 3 inches in circumference, and the pressure of s team on the boilers to be 80 lbs. per square inch.

Tons per hour, iii'i

Taking the speed of the rope to be miles per hour ; as the oad is one mile long, an amount of coal equal in weight to 11 the coal on the rope is landed at the top of incline times

1 t , . III'I

ti hour, hence the quantity on rope must average — ; —

44*4 tons 888 . Number of full corves on rope, =88*8, say 89 full, and the same number empty.

Weight of rope per yard — 4*5 lbs. ; total weight,

4*5 X 1760 X 2 15,840 lbs.

Total resistance gravity of coal (the corves balance each other) plus friction of full and empty corves and friction of the whole length of rope.

Weight of coal in pounds, 44*4 x 2240 99,456 Weight of corves in pounds, 89 x 2 x 4*5 X 112 89,712

Total ... ... ... 189,168

/ /

r

344 Coalmtning.

The height of the plane is 660 feet, and tlTei 5280 feet, so effect of gravity is of load,

Resistance due to gravity of coal, ""a — 12,432

„ ,, friction of coal and corves, 3,37*'

11 11 11 rope, '"a - a-" - 56*

Total resistance ... ... 16,37

The speed of rope is miles per hour; that is, x S5 22Q feet per minute.

So that a resistance of 16,376 lbs. is being moved through a space of 220 feet per minute. Hence foot-lbs. of work done per minute are 16,376 x 220.

If the efficiency of the plant is 70 per cent., and a pair of engines are employed working at a piston speed of 360 fet per minute and having aa average steam -pressure in the cylinder of half the pressure on the boiler, the diameter their cylinders should be —

16376 X 2

C 360 X 2 X 0-7854 X 70

155 inches

Wherever mechanical haulage is employed, means of communication with the engine-man must be provided. This is now universally accomplished by the use of electric aigos'*' The current is carried by bare wires fastened upon insulatorSi ' which are secured to props fixed alongside the road, By bringing these wires into contact with each other, or by connecting them by a metal conductor, a bell is rung in the engine* house. Signal wires can also be made to carry telephone* messages by connecting them to small portable telephones.

Pumping. 347

equal to that of a head of water 15 feet high, and is 15 x 0-434 6'5i lbs, ; and the downward pressure at c is equal to that of a head of water 20 feet high, and is 20 X 0-434 8'68 lbs. per square inch. The net upward pressure on either end equals the total upward pressure minus the total downward pressure, which is 15 — 6'5i 8'49 lbs, per square inch on b, and 15 — 8-68 6-32 lbs, per square inch on c. The effective pressure on the valve at a is the difference between these two pressures, and is 8-49 — 6-32 a'ly lbs. per square inch in the

I direction of the arrow ; so that if the valve is opened the water flows from the liigher to the lower pressure, that is, in the

! direction of the arrows.

To start a syphon, the whole of the pipes have to be filled with water. This may be done by fixing a hand-pump on to the delivery end, or by pouring in water through a funnel fixed on the pipes at their highest point. Great care must be taken to keep the pipe joints air-tight, or air will enter, as the pipes are under a partial vacuum. The pipes should have as uniform a gradient as possible, or air is apt to lodge in the high points and stop the flow by breaking the column of water.

Classification of Pumps. — Pumps used in mining may be divided into two classes : (i) Shaft pumps, and (2) dip I pumps. Shaft pumps may be worked by rods actuated by ' engines placed on the surface, or they may be worked direct by steam, compressed air, or electricity. When worked direct, shaft pumps are similar in design to those used for pumping water from dip workings to the shaft bottom.

Pumps driven by rods take up much more room in a shaft

than direct-driven pumps ; they are, however, economical in

Bteam consumption, and if the water should rise above them

, in the shaft, they are not affected, but under favourable

conditions can be kept at work for a considerable time.

Bucket Pumps, — An ordinary bucket lift is shown in I section in Fig 173, a is the windbore, b the pump clack, e the clack door, d ilie bucket, e the knock-off joint, / the

pump rods, g the bucket door, h the working barrel, and j the pump trees.

W'iWcrc.— The pump trees below the working barrel terminate in a windbore, through which the water which comes to the pump has to pass. The end of the pump is enlarged, closed at the bottom, and pierced with holes, All the water has to pass through these holes, which act as strainers and prevent solid substances from being drawn in.

Clark. — There are many forms of clacks; the one shown below (b, Fig. 173) is suitable for pumps up to a diameter of about 15 inches. The clack has two lids opening upwards; these lids are formed of leather strengthened with iron plates. They open to allow the water lo pass upwards to the working barrel, but close and prevent it from returning.

Clack Door. — The clacks are changed, when worn, through the clack door c. This is a strong cast-iron door bolted to the clack piece, a watertight joint being made by means of an iron ring wrapped round with tarred flannel, or some other packing material

Bucket — This is usually similar in construction to the clack, and has lids opening upwards. Arrangements must be made to allow ' the bucket to move up and down in the working barrel without water passing it The bucket shown in the figure is provided with a ring of leather, Bucfcet'purnp. which projects above the bucket shell; the weight of the water upon liiis leather presses it tightly against the working barrel, and so prevents water passing it.

Knock-off Joint. — The bucket is connected to the rods by means of a wrought-iron knock-off joint. By knocking the two hoops up, the bucket is freed from the rods, and can be witlvdrawn through the bucket door when the pump is at the lop of its stroke.

r PUMPING. 349

£ods or Shears. — Square pine rods are employed, the lengths being coupled by means of wrought-iron fish-plates and square through bolls. The rods for bucket lifts are wet ; that is, they work inside the pipes, which are always full of water. The stress upon pump rods should not be more than about 5 . per square inch sectional area.

Working Barrel, — This is a cast-iron pipe, turned inside to a true circle. If the water is corrosive, the working barrel should be lined with brass, as if the inside becomes rough the bucket leathers are destroyed very rapidly.

Pump Trees. — These are usually of cast iron, made in 9-feet lengths, and a little larger in diameter than the working barrel. By increasing the diameter of the pump trees, it is possible to draw the bucket through the pipes and change it at bank, in case the water rose above the bucket door.

Action of a Biuket Pump. — The action of a bucket pump is as follows : As the bucket is raised a vacuum is formed beneath it, and the atmospheric pressure forces water into the working barrel from the sump. The clack lids open for the upward passage of the water, but as soon as the upward stroke is completed they close and hold the water in the working barrel.

At the downstroke the water in the working barrel remains stationary, but passes through the lids in the bucket as it descends. At the next upstroke the water in the working barrel is raised the length of the stroke, because the bucket lids close, and if the pipes are full, a volume of water equal to the contents of the working barrel is discharged at the top, and at the same time water is drawn into the working barrel from the sump.

The vertical height from the level of the water in the sump to the top of the bucket, when at the highest point in its stroke, should not be more than about 25 feet, as the water is forced up by atmospheric pressure.

Bucket pumps will not satisfactorily raise water more than 100 yards in a single lift ; if the shaft is deeper than this, two or more lifts should be employed, the bottom one delivering into a tank, from which the next takes its water.

r

COAl-M/NING.

pump rods, g the bucket door, h the working barrel, and j the pump trees.

Winddare. — The pump trees below the working barrel terminate in a windbore, tlirough which the water which comes to the pump has to pass. The end of the pump is enlarged, closed at the bottom, and pierced with holes. All the water has to pass through these holes, which act as strainers and prevent solid substances from being drawn in.

Clack. — There are many forms of clacks ; the one shown below {h. Fig. 173) is suitable for pumps up to a diameter of about 15 inches. The clack has two lids opening upwards ; these lids are formed of leather strengthened with iron plates. They open to allow the water to pass upwards to the working barrel, but close and prevent it from returning.

Clack Door. — The clacks are changed, when worn, through the clack door e. This is a strong cast-iron door bolted to the clack piece, a watertight joint being made by means of an iron ring wrapped round with tarred flannel, or some other packing material

Bveket. — This is usually similar in construction to the clack, and has lids opening upwards. Arrangements must be made to allow ' the bucket to move up and down in the working barrel without water passing it The bucket shown in the figure is provided with a ring of leather, Backot'puriip which projects above the bucket shell; the weight of the water upon this leather presses it tightly against the working barrel, and so prevents water passing it.

Knock-off Joitil. — The bucket is connected to the rods by means of a wrought-iron knock-off joint. By knocking the two hoops up, the bucket is freed from the rods, and can be withdrawn through the bucket door when the pump is at the top of its stroke.

Pumping.

ion clack, e the top or delivery clack, d the ram or plunger, ; stuffing-box,/ the pump rods, g the rising main, and h barrel.

Clacks, — Both the clacks b and c are of the same design, each is fitted with lids opening upwards. When the lift

'ery long, double-beat or equilibrium valves are often iloyed ; they give a large opening with a low lift, and e with little shock. It is now becoming common to loy a number of small valves instead of one large one.

353 Coal-Mining.

Rams and Stitffing-hoxes. — The ram d a shell of cist iron, having its outer surface turned in a lathe. It is secured to the end of the pump rods /, and passes through the stuffing-box, which is packed with hemp or hydraulic packing, to prevent the leakage of water from the barrel. The stuffingbox and gland are usually lined with brass, and the ram may also be brass lined if the water is very corrosive.

Action of a Ram Pump. — As the ram makes its upstroke, water is forced through the bottom clack into tbe working barrel by atmospheric pressure. When the downstroke commences, the lids of the bottom clack close, and the ram forces the water in the barrel through the top clack into the rising

Pumping by Several Lifts.— Rams similar to the above are now made to force water to a considerable height in one lift ; formerly it was the practice to limit the height of escb lift to about loo yards, and to pump from a deep shaft by a series of lifts. This is convenient where feeders of water ae met with at different points in the shaft, as they can be dealt with by increasing the size of the rams,

A bucket pump does practically the whole of its work at the upstroke, whereas a ram delivers water at the downstroke only, so that by combining the two, the work done at each stroke can be to some extent equalized.

A common arrangement is to have a bucket lift at the bottom of the shaft, and ram pumps above.

The arrangement of rods and pumps in a shaft where the pumping is being done in two lifts, one a bucket and the other a ram, is shown in elevation in Fig, 175 and in plan in Fig- 176, which is an enlarged section on line de, Fig. 175. The main rod a is taken down the shaft to the bucket pump, whilst the ram b is driven by an offset rod.

Rods and pipes are secured by buttons placed across the shaft and let into the sides.

Catch-pieces, g, are bolted on to the rods at intervals, in order to catch them in case the pumps missed a stroke, 01 tbe

Pumping.

*nction clack, c the top or delivery clack, d the ram or plunger, t the stuffing-box,/ the pump rods, g the rising main, and h the barrel.

the clacks b and c are of the same design, Bnd each is fitted with lids opening upwards. When the lift

Fig. 175.— Pumping

' very long, double-beat or equilibrium valves are often **iployed; they give a large opening with a low lift, and 'we with little shock. It is now becoming common to ploy a number of small valves instead of one large one.

Coal-Mining.

Rams aiid Shiffing-boxes. — The ram is a shell of crt iron, having its outer surface turned in a lathe. It is secured to the end of the pump rods f, and passes through the stuffing-box, which is packed with hemp or hydraulic packing, to prevent the leakage of water from the barrel. The stuflfioS* box and gland are usually lined with brass, and the ram ma-y also be brass lined if the water is very corrosive.

Action of a Ram Pump. — As the ram makes its upstrote, water is forced through the bottom clack into the workicmg barrel by atmospheric pressure. When the downstroke cotaraences, the lids of the bottom clack close, and the ram forces the water in the barrel through the top clack into the risir£ main.

Pumping by Several Lifts.— Rams similar to the abo-f are now made to force water to a considerable height in oce hft; formerly it was the practice to hmit the height of eac=h lift to about loo yards, and to pump from a deep shaft by series of lifts. This is convenient where feeders of water met with at different points in the shaft, as they can be deaJt with by increasing the size of the rams.

A bucket pump does practically the whole of its work the upstroke, whereas a ram delivers water at the downstrolte only, so that by combining the two, the work done at eacn stroke can be to some extent equalized.

A common arrangement is to have a bucket lift at the bottom of the shaft, and ram above.

The arrangement of rods and pumps in a shaft where the pumping is being done in two lifts, one a bucket and the otter a ram, is shown in elevation in Fig. 175 and in plan in Fi& 176, which is an enlaied section on Hne dc, Fig. 175. The main rod a is taken down the shaft to the bucket pump, wli'*' the ram b is driven by an offset rod.

Rods and pipes are secured by buntons placed across shaft and let into Ihc sides.

Catch-pieces, g, are bolted on to the rods at inlervaXSi order to catch them in case the pumps missed a stroke ox*

Pumping.

rods broke. Strong timbers or girders are let into the shaft just below the bottom of the catch-pieces, to hold the rods if they should fall.

When rams are worked by single-acting Cornisb engines, the engines raise the rods and ram, but the downstroke — that is, the working stroke — is accomplished entirely by the weight of the rods. In very deep shafts the rods may have siderable excess of weight, and this must be counterbalanced. Fig. 177 shows a balance bob, which may be placed either on the surface or in a chamber got out for it in the shaft side. One end of the tee bob is coupled to the pump spears by

shaft

sdsif

gines,

-that

'eight

FiG. 175.— Section showing ram and bucket lifts.

a timber connecting rod, and the weight is secured to the other end.

The weight required to force a ram down may be calculated as follows :—

A ram 22 inches in diameter is delivering water against a head of 500 feet : find total weight of rods necessary.

Area of ram, 22 x 07854 3803 sq. in. Pressure per square inch on ram, 500 X 0-434 217 lbs.

Total pressure on ram, 217 x 38o'i3 82,488 lbs.

Add lopercenl. for friction instuffing-box.etc. 8,249 lbs,

Total pressure required 90,737 Iba.

Coal-Mining.

This amounts to 40 tons 10 ., which is equal to o?M

ig cwL per lineal foot of the rods.

Pump rods for deep shaJts should be made largest at the shaft top, where the weight upon them is the greatest.

Arrangement of Engines to work Shaft Pumps. —

Shaft pumps may be actuated by either rotary or reciprocating engines. The Comish engine is a good example of the re-

FlG. 177.— Balance bob.

ciprocating type. The pump rods are hung at one end of a beam, and the piston rod is coupled to the other; the engines make a pause at the end of each stroke, giving the pump valves time to close, and ensuring steady working.

Fig. 178 shows a reciprocating horizontal engine arranged to work two buckets or two rams by separate rods ; both pumps may be at the pit bottom and deliver to the surface, or one may be at the pit bottom and the other halfway up, pumping the water in two lifts. The pump rods are hung from the horizontal limbs of the two bell cranks, and the

Pumping.

engine piston rod is coupled to the vertical legs ; by this arrangement the strain on the engines is balanced, as one rod IS making a downstroke while the other makes an upstroke. A balanced arrangement suitable for a rotary engine is ,

Fig. 178. — Horizonla.1 engine working

shown in Fig. 179. Here the two bell cranks a and b are placed side by side, and driven by cranks from either side of the large spur-whee! c, c being driven through gearing by a horizontal engine.

Capacity of Single acting: Pumps. — The pumps shown in Figs. 173 and 174 are single-acting — that is, they do not deliver water at both up and down strokes. The effective speed

Fig. 179, — Pumps driven by rosary engine.

at which pumps of this class run is about 50 feet per minute ; the ram or bucket actually travels twice this distance, but delivers

water during only one-half of its time.

The size of a single-acting pump required to deliver a given

quantity of water may be found as follows ; —

Coal-Mining.

Find diameter of bucket pump necessary to pump 600 gallons per minute.

Eflective speed of ram 50 feet per n Gallons per foot of stroke, — - By formula given on p. 350, G rf X 0-034

Hence d /— , and /ji;! 19.7 inches dxar V 0-034 O'o34

Direct-acting Pumps. — A section through a double-acting pump is shown in Fig. iSo. a is the pump rod, which is a

Fig. i3o.— Double-acting piston pump.

extension of the engine piston rod ; b is the steam cylinder, which is fixed on the same bed-plate as the pump ; c is the pump bucket ; d and e are the suction, and / and g the delivery valves ; k is the air-vessel ; and m the delivery branch, on to which is bolted the rising main.

BtKket. — This is really. a piston, and differs from the bucket used in single-acting pumps by having no valves. It consists

Pumping.

3S7

of a solid cast-iron block fitted with a cup leather at either side ; these cup leathers are forced against the pump barrel by the water-pressure, and so prevent the water from passing the bucket.

Valves. — The valves shown in sketch consist of flat rubber discs working upon grids, and provided with a guard to , prevent them from opening too far. The disc is fixed at the i centre, and is raised by the pressure of the water upon its underside, whilst pressure from above closes the valves by forcing the rubber down on the grid.

Valves of this type are very efficient for lifts of moderate I height. When the head of water is great, groups of small ' circular brass valves are employed.

Air-vessel. — As water is incompressible, the flow in the rising main would stop and start at each stroke of the pump were it not for the air-vessel. This would cause a loss of I power, owing to the inertia of the water, and would lead to an ( irregular discharge, and to greatly varying strains on the pump. I

The air- consists of a cast-iron vessel, closed at the top and fixed vertically between pump and rising main. It iicts as a regulator by interposing an elastic body of air i between the pump and the rising main.

As the pump delivers its water, the air in the upper pait of 'j Ihe air-vessel {k. Fig. i8o) is compressed, and part of the water I is driven into the air-vessel. The moment the pump stops to ' reverse its stroke the pressure is relieved, and the air in the air-vessel expands and drives pirt of the water out of the ''essel into the rising main. In this way the flow of water is made fairly constant, and as the water is always kept in motion, the pump has not to start it from a state of rest at each stroke.

Air-vessels on large pumps are sometimes charged with air by means of a small air-pump, but those on smaller pumps are diarged automatically, the air which is drawn into the pump with the water rising to the highest point.

Pumps similar to that shown in Fig. iSo ate not suitable

3S8 Coal-Mining.

for high lifts or for bad water. When tlie leathers become worn the water slips past the bucket, and as this leakage is internal, it cannot be seen, and is difficult to detect. When the lift is high and the pump barrel roughened by wear or corrosive water, the leathers may require changing every few hours.

Action, — Sleam is admitted into the cylinder b (Fig. iSo) by valves, usually worked by some form of tappit. The steam presses first on one side of the piston, forcing it to one end of the cylinder and then to the other side, driving it back, and as the pump bucket is coupled to the steam-piston, it moves to and fro with it.

When the pump bucket is moving in the direction of the arrow, water flows through the suction valve d, and fills the space behind the bucket, whilst the water in front of the bucket is forced by it through the delivery valve g. In the return stroke, water is drawn in through the valve c, and expelled into the rising main through the delivery valve/.

Pumps of this class run at a piston speed of about loo feet per minute ; the si/.e of pump and steam-cylinder for a given duty can be calculated as follows : —

Example.— size of pump and engine to deliver 300 gallons per minute against a head of 150 feet, the available steam-pressure being 6o lbs.

Gallons per minute ... ... ... 300

Add 10 per cent, for slip 30

Gallons per foot of stroke, 3-3

Diameter of pump, 9'8s, say 10 in.

Pressure per sq. inch on bucket, 150 X o'434 65-1 Iba,! Area of bucket, 10 x 07854 78-54 ia,

Total pressure on bucket, 78-54 X 65*1 5113 lb&4

Add for friction in pump and in pipes, i

Total resistance 6

Pumping.

Take average pressure on piston at

, ., 60 X 2 Doiler pressure,

Area of steam-cylinder, - Diameter of steam-cylinder x/ -.

170-4 sq. in.

145. say I

This shows that the pump bucket should be 10 inches in diameter and the steam-cylinder 15 inches, the piston speed being 100 feet per minute.

Pipes. — The pipes should be of ample size, because the friction of water when passing through pipes varies with the square of the velocity. They should be of such a diameter as to keep the velocity of the water down to from 200 to 250 feet per minute.

Example. — Find diameter of pipes required for pump given in last example, allowing a velocity of azo feet per minute.

Cubic feet of water per minute, 7, Area of pipe

Area of pipe in square inches, 144 x o'liSa

Diameter of pipe

, / 3f42

When a pipe line is inclined, tlie pressure is the same as if the pipes were vertical, and of a length equal to the total nseof the incline; but as the length is greater for a given head *iien inclined, the friction is correspondingly greater, and allowance should be made for this by slightly increasing the wea of the pipes.

Double-acting Ram Pumps,- — -In the arrangement shown in ig. 181, two solid plungers, a and h, are connected to each other, and are given a reciprocating motion by means of a forked connecting rod, which is driven by a crank from a spur-wheel. The action of the pump is similar to that of

Coal'Mining.

a bucket or piston pump, one ram delivering whilst fhe o&er is drawing in water through the suction. The two rams work

Fic. i8i.— Double

through the stuffing-boxes /, /, and as they are externally I packed, leakage is readily detected. Ram pumps ate less

Fig. 182.— Section through one side of a WortliinBlon pump.

compact and more expensive than pumps of the bucket or piston type, but are much better suited for high lifts.

Duplex Pumps. — This arrangement consists of two Pumps placed side by side and mounted upon one bed-plate. The valves of one of the pumps are operated by levers driven ihe other ; thus one piston gives steam to the other, then finishes its own stroke and pauses until its valve is opened in *ts turn by the other engine.

Fig. 182 is a sectional view of one side of a Worthington Iump. E is the slide valve, driven by a lever from the engine tij its side ; F is the lever which operates the valve of the other Engine. The double-acting plunger B works through a deep JTnetallic packing ring ; the water enters the pump through the Suction C, and has a nearly straight course into the delivery D.

Three-throw Pumps. — These pumps are suitable for teiQg driven either by electricity or by wire ropes, and are ow very largely employed. They consist of three ram pumps IS laced side by side on one bed, and driven by connecting rods from three cranks, which are arranged on one shaft and set at a-K angle of 120° with each other. By having three pumps, the strain on the driving shaft is kept almost uniform, and the <delivery of the water nearly constant. Fig. 183 shows a three- tVirow Deane pump, as made by the Worthington Pump Com- i:>any, suitable for being driven by a belt from an electric motor.

Hydraulic Pumps. — In general arrangements hydraulic la-umps are somewhat similar lo the pump shown in Fig. r8o, the motive power is water at a high pressure instead of steam or compressed air. The hydraulic cylinder, which

|<2corresponds to the steam-cylinder d. Fig, 180, is usually of Smaller diameter than the pump, as the water-pressure which lives the pump is in most cases much greater than the pressure against which the pump delivers its water. The pressure of J the water employed for motive power may be either obtained artificially by a force pump, or from a natural head.

When worked by a natural head, a small volume of water at a high pressure is employed to raise a larger volume against a lower pressure. If, for example, water were piped down

'a shaft 400 yards deep, the pressure at the bottom of the pipa Would be 400 X 3 X o'434. sao'S lbs, per square inch.

If the volume of water amounted to 50 gallons per minute ' e horse-power due to this weight of water falling this distance

Pumping. 363

plied by vertical distance in feet divided by 33,000). About alf of this power would be absorbed by frictional and other *OEses, but the remainder could be utilized to pump water [&om dip workings to the shaft bottom.

Pulsometers. — These pumps are designed to lift large lumes of water against a low pressure. They are seldom are much used lal washeries, and sometimes isiDking pits. They have no Me parts, with the exception simple automatic valves, so not apt to get out of order. ;y will pump very dirty water lout trouble, but are rather Mtravagant in steam, and cannot ileal with high lifts. Fig. 184 is a sectional view of a pulsometer. It consists of a large pear-shaped casting, divided longitudinally as llo¥n. a is the suction pipe, k and c the inlet valves, d and ( the outlet or delivery branches, jf the steam-valve, and g the Ream inlet

To start a pulsometer, it is lUed with water, and the steam nrned on. The steam-valve / ttanged that it must cover one or other of the openings, but tarot cover them both, so that as soon as the steam is turned I, it rushes through the opening which happens to be covered into one of the chambers, and by its superior sure forces the water in the chamber through the delivery LOch into the rising main. The two delivery branches and are provided with valves, which open for the passage

IG. 184. — Pulsomeler pump, rubber ball, and is so

CHAPTER XXVr.

Surface Arrangements.

Engine-houses and Boilers.— The position of the engines, boilers, and other surface erections should be carefully chosen, so as to allow ample space, but with due regard to convenience and economy.

The boilers should all be set in a range, and room provided for extension ; they should be placed with the view of avoiding long ranges of steam-pipes, and provision should be made for the economical conveyance of coal to the firt holes, and of ashes from the ashpits. Each winding e should have a separate house, but whenever possible all the other engines should be under one roof. It is now becomii the practice to drive haulage, screens, pumps, washeries, etc, i by electric motors, so that the only engines absolutely necessary are the winding, electric generator, and fan engines, and shortly fans also wdl no doubt be driven by eJectric motOR. Some of the older collieries have an enormous number of small engines running for various purposes, but this leads to large steam consumption, on account of the great length of steam-pipes and inefficient working of small engines.

Shops and Stores.— The workshops and store-rooms should be built in one block, and should have a waggon road running alongside them, and a corf road running into each shop, so that heavy machinery can be loaded on a corf in the shops, and sent straight down the pit.

The shops should consist of carpenters', smiths', and fitters' shops.

Pumping.

from a sinking pit by a series of independent pumps is the ''regulation of the water. If one pump delivers more water than the pump above, part of the water must run back, and the upper pump dehvers more water than the lower, it will the cistern dry, and run on air.

Winding; Water.— Small quantities of water may be dealt with by the winding engine. The water is allowed to accumulate in the sump and water-levels during the day, and is wound to the surface at night. An iron water-barrel is either hung below the cage, or is provided with wheels and run on to the cage in place of the corves, and is dipped into the sump. At the bottom of the water-barrel a valve opening inwards is fixed, through which the water enters when the cage is dipped. The discharge at the surface is effected by a lever, one end of which is connected to the valve by a rod ; this lever strikes a bar when the cage is drawn above bank-level, and opens the valve.

Except when the quantity of water is small, winding should not be resorted to, as the shaft and fittings are damaged by tlie escaping water and by the vibration.

When a shaft is used exclusively for water winding, cigarshaped barrels are often employed, as they run steadily, and enter the water without shock,

Riedler Pumps. The chief feature of this class of pump is that the valves, instead of being left to close by the reversal of the stroke, are closed mechanically just at the proper moment. By this means these pumps can be run at a very high speed, without risk of injury. A piston speed of 300 to 400 feet per minute can be attained, which, of course, results in a large reduction in the size of pump required for a given

k

r

368 COAL-MrmNG.

Sidings. — Ample and well laid out sidings are of flie utmost importance in dealing expeditiously with a large output. An example of the general arrangement of collieij sidings is shown in Fig. i86. These sidings are arranged to work entirely by gravity, so that the colliery company require no locomotive. The railway company's locomotive pusha the empty waggons into the empty sidings, which have a grade of about I in 60 towards the screens. When empty waggons are required, they are lowered by their brakes to the screens where they are loaded, and when full they are lowered into the full sidings, from whence they gravitate over the weighing machine, and are taken away by the railway company.

Screens. — The pit bank should be raised from jo to 30 feet above the level of the sidings, to enable the aal to gravitate over the screens and belts into the waggoni' Modern pit banks are in almost every case constructed of iron or steel, ordinary steel girders of H section being usually employed, though some pit banks are built on cast-iron columns. It is desirable to have landings at the siding level as well is at the level of the pit bank ; the former being employed for winding horses, timber, etc., and the latter for coaL

Banking: the Corves, — The arrangements at a pit top must be well designed, in order to cope with the large outputs which are now required ; there are collieries now at woA which are turning over 500 corves per hour from one shaft. The full and empty corves should run on separate roads, and have a definite direction, all the roads being graded to enable

SUJtFACE ARRANGEMENTS.

The blacksmiths' shop should contain single and double hearths, and should be provided with a good steam hammer ; the fitting shop should contain lathes, shaping, drilling, and shearing machines.

A small foundry is a most valuable adjunct to a large

I. Downcast shaft, t Upcast shaft, i. Coko ovens.

J. Wiadlng engines, downcast shaft, X Winding engines, upcast shaft. L Fireholes.

Fic;. 185,— Surface arrangemonv

Econ

lain flue

Time office and lamp-root. Saw-mill. Carpenlers' shop, Blacksmiths' shop.

22. Locomotive shed.

23, Waggon- repairing shed. 04. Timbar yard,

25. Conveyor to fire-holes. e6. Conveyor to washer,

>3. Feedpumps.

Colliery, as repairs have often to be made as quickly as possible, and much time may be lost when small castings have to be made at a foundry situated some distance away from

the colliery.

An example showing a compact arrangement of the surface

sections necessary for a large colliery is given in Fig, 185.

Coal-Mtntng.

the platfonns. In the examijle given in Fig. 187, the might be raised to the upper platforms by additional creepers, and iJie full corves run to the weighing machine by separate roads. As these roads would be steep, the velocity of the corves would have to be checked ; this is usually done bj fixing long springs on cither side of the road. When the ' corves pass between the springs they must push them apart and are almost pulled up by the pressure.

Fowler's Hydraulic Decking Arrangement, — This is as arrangement for changing several decks simultaneously bf

I. — Fowler's hydraulfi; cage decking arrangement.

means of hydraulic rams. Fig. i88 shows the arrangement as adapted for a three-decked cage. The corves on the upper deck are changed by hand, and on the two lower decks by hydraulic rams, a and b are subsidiary cages resting on the rams c and d; e and / are the horizontal rams by which the cages are loaded. When the winding cage reaches the bank, the corves on the top deck are changed by hand, and whilst this is being done the empty corves, which have previously been placed on the cage are pushed off it on to the windii cage by the rams c and f, the full corves at the same time

SURFACE ARRANGEMENTS. afijfl

tte corves to run without manual labour. A good fonii of pit bank is shown in Fig. 187, the direction in which the corves circulate being indicated by arrows. When the full con'es are pushed off the cage, they run down to the switchback b in Fig. 187 ; the road across the points rises sharply, a.nd the corves mount the incline on account of the momentum they acquire in running down the grade. They run into spring buffers at the dead end, and are switched back automatically on to the road leading to the weighing machine. TTiey are steadied at the machine by a man or lad, who them off the platform when weighed ; they then run to the tippler, and are tipped and pushed out at the other nd, whence they run to the point A, which is the foot of the creeper. The point A is considerably lower than the

<iage bottom, because the corves have been running downhdl for the whole distance; they are, therefore, raised by the Creeper to a point above the level of the cage. From the Creeper top they run into one or other of the roads from which the empty corves are run on to the cage ; as a corf runs into One of the roads it pushes back a lever which moves the points to turn the next corf into the other road, so that a corf runs into each road alternately.

The weak point in the arrangement shown in the figure is thai it provides no stand-room for corves, so that winding Would have to be suspended whilst any small accident that might occur to the screens was being remedied.

Most cages have more than one deck, and the corves on each deck should be changed simultaneously. For this purpose platforms must be erected at the level of each deck, and arrangements made for conveying the corves to and from

r

37a

Coal-Mining.

or part of a circle. The corf is pushed on Lo rails on the tippler, and the tippler is revolved, discharging the contents of the corf over its end. The axis upon which the tippler turns is fixed parallel lo the ends of the corf. End tipplers are now seldom used in modem screening plants, the objections being, that the corf has to be pushed in and pulled back out of the tippler. This results in loss of time and adds to the labour ; raoreoFcr, the coal has to fall a considerable distance on to the screen, which leads to unnecessary breakage, especially when it is of a tender nature.

Side TippUrs. — An end elevation of a side tippler is shown in Fig. 189.

Tlie tippler consists of two cast-iron rings, a, connected bj

ironwork, and provided with rails for the corves to run on and projections to hold them in position when being tipped. The rings a are carried by the rollers /', b, upon which they are free to revolve. The wheel d is driven by a belt from the shafting which drives the screens, and revolves continoooslj. d is carried on sliding pedestals, and its circumference is grooved to fit the edge of the ring a. When the tippler is oul of action, the wheel d is kept clear of the ring a by means of the balance weight e. To start the tippler, the lever/is pushed in the direction of the arrow; this forces the sliding pedestal towards the tippler, and the grooved wheel d binds against the ring a and carries it round as it revolves. The tippler is

Surface Arrangements. 371

being pushed off the winding cage on to the subsidiary cage 1 The winding cage then descends, and whilst it is in the shaft the subsidiary cages are raised to bank, deck by deck, by nieins of the rams c and d, and fresh empty corves ate pushed on to a, and the full ones removed from b. Both subsidiary cages are then lowered to the position shown in Fig. 188, in readiness for the next load. Four subsidiary cages are employed inallj two for each of the winding cages.

Creepers, -For raising coives from one level to another either hoists or creepers may be employed ; creepers are now Oore common, as they are automatic in action, whereas the hoist requires a lad to drive it.

A creeper consists of an endless chain, which travels slowly up an inchne, and runs in an iron Irough. The chain i s composed of flat links, some of which are provided with fingers," or projections. The "fingers" stand above the top of the trough, whilst the chain itself is kept in the trough ty flanges. When a corf runs to the bottom of the incline, of its axles is caught by one of the fingers, and the corf s dragged up the incline, beyond the (op of which the road is etwith a slight gradient downward. The chain delivers the *:::orf on to the top of the incline, and is then led below the level, so that the "finger" leaves the axle and the corf is *iee to run.

A hoist in its common form consists of a vertical cylinder 'Sarrying a light cage or platform on its piston rod, the load iDeing raised by the admission of steam under the piston. I Hoists take up less room than creepers, but require more steam I and labour.

Tipplers. — The coal is emptied from the corves to the screen by means of tipplers. End tipplers are arranged to empty the coal over the end of the corf, and side tipplers over the side.

Eitd Tipplers. — These consist of a framework or platform of iron suspended by pivots, and free to turn through the whole

COAL-MmiNG.

Fixed-bar screens are now seldom erected at important collieries, as they do not separate the coal thoroughly, and offer DO facilities for picking out ihe ditt.

Jigging Sa-eens. — Fig. 190 shows a simple arrangetneat of jigging screen suitable for making three sizes of coal, namely, nuts, dust, and cobbles.

The screens themselves consist of iron pans, the screening being done over wire meshes or perforated sheets of iron. la the figure, a is the main screen, upon which the whole of the

Ouat Cobbles

coal is tipped ; it is hung from girders by the suspension rods /', and is given a reciprocating motion by means of the cam or eccentric c: The upper portion of this screen consists of a mesh sufficiently large to admit the nuts and dust ; the lower portion is a steel plate, and acts only as a shoot. An iron shoot, is suspended below the mesh, and extends to the top of the lower screen, as shown in the figure.

The smaller screen e is also suspended on rods, and is vibrated by the eccentric /; the bottom of the upper portion of this screen is composed of a wire mesh, which allows the

Surface Arrangements. 373 ,

turned through a whole revolution, and may either revolve backwards or forwards, according to the design of the screen.

It will be noticed that the tippler shown above does not stop automatically after a complete revolution has been made, but continues to revolve as long as pressure is kept upon the lever. There are now many patent tipplers at work which, when started, continue to revolve until a complete revolution has been made, and then stop automatically.

The corves run in at one end of the tippler and pass out at the other after being tipped. If a very large tonnage has to go over one tippler, it should be made of sufficient length to j hold two corves, end to end.

Sorting and Cleaning the Coal, — Before the coal is sent to the purchasers it must be cleaned and sorted into Various sizes and qualities. In some districts the large housecoal is picked out and loaded by hand, and the remainder separated into sizes by screens,

The smudge used for coke-making is usually washed to remove the dirt and other impurities, and it ia now becoming the practice to wash the smaller sizes which are used for steam and gas coals.

Fixed-bar Screens. — These consist of fla!t spouts, having bottoms composed of steel bars ; the bars ate set in combs, and have spaces of any desired width between them. They <iip from the pit bank to the waggons at the rate of i in 3 to I in 3. As the coal passes over the bars, the small slips through the spaces and the large passes over the bars. Thus, to make three sizes, slack, cobbles, and large, the upper portion of the screen would have bars fairly close together ; in the second portion the bars would be spaced further apart, and the remainder of the screen would have a plate instead of bars. The large coal and cobbles would pass over the first portion of the screen, but the slack would fall through into a waggon ; the cobbles would fall through the next set of bars into second waggon, and the large coal would the screen into a third

:he end of

Coal-Mining.

Fixed-bar screens are now seldom erected at important collieries, as they do not separate the coal thoroughly, and offer no facilities for picking out (he dirt.

Jigng Sa-eens. — Fig. 190 shows a simple arrangement of jigging screen suitable for making three sizes of coal, namely, nuts, dust, and cobbles.

The screens themselves consist of iron pans, the screening being done over wire meshes or perforated sheets of iron. In the figure, a is the main screen, upon which the whole of the-£=

JigSing screens.

coal is tipped ; it is hung from girders by the suspension rods - b, and is given a reciprocating motion by means of the cam or " eccentric c. The upper portion of this screen consists of a mesh sufficiently large to admit the nuts and dust ; the lower portion is a stee! plate, and acts only as a shoot. An iron shoot, d, is suspended below the mesh, and extends to the top of the lower screen, as shown in the figure.

The smaller screen e is also suspended on rods, and ts vibrated by the eccentric /; the bottom of the upper portion of this screen is composed of a wire mesh, which allows the

Surface Arrangements. 373

alack to pass through, but not the nuts ; the lower portion i of sheet ii

The coal is lipped on to the top of the screen a and passes gradually down the screen, being welt shaken about as it does so by the action of the eccentric. The outs and dust pass through the mesh on to the shoot iand the cobbles pass over the end of the screen on to a picking band, g, and from thence to the waggon. The nuts and slack are conveyed by the shoot to the top of the smaller screen, where the slack passes through the mesh into the waggon and the nuts fall over the end of the screen on to another picking band, or direct into the waggon. There are many varieties of jigging screens ; some vibrate sideways instead of endways, and the screens themselves can be arranged in many ways.

Picking Bands. — In appearance a picking band is similar

to a long iron trough having a bottom composed of sheet-iron plates, which travels slowly along. The coal is tipped on to one end of the trough, and is conveyed slowly to the other end. Men and lads are stationed on either side of the belt, and pick out the dirt and other impurities from the coal as it is carried past them. The speed of the belts which form I the bottom of the trough is usually from 30 to 50 feet per I' minute ; and they are usually horizontal or very slightly inclined.

I At many collieries in the Midlands belts are not only employed for picking out the refuse, but for picking out the various qualities of coal. For example, a seam may consist of several different qualities of coal — -say house, steam, and gas. As the coal comes out of the pit the corves are tipped upon the belt, and a mixture of the coals covers the surface of the belt in a thin layer. The waggons are loaded on either side of the belt, and each is in charge of men and lads, who confine their attention to picking out one class of coal.

Thus one man might be filling a house-coal waggon, and would be stationed close to the belt, and to a waggon to be loaded with house-coal. As soon as a lump of house-coal is carried up to him, he it off the belts and puts it into the

Coal-Mtntng.

Two troughs are employed, being placed side by side, so Ihal one can be cleaned out whilst the other is being used.

Washers of this description are rather costly in labour, and require a large quantity of water ; there is also a danger of part of the very fine dust being lost.

The Mitrion Waslur. — This machine is similar in principle to the ordinary trough washer, but is more elaborate, aad, being automatic in action, requires much less labour.

The general design of the Murton washer will be understood from Fig. 192.

rt is a travelling steel trough ; it is about 60 feet in length, 18 inches in depth, and 3 feet in width at the top, which is

rather wider than the bottom. This trough is made ap of sections, each about 3 feet in length, and joined together by a watertight joint ; at the end of each section there is stopping 2 inches in height. The trough has an inclioatioD, which can be varied to suit the coal which is to be washed, but averages about i in 20. It is carried by rollers, and travels uphill at the rate of 8 or 10 feet per minute ; the driving arrangements are similar to those of an ordinary picking belt, except that the drums are very much larger. The slack to be washed is raised by an elevator to the hopper b, from which it is fed on to the belt.

A jet of water from the nozzle c meets the slack and carries it down the belt, whilst the dirt falls to the bottom, is caught by the stoppings, and carried uphill with the belt, A

Surface Arr4Ngemewts

second jet of water issues from the nozzle d, which is a few feet above c; this stirs up the dirt on the trough and washes back any coal there may be among it In this manner the washed coal is carried downhill by the witer, and the dirt which settles on the bottom of the trough is earned up with it

As the trough turns at its upper extremity the dirt falls off into a waggon, whilst the washed slack which is earned to the bottom of the trough by the water passes through a shoot, where the water is drained off into a hopper The water passes through settling-tanks, where the sediment is deposited and the clear water is pumped back and used over again, with the addition of a little fresh,which must be added to make up the loss.

The slack is divided into various sizes before being washed, and each size -is treated on a separate belt.

The Elliot Washer. — This is a form of trough washer in w-liich the trough itself is stationary, but is provided with movable scrapers, which are fixed to chains and travel slowly uphai.

There arc usually three troughs placed side by side ; they are supplied with the slack which is to be washed by means cf a revolving screen, which divides the slack into three sizes, and deposits each size in a separate trough. The washed slack is suspended in the water, and delivered by it at the lower end of the trough ; the dirt falls to the bottom of the trough and is conveyed uphill by the scrapers, so that the clean Coal is delivered at the lower end of the trough, and the dirt at the upper end.

Rotary Washers.If a mixture of slack and shale is stirred together in water, the shale, being heavier, falls to the bottom before the coal ; it is upon this principle that washers of the rotary class separate the coal from the dirt. Fig. 193 IS a section through the Robinson washer, which is the best- Itnown example of this class of machine, a is an iron pan, in the shape of an inverted cone. The vertical shaft b is fixed in the centre of the pan, and carries a crosshead, e, to which

Coal-Mining.

are attached two sets of arms or stirrers, d. The shaft and arms are driven by an engine through bevel wheels, and make about ten revolutions per minute, e is a water jacket supplied with water at a slight pressure ; it is an iron ring, surrounding the bottom of the cone, and provided with perforations in its inner circumference, through which the water issues to ihe interior of the cone. The slack to be washed is supplied

through the shoot / and falls into the cone, where it is agitated and thorouglily mixed with the water by means of the stirrers. The water entering through the perforations in ihe waler jacket rises up the cone on account of its pressure, and flows over the top, carrying with it the clean coal, whilst the dirt gradually makes its way to the bottom. To discharge the dirt the lower slide k is closed, and the upper one g il opened ; the dirt then falls into the space between the two slides, g is then closed and k opened, allowing the dirt to fall out into a waggon. By having the two slides il is

Surface Arrangements. 38

possible to remove the dirt without stopping the machine losing the water.

The action, then, is briefly this : The water, in passing upwards, carries the clean coal with it and washes it over the top of the cone ; whilst the dirt falls through the rising water, settles in the bottom, and is withdrawn by opening the slides. These washers are very simple in construction, compact, and cheap, and are much used for preparing slack for coking.

Jiggers. — Various designs of jiggers are employed in ( elaborate and costly washing machines of the Luhrig and I Humbolt type, a considerable number of which have lately I been erected in the Midland and other coal-fields. These r Wachines are designed to wash coal up to about 3 inches in (diameter, as well as slack.

The coal is first carefully sized by revolving or other screens, and each size is dealt with by a separate jigger.

Jiggers were originally introduced for dressing metalliferous

Tes, and are still very largely used for that purpose. Fig. 194

hows the ordinary jigger ; it consists of a rectangular box

I *divided into two compartments, a and i, connected at the

"ottom as shown, a is fitted with a piston, c, which receives

ti up-and-down motion from the eccentric and rod d. The

ther compartment is divided horizontally by the sieve t

trainer e. This sieve is slightly inclined, and is of just

Sufficiently small mesh to prevent the material which is to be

hashed from passing through it. The water is introduced

through a pipe below the piston, and the coal to be washed is

1' *delivered on to the higher end of the sieve. Both the chambers

and b are kept full of water to a height of about 12 inches

il above the sieve. As the piston makes a down-stroke it forces

'ater from a to thus raising the coal and shale lying upon

the sieve, and allowing it to drop at the up-stroke. The piston

makes from sixty to eighty strokes per minute, so that the

L ttJalerial upon the sieve is rapidly lifted up and down, and as

M the coal is lighter than the shale, it is lifted higher and falls more

K slowly. The final result is, that coal and shale separate into

Coal-Mining.

two layers, the coal of course being the uppermost. The coal is washed out at a wide opening about 12 inches above the sieve, and the shale is discharged at another opening situated a little lower down,

For washing the smaller sizes a felspar jigger is employed. In this case the openings in the sieve are sufficiently large to allow the material which is to be washed to pass through, but a bed of felspar about 3 inches in thickness is laid upon the sieve. The jigging action resuUs in the shale finding its way below the felspar and through the meshes in the sieve, whilst the coal is washed over the opening in the side of the box as before.

The Bmiin Waslur. — This machine differs from other washers in that the coal is washed before it is sized, whereas a complete sizing of the coal before washing is an essential feature of most other machines. By washing the coal before sizing only one jigger is employed instead of severaL Another feature is that the water in the jiggers is pulsated by blasts of compressed air instead of by pistons. This does away with the eccentrics and pistons, and tends to make the machine simpler and less hable to derangements.

The Baum washer is conaparatively new in England, but it has met with much success on the Continent, and is likely to be extensively used in this country in the future.

Chapter Xxvii.

Coke-Making.

Coal is composed of fixed and volatile matters. By heating coal, the volatile nialters are driven off, and the fixed remain in the shape of coke. Some coals, when heated, are resolved into a pasty mass which forms coke, quite unlike the coal in.

I appearance, whilst others do not run together in this manner, but retain something like the original farm of the coal. The former are termed caking coals, and can be used for cokelaking, and the latter are known as non-caking coals, and

1 will not coke. The coking properties of a coal cannot rately be determined by its chemical analysis, hut good coking coals contain from 3 to 4 per cent, of disposable hydrogen. By disposable hydrogen is meant the excess of

! hydrogen contained in a coal over that amount which can

[ enter into combination with the oxygen there is present to

form water.

The average composition of ordinary coking coal and of coke are as follows : —

Coal p=r MM.

Colu pet nl.

Carbon

Volatile matters ...

Ash

Sulphur

Wstet

60 to 85

3 to S 3 to 6

85 W90

S loio

A certain amount of ash is necessary to give the coke mechanical strength. Sulphur is very harmful, especially in

Coaimining.

the case of steel coke. Much moisture also should he avoided, as it is not only a source of loss commercially by displacing its weight of carbon, but a certain amount of the carbon has to be employed when the coke is used, to drive the moisture out in the shape of steam.

The chief varieties of coke are Furnace, Steel, and Foundry. Furnace and steel cokes should be very hard and porous, of steel-grey colour, clean and crystalline, and formed in columnar masses. They should be as free as possible from sulphur, and should not carry too much ash or water. Foundry coke should be very pure and compact.

Coke may be made either in ovens, into which air is admitted during the process of coking, such as the ordinary beehive oven, or in retort ovens, from which the air is enlirelv excluded.

Beehive Ovens. — The ordinary beehive oven is shown in section in Fig. 195. The oven itself is dome-shaped, usually 1 1 feet in diameter and from 7 to 8 feet in height. It is lined with a 9-inch thickness of firebrick, and built with ground fireclay instead of cement or lime. The floor is paved with hard red bricks,

The charging hole a, in figure, is a circular aperture about 12 inches in diameter, situated at the apex of the dome, and closed with a movable tile. The flue i is 9 inches in diameter, and connects the oven with the main flue c. The communication between oven and flue can be closed or regulated by means of the damper e. The doors / are 3 or 4 feet high, measured from the floor of the oven, and from 3 to 35 feet in width.

The oven floor stands about feet above the level of the bench, and inclines slightly from back to front. The bench is a paved platform, about zo feet in width, occupying the space between the front of the oven and the sidings,

Coke-buritiiig. — The smudge to be coked requires washing, unless it is very pure and clean, or the coke will contain too much ash, and perhaps sulphur. In some places the smudge

Coke-Mak/Ng. 385

er slack is ground and not washed, whilst at others it is both as!ied and ground. VVlien both grinding and washing are done, opinions differ as to which should be done first. If the coal is ground first, it is difficult to wash, owing to its finely divided state; and, on the other hand, wet slack is more (Wkward to grind than when dry.

The ovens are charged through the holes in their tops, by jeans of iron hopper-bottomed waggons ; the waggons are filled

. 195. — Beehive

im the main hopper, and run on rails laid on the ovens, to ; oven which is to be charged. As soon as the waggon is ictly over the charging hole, a slide is withdrawn and the tents fall into the oven. The haulage on the ovens may

performed either by ropes or by a small locomotive.

After an oven is charged and the smudge levelled down, door is built up with bricks and plastered over ; a small

e is left at the top of the door to supply air for combustion.

386 Coal-Mining.

This hole is enlarged or diminished as required, during the process of burning. The ovens are never allowed to cool, so that after one has been charged, it is quickly tired by the heal of the walls and of the adjacent ovens. The ovens are not drawn in blocks, but alternately, in order to keep the temperature as unifonn as possible. The time required for coking varies somewhat with the nature of the coal, size of charge, and construction of the ovens. With ir-feet ovens of ordinary construction, charged with 6 or 7 tons of smudge, from 2 to 3 draws per week should be obtained.

When the coke is ready for drawing, it is cooled off with water before being drawn from the ovens; this is done by means of an iron pipe 12 or 14 feet long and about f inch in diameter. This pipe is connected by a flexible hose to the water main which runs along the ovens, and water is sprayed on to the burning coke.

When ovens are drawn by hand, the contents are pulled through the door by means of long iron rakes and scrapers.

The heat and smoke given off during burning pass from the oven into the main flue, and are drawn under boilers and used to generate steam. The number of ovens per boiler varies very greatly at different collieries. At some collieries there are as many as 45 ovens to one boiler, whilst at others there are only from 10 lo 15. Under average conditions, die heat given off from each colce oven will evaporate from 15 to 25 gallons of water per hour.

Beehive ovens are always built in a double row ; two rows of ovens back to back, discharging their heat into one flue, is the usual arrangement.

Fig. ig6 is an example of the manner in which beehive ovens can be arranged to heat Lancashire boilers.

Beehive ovens are sometimes built with a system of internal flues, either for heating the ovens themselves or the air used for combustion.

Mechanical Drawing. — The cost of labour on beehive ovens, when drawn by hand, is from u. 6rf. to 2s. td. per ton 0/ coke made. This cost may be reduced by drawing the

ovens by machinery in the following manoer. A small engine ind boiler propels itself upon a road laid alongside the ovens. The engine carries a shovel-shaped extractor at the end of a ong arm. The arm is fitted with a rack, which engages with paring on the engine, and can be run in and out or swung round at an angle. To draw an oven, the engine is stationed Posite the oven door, and forces the estractor under the Mke, by the rack. As the extractor is withdrawn, it brings le coke out with it, owing to the barbed shape of the shovel, lometimes the coke is drawn on to a belt which runs just elow the oven doors, and delivers the coke on to a bar

Coke-Ma K/Ng.

from which it gravitates into waggons. These belts are Ot now used so much as formerly, owing to the cost of up- Bep, caused by their great wear and rapid corrosion. f In beehive ovens the yield of coke is usually from 50 to IP per cent, of the coal carbonized. Nearly the whole of the volatile matters and part of the carbon are consumed, and, kept for the steam generated at the boilers, they are wasted.

Retort Ovens. — In making coke in retort ovens, the latile matters are not burned away, but are driven off by heat pnsmitted to the coal through the walls of the ovens, and t all fiir is excluded from the coking chambers, there is no

Coal-Mining.

combustion and no loss. Retort ovens are usually employe in conjunction willi by-product recovery plants, by whici the valuable products contained in the volatile matters ari I recovered.

There are now many batteries of retort ovens working in I Great Britain, and in Germany they have entirely superseded ' beehive ovens.

A battery of retort ovens consists of a series of long nanw I chambers, having flues between and under them ; heat is tianamitted from the flues through the walls of the ovens, which are I constructed of firebrick, and must be very thin. The ovens are ' connected by an ascension pipe to an exhaust pump, which draws the gases off as they are generated by the decomposition of the coal. The gases are drawn through condensers and scrubbers, where they deposit tar and ammonia, and the incondensable gases which remain are led back to the ovens and burned at the flues to generate the heat necessary for coking the coal. There is practically no waste ; the whole of the carbon should remain in the ovens in the form of coke, the heat which I escapes from the ovens is taken under boilers to geoeral steam, the valuable by-products are recovered in the condensers, and any incondensable gas which remains after the ovens are heated is either burned under boilers, or used W drive gas-engines.

There are several diflferent classes of ovens at work, iU similar in principle, but differing greatly in detail. The flu* between the ovens are sometimes horizontal and sometimes vertical; to the former class belong the Simon-Carv& and Semet-Solvay, and to the latter the Otto and Koppers ovens.

In the Yorkshire Coal-field the Simon-Carves oven is more used than any of the others, and is giving very good results.

Fig. 197 is a cross-section of the Simon-Carves oven. " is the oven itself, which is 33 feet 9 inches long, 8 feet a inches high, and from ao inches wide at the front to 32 inches at ih* back. The oven is heated by the horizontal flues ; gas is brought from the by-product plant in pipes into these flueSi i meets the air for combustion at various points, where il

Coke-Making.

and heats the flues. The xix for the combustion of the heated before it enters the side-flues, by being drawn h arches in the oven dons and along the sole- The heating is divided vo distinct zones, each ndent of the other; the tone heats the lower part

side walls and the upper le upper part After the les have heated the ovens ass into a main flue, and bence to a chimney, heatilers on the way. c ovens are charged either lans of a compressor, or h three charging holes, d,

at equal distances along /en tops J the charge is to to 11 tons of coal. kSes are exhausted through cension pipe, having an at the top of the oven. le ovens are closed by at either end; these doors t of firebrick built into frame, and are raised Jly by chains and balance they are luted with keep Eur from entering vens. The process of : is completed in about forty-eight hours. To empty the

both doors are raised, and the coke is pushed out by a The ovens are made a couple of inches wider at back than Co enable the coke to be pushed out without jamming, mpressors. — By these appliances the smudge is com- d and put into the oven in the form of a solid cake. They

Fig. 197. — Simon -Carv&

Coal-Mining.

are working successfully at several Yorkshire collieries, and result in a better coke.

Fig igS is the front view of a compressor j that is, the view which is presented to the ovens. The whole apparatus travels on rails in front of the ovens, and is driven by an electric motor, taking its power from trolley wires, like an ordinary tramcar. a is the hopper, which is filled from the large storage hopper, b is the discharging ram ; it is carried by a rack, and can be pushed forward by a motor, c is the chamber in which the cake is made ; this chamber is a little less every way than an oven, and has one side which can be slackened a little to liberate the cake. The bottom of the cakechamber is an iron plate, having a rack on its under side ; spur-wheels driven by the motor engage with this rack, so that the bottom of the chamber can be racked forwaidi carrying the cake with it. d is a stamper; it is continually raised and dropped, travelling backwards and forwards along the whole length of the chamber at the same time: The process of charging and discharging an oven by means of a compressor is as follows : —

The compressor is run to the main hopper and takes a charge of slack into the hopper a ; this hopper feeds the cakechamber c, and as the cake-chamber is gradually filled, its contents are rammed by the stamper into a solid mass, water being added to make the smudge bind. The compressor is brought up to the oven which has to be discharged and is stopped with the ram b exactly in line with the oven. Both

Fig. 19B. — Coke compressor.

Coke-Making.

the oven doors are then raised, and the ram is racked forward, pushing the coke out of the oven on to the bench behind it, where it is cooled with water and loaded up. After the discharging ram is racked back, the compressor is moved until the chamber c is exactly in line with the open oven. The door of the chamber is then raised, and the bottom plate is racked slowly forward into the oven, carrying the cake with it. When the whole of the cake is inside the oven, the doors are lowered, and the bottom plate drawn back, leaving the cake in the oven.

I By-products. — Tar, ammonium nitrate, and benzol are I the usual by-products which are collected from the volatile ! matters in the coal.

The gas given off when the coal is heated is drawn from the ovens by an exhaust pump. It first passes through the hydraulic main, where it is drawn through water and deposits part of its tar ; it is next drawn through condensers, where it is further cooled and deposits more tar ; it then goes through the eiihausters, and is forced through scrubbers and washers, in which the ammonia is extracted ; then through a second series, for the recovery of the benzol ; and finally through an acid wisher, which removes the last trace of ammonia.

The incondensable gas that remains is burned in the oven Sues, and the surplus used to drive gas-engines or burned under : balers.

CHAPTER XXVni. ACCIDENTS.

The following Uble shows the number of fatal accidents per thousand persons employed at the mines in Great Britain, classed under the Coal Mines Regulation Act, under different heads and extending over various periods : —

Updcrgro

.d:

wkcri.

1[

l(.

Period.

.

M

lo years ending

"

0-47 a

o-g*

a-a4

10 years ending

0'33

'9

o'so 2

I-Si

Year 1893 .-

0-iS

„ 1S94 ...

o'54

. iS9S -

, 1896 ...

o'3o

H

, 1897 ...

ss

o"53 I

S'

, 1S98 ...

o-os

0'44 I

, 1899 -

o'09

0'43 I

, 1900 ...

'3

0'4S I

, 1901

, 1902

o'ls

10 years ending

o'i7

o'i4

o-,S .

S3

These figures s

how t

hat th

e dea

h-rate fn

am

accidents is

g

adually decrea

sing.

D

rin

?

le

en years

end

°g

s, out

A Cc We Nts.

of every thousand workers underground over Z5 were killed annually, whilst only per thousand were killed during the ten years ending 1902.

Explosions. — Statistics show that there are now fewer colliery explosions than formerly, but that those that do occur are more extensive. Hence, the loss of life per explosion is now greater than it U5ed to be. The decrease in the nunnber of explosions is due to the better ventilation, the reductic the use of blasting-powder, and the extended use of safetylamps ; whilst the greater death-rate per explosion is owing to the fact that mines ace now larger, deeper, and drier than they were.

Until comparatively recently, it was thought that gas alone was responsible for explosions ; but it is now proved beyond doubt that this is not so, and that coal-dust has played the most prominent part in many of the large explosions of recent years.

The fact that coal-dust alone could give rise to an explosion was doubted by many until recently, although it was universally acknowledged that if, in addition to the dust, a very small percentage of fire-damp were present, a disastrous explosion right be occasioned.

That coal-dust and air can cause all the eHfects of a violent explosion without the presence of gas is proved by the following ;—

I. A violent explosion can readily be caused by the experi- tQental firing of coal-dust and air.

z. Explosions of coal-dust and air have taken place on Screens, etc, on the surface.

3. Violent explosions have taken place at collieries in which no gas has ever been seen, either before or after the explosion.

4. Many recent explosions have originated in the main Intakes, in which dust in its most dangerous form was most ely to be found, and in which it was impossible for large

Volumes of gas to have been present.

Coal-Mining.

Sourm of Dust. — The downcast shaft of a colliery is, as a rule, closely surrounded by the screens. Consequently a large quantity of the fine dust that is always present on the screens is drawn into the mine with the air. This dust is carried along the roadways, and as the velocity of the cunent slackens, is deposited on the roof, floor, and sides of the intake airways. Much dust is also made whilst the coal is in transit from the workings to the shafts. The roads along which the coal is drawn are always more or less uneven, so that the lumps of coal are shaken and ground together, thereby forming dust. The corves, too, are frequently in bad repair, and allow small lumps of coal to fall out on to the road, where they become trampled and ground into dust. The heavier dust settles on the floor, and the lighter, which is the more dangerous, lodges on roof and sides.

As the main haulage roads are usually the intakes, it follows that the dust made in the transit of the coal settles in the intakes, in addition to the dust which is carried down the shaft from the screens.

A certain amount of dust is made in the workings by the breaking up and loading of the coal.

Dangerous Conditions of Dust.— The following are the factors which have the chief influence on the explosiveness of coal-dust and air : —

1. Nature of the dust : The dust from some seams is more dangerous than that from others.

z. Fineness: The fine dust is more dangerous than the coarse.

3. Dryness: The danger of coal-dust depends greatly upon its dryness. Air at a given temperature can only hold a given quantity of moisture in suspension ; but this quantity increases as the temperature rises. Air may enter a deep mine at a comparatively low temperature, but as it traverses the roadways its temperature increases, and so docs its capacity for absorbing moisture. This being so, any moisture there may be present is taken up by the air, which dries everything it comes in contact with, including, of course, the coal-dust For this reason

Accidents. 39S '

the coal-dust in deep mines is usually drier and more dangerous than in shallow ones.

4. Quantity : The quantity of dust in the air necessary to give rise to an explosion depends upon various circumstances "but the dust must be intimately mixed with the air in the shape of a cloud, though the cloud need not necessarily be very dense.

Action of a Coal-dust Explosion. — There is no actual <liffercnce, except in degree, between what is known as " com- "bustion " and an " explosion." With the latter the combustion 3s extremely rapid, and if tliere is not ample room for the expansion caused by the heat and combustion, great pressure 3S generated. What actually happens when an explosion of *;oal-dust and air takes place is this : A cloud of fine dry :oal-dust is raised in the air, either by a blown-out shot by a small explosion of fire-damp. As soon as the ust is raised, it is instantaneously burned. Great heat lis generated, causing the air to expand, and this expansion is increased by the addition of the gaseous matters formed by the burning of the solid particles of coal, As the space is confined, the result of this expansion is to cause eat pressure, and to drive the flame along the road at a high "velocity. As the flame advances, it raises fresh clouds of dust in front of it, upon which it feeds. Thus the flame rushes through the roads at ever-increasing pressure, raising a cloud of dust before it, and continuing until the shafts are reached or the supply of dust fails.

Coal-dust explosions usually originate in the main haulage loads, because it is there that the chief supplies of fine dry dust are found, and they are generally started by blasting operations. It will be noticed that the Explosives in Coal Mines Order, 1899, is drafted almost entirely with a view to guarding against the dangers of blasting in dry haulage roads. Rmudies. — To combat the dangers of coal-dust explosions, , the dust may be removed at frequent intervals, or may rendered innocuous by being kept thoroughly weL There are, however, practical objections to both of these courses.

be I

1 396 Coal-Mining.

in many cases impossible to remove all the fine diy dusf the whole length of haulage roads, and to thoroughly wet the loads in some seams would set them "working" and add enormously to the cost of maintenance. Watering may be done by means of stand-pipes, hoses, or by water-barrels. At some collieries stand-pipes connected to mains containing water and compressed air are erected at intervals along the main roads, and send out a continuous and very fine spray. It has, however, been found that in order to wet the roads thoroughly these stand-pipes must be nearer together than is practicable. Water-barrels, as usually employed, are very inefficient, and are apt to interfere with the haulage. They are of no value unless they provide for the thorough wetting of the roof and sides, as it is there, and not on the floor, that the finest and most dangerous dust is found. In several instances explosions have been stopped by lengths of road happening to be naturally wet, and this has suggested the idea of keeping lengths of road thoroughly wetted. This expedient is not to be relied on, as j there are cases on record in which explosions have p considerable lengths of wet road.

The best method of avoiding coal-dust explosions is to fire I

! no shots in the main roads. If the provisions of the Explosives 1

I in Coal Mines Order are rigorously carried out, the risk of j explosions from blasting are very small.

Whenever a large explosion takes place, it is found that the J majority of deaths are caused by the effects of after-damp, and 1

I not by the force of the blast. Most explosions originate ii

I main intake, and travel in the direction of the shafts. This j causes the main intakes to be filled with poisonous gases, and I disarranges the ventilation by blowing out doors, stoppings, and overcasts. The men working at the coal face usually hurry I into the main roads and are overcome by the after-damp; ' whereas if they remained in the workings until rescued, or cjme out by the returns, they might in many cases be saved.

The composition of after-damp has been found to vary very I I considerably, but the most important poisonous element is in I all cases carbon monoxide.

Accidents. 397

The Pneumataphor.— To facilitate the exploration of wines after an explosion has occurred, apparatus have been devised by the use of which explorers carry the air they require with them, and are enabled to penetrate the most jjoisonous of atmospheres. One of the most recent inventions for this purpose is that known as the Pneumataphor. It consists of an indiarubber bag, about 24 inches by 20 inches by inches, which is carried on the chest of the user, and is fitted with a mouthpiece. Inside this bag is a cyhnder of sheet iron, 8 inches in length by 3 inches in diameter, containing in a glass bottle a 35 per cent solution of caustic soda; and below this is a cylinder 12 inches long containing oxygen at a pressure of igoo lbs. per square inch.

To use the apparatus, the bag is strapped upon the chest <jf the user, who fixes the mouthpiece firmly into his mouth, and lightly clamps his nostrils with a small clip, to prevent air "being drawn in through them. He then breaks the bottle of caustic soda by means of a screw provided for that purpose, and turns on a supply of oxygen. The whole of the breathing ds done through the mouthpiece into the bag ; the air which is — breathed into the bag is polluted with carbonic acid gas whiclil is absorbed by the caustic soda, and a small quantity of oxygen " is added, making the mixture in the bag fit for respiration. Sufficient oxygen is carried for about hour's respiration, but if the wearer is exerting himself to any extent, this period is much shortened. Two smaller cylinders of oxygen may be carried instead of one, so that the explorer may know when half of his supply is exhausted.

In some of the apparatus of this class a helmet is worn instead of the mouthpiece and nose-clip. This prevents the mouthpiece being accidentally pulled out of the mouth, and the glass front protects the eyes of the wearer from smoke, if any should be present.

Although these appliances have been of great service in many cases, they are still very imperfect The bags are very clumsy, and could hardly be used in rough low roads, and the carbonic acid gas is not completely eliminated from the

Coal-Mining.

exhaled air, which gives rise to s of the w

; headaches on the part

Falls of Roof and Sides,— During the last ten years, falls of roof and sides have caused one-ha!f of the dea.lhs which have resulted from accidents underground, the mortality from this cause amounting to 076 per thousand workers underground. The accidents generally occur singly, and happen for the most part at the coal face. Thick seams, and seams lying at a high inclination, are generally more dangerous to work than thin and flat seams ; the amount of danger also depends to a great extent upon the nature of the roof which overlies the coaL It does not by any means follow that the most dangerous work gives rise to the greatest number of accidents, a large proportion of the fatalities being caused by carelessness on the part of the workmen. The most efficient method of preventing accidents from falls is undoubtedly the introduction of systematic timbering. The timber at the face should be set at stated intervals, and not merely where it appears to be required at the moment ; because the object of timbering is not only to support a bad roof, but also to prevent a good roof becoming bad.

One of the most dangerous operations in coal-mining is the withdrawal of props from goaves. This danger is greatly lessened by drawing the timber regularly, and before it has been left far behind, and almost disappears if the ringer and chain are properly employed, as then the timber drawer may stand under a good roof.

Shaft Accidents.— The fatalities caused by accidents in

shafts during the last ten years amounted to o'i4 per annum per thousand persons employed, which is less than r fatal accident for 7000 employees. A portion of these accidents occur to men whilst being lowered or raised to or from their work, and the remainder to sinkers, or to men employed ii shafts, attending to pumps and similar work.

Considering the laie number of men who are wouiu

Accidents.

and down shafts every day, the number of accidents that happen is very small. The accidents that do occur are occasioned either by the engine-man overwinding, by the breakage of ropes or chains, or by men falling from the cages.

Detaching hooks (see Chapter XXIII.) save many lives, but ihey are of no avail if the cage is pulled into the head-gear at a high velocity, and in no case can they save the men in the descending cage, who, when an overwind occurs, are dashed violently into the pit bottom. There are now several different appliances in use by which engines are stopped automatically at the end of the wind, but arrangements of this kind are not at all general.

The breakage of winding-ropes or chains is rare, but occasionally serious accidents do arise from this cause, even when the tackle is of the best, and has been well cared for and properly examined. Wire ropes sometimes sufferfrom internal corrosion, and this may be very difiicult to detect, the seat of the injury being in the inner wires. A very severe strain may be put upon the winding-rope if the engine-man suddenly checks the speed of the descending cage.

The weakest part of a rope is the capping ; this should be renewed frequently, and a few yards cut off the rope at each I'renewal. The cage chains should be annealed every few months.

At many Continental and a few British collieries, the cages are fitted with appliances which wedge them to the conductors ™ the event of the rope breaking. These safety cages are Srierally employed in conjunction with timber conductors, though they can be applied with rope guides ; they have not ''come popular in this country on account of their liability to *Cknie into action when the velocity of the cages is unusually

It is generally considered desirable to rely for safety upon employment of ropes having a high factor of safety, and 'Eon careful and frequent examination.

Miscellaneous Accidents,— About one-third of the

Coal-Mintng.

fatal accidents which occur underground are classified under this head. They may be subdivided as follows :—

1. Accidents on haulage road.

z. From sufibcative gases.

3. From the use of explosives {see Chap. X.).

4. From eruptions of water, Accidents on haulage roads are due to lads being run over

whilst driving, and to persons being run over on engine planes and inclines. It is now becoming customary in large collieries to have a separate travelling road for the men, and to allow no one on the haulage roads except the men employed upon them. This is a very good practice, especially where the seam is steep. Where no separate travelling road exists, good manholes should be provided.

The fatalities occasioned by suffocative gases — leaving after-damp out of the question — are frequently due to the fumes given off from underground fires. These fires may arise either by accident, or by spontaneous ignition. Accidental fires may be caused by the use of furnaces or underground boilers, by the heating of brakes on hauling engines, by the careless handling of naked lights, or by the insufEcient insulation of steam-pipes or electric machinery. No accumulations of oily waste should be allowed in engine-rooms either on the surface or underground.

Spontaneous Ignition. — Some seams are extremely b'able to spontaneous ignition, whilst in others it is never known to occur. As might be expected, gob-fires are almost entirely confined to the thick seams in which much small coal is left in the wastes. The principal agent in spontaneous ignition is the property that all coal possesses of absorbing oxygen from the air. The chemical action that this gives rise to is accompanied by the generation of heat, and the hotter the coal becomes, the greater is its affinity for oxygen, so that as the coal absorbs oxygen, it becomes heated, and as it becomes heated it absorbs still more oxygen and generates still more heat, until finally the temperature of ignition is reached, and the coal gives off dense smoke and bursts into flame. The

Accidents. 401

iron pyrites which some seams of coal contain was once thought to he the principal factor in spontaneous ignition, but it is probable that the chief part that pyrites play in the matter is to assist in the disintegration of the coal, thereby exposing fresh surfaces for the oxygen to act upon. Solid coal never ignites spontaneously, though fires may occur at the edges of pillars which are crushed by the weight.

Seams liable to gob-fires should be worked by the longwall retreating method, wherever it is possible to do so, as by this method of working the goaves are left behind. It is also most desirable to arrange the pit in such a manner that any district can be readily isolated by the building of two or three dams.

There are two methods of deaJing with gob-fires. One is to seal them off by the erection of dams, and so extinguish them by cutting off the supply of oxygen ; and the other is to cool them down with water and send the smouldering material out of the pit, filling in the space it occupied with sand or flue dust.

Fig, 199 shows the class of dam that should be built to seal off a gobfire. In building dams of this description, it is most important that the surrounding strata should foe perfectly solid and free from breaks, as the dam is quite useless if air can get past it through the measures.

The dam shown in Fig. 199 is constructed of two brick walls, the one nearest the fire being convex in plan in order to resist the force of an explosion if one should occur in the vicinity of the fire. The space between the two walls is tightly packed with sifted sand and the outside of the outer wait kept well whitewashed.

A pipe should be taken through the whole of the dam and fitted on its outer end with a valve which allows the air or gas &om within the dam to escape, but prevents the passage of air from the mine to the fire. The walls should be built in trenches cut right into the solid in roof, floor, and sides.

ff,

Coal-Mining.

When fires occur in ordinary longwall workings it is

impossible to dam them off, as there may be no solid ground

in which to place the dams. In this case roads are scoured

through the goaves to the seat of the fire, which is cooled down

by water and filled out.

In a few instances carbonic acid gas has been generated

either by passing air over a coke and lime fire, or by the action

of hydrochloric acid on limestone, and has been piped into the

burning district which has been closed up. This procedure

has not met with great success.

Eruptions of Wafer.— The Coal Mines Regulation Act

provides that, " where a place is likely to contain a dangerous

accumulation of water, the workings approaching that place

shall not at any point within 40 yards of that place exceed 8

feet in width, and there shall be constantly kept at a suiEcient

distance, not being less than 5 yards in

advance, at least one borehole near

the centre of the working and sufficient

flank boreholes on either side."

The arrangements that might be

adopted when a longwall face ap-

Fio. zoo. -Boring in ad- proached old workings filled with water vance to prove old work- ... , . „. ,

ings. are indicated mFig, 200, The heading

and boreholes must be driven continuously as the face advances, and in no case must the boreholes be less than 5 yards in advance of the heading or the heading less than 40 yards in advance of the face. If the pressure of the water in the old workings was at all considerable, boreholes of a much greater length than 5 yards should be provided.

The long holes are usually drilled by means of auger drills and rotary machines worked by hand. The lengthening rods should be composed of pipes, and the drills hollow, to enable the hole to be cleaned by pumping water through the rods. When the water pressure is expected to be great, boring should be conducted through a pipe firmly wedged into the hole and provided with a valve, so that when the water is tapped it can be shut off.

Accidents. 403

In every case when boring against water, long wooden plugs should be in readiness. These plugs should be fitted with crossbars, to enable the men to force them into the

e against the pressure.

In some cases ancient submeied workings have been found to have become almost entirely closed up, and to contain but little water.

Dams. — It is sometimes necessary to shut off a feeder of water by closing the roadways along which it flows by means of dams.

These dams must be very substantial, as they may have to resist enormous pressure, and their failure might be disastrous to both life and property. The total pressure upon a dam depends upon the area exposed to the water, and upon the head of the water. For example, what will be the total pressure upon a dam 9 feet 6 inches wide by S feet high, the height to which the water will rise when the dam is built being 530 yards ?

Area of dam, 9J X 8 X 144 10944 sq. inches Pressure per square inch, 230 X 3 X '434 - 299'5 lbs.

Total pressure in tons, 1463-3 tons

The best dams to resist very great pressure are those constructed of solid timber. Each piece of timber must be carefully shaped and of taper form, the thicker end being *posed to the pressure. The timber should be built in the !>nn of an arch, and the joints well wedged up from behind. )ams of this construction, though very efficient, are extremely ostly, and are only built in exceptional cases.

Fig, 201 shows a masonry dam. It consists of two rows f brick arching, built of hard bricks, set in cement. Each ring lould be built independently of the others, and a small space ift between, which should be filled in with cement as the dam being built. The site of the dam must be very carefully losen, and a trench excavated for it beyond all breaks. It is ;ry difficult to make a satisfactory joint between the top of a

J

404 COAL-hflNTNG.

masonry dam and the roof, as a slight settleinenl takes place, especially if the dam is built up quickly and the joints in ttie brickwork are not kept veiy thin. An iron pipe should be built into the bottom of the dam, to allow the water to flow through whilst the dam is being built, and to enable the workmen engaged in the erection to pass out when it is completed. A. small pipe should also be built into the dam near the top, to allow the air to escape as the space behind the dam becomes filled with water, afler which it can be gradually closed to allow the dam to take the full presniie by degrees.

Diseases to which Miners are liable.— Coal-mining is not considered an unhealthy occupation, in fact the rate of mortality among coal-miners compares favourably with that of most classes of manual labour.

Phthisis, — Lung troubles are usually prevalent among men who work in an atmosphere impregnated with dust, but coalminers, as a class, suffer little from consumption and sirailar maladies, because coal-dust is free from hard grit. Men who work in metalliferous and ganistec mines are very liable to lung disease, especially where rock drills arc employed, as the dust made by the drills is composed of sharp, hard partidei, which cut the lungs.

Ankylostomiasis. — Extensive outbreaks of this disease have recently occurred in Westphalia; it is extremely contagious, and drastic methods have had to be resorted to in order lo cope with it. This disease takes the form of intestinal worms, the growth of which are favoured by the prevalence of await, moist atmosphere. When an outbreak occurs, the affected

Accidents, 405

persons should be carefully isolated, and all the underground workers periodically subjected to medical examination. All collieries should be provided with portable sanitary appliances, placed in convenient places underground, and their use insisted upon.

Nystagmus. — This is a disease which aflfects the nerves of the eyes ; it is more prevalent among those who work by the light of safety-lamps than among those who use naked lights. The cause of nystagmus is thought to be either the constant dazzling of the eyes by the bright concentrated light of safetylamps, or the strain put upon the muscles of the eyes by work such as holing. The symptoms of this disease are a twitching of the eyes and impaired sight.

Electricity is in itself so Large and important a subject that a detailed treatment cannot be attempted in this volume, but the employment of electricity in mining is now so general that a few notes on the subject seem desirable.

The exact nature of electricity is not known, but it is evidently a condition of matter which exists to a greater or less extent among the atoms and molecules of which all bodies consist. Electricity in its quiescent state can do no work ; it is only when its equilibrium is disturbed that power can iw obtained from it. In like manner, water in itself has no power, but if raised and allowed to fall to its original level, power can be generated by leading it over a water-wheel or through a turbine. Electricity must not be regarded as a source of power, but only as a means of transmitting power ; and the power given off by the motor is always less than that put into the dynamo.

Electric Terms. — The following are the most important of the terms used in electrical engineering.

The volt is the unit of pressure, potential, or electron force (E.M.F.).

The coulomb is the unit of quantity.

The ampere is the unit of current.

The ohm is the unit of resistance.

The watt is the unit of power.

The Board of Trade Unit (B.T. Unit) is the : energy.

Electricity. 407

TJii Voll. — The pressure at which electricity is generated is measured in volts, in the same manner in which pressure of steam or water is measured in pounds per square inch. The usual pressure generated at collieries is from 500 to 600 volts. ; T/i£ Ampere. — The rate of flow of electricity is measured

I in amperes, Water is said to flow at so many gallons per minute ; electricity at so many coulombs per second. One coulomb per second equals one ampfere, hence if 5000 coulombs per minute flowed through a circuit, the current would be Sigs 83'3 ampferes. For commercial purposes the quantity flowing per hour is taken as the unit, and quantities measured in vampire hours.

I The Ohm. — The resistance offered to the passage of

electricity is measured in ohms. Wiien a given quantity of water passes through a pipe it encounters a certain amount of resistance ; the amount of resistance depends chiefly upon the quantity of water and size of pipe. In like manner when electricity passes through a wire it encounters resistance, which is measured in ohms. The resistance depends upon the size and length of the conductor, the material of which it is composed, and upon the quantity of electricity passing, but does not vary with the voltage or pressure of the current.

The Watt. — Mechanical power is measured in foot-pounds per minute and in horse-power ; electrical power is measured in watts. A current of one ampere at a pressure of one volt gives out power equal to one watt ; thus ampferes multiplied by Volts equal watts. 746 watts equal one electrical horsepower. So that a current of 40 ampferes at a pressure of

[t 500 volts equals °— 5— - 268 H.P. One kilowatt I 1 000 watts.

Board of Trade Unit. — An electric supply of 1000 watthours is known as a Board of Trade Unit (written B.T. Unit). This is really a commercial term, the electric light and power i Stations supplying their customers at so much per B.T. Unit,

Example. — If a current of 60 ampferes at a pressure of I 400 volts were employed for 24 hours, what is the total

4o8 COAL-MINING.

number of units consumed) and what is tlie cost per horsepower per hour at per B.T. Unit ?

Watts, 60 X 400 24000 Watt hours, 24000 X 24 576000

Units per hour, 24 Cost per hour, 24 x 2'd. 6od,

Horse-power, -

Cost per E.H.P. per hour,

r86rf.

One B.T. Unit '"34 working for one hour.

Ekctrlcal Conductors. — Some materials offer very little resistance to the passage of electricity, whilst others offer so much as to altogether |irevent it from flowing under ordinary pressures. The former materials are termed conductors, the latter are known as non-conductors or insulators. All the metals are conductors, though in varying degrees, while indiarubber, silk, oi), porcelain, mica, ebonite, glass, etc., are insulators. Water, wood, and several other substances are classed as semi-conductors, as they allow electricity to pass through them, though not very readily.

The Dyjiamo. — Electricity, when employed on a large scale, is generated by means of dynamos. The dynamo or electric generator depends for its action upon the fact that electric currents are generated whenever the lines of force, which pass from one pole of a magnet to the Other, are cut by a conductor.

A magnet is anything which possesses the power of attracting iron or steel or other magnetizable bodies. There are two kinds of magnets. Permanent and Electro. The former are made of hard steel, and retain their magnetism for a consider- ;ible period, and the latter owe their magnetism to an electric current, and are magnets only so long as the electric current passes round them.

If a length of insulated wire is coiled round a bar of soft

ffon, as showr

i,as shown in Fig. 202, this bar becomes an electromagnet

Kenever a current of electricity is sent through the wire. le end of the bar is tnowo as the " North ble," and the other as he " South pole." Lines of force" flow

i gMisiy

bm the ends of the Ugnet, passing from the forth to the South pole, as shown in figure. These " lines of wee" are really currents of magnetism. If the magnet is ent into the shape of a horse-shoe, the lines of force will pw from one pole to the other, and the space between the inds of the magnet through which these Jines of force pass I known as the magnetic field,

f Whenever a wire is moved through a magnetic field in inch a manner as to cut the lines of force, an electric current ts induced, which flows through the wire.

In Fig. 203, N and S are the two poles of a magnet ; consequently, lines of force pass through the magnetic field

Fig. 203. — Principle of the dyn:

*ween them, abed is a wire frame, mounted on the spindle t by which it can be rotated. One end of this frame Uiinates in an insulated copper ring, g, and the other ter- Wiales in a similar ring, /;. Brushes of copper, k and I, are pt in contact with the rings, and from these brushes the

4Io Coal-Mining.

electric current is led off as it is generated. When the frame is in the position shown in Fig. 203, no lines of force are cut; but if it makes half a turn in the direction of the arrow, the part ab descends through and cuts the lines of force, whilst the part of the frame cd ascends through them. This cutting of the lines of force generates an electric current in the frame, which passes from one brush through the estemal circuit, where it does work, and back to the machine through the other brush.

If the frame is rotated through the other half of the revolution, cd descends through the lines of force and fli ascends. This induces a current through the frame, but in the opposite direction, so that for each complete revolution of the frame two currents of electricity are generated, fiowmg through the frame in opposite directions. Machines of this class are known as alternators.

Alternating cuireatsare changed to direct by means of an apparatus known as a " commutator." The principle upon which this is constructed is shovfn in Fig. 204. The ends of the frame or coil are not joined to copper tubes as ia Fig. 203, but each end is connected to one half of a split tube, each half being insulated from the other and from the spindle. In Fig. 204, the end of the coil a terminates in one insulated half-tube, g, and the end of i in the other half, h. The brushes k and / are set exactly opposite each other, so one presses on the one segment and the other on the other segment.

During one half of a revolution the current through the frame travels in one direction, and is reversed during the other half, but the current in the opposite direction is taken by the opposite brushes, because the segments have turned round, so that the reverse current, being taken by the opposite brushes.

Electricity.

results in a continuous current Or, in other words, as soon as the direction of the current changes, the connection to the external circuit is also changed, and the one change negatives

I the other, so the current travels through the outer circuit in , the same direction as before.

For the sake of simplicity, the fratne or armature shown in

I Fig. 204 has only one coil of wire, but in practice armatures are constructed of many coils, each insulated from the others,

' and each connected to a separate insulated bar on the

commutator.

' The main organs of a dynamo are shown in Fig, 205. a

Fig. 205,— Dynamo.

iis the magnetic yoke connecting the magnetic coils h ; c is the ] Armature revolving in the magnetic field between the field *magnets d; f is the commutator, which changes the currents from alternating to direct;/, /are the brushes through which the current is led round the coils and external circuit.

The armature is rotated at a high speed by means of an engine and belt, the pulley on the engine being large and that on the dynamo small, in order to increase tlie speed of the latter.

Tn the apparatus shown in Fig. 203, the armature abed is j rotated between the poles of permanent magnets, but in large

r

41a COAIMINING.

dynamos electro magnets are employed, as shown

As has already been explained, electro magnets are fanned by sending a current of electricity through coils wrapped round an iron core. The coils and core are shown at W, Fig. 205, and the electric current which passes through them may be supplied either by a small dynamo, in which case the machine is said to be separately emted, or, as is more usual, the current which passes through the coils may be taken from the machine itself. When the armature is revolved, the slight amount of residual magnetism in the pole pieces causes 30 electric current to be generated in the coils of the arniiture, which is collected by the brushes and allowed to pass through the coils encircling the soft iron magnets, and the magnetic field becomes stronger and stronger, until the field pieces are saturated.

There are three different methods of winding dynamos- Series, Shunt, and Compound.

Series Machines, — The connections of a series dynamo are shown in Fig. zo6. The current passes from the commutator through one brush, round the external circuit where the work is done, and back round the coils to the other brush. The whole of the current passes round the coils, so that in series machines the voltage given out varies with the current because, when more current is generated, more passes round the field magnets, which are thereby strengthened.

Shunt Machines. — The coils of these machines are magnetized by being wound with a great length of fine wire, and only part of the current goes round them, the remainder serving the external circuit. It foUoivs, therefore, that if the resistance on the external circuit is increased, more current flows throu the shunt, thereby strengthening the field and increasing the voltage. I

Compound Machines. — These machines are wound both in I series and by shunts. In series machines, when the speed is ' constant, the voltage rises as the external current increases ; in shunt machines the voltage falls as more current is employed,

slnhat by

Electricity.

i by combining the two windings on one machit stant voltage can be maintained under varying loads.

Fig. 207 illustrates the winding of a compound machine. , The thick line represents the series coil, and the thin one the shunt. As the current leaves the + brush it splits, and a small I of it goes through the shunt, and the remainder through I tlie series coils; both series and shunt coils are taken round the field magnets, but the series coils only form the external c;circuit. If the load increases and more current is required, tlie voltage due to the series coils is increased, but that due to the shunt coils falls, and vice versA. In this manner com-

he

pound machines give a constant voltage under varying loads, if they are run at a constant speed.

Compound-wound dynamos are the best for colliery work, as, by keeping their speed constant, a constant voltage is generated under the varying loads which occur when coal-cutting machines, hauling engines, etc., have to be driven.

Driving Dynamos. — Three methods of driving electric generators are in general use.

(a) By low-speed engines, through belts or ropes.

(b) By high-speed engines, coupled direct,

(c) By steam turbines. I

414 Coal-Mining.

The two latter methods aie now generally preferred, fiimb ' low-speed engines and belt drives have considerable advantages as regards simplicity and smooth running.

Steam turbines are now coming more to the front; they are extremely compact, and require little attention. They run at a very high speed — from 3000 to 30,000 revolutions per rainule. When worked in conjunction with condensers they are not uneconomical as regards steam consumption.

Cables. — The electric current is conveyed from the dynamo to lamps, or motors, by insulated cables ; for continuous currents two cables are required— one to take the current &om the dynamo, and the other to conduct it back in order to complete the circuit. If the insulation on the conductors were destroyed, and the bare cables allowed to touch, what is known as a " short circuit" would be formed, and the whole or part of the cuneni would go back to the generator through the point of contact. Short circuits may also occur in the dynamos or motors, and may give rise to heat and cause the insulation to bum.

The resistance that different metals offer to the passage of an electric current varies very greatly ; silver has the least resistance, and is, therefore, the best conductor. Copper is almost universally employed for electric conductors, as it offers low resistance to the current, and is very durable. Taking the resistance of silver as i, the resistance of copper is I'or, and of iron 6-25 ; so that, under similar conditions as to length, a conductor of iron must have more than six times the area of one of copper to offer the same resistance to a current of electricity. Although the price of copper is much niore than sw times the price of iron, copper cables are the more economical, because, being so much lighter, they' are cheaper to fiit, and, being so much smaller in diameter, a less weight of insulation is required for a cover of equal thickness.

Cables are insulated with rubber, ozokerited tape, or with some material impregnated with oil ; when used in damp places they should be protected by a lead covering, and, if exposed to rough usage, armoured by being wrapped roimdj" galvanized wire.

Electricttv.

The two cables may be either separate or concentric; a SKlion through a cable of the latter type is shown in Fig. zo8. i is an internal copper strand forming one cable ; i is a layer of insulation to prevent leakage of current from one cable to the other ; c, c are copper strips forming the second cable ; a ' second layer of insulation ; and e wire armour.

Oa the surface cables are carried by being Jiung from poles, to which they are attached by insulators ; down shafts they inay be carried side by side in a grooved wooden casing, as shown in Fig. 209. The cables 6t tightly into the grooves, a 'over is nailed over them, and the whole spiked securely to the Aaft side.

In the workings cables are usually hung from insulators

f IG. 20B.— Cone

ruled on to the timbers; they should be hung loosely and owed to form loops, so that a fall of roof would drag them lown, and not break them. Sometimes both cables are hung n one side of the road, but it is better to have one on either

of loss of pressure in the cables depends pon their length, and upon tJie number of amptjres carried per ijaare inch sectional area of copper. The usual allowance of rea is at the rale of one square inch of copper for 1000 tnp&res ; this leads to a loss of about ai volts per hundred ards. If the cables are too small, the loss in voltage, and consequently power, may be serious ; the power being expended 1 heating the cables.

Large cables are made up of a number of small wires nited into strands ; their size is expressed in the number

r

Coal-Mining.

and gauge of the wires of which they are composed; A) yj cable means a cable composed of seven wires each of No. 16 standard wire gauge (s.w.c.)

Cables are usually made up of wire of from Nos. 12 to 11 standard wire gauge.

The following table gives the sectional area of wires of various gauges, together wilh their carrying capacity at the rate of looo ampferes per square inch : —

Number of

O'oo66

'4

0'0D4I

S'o

o-a3o6

Cables are usually constructed of 3, 7, 19, or 37 wires.

From this table the size of cable necessary to carry a given current can be determined.

Example. — What size cable would be required to carry a current of thirty-five ampbres ?

Area of copper in square inches, 0-035 square inch.

If the cable has seven wires, the area of each will be —

The gauge of a wire o*oo5 square inches in area is No. 14. so that a cable is required.

Motors. — The construction of a motor is similar to that of a dynamo, and machines built for dynamos will run as rooton, or vice versd.

A dynamo generates current when its armature is revolved.

Electricity.

whereas a motor is supplied with current, which armature to rotate. The rotation is produced by the action of the lines of force in the magnetic field upon the coils in the anaature.

The magnetic currents tend to turn the coils until they coincide with ihe lines of force, but as soon as one coil is pulled into this position, another takes its place, and is pulled round in its turn, and so on, the result being a continuous rotation of the armature.

Motors, like dynamos, may be wound in series, shunt, or compound.

In series motors the speed varies with the load, hence they e only suitable for constant loads. The "torque" or turning power of a series motor is greatest at the moment they are started, so that they are suited for starting against a heavy load, which is maintained at a fairly constant pressure: after it set in motion, such as pumping or hauling up an incline. The starting torque of a shunt motor is low, but they run

at a fairly uniform velocity against loads varying within certain

litnits. Com pound- wound motors start against a heavy load , by reason of their series coils, and maintain a uniform velocity '. by virtue of their shunt coils.

f Distribution. — Where a large amount of power is generated M a central station, and used to supply numerous lamps and ; Motors, as is usually the case, the whole current should not be Esnerated by a single engine and dynamo, but by several. For example, if a maximum load of 800 horse-power had to be provided, five machines might be employed, each driven by a separate engine, and each capable of supplying 200 horse- Poffer. This would allow one machine for reserve in case T repairs or break-downs. If only one large machine were 'ected, there would be no provision for accidents, and the 'ge machine would have to run at times when only a small ountof power was required, consequently with less efficiency. The cables from the various machines are led to the main ' itch-board, from whence the current is distributed among ! *He different circuits.

%

COAL-MINfNG.

Switches. — The current is turned on or off the different circuLts by means of switches. One design of double-pole switch is shown in Fig. aio. One cable is attached to the tenninal c, where it is broken off and attached to a. The space between a and c is bridged by the bar e, as shown in the figure. If the current is to be switched off, the handle is pushed sharply in the direction of the arrow ; this moves the bar clear of the terminal c, and the contact is broken. As this is a double-pole' switch, both wires must be disconnected; the manner in this is done is shown in Fig. 210. The switch is mounted on a slate base, the cables being connected from behind.

Cut-outs. — If through any accident the current should rist

Double-pole

much beyond the normal, the insulation on the machin be burned by the heat generated. To prevent this, cut-out are placed in each circuit. A cut-out of ordinary form is showW* in Fig. an. The cable is broken off at a and reconnected W b, the space between a and b being bridged by a tin or lead fuse — wire c. This wire is of sufficient size to carry the maximurtK"* current that should pass ; but, if this maximum is exceededthe heat generated by the passage of the current through wire melts it and cuts out the circuit.

Magnetic cut-outs are also employed, the contact bein 'S broken by the action of an electro-magnet when the curren becomes excessive.

F.Lectrtcity. 419

Starting Switches.— In order to start a motor gradually and without shock, resistances are employed. These resistances may consist of thin wire coiled into spirals. When the motor is started, the current is passed through all the coils, and the resistance they offer to its passage lowers the electro-motive force, as part of the power is spent in heating the wires; so that the whole power of the current is not turned into the motor. The resistance coils are gradually thrown out of the

I' circuit by moving a lever, BO that the potential gradually increases. [ In Fig. 212, a, b, c, etc., are contact blocks connected to the coils. In the position shown in figure, the current enters at g, passes through the bar k, contact block it, and through the whole of the resistances to the motor. By moving the switch to h, some of the resistance coils are thrown out, more are thrown out by moving it to e, and so on, until all the coils are out of circuit, and the motor gets the full pressure when the bar is moved to/.

Electric Lamps .—There are two classes of electric lamps, incandescent and arc. Tlie former are usually employed for lighting engine-houses, offices, pit bottoms, etc., and the latter for large open spaces, such as sidings.

Incandescent lamps consist of a thin thread of carbon enclosed in a glass bulb from which the air has been extracted. When the electricity flows through this thread it raises it to an intense heat on account of the resistance offered to the passage of the current ; this causes the lamp to glow. The carbon is not consumed owing to the absence of oxygen in the bulb. Incandescent lamps are commonly made of small candle-

430 COAjL-MIA/NG.

power, i6 candle-power being a common size, but they are also constructed for very high powers.

I horse-power will supply current for ten i5 candle-power lamps. Their usual voltage is from jqq to 200.

Arc laEips consist of carbon rods about inch in diameter. The rods are brought together and then separated by a space of about 5 inch. A continuous discharge is then maintained through the space, causing a bright light. As the arc burns the carbon rods are consumed, and means are provided for feeding the rods forward as their length is shortened, i horsepower provides current for about rooo candle-power when arc lamps are employed. I S)'stems of Wiritig. — There are several methods by which

I electric energy is distributed. The most common method is

I by the two-wire system, arranged either in parallel or series.

k

:. 213.— Wiring in parallel and

In Fig, 213 the two motors M' and are connected parallel, and the five lamps in series with each other. If the dynamo is generating electricity at a pressure of 500 volts, the motors being connected in parallel, each receive a current of 500 volts ; but the lamps, being in series, divide the pressure among them, so that the pressure on each lamp is 100 volts only. Motors are always arranged in parallel, but if it is desired to run 100 volt lamps on a 500-volt circuit, they may be arranged in series as shown. If one lamp fails, the others which are connected in series with it go out also.

Polpyhase Plants. — Three-phase alternators have been recently put down at several collieries, and their application is likely to extend. Their chief advantage is that they have no commutators, and can give oif no sparks.

Electricity. 421

Three cables are employed instead of two, as with continuous currents, but they are smaller in sectional area. The machines themselves are very simple in construction ; the motors can start against a heavy load, and do not race and bum up if they are suddenly relieved of their load.

Dangers of the Employment of Electricity in Mines, — The

chief danger introduced by electricity in mines is the possibility

of sparks from brushes or switches lighting any gas there may

be present. There is also a possibility of a short circuit

causing a fire. If the plant is well arranged, this danger

is not great; but in several cases fires have been caused

in this manner. Another source of danger is the risk of

shock to those handling the apparatus. Under ordinary

conditions a shock firom a current of 500 volts would do

little harm, but under exceptional circumstances men have

een killed by shock from a current at a considerably lower

voltage.

Size of Electric Machinery, — Electric machinery should ways be made of ample size for the work it has to do, otherise there is constant trouble from over-heating, which results in a final breakdown.

The size of motor for a given duty may be calculated as follows : —

Find size of motor to drive a pump delivering 240 gallons per minute against a head of 500 feet.

. 240 X 10 X 500 Horse-power m water, — 36*36

Taking the efficiency from motor to water raised j

at 75 per cent., the horse-power of motor [ o. .0

must be

Watts required, 48*48 x 746 =36166

Assuming E.M.F. at motor to be 450 volts,

3(!ifi6 r — 80*4

amps, required,

Size of motor required, 450 volts and 80*4 amps.

422 Coal-Mining.

Cables, — Sectional area of cable in square inches at looo amps, per square inch, 0*0804.

Area of each wire if nineteen are employed, 0*0042

The standard wire nearest to this in size is No. 15, so that the cables should be yf.

Index.

ACCIDENTS in mines, 392 Air compressors, 242 Air, friction of, in mines, 259

— crossings, 276

— current, measurement of, 287

— distribution of, 275

— properties of, 256

— vessels on pumps, 357

— weight of, 256 Alum shale, 13 Ammonium nitrate, 391 Amperes, 406 Anemometer, 286 Aneroid barometer, 281 Ankylostomiasis, 404 Anthracite, 40 Anticlinal curve, 16 Arching roadways, 186 Arsenical pyrites, 13 Atmosphere, pressure of, 279

BALANCE bobs, 354 Balance inclines, 332 Balance ropes, 316 Banking corves, 368 Bamsley bed, 36

method of work, 162

Barometers, mercurial, 279

Barytes, 13

Basins, 17

Baum washing machines, 382

Bauxite, 13

Beard-Mackie fire-damp indicator,

Bedding, 20

Beehive coke-ovens, 384 arrangement of flues, 387

Benzol, 391 Bitumindus coal, 39 Black-shale coal, 36 Blasting, electric, 135

— in sinking pits, 83

— tools used in, 124

Board of Trade unit of electricity,

Bog ore, 13 Boilers, Lancashire,. 237

— water-tube, 240

— work of, 239 Bord-and-pillar method of work,

Boreholes, method of proving true

dip by, 52 Boring, percussive method of, 53

— rotary methods, 60 Boyle's law, 257

Brakes for winding engines, 320

Brattices, 276

Bristol coal-field, 46

Bucket pumps, 347

By-products from coke-making,

CAGES, attachment to rope, 305 Cages, indicator to show position of, 319 Cages, winding, 303 Calorific value of coal, 41 Cannel coal, 39 Capell fan, 273 Cappings, rope, 239 Capstan engines, 80 Carbonic acid gas, 253 — oxide gas, 254

"TAMS gainst gob-firw, 401 1 LJ Dams against water, 404

Coibonite, 131

Caiburelted hydrogen, 252

Davis anemometer, 286

Centrifugal fans, 268

Davis-calyx method of boring,6a 1

— pumps, 364

Chains, strength of, 313

Chalk, 13

Detaching hooks, 320

Champion coal-cultinfi machine,

Dip, mode of ascertaining, 17

Charles's law, B56

Direction of main roads, 116

Chert, 13

China clay, 13

Doors, ventilating, 275

Clanny lamp, 291

Double-Bctiog pumps, 356

Clark-and-Steavenson coal-culling

Double-stall method of work,

machine, 197

Dover coal-SeM, 47

Cleat, 38

Clinomeler, 18

Drifts, calculating length of,

Clowes' fire-damp iodicalor, 299

Coal, annual output of, 33

— calorific value of, 41

— mode of occuirence of, 9

— uses of, 41

- varieties of, 35

Coal-cutting machinery, 190

— series-wound, 41a

Coal-seams, produce of, 33

— typical examples of, 36

(Jockermeg, 182

Coefficient of friction of air, 261

TT CONOMIZERS, 240 XL Electric blasting, 13;

Cofiering in sinking pits, 97

Coke, manufacture of, 383

Electric cables, 414

1 — o\-ens, beehive, 385

Simon-Carves, 387

Combustion, Z95

Compound engines, 234

Compressed air, 24I Condensers, 235

Conforronbility, 20

Contiguous coal-seams, method of working, 174

- switches, 210

Contorted strata, 29

Elliot coal-washer, 379

Contour lines, 30

£endless-rope haulage, 337

Copper ores, 13

Engines, steam, 233

Corves, 324

— friction of, 327

Coulomb, 406

Explosions in mines, 393

Courriires method of limbering.

Explosives, 12S

Iss

- Mines Order, 129

Creepers, 371 Cumberland coal-field, 42

1 Curbs, walling, 96

TTALLS in mines, 39S r Fans, centrifugal, 268

1 Curves, setting out, 336

Index.

, reversed, 26

gh, 26

,mp indicators, 298

underground, 400

par, 13

of Dean coal-field, 46

, carboniferous, 12

cage decking arrangement,

1 clutches, 340 r in mines, 259 )rves, 327 )lids, 222

2, ventilating, 265 cut-out, 418

LLOWAY'S pneumatic vater-barrel, 99 r, II

J, 41

1 mines, 25 1

)ads in longwall workings,

cal maps, 29 value of, I

and - Copley coal-cutting ine, 196

is, 400 e, 14

ts, measuring and express-

*an, 271 "or shafts, rail, 307

ropes, 307

timber, 306 der, 130

, 14

)E of faults, 24 Eiammers, 120 achine drills, 122

:, endless-rope, 337

,329

and tail, 335

J-rope, 333

ar, 302

ichanical equivalent of, 209

er of, 227

Heat, unit of, 225 Hepplewhite-Grey lamp, 294 Hoppit for sinking, 82 Horse-power, 210

— of ventilation, 259

Hind coal-cutting machine, 198 Hutton seam, 36 Hydraulic power, 220

— pumps, 361 Hydrogen sulphide, 254 Hygrometer, 286

IGNEOUS rocks, 2 lUuminants for safety-lamps,

Inclined planes, 218

Inclines, self-acting, 330

Indicator diagrams, 231

IngersoU - Sergeant's coal-cutting

machine, 2(

Iron ore, 14

Iron pyrites, 14

JEFFREY chain coal-cutting machine, 205 Jeffrey disc coal-cutting machine, Jet condenser, 235 Jiggers, washing, 381 Jigging screens, 374 Jinney wheels, 331 Joints, 20

KIND-CHAUDRON of sinking, 104 King's detaching hook, 321

process

LANCASHIRE boiler, 237 Lancashire coal-field, 43 Latent heat, 226 Lead ore, 14

Lee coal-cutting machine, 199 Leicestershire coal-field, 44 Levels, driving, 114 Levers, 212 Lignite, 39

Longwall method of work, 148 — retreating, 158 Lower coal-measures, 10

TV It ACHINE rock diills, 89 IVi Main coal seam, Sov.th

Derbyshire. 37

Main and toil rope haulage, 335

Mangane ate, 14

Picks, 120 1

Marsaut safety-lamp, 293

Pieler gas indicator, 299

Mather and Piatt method of boring.

Piling through loose ground, 67

Pillar-and-stall method of work, vmfa .

Meelianical powers, 2 1 1

Pipes, air, 276

Metaroorphic rocks, 5

Methods of opening out coal -seams.

Pit hank, anangemenl of

Pit bottom. Ill

— of working coal. 141

Mica, 14

Midland coal-field, 42

Poelsch method of sinkil, 72

Millstone grit, 1 1

Props, setting, 177

Miners' phthisis, 404

— strength of, 177

Morgan-Gardner coal-cnttinc ma-

Pulley blocks, 217

chine, 200

Pulleys, winding, 214

Motive column, 259

Motors, electric, 416

Mneseler safety-lamp, 293 Multiple wedge, 126

Munoii coal-washer, 37S

ATURAL venlilalion, 267 Nitrogen, 251

Normal fault, 23 Northern coal-fields, 41

Retort coke-ovens, 3S7

Reversed faults, 26

— Wales coal-field, 44

Nystagmus, 405

Robinson coal-washer, 379

/CHRE, 14 KJ Ohm, 406

Rocks, age of, ;

Oil shale, 14

Outbursts of gss, 253

Outcrop of beds, 19

Output of coal from Great BriUin,

Overlap of strata, 23

Ropes, Lang's lay, 308

Overwinding, prevention of, 320

Oxygen, 250

- strength and weight of,

- windTng, 30S

DACKS, 14S r Peat, 3S

Percussive bomig, 53

Permian system of rocks, 8

Index.

for sinking pit, 87 n, 270 al-fields, 46

y inclines, 330 t mine, 37 dents, 398

m and size of, 66 n of, 65 ig tools, 123 i stores, 366 g by electricity, 135

e coal-fields, 45

jves coke-ovens, 388 ;ous blasting, 140 pe haulage, 333 y the aid of compressed air,

js, 67

cts, 109

t*s method, 76

Chaudron method, 104

erg process, 105

ds, 87

5 arrangements, 79

ds, 108

Is, 349

irough loose ground, 187

urns, 317

the air, 21

ous ignition, 4CX)

leading machines, 204

igines, 233

pound, 234

grams, 232

licators, 230

roperties of, 228

iers, 184

:ring, 123

ams, method of working,

on safety-lamp, 291 ire-damp indicator, 300 ' beds, 17

stated hydrogen, 254 arrangements, 367 users, 236

Swellies, 23

Switch, double-pole, 418 Synclinal curves, 16 Syphon, 346

Sylvester's patent prop withdrawer,

TAMPING shot-holes, 138 Tapered props, 184 Tar, 391 Temperature and pressure of steam,

Tempering steel, 123 Ten-yard coal, method of working,

Thermal units, 209 Thermometers, 282 Thick seams, method of working,

Thinning out of beds, 22 Thomeburry safety-lamp, 294 Three-throw pumps, 361 Tightening pulleys for endless

ropes, 339 Timber, methods of preserving, 176

— strength of, 178 Timbering roadways, 148

— shafts, 84 Tin, 14 Tipplers, 371 Tramming, 328

Trias system of rocks, 7 Trough faults, 26

— washers, 377

Tubbing, method of fixing, 93

— strength of, 94

Tubs, construction of, 324

UNCONFORMABILITV 20 Underground dams, 404 Underground fires, 401 Units of work, 209 Unstratified rocks, 2 Upcast shafts, closing in, 275

VALVES for pumps, 357 Veins, mineral, 24 Ventilating fans, 268 — furnaces, 265

Index.

Ventilation, calculations relating to,

— natural, 267

— of mines, 275

— of sinking pits, 81 Vernier, 280

Volt, 406

WADDLE fans, 271 Walker's patent sinking frame, 90 Warwickdiire coal-field, 45 Washing machines, 376 Wash-out, 29

Water, occurrence of in mines,

Water-gauge, 284

Water-levels, 114

Watt, 406

Wedges, 120

Wedging curbs, 95

Wheels, toothed, 216

Winding cages, 303

— engines, 314 size of, 321,

— pulleys, 302

— ropes, 308

Wire ropes, cappels for, 311 Worthington pumps, 260

The End.

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PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, LONDON AND BBCCLBS, h!

Aug 3 I 1937