Rudimentary treatise on the blasting and quarrying of stone for building and other purposes

Burgoyne, John Fox, Sir, bart. · 1849 · Historical

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'J

Rudimentary Treatise

ON THl

Blasting And Quarrying

09

Stone

Fob Buildiko And Otheb Pubposes.

Bt

Maj.-Gen. Sir John Burgoyne, K.O.B.,

BTOv ETC.) BTO.

WUt| niimiioiui m<wli W/ngfMutiB*

Togetheb With Otheb Useful Additions Belatino

To The Same Objects.

London: John Weale, 69, High Holborn.

1849.

S^^

Jun 20 1917

iRANSFtRRtO TO "».A|^AKw COUUOfi tlURARy

Londoh : 6E0Bob Woodfall And Son,

Advertisement.

For the present Volume, on a subject hitherto little treated of, T am indebted to Major-General Sir John Burgoyne, who published the same as a contributory Paper in the elaborate and continuous Work, entitled " Professional Papers of the Corps of Boyd Engineers," of which there are at this period 10 vols, large quarto. Sir John Burgoyne, with his usual urbanity, to aid its more general diffusion, has kindly sanc- tioned the reproduction of this Paper in the Eudimentary Series. For the very useful additional matter, which will be found in pages 78 to the end, I am indebted to Mr. Dempsey, who has before acquitted himself to the satisfaction of those who are engaged in the professional pursuits of the Useful Arts.

John Weale.

Contents.

Paet I.

Quaehying And Blasting Books.

Inteoductoey Obseeyations Page 1

Boeing the Holes 2

Results in Granite Quarries at Dalkey^ 2. — Chum Jumpers, 3. — Boring with Augers, 4. — German Boring Apparatus, 5.— Position of the Holes^ 5. — Line of Least Resistance, 5. — Charge of Powder required, 6. — Best Positions in which to operate on the Rock, 9— . Instance of the Force of Powder at Dunmore East, near Waterford, 14. — Table of Space occupied by given Quantities of Powder, 16.

The Powdee and the Chaege 17

Strength of Powder used, 17. — Table of Comparative Results of dif- ferent Qualities of Powder, 18. — The Eprouvette Gun, 19. — ^Table of Experiments on Powder by Bursting of Spherical Case Shells, 20. — Advantages of Using Superior Powder, 21. — Mixture of Saw- dust with Powder, 22. — Leaving an Air-space adjoining the Charge, 23. — Mixing Quicklime with the Powder, 24. — Mode of operating on the Hard Limestone of Gibraltar, 25.

Loading 26

Ordinary Methods of Loading, 26. — Marked Copper Measures for Charges, and Copper Tubes and Funnels for Filling, 28. — Tamping- bar to be tipped with Brass, 29.

The Teain and Fieing 29

Safety Fuse, 30. — Account of its Use at the Kingston Harbour Works, and Description of the Invention, 30. — Firing by a

Voltaic Battery, 34. — Mode of Lighting a Train in Shafts, 35

Means for preventing Small Stones flying about in Blasting, 35. — Quarry Shields, 36.

Tamping 37

Different Materials employed, 37. — Experiments upon the Com-

Vi Contents.

parative value of Sand and Clay for Tamping, 40. — Experiments on Tamping with Packed Sand, 44. — Sand Tamping inferior, or worth- less, 45 Experiments with Tamping of Clay, broken Brick, and

broken Stone, 47. — Tamping Pluys, 50. — Iron Plugs, 51. — Objec- tions to Plugs, 51. — Pins and Cones, 52. — Iron Cones and Arrows, 53. — Experiments on Tamping with iron Plugs or Cones, 55. — Conclusions from preceding fixperimenti, 5d.

Tunnelling Page 60

Disadvantage of the Work, 60. — Mode of Proceeding, 61. — A Good Record of Results of Working Tunnels much wanted, 62. — Assumed Advantages of constructing Double Tunnels, 63. — Denied, 64. — Sinking Shafts, 66.— Effects of Strata, 67.— Drainage, 68.— Ven- tilation, 69 — French Method of Ventilating Tunnels, 71 Cost of

Tunnelling, 72. — Cost of Road Tunnel at Drenodrohur, in Kerry, 72. — Cost of Railway Tunnel at Liverpool, 73.

Appendix 74

Mode adopted at Marseilles for enlarging Inner End ot Hole, 74. — Patent for ditto to Baron de Liebhaber, 75. — Blasting in the Jumtia,

and at Delhi, 76 Blasting Plymouth Limestone, 77 and 79. —

Quarrying the Granites of Aberdeen and Peterhead, 78. — Imple- ments and Cost at Plymouth Quarries, 79.

Slats QtrAERTiNo 81

Geological Features of the Strata, 81. — Quarries at Bangor, 82. — French Slate Quarries, 83. ^Quarries in Germany, Switzerland, Italy, &c., 83.— Slate hardened by Baking, 83.

PiEiNG Mines by Voltaic Electricity .... 84 Removal of Round- Down Cliff at Dover, 84.— Charges, 85. — Chambers, Shafts, and Galleries, 85. — Voltaic Batteries, Danieirs, and Plate Batteries employed, 86. — Cartridges, 86. — Tamping, 87 — The Firing and Results, 87.

Pabt Ii.

Stones used in BtJiLfiiNG .88

Division of Stoned into Oranitey 3late9, lAmegtonesy Ittd Sandstones^ 88. — Granite, 89.— Constituents, and Districts where found, 89. — Hetm (Guernsey) Gfanite, 90.— Table of Results of Wear of different Granites, 92 — Table of Experiments on Crushing Granites, 94. — Experiments upon Irish Granites, 95. — Serpentine and Por- phyry, 95.

CONTENTS. Vll

Slate. — Constitutent Substances, 96. — Districts where worked, 97. — Irish Slates — Results of ESperiments, 97.

Sandstones. — Chemical Analysis, 97. — Weight and Composition, 96. — Mode of using and selecting best description for Building Purposes, 98. — Examples of Durability of Sandstone Buildings, 99.— Experi- ments upon Crushing Sandstones, 100.

Limestones, 101 < — Analysis of Oolites and Limestones, 101.— Weights of ditto, 101. — Composition of ditto, 102. — Analysis of Magnesian Limestones, 102. — Weights and Composition of ditto, 102. — Build- ings of Magnesian Limestone, 103. — Buildings of Oolites and other Limestones, 103. — Summary of Results upon Sandstones and Lime- stones, 105.

Quarrying

And

Blasting Rocks.

In a ** Rudimentary Series," such as the one to which this volume belongs, perhaps no subject can be introduced with greater fitness than that of quarrying or stone-getting, — cer- tainly one of the rudimentary arts connected equally with the duties of the engineer, the architect, and the practical builder. Any attempt to recount the history of the art would oblige us to extend our retrospect to a very early date, perhaps we should rather say to a dateless period ; to call to mind the structural wonders of Tyre, of Sidon, and of Thebes ; and to close the history with the confession that, however the mechanical modes of wielding the wrought masses may have received improvement in modem times, the primitive methods and tools of the quarryman and of the mason have, if we except the introduction of gunpowder, become no more altered in our hands than have the chiselled works of the ancient sculptors been surpassed by the productions of later ages. The one powerful assistant, however, to which we have referred, has been enHsted in the service of the quarry within a comparatively recent period, and its aid has certainly sup- planted to a great extent the action of the wedge and the hammer.

Without this valuable auxiliary, the work of separating large masses of stone from their native blocks or beds must have been infinitely more laborious, and have needed also a skill of no mean degree. The art of applying gunpowder to this purpose has, however, remained very nearly the same since the first experimenter "jumped" and "charged" a bore in the stubborn rock, which till then had been attacked only with the chisel and the wedge.

2 Quabbting And Blasting Bocks.

The implements employed for quarrying by mere manual labour are simply the sledge hammer or mallet, the borer or chisel, and the wedges, besides trucks, and such gearing as may be required to facilitate the removal of the blocks when detached. Of these, the only one which needs any description is the chisel, which is an iron rod with a steel cutting end, welded at one extremity, and flattened to a wedge- like form at the other. The implements used in blasting are of a similarly simple character, and consist of the borer or jumping tool, the scraper for clearing the hole of the chips produced, the claying bar for driving in dry clay if the hole be too damp for the immediate introduction of the charge, the needle, which is driven into the charge, and remains while the hole is filled up with stones, &c., so that, when ultimately withdrawn, a channel is preserved communicating directly with the powder. While the needle, which is a long thin copper rod, remains in its place, the space around it is filled up, by means of the tamping bar, with stones, &c.

In the following paper, which is from the pen of Major- General Sir J. F. Burgoyne, we have a most useful collection of facts upon the subject of blasting, together with a complete account of the process and the materials employed, and seve- ral hints for the improvement of both, which we trust will receive all the attention due to their high authority and intrinsic practical value.

The operations which constitute the entire process of blast- ing are, boring the holes, loading, and firing.

Boring The Holes.

The best means of expediting the operation of blasting, would be by any contrivance that woiQd render the boring of the holes more quickly executed.

The ordinary implements used for this purpose are, the jumper or cutting-tool, the hammer, and the scraper.

There is much discrepancy in the account given in dif- ferent places, of the time required for boring holes ; arising from differences in the precise quality of the rock, the mode of working, and the different bases of calculation.

The following, obtained from John Mac Mahon, Esq., of Dublin, is the result of some considerable experience in quarries of granite of good quality at Dalkey, in the neigh- bourhood of Dublin.

*' 3-inch jumpers, used in boring holes from 9 to 15 feet

QUARBTINa AND BLASTINa BOOKS. 3

deep; ^ men striking, and 1 man holding and turning the jumper, bored on an average 4 feet in a day, or 5 feet with a 2|-inch jumper, which was frequently used for boring the same depth.

" 25-inch jumper, for holes from 5 to 10 feet deep ; 3 men as above would bore on an average 6 feet each day.

"2-inch holes from 4 to 7 feet deep; 3 men would bore

8 feet of such holes.

"l|-inch holes from 2 feet 6 inches to 6 feet; the

3 men bored 12 feet.

" In working the two last classes, a strong boy will answer to turn the jumper instead of a man.

" 1-inch jumper, for breaking the fragments of rock to smaller pieces ; 1 man bored 8 feet per day.

"The waste of steel and iron was nearly as follows: — a 3-inch jumper took for its bit 2 lbs. of steel, with which it would bore 16 feet, on being dressed or sharpened 18 times; waste of iron 18 inches to each steeling, or 1| inch for each foot bored.

2-inch jumper took 1 1 lb. of steel. l|-inch „ „ fib. 1-inch „ „ 3 oz.

" They would all bore from 18 to 24 feet with each steel- ing, and require to be sharpened about ouce for every foot bored.

"The weight of the hammers used in boring with each class of jumper was as follows : —

18 lb. hammers for 3-inch jumpers,

161b. „ „ 2| and 2|-inch,

14 lb. „ „ 2 and l|-inch,

5 to 71b. „ „ 1-inch, used by one man.

" Chum jumpers, so called from the manner in which they are worked, from 7 to 8 feet long, with a steel bit at each end; general diameter, 1| to 1| inch. Two men would bore with them about 16 feet per day."

These last are much more efficient than those struck on the head with a hammer, and are sometimes used with a spring rod and line. They are applicable to holes that are vertical, or nearly so, and to rock that is not too hard : in the granite at Kingstown they were abandoned on account of the edges turning so fast, that the frequency of the necessary sbarpenings gave the advantage to the use of the hammer: where they can be used, the work will be performed at a far

B 2

4 Quarrying And Blasting Rocks.

more rapid rate than even above mentioned. In boring Artesian wells to great depths the application of the tool is entirely on this principle.

A ^till quicker mode of boring would be by drilling the holes, if it were feasible. It has often been proposed, but the cutting edges of the tools will not stand in any kind of stone.

Where charges have been exploded without blowing out the tamping *, it may be very desirable to bore the latter out for the purpose of introducing another charge ; in such case the hole need not be of the size of that originally made, as 1 inch bore will be adequate at any time.

In clay tamping, a hole may be bored out with the jumper and hammer at the rate of about 26 minutes for 3 feet. Broken stone tamping will be bored out at the rate of 20 minutes for 3 feet.

A very few trials were made to bore a hole through clay tamping with an auger ; the labour was less, as fewer men were necessary ; the time consumed was somewhat more, but the tool was capable of improvement, and the men were new to its use.

It is conceived that augers, properly constructed, may be used to advantage in re-boring through clay tamping for suc- cessive blasts from the same hole, to the gain of a saving in time and labour, and avoiding the application of water, which is necessary with any kind of jumper.

In case of a miss-fire it is a very dangerous practice to re- bore the hole, and has occasioned very many bad accidents ; it is very properly usually forbidden altogether. If the hole be vertical, or nearly so, and the needle or fuse hole can be cleared, so as to ensure a thorough wetting of the charge, by pouring water down, it might be done with safety ; but some- times flie very object of the quarry man is to save the powder, — a very unworthy one for which to incur the great risk of killing or maiming two or three workmen.

To prevent the loss of any large charge in this way, a hole is sometimes bored on one side, and within a few inches of the one that has failed, to the same depth as its charge, and being loaded and exploded, has had the effect of igniting the other also.

An apparatus for boring to considerable depths has re-

• The ** tamping** is the filling up of the hole in which the chai^ of powder, &c., is deposited. .^.Ei).

QUARBYIKa AND BLASTING BOCKS. 5

cently been introduced into this country from mines in Ger- many* by Charles Vignoles, Esq., O.E., which it is believed is fieir more efficient than any hitherto employed in Great Britain.

This machinery has been in operation, it is believed, on the Manchester and Sheffield Railway, of which Mr. Vig- noles was the engineer ; its direct application being to bore into and ascertain the precise qualities of the strata through which the great tunnel (8 miles in length) will be carried, which is to form the communication through the moimtain ridge that divides the eastern and western inclines of England.

The principal feature in the process is that the cutting tools are attached to a heavy weight, and worked by a rope, instead of by rods with screw joints.

The rope is wound round a cylindrical roller by a winch, and there are several ingenious contrivances in the details and parts of the machinery, that tend to facilitate the ope- ration.

Upon the judicious selection of the position of the holes will in a great measure depend the useful effect of the blast ; but two leading errors are committed by quarrymen or miners in general, viz., selecting an injudicious position for the charge, by which the action of the powder is exerted in the direction of the opening where it was introduced; and the adopting as a rule for the several charges, to fill a certain number of feet or inches of the hole bored, usually one-third of its depth, instead of employing given weights adapted to the lines of least resistance.

The line of hast resistance is that line by which the ex- plosion of the powder will find the least opposition to its vent in the air. This need not necessarily be the shortest line to the surface ; as, for instance, a long line in earth may, from the same charge, afford less resistance than a shorter line in rock.

Supposing the matter in which the explosion is to take place to be of uniform consistence in every direction, charges of powder to produce similar proportionate results ought to be as the cubes of the lines of least resistance, and not according to any fanciful depth of hole bored.

Thus, if 4 ounces of powder would have a given effect upon

* It is said that boring on a similar principle has been long used in China.

ft solid piece of rock of H feet thick to the BurfiuM, it ought to require 13^ ounces to produce the same effect upon a piece of similar rock 3 feet thick ; that is.

Cube of 3 feet

37

18J

or, what is the same thing, half the cuhe of the line of ]east resistance expressed in feet, will, on thU particular datum, be lie charge in ounces, as follows : —

Linei of least resiitance Ctiarge of poirder.

in feeL ^'

tiane of ]

1 . . . . Oj*

4 ]3|

3 3 U| 6 13 10 llj 18

These quantities being of common merchants' blasting powder, will be found adequate for any rock of ordinary tenacity; but a precise datum should be ascertained by a few actual experiments on the particular rock to be worked |.

Thus, with a 2-feet line of least resistance, (a to B, Fig- I— {Section,)

fig. 1,) whether 4 ounces, or 8 ounces, or 8 ounces, are requisite to produce a good effect ; with 3-feet line of least resistance, whether 13^ ounces, or 18 ounces, or 27 ounces, &o.

On the results of these trials a scale may be adopts ed for guide in the service. With regard to the first error above mentioned, that of leaving the action of the pow- der to be exerted in the direction of the hole bored, one con-

■ To 80 BmaU a quantity as 4 ounce a lillle eiceu might be added, but } ounce, or J ounce more, will be sufficient.

t In tbe granite quarriea of Kingaloim (near Dublin) these chattel Here sufBcienI to open the rock wbere there were no Gssures, apparent

Q(7ABBTINa AND BLASTING ROOKS. 7

sequence is that, with small charges, commonly a part of the explosion finds comparatively easy vent hy that opening, (in spite of the best tamping,) and is wasted ; and it is only the excess that acts in producing the effect required on the rock ; whereas, if the explosion were forced through another direction, the whole of its power would be exerted beneficially. But the great objection is, that the rock is then so much more firmly bound aU round the charge, as to oppose and lessen in a very great degree the extension of the effect of the ex- plosion.

It must be understood that, even although the line of least resistance should be in the direction of the hole bored, the depth of the hole will by no means be the measure by which the proportions of powder for the charge can be taken accord- ing to tiie above rule, namely, as the cubes of the lines of least resistance.

1st, because the tamping, however good, or by whatever contrivance strengthened, cannot be equal in strength to the solid rock.

2ndly and chiefly, because of the various proportions of the entire depth of the hole occupied by different charges of powder : thus, i ounce of powder will occupy an insignificant proportion of the depth of even 1 foot of a 1-inch hole, and also the 4 ounces for a 2-feet line of least resistance would fill only 2 inches of a 1-inch hole, and consequently occupy one-twelfth of the 2 feet, and leave 1 foot 10 inches of tamp- ing; while the 18| ounces for a 3-feet line of lesist resistance would occupy of a 1-inch hole above 6 inches, that is, more than one-sixth, and leave only 2 feet 6 inches of tamping, and consequently of resistance, such as it is.

This might be remedied in one way, by applying holes of larger diameters for increasing charges, but, by so doing, an increased amount of the less resisting medium (the tamp- ing) would be the consequence, which again renders the cal- culation, founded on a resistance of solid rock, incorrect.

There is another reason why the powder is ill applied when the explosion takes place in the same line as the bore, which is, that it is placed longitudinally with the line of least resistance, as at o, in fig. 2, and not perpendicular to it, as at

weakness, or other advantage ; but where the line of least resistance was not that of the hole bored, the effect was either to bring it down, or only to Click it, according to the quality of the powder used.

8 aUABBIlNO AHD 8LA8IIN8 EOCKfl.

P ; when much extended, the elongated fonn in either is bad, bat it is worst in the former case.

Fig. 2.— (Section.)

When the common mode of blasting is adopted, a loud report is heard like a gun, (louder in general in proportion to the less mefid effect produced,) and fr^ments of stone are frequently ^rown to a considerable distance ; but when done judiciously, the report will be trifling, and the mass will be seen to be lifted, and thoroughlj fractured, rent, or thrown over, without being forciblj projected.

It is the irregularity and extent of the TJolent explosion following the ordinary process, that renders it so peculiarly difBcult to form an accurate judgment on the proper charges for each circumstance ; the consequence is a practice purely empirical. The miner or quarryman will give as his rule either a proportionate depth of hole, or, aware how frequently that must prove erroneous, is driven to his usual answer, that he knows &om the appearartce of the situaljon what to apply ; that is, in fact, admitting that it is a matter of ca- price, and provided a certain effect is produced, he is little aware how much time, powder, and labour, may have been wasted.

It is difKcult to make ordinary quanymen, oi even over- seers, understand correctly the meaning of the lines of least resistance: after appearing to comprehend it, they are fre- quently observed to confound it with the length of hole bored, or with soma conceived necessary direction either vertical or horizontal.

With respect to the second error mentioned, it can easily be shown how very erroneous miat be the rule of measuring

Quabbying And Blasiing Books. 9

the charge by any given proportion of the depth of the hole, since the quantity of powder will in that case depend, not only on the depth, but also on its diameter, with which it c!)Bin have no relation : thus, if a 6-feet hole is to be bored, it may be an act of chance or caprice whether a jumper of Ig-inch gauge, or of 2 inches, or of 2 J, were used ; whereas the third of the depth, or any given number of inches of the 2-inch, would hold very nearly double the quantity of powder that would be contained in the l|-inch ; and of the 2 J-inch, one half more than in the 2, and nearly three times as much as in the 1^.

Such a rule also takes no account of the quality of the rock, which in reality will cause the greatest difference in the effect ; a given depth of hole being applied to hard or soft rock indis- criminately.

Although some allowances may be made in extreme cases, yet it will be found in most books and papers on blasting rock, that a tistLal charge is one-third of the depth of the hole ; and the same will be found to be the actual prevalent practice.

As to the experience by which it might be assumed, that the miners will modify this rule* and regulate the proper charges to give in each case, the value of such practice, unaided by better principles, must be small, where the results are so indistinct. A loud explosion takes place, and the rock is more or less separated, but no proof whatever is afforded that the charge has been precisely, or even nearly, what it should have been ; and being regulated by no rule, (for in this case of leaving it to the miner's judgment, the only rule is abandoned,) the experience, to be valuable, should be of precisely similar cases, whereas in blasting they are constantly varying, in size and depth of hole, and in many other circum- stances. If the rock were uniform, and the application of the charge always in similar holes and situations, a tolerable rule of thumb experience might perhaps be obtained; but it is quite otherwise, and among the circumstances 'that must tend to perplex an ordinary miner workman, would be, that the true principle for charges is, as the ctibes of the thickness of the resisting medium, but which he would certainly regulate by a much more gradual proportionate increase, such as doubling, trebling, or squaring at most.

In order to quarry with good effect for saving labour and powder, an exposed front, either vertical or horizontal, should, if possible, be established on the rock on which to operate,

B 3

10

QUABBYINO AJiD BLASTINa BOOKS.

principally to obtain a line of least resistance in a different direction from that of the hole bored.

Thus, if a charge of powder were JV. .—3( Section.) placed at p, fig. 2, with a line of least resistance to b, the explosion would force its way through at b, shatter and loosen the whole mass at D, and make cracks to a great extent towards e; whereas if the hole had been bored direct from b to p, or as at o, (as ' is usually prac- tised by common quarrymen,) the re- sistance being excessive in every direc- tion, except in the direct line of the hole bored, it may be easily conceived that the same charge would produce fax less effect.

Or, to adopt a more practical illus- tration, suppose ledges of rock require to be cleared away to a certain level for a road, navigation, or other object ; instead of boring holes + + +, the effect would be far better by inclined holes. A, b, c, fig. 3, applied in suc- cession after the above-mentioned prin- ciple.

Where there is a high face of rock, a system of undermining may be ad- vantageously employed: thus a blast at A, hg. 4, would make an opening easy from c to d, and the mass e, if not shaken, which it probably would be, so as to be worked on with crow-bars and wedges, would be brought down by very slight subse- quent blasts.

When the rock is stratified, and in close parallel beds and seams, the holes should be bored in the direc- tion of the joints, and the powder laid along them as at a, fig. 5, which will have much more effect in lifting large masses than if placed across the grain, and the operation of boring will be easier.

QtAKBTtNG AND BLABtINO BOCKS. 11

The worst aitoatioti for a chai^ of powder ia in & te-enter- ing angle, as at a, fig. 6 : the rook exerts Buch preBSure all

J^, 4.— < Section.)

Fig. 5 (Section.)

Fig. 6,~( Horizontal Section.)

13 QUARBYIHe ADD BLAHTINO BOCKS.

aroand it, ihat very little effect can be expected ; nor is the position much improTod at b.

This situation of a re-entering angle occurs very frequently, and should be avoided aa much as possible. Thus a charge may be lodged in a hole c, fig. 7, having the same length of line of least resistance as at other holes, a or b ; but the effect of the explosion will be greatly reduced by the mafises d, e. Fig. 7.-(Pl«..)

An important illus- J^. 8.— (Sedion.)

tration of this disad- vantageous position for the charge will be ex- perienced in cutting through any narrow con- fined space A, B, c, D, fig. 8, either horizon- tall;, as in the first drift, or opening, all through a tunnel, or vertically, as in sinking a shaft; blasts at a, h, or c. must be extremely ineffective.

A projection, on the contrary, is the most favourable

situation to produce the greatest effect with the smallest

Fig. 9.— (Secdons.)

means i a given quantity of powder, for instance, at x, fig. 9, would remove the mass b, b, a, c, and make partial cracks on

Quabbting Akd Blasting B0Ce8. 13

the side e, but the same quantify at d would remove e, f, g, h, or nearly double the mass *.

Gases, however, frequently occur requiring a deviation from what, under ordinary circumstances, woidd be the most favourable application of the charge, either owing to the quality of the rock, or where other objects are of more importance than the consumption of powder, or of labour in boring.

The rock may require to be cut to a particular form, as, for mstance, when preparing it to receive foundations of masonry ; or certain blocks of the stone may be required of particular forms or dimensions : an excess of powder may be applied to increase the shock for bringing down any loose mass in a peculiar state, or vice versd, smaller proportions may from circumstances be sufficient to produce as much effect as is required : these irregularities are very frequent, but it is not the less necessary to understand the correct principles, and not to be carried away with the idea that the whole is a mystery.

It may also be urged that there are cases where the system of working on a line of least resistance, different from that of the hole bored, cannot be followed ; such, for instance, as in sinking a shaft, or cutting the first driftway of a gallery or tunnel.

This is very true, and must cause such operations . to be peculiarly costly and slow; and though the rule above re- commended for regulating the charges would be inapplicable, still that of taking any proportionate depth of the hole would be quite erroneous.

The system to be adopted in such instances should be to apply the mode of tamping that would give the greatest possible resistance, and to endeavour to obtain by trials the amount of charge by weight that will barely disturb such tamping ; in this way the fiill effect of the powder will act upon the rock, and where that is not very great, a second shot from the same hole will be sure to be very decisive.

Among the cases not admitting of fixed rule, and where a great deal miLst depend upon the intelligence and experience of the directing quarryman, is that of irregularity of joints, or seams.

* It will not have quite this effect, as the greater resistance on the side K, in the one case, will increase the effect towards c ; but that circum- stance does not affect the general consideration of the principle here ad> verted to.

I<t qUABB'fIKO iXB BUSTDtS BOOKS.

Tha following iast«nce will explain this : —

A hole A, B, fig, 10, of 4 ioches diameter and 10 feet deep, was bored to tlie back of a projecting ma§g of granite, and 6 feet above a natural slide joint, aa ehown in the plan and

section.

Pint. .F^. ]0. Section.

Had there been no projection, nor any joint to afibrd an advantage, it would have required probably 182 lbs. of powder to break through a reaiiitance of 18 feet; but as it was cir- cumstanced, between 35 and 36 lbs. (occupying 7 feet of the hole) broke off and overturned an enormous mass c, cutting it down as shown by the dotted Uses : the fragments of course were large, one piece containing 80 cubic yards; and were very appropriate for cutting into ashlar of large dimensions.

Another instance, tried at Dunmore East, near Waterford, may be given of the force of the action of powder, even in an open joint: the same experiment also incidentally serves to illustrate another object of inquiry.

The rock was a very hard conglomerate, in &ir partdlel beds ; the surface was even ; the side h, h, fig. 11, had been already excavated ; there was a joint or bed, parallel to the surface, and 7 feet below it. A hole a, of 3 inches diameter and 6 feet deep, had been loaded with 1 lb. 14 oz. of powder, (t 5 inches,) and made a straight crack c e, and to k, of 14 feet long, and down to the bed.

Qvabryino And Blasting Bocks.

15

1%. 11.— (Plan.)

/

A trial was then made, whether openings might not be directed to particular lines : 13-plug holes were dnlled along the line + + + 8 inches deep and 1| inch diameter; a ^^-inch hole was then bored at &, to a depth of 6 feet 10 inches, and loaded with 4 lbs. (2 feet) of powder : when fired, the line was opened very nearly along the line of the plug-holes ; the separation did not exceed half an inch.

The hole b was then cleared out, and loaded with 8 lbs. of powder, and the explosion sent the whole mass forward upwards of 2 feet without any new fracture ; the cubic con- tents of the mass being 663 feet, weighing about 51 tons.

In most extensive quarries of stone, much of the practice must depend upon the intelligence with which advantage is taken of the position and nature of the joints and fissures : still many errors are committed from a want of knowledge of the best application of powder to a perfectly solid mass ; and in cases where the mass to be removed is small, or the open- ings to be made, confined, but little advantage can be gained by the joints, and the application should be chiefly to given charges for lines of least resistance.

The advantage obtained by joints is one reason for rather reducing the calculated amount of charges, particularly in large explosions ; because, although nothing that is not per- ceptible can well augment the force of resistance, fissures or joints that may not be seen on the surface may have the effect of reducing it.

It would be of much advantage in many cases, if the pow- der could be placed in a more compact form, than occupying

16

Quabbtino And Blasting Bocks.

a considerable length of a hole of comparatiyely small diame- ter : the position it must assume in these holes is generally unfavourable for producing the best effect, and in some cases renders it impossible to apply so large a charge as would be desirable; but no practical mode of enlarging the space at the bottom of the hole has yet been contrived, except perhaps by successive explosions from the same, as practised at Gibraltar *.

It may be assumed that 1 lb. of powder loosely poured, but not shaken or compressed, will occupy about 30 cubic inches ; a cubic foot weighs consequently about 57^ lbs., although dif- ferent quantities are given in different Tables of specific gravity : if close shaken, powder will go into a smaller com- pass.

The following Table from Colonel Pasley's (now M^jor- Gen. Sir Chas. Pasley, E.C.B.) Memoranda on Mining will give the means of calculating the space occupied by any given quantity of powder in round holes of different sizes from 1 to 6 inches : —

Diameter of the hole.

Powder con- tAined in one inch of hole.

Powder contained

in one foot of

hole.

Depth of hole

to contain 1 lb.

of powder.

Inches.

1

14

2

24

3

84

4

44

5

54

6

lbs. oz. 0-419 0-942 1 676 2618 3*77 5-131 6-702 8-482 10-472 12-671 15-08

lbs. oz. 5*028

11-304

1 4112

1 15*416

2 1324

3 13-572

5 424

6 5*784

7 13'664 9 8-052

11 4-96

Inches. 88197 16-976 9-549 6112 4*244 3*118 2-387 1-886 1-528 1-263 1*061

In practice, the holes are somewhat irregular ; this Table, however, will be sufficient to ascertain, nearly, the depth re- quired for any charge.

* In the Appendix will be found a memorandum by General Burgoyne on the use, at Marseilles, of nitric acid for the purpose of enlarging the inner end of the hole ; and also a brief description of a patent obtained by the Baron Liebhaber for an apparatus for this purpose. — Ed.

Quarrying And Blasting Rocks. 17

Of The Powder And The Charge.

Gunpowder used for the blasting of rock is notoriously of inferior strength to that^sold for sporting, or manufactured by Government for the army and navy ; and there is an im- pression (I believe nearly universal) that it is right that it should be so, not merely because pound for pound it is cheaper, but because it is thought to be positively better for the object, on account of its less rapid ignition, and assumed quality of giving what the miners call a heave. This opinion appears to be founded on a Mlacy. Inferior powder cannot be used in war, or for sporting, without the disadvantage being immediately apparent ; while in blasting it can be made to answer the purpose : this, with its comparative cheapness, has led, no doubt, to its being introduced and constantly made use of, without much investi- gation as to the policy of its employment in preference to a material of superior strength.

The argument used in its favour is, that, by igniting slowly in comparison with the other, the power is more forcibly and efficiently applied for the required object, than by the rapid shock of the superior powder, such as is undeniably requisite for impelling projectiles.

This reasoning would seem to imply that the rock will be opened better by a force of pressn/re than by that of a sudden shock or blow; which, however, may be disputed, even sup- posing, what is probably not the case, that the elastic vapour generated by either is the same. Rock being of a brittle nature, it is reasonable to suppose that the sudden violent shock would make more extensive cracks, which is the great object, than a more slow action.

The following are the observations I have been able to collect on this head ; and they tend to confirm the impression of the good policy of employing stronger powder for blasting, even at increased prices : more research, however, would be necessary to establish the fact entirely, and to fix the relative value of each gradation in quality.

Having procured from great contractors and respectable dealers eleven samples of Merchants* blasting powder, stated to be that of the principal manufacturers, they were analysed, proved with the Iprouvette mortar and eprouvette gun, and compared by the bursting of shells : the results will be seen in the annexed Tables.

18

Quabbting And Blasting Books.

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Quabbtinq And Blastin0 R0Ge8. 19

The best proportion of nitre (the most valuable ingredient) is 76 per cent.

The eprouvette mortar is 8 inches in diameter, and is charged -with 2 omices of the powder, and, an iron ball of 68^ lbs. weight ; the Government good cannon powder gives an average range of 265 feet. The Government powder somewhat deteriorated, and reserved for blasting, gives a range of 240 feet.

The eprouvette gun is of brass ; its bore If inches in diameter and 27*6 inches long; it weighs 86|lbs., and is suspended from a frame : being charged with 2 ounces of the powder, without any shot or wadding, it is fired, and the extent of the recoil is measured bj an index on a graduated arc.

The eprouvette gun is considered to be rather adapted to try the strength oifine grained powder than of the coarse ; the fine grained Government Rifle powder will give 26 or 26 degrees ; the Government good cannon powder 21 degrees ; that tried at the same time with the above, 20*6. It is extremely probable that in many instances of these coarse grained qualities, and of the Merchants' powder, igniting slowly, much of the charges may have been thrown out from the gun in each case unignited, and perhaps in some degree from the mortar.

Some discrepancies will be observed in nearly all proofs of gunpowder, but rarely to the extent that will be noticed in this Table : they show, however, how very unequal may be the qualities of the article as obtained at different times, from different dealers, and subject to a variety in their condition from modes and time of keeping ; and they also exhibit a very strong presumption of universal inferiority.

20

Quarrying And Blasting Rocks.

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Quabbting And Blasting Bocks. $21

The comparative strengtli by this mode of trial would seem to be about 9 parts of the Government, equal to 13 of the Merchants' powder.

It is very difficult to obtain any very precise results from trials on the rock itself: the effects vary so greatly under circumstances to all appearance precisely similar, that we are driven to reason very much from analogy; and where the blasting is judiciously performed, the tamping but slightly, if at all removed, and the rock merely opened and not violently ejected, it certainly would appear reasonable that the powder showing such superiority of strength in the above-described experiments would be by far the most efficient in its action on the rock.

A few trials that were made at Eongstown to elucidate the point seemed to prove the truth of this reasoning.

Charges calculated on tbe basis of ^ ounce ^r 1 foot, and augmented in proportion to the cubes of the lines of least resistance, were exploded in a high face of very solid rock ; and the result in every case was very marked in favour of the Government powder, even to the conviction of the miners present, who had previously expressed doubts on the subject.

Although the Government powder was applied to the cases which seemed to present the fewest advantages, the effect was decidedly superior, to the extent of usually dislodging a mass of rock ; whereas the Merchants' powder in no instance did more than make cracks and fissures.

If the truth of this suggestion be acknowledged, the follow- ing advantages would attend the use of the superior powder.

1. As smaller quantities would go farther, the stock for consumption would be easier to stow away and to carry.

2. Greater effect would be produced with a smaller amount of labour, and, what is of more consequence in many cases, of time in boring holes.

3. By occupying a smaller spacie in the bottom of a hole, an increased resistance in the tamping would be obtained by its greater proportionate extent.

4. The Government powder, and the superior kind made for sporting, (the former in particular,) are much less subject to deterioration from keeping, than the ordinary blasting powder ; this would effect a very desirable improvement, but it is not an absolutely necessary consequence of their being stronger, because the best preserving powders are not always the strongest.

Accordmg to Dr. Ure's Chemical Analysis, there is not

S2 Quabbying Ahb Blastiko Bocks.

moch difference between the mixtures of the Government Waltham Abbey powder, and those of the first class of sport- ing powder of the private manufacturers; the Government powder, however, resisted rather the best the hygrometric in- fluence, that is, would absorb less atmospheric moisture, and consequently be best for keeping.

In the works carried on by the Eoyal Engineer department, the powder is usually from the Ordnance stores, sometimes being perfectly good, or even if deteriorated to the degree for its being appropriated to blasting, it is still much stronger than the Merchants' blasting powder.

Fine grained powder made with very superior care, and at superior cost, is manufactured for the Rifle Service by Govern- ment, and for shooting by private manufacturers : but it would be too costly in proportion to its increased superiority, and some of its properties not being necessary for blasting, it is considered that the best cannon powder would be the most advantageous to employ.

Blasting powder is sold by dealers in the country at from 60a. to 75a. per 100 lbs.; while nearly as good powder of this nature as can be made, such as the Government cannon powder, might be sold hy the manufacturers at between 60a. and 60a.: supposing, therefore, that the cost, including the removal, the dealers' expenses and profit, should be one quarter or one third more than at present, the question will be, con- sidering the advantage of using this superior kind, and the proportion which the cost of the powder bears in the general expenditure of blasting, how far, and under what circumstances, it might be desirable to incur that increased expense, making allowance at the same time for the smaller quantity that would be consumed.

Founded on the same reasoning of the advantage of more gradual ignition, and almost leading to the assumption that the blasting'powder in its present state is even too goody is the assertion that will be found in all books on the subject, namely, that a mixture of fine and dry sawdust of elm or beech with the powder, in the proportion of ^ of sawdust for small charges, and \ for large, will produce as good results as equal quantities of powder alone.

It is not assumed that the effect is produced by any de- composition of the sawdust, but simply by giving a little more space, and by dividing the particles of the charge, causing them to ignite more gradually, and thus to act with greater force on the rock, than by the more sudden explosion.

QQA&BYnra iom bljutihO bockb. 33

No account ia given of any defined experimeste tending to prove tliis fact ; on the contrary, every tnal affording positive resolte is Bgainst it : such a mixtnre has been tried in gous, and produced no useful effect whatever ; and though of very Bimple application, it doea not appeir that in any place tliere haa been a continued nae of it.

There is indeed a deception in tlie first instance in the sup- posed pToportioQB ; for a mixture of two eijual measures of tite two ingredients, the sawdust being, as required, very fine and dry, and the powder of the usual large grain, will not fill above If of the same measure ; consequenuy two tneesurea of the mixture will contain nearly ^ more powder than calculated upon : thus if two measures, each capable of containing 8 ounces of powder, be filled with the mixture of equal measi^ed proportions, the quantity of powder will be nearer 9 onnces than the 8 calculated upon.

Altogether I feel little doubt of the application of sawdust being of no real value.

Another theoretical refinement, that is tA be found in all works on blasting, is, that if a hollow space be left adjoining the chaise, a much greatw effect will be produced, provided always {and it ia essential to bear it in mind) that (he tamping be as substantial, and to as great extent, in Uie one case as in the other.

Thus, in two holes of similar dimensions, the charge o, fig. 13, with a hollow space i> over it, wUl produce as good an

Fig. 12.

effect with i or } the quantity, as at the full charge e fully tamped, provided the tamping b, from e to h, be as good and as deep as that at a. An increased effect will certainly be produced by bu<^

24 Quabbting And Blasting Rocxb.

hollow, in the same manner as with guns which are frequently burst by the occurrence of a hollow between the powder and the shot, but there must be great reason to doubt its practical utility : no accounts are given of the well-defined result of actual experiment, nor are any rules attempted to be laid down for the extent of the hollow spaces in proportion to the quantity of powder in the charge, &c., to produce useful eflFect ; and yet these must be matters of consequence ; nor is it any- where stated that it has been ever practically continued to be used, notwithstanding the great saving of powder professed to arise from the adoption of this principle.

In large charges, the space that could be left would be too small to produce any useful effect ; and in small charges, the more simple, quick, and cheap way, would be by using the full charge of powder.

This and the sawdust are among the refinements adverted to in books (on this as on many other subjects), but seldom, if ever, put in practice.

Another mode of improving the power of the charges of powder has been employed, it is said, in America. It is the mixing of a quantity of quicklime in a proportion of about \ with tibe powder, on the principle that it will absorb any little moisture in the powder, and itself produce some ad(£tional vapour in the explosion, It is stated, however, that it must be used soon after the ingredients are put together, it having been remarked that if left mixed for a whole night the powder was deteriorated, owbig, as imagined, to the impurities of the saltpetre of which the powder was composed*.

Witb reference to the quantities of powder to be employed in blasting, different systems igu:e adopted.

In quarries worked for large stones, and in great quantities, sometimes very large blasts are considered advantageous.

In those near Kingstown, where the granite stones for ashlar work are squared by the contractors to from 40 to 60 cubic feet each, 50, 60, and 70 lbs. of powder were frequently exploded in a single blast, sometimes filling two-thirds of a hole of 4 or 3^ inches diameter, and perhaps twenty feet deep.

* There are other reasons against this practice. The absorption of water must be attended with the evolution of heat; and it is highly pro- bable that, under such, circumstances, there would be a reaction between the sulphur and nitre, in the presence of so powerful a base, and the ulti- mate production of sulphate of lime. Whilst, then, the simplicity of the operation is diminished, the powder is deteriorated ; and, if much moisture be present, not without danger.

Quabbtino And Blastikg Bocks. 35

They have been applied generally where a projection of considerable height or length, showing joints in large features* offered a prospect of bringing down some enormous mass; and in this way they were usually very successful.

To give an instance of one : —

The hole was 19 feet 7 inches in depth, and 5^ inches diameter ; the charge, 75 lbs. of powder, filled 8 feet 10 inches of the hole, having consequently 10 feet 9 inches of tamping.

The mass that was brought down, or thoroughly shaken and rent, measured, on a rough calculation, 1200 cubic yards, or 2400 tons. The cost was calculated at £6 i5«. Sd,, ihus :

2 men, 14 days, at Is, Sd, each ... £2 6 8

1 ditto, 14 days, &tU.6d 110

75 lbs. powder 200

Fuse 2

Smith's work, iron, steel, &c. . . . 16

M 15 8

Of course there was a great deal of after-work and small blasts required for the separation of the large masses of which this shaken rock consisted, and reducing it to manageable shapes and sizes ; but the work was greatly facilitated by this first effect.

At Gibraltar, the military miners under the Royal En- gineers work on quite a different system.

The rock there is a peculiarly hard limestone marble : to bring down large masses, they bore their holes usually to about the depth of 9 feet with 2i-inch jumpers, and load them with about 4 lbs. of powder ; the explosion has no apparent effect, but the rock is shaken below: the needle hole is cleared out, and the hole again filled, when it will take per- haps from 8 to 12 lbs., and is fired again; a third charge, with perhaps 20 to 30 lbs., is fired in the same manner, and some* times a fourth, till the rock is very greatly separated and rent to the extent of 10, 20, or 30 feet in different directions. If the needle hole or tamping be deranged before the final ex* plosion, it is bored out and re-tamped.

Under all ordinary circumstances I should much prefer thid principle of this system to the other ; it is more gradual and systematic, would require less labour in boring, and is less subject to waste of powder, or the violent projecting of stones^

In some rocks it may be liable to one objection, which is,

36 Quarrtino Anb Blasting Bocks.

ike chance of sm.j of the preliminary explosions tapping a spiring or yent far water into the hole ; no such springs are found at Gxhraltar, hut thej are at Eangstoire.

If the holes should not he vertical, or nearly so, (which it seems they always are at Gihraltar,) the tamping must he hored out at each explosion, to enable the next charge of powder to he introduced.

The prevailing feuilt in blasting is the using too much powder.

If the tamping be not blown out by the smaller charges, a very useful effect will have been produced on the rock by every explosion, even although the rock be not apparently much affected; the tamping will be easily bored out suf- ficiently to admit a fresh charge, which, being introduced and re-tamped, will be found to be very efficient.

The object is generally to loosen and bring the rock down in large masses, and not to shatter it into fragments : even for small stone, such as for road metalling, &c., it is better to bring out first large masses, and subsequently to divide them, either by small blasts with powder, or by crowbars and wedges.

OF LOADINa«

The ordinary manner in quarries of loading and firing the holes that have been bored is,

I. To dry out the bottom, if necessary, with little wisps of hay.

II. To pour in the powder till it fills a certain number of feet or inches of the bottom of the hole. If the hole be vertical, or very nearly so, the powder will drop in pretty clear to the bottom ; but if it be on an inclination, and not very steep, the powder must be scraped down, professedly with a wooden ramrod, but frequently with an iron scraper. If the bole be horizontal, a scoop is used, which is open at top, and by being turned round at the end of the hole leaves the powder there. If the hole incline upwards, a cartridge is employed.

III. A needle is then introduced, the point of which is let well into the charge of powder, and the top with a handle or eye extending to the outside of the hole.

IV. A little wadding, either hay, or straw, or turf, is in- serted over the pawder.

V. The tamping over the wad is very generally of the moaXX fragments of the quarry stone and its dust, (unless there be in it flint or other substance that nototiotusly strikes fire^ m which caae broken brick is commonly used,) rammed down.

Quasbting And Blastiko Bocks. %7

by 0D6 or two inches at a tinie, by means of an iron rod or tamping-bar; the needle k frequendj turned to prevent its becoming fixed.

VI. Tke last indi or two is filled with damp claj.

YII. The needle is carefully pulled out, and the opening it has left is filled with loose fine-grained powder; or with a long series of connected straws filled with powder, into the upper end of which is inserted a small piece of touch-paper that will bum about half a minute, which is lighted and com- municates the fire.

The touch-paper is made by the quarrymen themselves, by soaking coarse paper in a strong scdution of saltpetre, or gun- powder, and then drying it.

The following is an expressive account of the process, as written by a quarryman of much experience.

" The method of blasting is in every place nearly the same, as far as I have been able to make observations, and I have had charge of such work in Scotland, England, Wales, America, and, lastly, in Ireland. Different quarrymen may, it is true, not agree in everything ; for instance, some prefer a small piece of dry turf for a wad over the powder before they commence ramming ; others prefer hay or straw ; but in ramming every one uses the same kind c^ stuff, that is, small pieces of any stone (that has no fiint in it) that will go into the drill hole ; but, in deep holes, ramming sand wiU do as well as anything.

" The usual metiiod of blasting is very simple, and is as follows : first, to drill the hole, say 3 feet deep, ] ^-inch bore ; in common cases, 6 inches powder will be sufficient in the bottom ; then in with your needle, them your wad of turf or hay, &c. ; then two or three bbws with your rammer, and then in wit^ a handful of small stones ; four or five blows more of your rammer ; and so on till you fill up the vacuity above the powder within 1 inch of the top ; tiien fill said 1 inch with a bit of moist clay (not too wet), and then extract your needle ; lastly, fill up the needle hole with fine powder, or, what is safer, put down straws filled with powder, and apply your match, to which set fire, and run as fast as you can, and you have the whole of it"

Nothing con be more, 1st, uncertain, — 2nd, wasteful,-— 8rd, dangerous, — 4th, unscientific, than the whole of this process.

1st. Missinff fire occurs frequently, — some obstruction will arise in tne needle hole ; any moisture in the hole, or wetness in the atmosphere, will a&ct so small a quantity of

od

28 QUABBTIKG AND BLASTINa ROCKS.

powder as composes the train; loose powder for the train cannot be introduced into any but such as are vertical or very steep, and straws of any length are not easily passed through to the charge. All these and other circumstances must create much uncertainty.

2nd. To say nothing of the guess-work in the proportion of the charge, there must be much waste in the manner of introducing the powder, and in the occasional missing fire.

3rd. With regard to the danger, it manifestly pervades every step from the first handling of the powder.

4th. No rule is adopted for the charge, nor for the size of the holes, nor for the depth of tamping ; no knowledge ac- quired of the best material and mode of tamping, nor any contrivances for accelerating and simplifying the process, or reducing its danger.

To obviate in some degree these defects, the following pro- ceedings have been adopted with success :

To allot every charge by weight, according to a scale adapted to lines of least resistance, or to the circumstances of the case.

The overseer (or, if the work be sufficiently considerable, an express powderman) to have on the spot a strong copper canister containing from 3 or 4, to 10 or 12 lbs. of powder, with a large mouth or opening, but thoroughly secured by a well-fitted cover from spilling, accident, or weather, and with a lock and key.

He should have a set of marked copper measures that will contain, when fall, just 1 lb., 4 ounces, and 1 ounce of powder, respectively * ; a copper cylindrical tube of 3 feet, or 3 feet 6 inches long, by f inch diameter from out to out ; a set of three tubes of about an inch in diameter, 3 feet long each, with joints, so as to be screwed at pleasure into one length of 6 or 9 feet, or with more joints if deeper holes are employed, and so constructed that when together the interior should form one smooth surface ; a copper funnel, the bowl large enough to contain about 1 lb. of powder, and the neck 2 inches long, by somewhat less than f inch diameter; to- gether with some coils of Bickford's patent fuse.

By means of the measures, the tubes, and the funnel, any> specific charge of powder may be lodged char to the bottom

* Where the blasting is constant, and the charges vary but little, such as in sinking shafts, driving galleries, &c, it might be found convenient to have charges of the most usual quantities prepared previously in papers, cartridges, or perhaps even in little boxes or chargers.

Quabbyino And Blastinq Books. ^9

of any hole ; and if horizontal, or nearly so, by pushing it ift through the tubes with a wooden stick or ramrod*.

One end of a piece of the patent fuse is inserted well into the powder, the other end cut off about an inch beyond the outside of the hole ; a little wadding is then pressed down over the powder with the tamping'bar, and upon that the tamping in the usual manner (but with a proper material) to the top, without any necessity for the moist clay.

Most of the accidents that occur to miners arise from the first blows of the tamping-bar over the charge : to obviate this, the first 2 or 3 inches of the tamping should be merely pressed down gently over the wadding, and then the hard ramming commenced over that ; this cannot injure the effect of the explosion, as it is generally acknowledged that a small vacant space about the powder tends, if anything, to increase its power.

If the tamping-bar be tipped with brass, it will add more security, and at very little increased expense.

The outer end of the fuse is then lighted ; there is neither difficulty, loss of time, nor extra cost or labour, by using these precautions, and obtaining all the consequent advan- tages ; they should therefore never be neglected.

Whenever blasting is to be performed on an extensive scale within a limited space, it will be quite worth while to ascertain by a few experiments the value of the different ingredients that are to be used, or matter to be acted upon in the particular locality, as well as the best modes of applying them ; such as the strength of the powder, the tenacity of the rock, the value of the tamping material, &c. : it is clear that, by proportioning these judy, so as to obtain the greatest effect with die smallest means, much time and expense may be spared.

Of The Teain And Fibing.

The inconveniences and loss of time attending the ordinary mode of laying the trains for firing the charge in blasting holes have been mentioned above.

It is the very worst contrived part of the whole operation

* It affords one veiy important medium of security against accidents to depoBit the powder quite clear to the bottom of the hole by means of these tubes, instead of allowing grains to hang on the sides, as they must do when it is poured in in the ordinary manner, particularly in holes that are inclined, where it is easy to conceive that a regular train may sometimes be left fi'om top to bottom.

30 Quabbtino And Bxasting Bocks.

of blflstiBg ; but fortunately a most valuable improvement has been made of late years by the invention of Bickfbrd's patent safety fuse *.

The use of this article is extremely simple; it is ^^ cient in damp situations, and even under water, by using the quality prepared expressly for that object ; a miss-fire is scarcely ever experienced, unless there be great carelessness, and it is a very^ great protection against accidents.

Whenever accidents have occurred (which are eajtremely rare), they have been traced to oireumsteaices which could not be affected by the fuse ; namely, to the first applications of the tamping'bar over the powder.

So large an opening for the escape of the powder is not created by the fuse hole as by the needle f; and, taking every- thing into consideration, it is calculated dmt the use of the fuse is cheaper than the ordinary priming, even if the Yerj trifling cost, or at least difference of either, could be deemed of importance.

Safety Fuse.

At Kingstown Harbour it was employed constantly in working with a diving bell in blasting rock for foundations in from 20 to 30 feet depth of water, and with complete success.

The following account of the great value of this invention is from a Paper by B. MulHns, Esq., an intelligent member of the firm who have the contract for the Kingstown Harbour works.

*' Eock blasting operations have been for many years, and aro now, carried on extensively by my firm. Bid^ford's safety fuse has been invariably used in those operations since

* This patent was granted on the 6th September, 1831, to W. Bickford, of Tucking Mill, Cornwall, for '* an instrument for igniting gunpowder when used for blasting rocks, which he denominates the * Miners* Safety Fuse.' " This fuse was therein described to be a cylinder of gunpowder or other explosive compound, inclosed within a hempen cord, which is first twisted and afterwards overlaid with another cord to strengthen the casing thus formed, then varnished to preserve the contents fh)m injury by moisture, and finally covered with whitening, or other suitable matter, to prevent the varnish from adhering. — [Ed.J

f In firing very small ehargies, tb» openuig made by the needlie or fiise bole tends very much t» reduce the effect. In the tamping experiments ill will be observed that, of elay, and other eompaot tamping, portions of the top were frequently carried away ; in all these and other partial re* morals of tamping it was observed that the principal openings were always on the side where the fiise had been.

QUARSTING AKB BLASTING BOOKS, Si

the summer of 1833. It has our entire approval, as being more certain in its effects, less hazardous in its application, and ultimately cheaper, although not apparently so, than priming in the ordinaty mode. From the period of its intro- doetion np to the present time, we have not had an accident in Any of our worics from blasting, although within that period 73,600 lbs. of powder have been consumed, and labour equal to that of 288,719 days of one man expended; nor had we more than two or three cases of miss-fire that I can recollect, and those were caused by want of caution in using improper tamping material, having stones in it which onC the fase and severed the train. We have used of it in the interval 167,32d lineal feet.

" The cost of 167,822 feet of the fuse was £304 7». 9<i., while that of the actual quantity of powder required for the same amount of priming, namely, 35 barrels, would be £105, besides the labour of the application of the latter."

Then follows a comparison between the old system of loading and firing, and the mode with the fuse.

After describing in detail the old practice (that, indeed, still used in most places), the statement continues thus :

** In the appHeation of the fuse the charge mey be lodged at any required depth in the rock. We lately drove a hole with a (h-itieh gauge ^i feet horizontally into the face of the cliff at Dalkey, and <^rged it with 85 lbs. of powder, by which we released 2000 tons of solid rock, a quantity far exceeding what coidd be displaced by vertical or oblique bores. Straw tubes could hardly be made of so great lengths, and, were it practicable, there is so great a loss of time, and so much uncertainty in using them in horizontal holes of much less depth, that they bear no comparison in fftcility of use to the fuse, which effectually supersedes the tedious and hazardous employment of the needle, and is a perfect preventive against premature explosion or miss-fire, wherein the old methods are particularly defective.

** It has this further advantage, that any number of shots may be simultaneously fired, whilst with the straw tubes and match paper not more than three, with a probable chance of escape to the men employed.

" In wet quarries the fuse is quite as effective as in dry : where wet joints are met with in boring, which frequency happens, the holes fill with water, and nrast necessarily, by the old methods, before being charged, be rendered perfectly dry; this is accomplished bjr wrapping coarse tow or mop

32 QCABBTINa AND BLASTING BOOKS^

thrums round the end of a stick, and mopping out the water ; the finest argillaceous clay is then kneaded into a paste, and worked constantly upwards and downwards hy the tamper struck with the hammer, and continued until the blaster is satisfied of having staunched the leaky joints in the hole : this being done, the hole is then cleared out with an iron scraper, made dry, and charged ; and, after all this labour, success is doubtful. A man often spends half a day drying,, tamping, and charging a hole in this way to no purpose, the powder having got wet.

'' In these cases the fuse furnishes an effectual remedy ; a waterproof ha^ containing the powder, and having a sufficient length of fuse closely tied in its mouth, is pushed home to the bottom of the hole, which is then tamped and fired with as much certainty and effect as in dry work.

" Blasting in deep water by means of the diving bell is rendered comparatively easy by the use of the fuse, as com- pared with the tedious, costly, and ineffective process hereto- fore practised.

^^ In the old way, the charge was lodged in a tin canister in the bored rock ; in this canister a small tube was fixed; and raised joint after joint, until the bell was elevated above the water 8 surfELce ; then a small piece of iron made red hot was thrown into the tube to fire the charge in the canister^ What the effect produced may have been, I cannot say of my own knowledge, not having seen those operations ; but I have been informed that, except in insulated rocks, it was of little use. The canister and the joint of the tube adjoining were blown to pieces, and most of the joints more remote were flattened by the collapse of the water, so that new canisters and tubes were necessary for every shot.

" The fuse employed in blasting under water is somewhat different, and more expensive than the other, and is called sump-fuse ; it is used in the following manner :

" A waterproof charger or bag, containing the powder, with a piece of fuse 5 or 6 feet long closely tied in its mouth, is dipped in boiling pitch')' to secure the orifice from wet; the charge is then put into the bore-hole, which is tamped with sand, or the fine chippings of the stone-cutter's waste, and the fuse, the upper end of which is retained in the diving

* A perfect waterproof composition for this purpose is made of 8 parts by weight, pitch, ^

1 do. do. bees'-wax, > melted together, but not boiled.

1 do. do. tallow, )

Qt7Abbyino And Blasting Books. Ss

ben, being set fire to, is thrust out under its edge into the water: the bell is then, by signal, removed 8 or 10 feet out of the way ; the fuse bums through the water, and explosion follows ; the proximity of the bell to the blasted rock, without endangering the workmen, enables them to resume their operations with little or no delay.

" In founding the Commercial Wharf wall (a considerable part on rock) in 22 feet water at low water of Spring tides, and in clearing for abutment for setting frame for the eastern pier head in 28 feet at low water (the rise of tide 12 feet), we pursued the method above described with success.

" Having obtained a list of all the men who had been killed, or badly wounded, by the old methods of blasting at the quarries for the Kingstown Harbour works, previous to the use of the fuse, I annex it."

The list referred to of accidents under previous contracts, for the first 15 years, contains the names of 30 individuals, two of whom were twice injured, making 32 casualties, conse- quently more than 2 per year ; it includes 7 killed, 4 loss of one eye, I loss of both eyes, and 20 injuries ; while, during the 8 years of the present contract, there has been but one man injured, and that before the fuse was introduced.

In order to test the extent of applicability of this composi- tion for blasting under water, pieces of the quality prepared for it (called sump-fuse), which is somewhat thicker than the ordinary kind, being about -^^ of an inch thick, were kept im- mersed (except the upper ends) for different periods up to upwards of 16 hours, and were then found to bum throughout with their ordinary force ; no trial was made beyond that time.

Pieces 25 feet long (their usual dimension), having one end inserted into a few ounces of powder inclosed in a water- proof bag, were tied to long chains ; the powder bag was lowered mto the water by a weight, and, the other end of the fuse being lighted from a boat, the whole was lowered again until the weight touched the bottom in 39 feet depth, and each time burned through and exploded the powder in 13 or 14 minutes. In order to get a greater length, an extra kind was procured in 51 feet and 52 feet lengths; it was apparently expressly made, and thicker than the other, being about f of an inch in diameter.

This succeeded perfectly in every case ; but, being provided for the purpose, it was not considered so satisfactory a trial, and appears to be unnecessary, considering the e£&ciency of that usually sold.

c3

34 QUABBTiXO AKD BLA8TIN43t BOCKS.

The common fuse (diat not prepai:e(l for water) was tried, and on some occasions* when lighted yerj soon after being immersed, would bum through many feet imder water, but frequently only a short distance ; it is manifestly not adapted for water (and not assumed to be so), but it is perfectly effi- cient in damp situations, if fired without much delay.

There is one great merit in this fuse, namely, that the im- provement is gained without the least sacrifice of simplicity ; on the contrary, it is much easier to apply than any other process.

The only inoonyenience attending its use, of which I ma aware, is the length of time it takes to bum any but short pieces.

It bums at the rate of £rom 2 to 3 feet per minute ; and as a minute usually affords ample time for the person firing to remove to a sufficient distance, there is a delay and an im- patience created in watching the longer terms, particularly when it amounts to 3 or 4 minutes, or more*.

This lengthened time of burning would quite preclude its use for many military mines^ where the explosion must take place at a particular instant.

In blasting under water^ as it can only be lighted in the beU, or at l£e surface if the beU be not used in firing and the water deep, the time consumed in burning the fuse would be very inconvenient.

Fieing By A Voltaic Battery.

Charges of powder have been fired under ground, as well as under water, and to considerable distances, by the voltaic battery.

It is to be presumed, however, that the distinct machinery for this purpose, the expense, and probably some degree of nicety in its arrangements, even after all the improvements that have been made at Chatham by Colonel Pasley, would render it inapplicable to ordinary purposes; although for firing very large quantities of powder, under very peculiar circumstances, it has been considered very useful. The tamping by this mode would be much more complete and substantial, having only two thin wires through it; and by the very instanta- neous effect produced, even at varying distances, simultaneous

* The fase burns slower through a tamping of loose sand than through a tough material well rammed, but it is not extinguished by it

Qdabbying Avd Blasting Bocks. 35

explosions, that are impossible by any other means, might be effected by this mode of ignition ^c.

Mode Of Lighting A Train In Shafts.

Under many circumstances the manner adopted for lighting a train is a matter of some consequence.

At the bottom of deep shafts, or of long small galleries where there is no shelter for the man who applies the light, the touch-paper, German tinder, or match of whatever kind, must afford time for him to get completely out oi the way. It is attended with some difficulty to secure that object, with* out wasting time in doing so, by allowing too long an inter- yal ; but the latter must be the usual, as the only safe alter- native.

The safety fuse has an advantage in this respect, as its period of burning can be more regularly calculated than that of any other match usually resorted to.

A French engineer has proposed and employed a manner of remedying this inconvenience, as far as regards blasting in a shaft, which would appear to be useful where the safety fuse is not employed.

One end of a wire is fixed temporarily into a little powder connected with the train, the other end in a coil being at the surface of the ground.

The wire is carefully straightened up the shaft from any sharp twists or bends ; a piece of German tinder is passed round it, forming a veiy loose ring, and, being lighted, is let go, and drops down on the powder.

The wire may of course be constantly suspended to the side of the shaft, and fixed and applied from time to time as wanted, being lengthened from the coil above as occasion requires.

To facilitate the descent, if necessary, a small weight might be easily added, to the under part of which the lighted match could be fixed.

MEAKS HdR PltEVliNTlNlG SMALL STONES fLttSa ABOUT IN

Blasting.

A great loss of time and labour is experienced in quarries and other confined situations, arising from the necessity for the workmen to retire to a distance at every blast ; not only

* In the Appendix is given a brief account of' the successful application of the voltaic firing in removing the Round Down Cliff, at Dover, for the works of the Sou& Eastern Rulway. — [Ed.]

36 Quasbtimg Amd .Blastimg Bocks*

those engaged in the precise operation^ but all others who can be at all supposed to be within reach of its effects.

This is a greater evil than what is perhaps commonly thought.

' I have myself been in a great quarry, and in the course of half an hour seen SO or 30 men, at given signals, retire two- or three times from five or six different parts at which they were at work, to which they went leisurely back again after each explosion or ascertained miss-fire.

There is another occasion where the necessary retiring of the miner from the effect of a blast is attended with peculiar inconvenience ; that is, from the bottom of a shaft, in which case he has to be drawn up to the top.

When a better mode of applying the charge shall be gene- rally understood, there will be fewer occasions of the projec- tion of stones, but there must always be some ; any remedy for this waste of time, therefore, must be very valuable.

Quabbi Shields.

In some quarries in the neighbourhood of Glasgow they are in the habit of frequently applying a piece of old boiler iron, of about 2 feet 6 inches square and J inch thick, over the hole when fired, which acts as a shield, and, in small blasts, so far prevents any flying about of loose stones, that the men take much less precaution in moving out of the way on those occasions than when it is not used.

As they have horizontal as well as vertical faces to work on, the shield is suspended over the horizontal holes, and laid flat over those that are vertical ; in the latter case a large stone or two, if at hand, is frequently placed upon it.

This application might be very useful under particular cir- cumstances of blasting; for instance, where l^e blasts are generally small, and in confined situations. In a shaft, where the holes will be all probably vertical, or nearly so, and the blasts not large, a good shield could be placed over every hole, and weighted either with stones, or with one or two half-hundred weights, kept in the shaft for the purpose. On trial at the particular place, this might be found to give such certain security, that the miners would not require to be removed more than a very short way above, either by the bucket, or by a ladder, which would lead to a very great saving of time, labour, and expense.

Quabbying And Blasting Bocks* 37

On Tamping.

The desideratum in tamping is to obtain the greatest pos- sible resistance over the charge of powder ; if it could be made as strong as the rock itself it would be perfection.

If 12 inches of one species of tamping will afford as much resistance as 18 inches of another, the question will be — Does the former, in the application, require as much more time and expense as the operation of boring the additional 6 inches of hole ? If not, it will, under most circumstances, be better in the relative proportion of that expenditure.

Where other qualities are equal, that which can be applied in the least space of time will be feir preferable, particularly in such operations as sinking shafts, driving long narrow gal- leries or driftways, and other situations where the progress is necessarily slow.

Different materials are employed for tamping : —

I. The chips and dust of the quarry itself. This is what is most commoidy used, unless there be flint or other stone in it that notoriously strikes Are.

II. Sand poured in loose, or stirred up as it is poured in, to make it more compact. This is an approved material in many places, and is recommended to be very fine and dry.

III. Clay, well dried, either by exposure to the sun, or, what is more certain and more rapid, by a fire.

Wherever blasting is going on, there must be smiths' forges at work : the clay is formed by the hand into rolls of about 2 inches in diameter, and readily dried by the smiths' fires.

In the course of some experiments, clay was used that was in a state of powder, owing to its having been dried a long time previous, and was not thought so good as when applied in a state just caked enough to remain in lump.

lY. Broken brick is an approved material in some locali- ties, as being less liable to apcidents by striking fire than chips of stone.

It is used in small pieces and dust, and is improved by being slightly moistened with water during the ramming.

Vegetable eartH, or any small rubbish, is sometimes ap- plied instead of the stone chips, when the latter are considered dangerous. Such are the simple ingredients used in tamp- ing ; that is, exclusive of the addition of any mechanical con- trivance : of these, the most essential to analyze is the appli- cation of sand, since its use has been by many strongly recommended, and, if e£5caeious, would be most convenient.

38 Quabbting Akd Blasting Bocks.

on account of the rapidity and security with which it can be applied.

In Cachings Memoire snr la Digne de Cherbourg, printed in 1820, (a most interesting work as regards the construction of breakwaters,) it is thus stated in a note: —

" In blasting rock at Cherbourg, the use of the needle, and well-rammed tamping, has been long abandoned.

" The priming is in the usual mcuiner by straws, and the tamping is of very fine dry sand, poured in.

" It has been proved by long experience that the effect of the explosion is as great by this method as by the more laborious tamping in the usual manner."

And in the Journal of the Franklin Institute (United States) for July and August, 1836, after quoting a variety of experiments on the resistance of sand to motion through tubes, made as well in France as in America, and facts regarding the bursting of musket barrels, &c., by charges of sand over the powder, the conclusion come to is, that

" Experience proves that the resistance offered by sand is quite suflBicient for blasting rocks, and it is less troublesome, and more safe, than the usual mode."

It is added, that

" To ensure success, the space left above the powder should have a length of ten or twelve times as great as the diameter of the hole."

General Pauley, on the contrary, asserts that sand as an ingredient for tamping was found at Chatham to be utterly valueless; but acknowledges that the opportunities there of blasting were few and on a very small scale. Many other officers of the British Engineers have been long under the same impression.

It does not appear that any of these opinions have been formed upon any more precise experiments than the sensible effect upon stones or rock with the usual chai^ges; and as these effects are very different under circumstances that are jApparently similar, and as they might vary with different proportions of the powder and ingredients used, advantage was taken of the opportunity afforded by the works carrying on at Kingstown Harbour, near Dublin, to try a few expe* riments that should be somewhat more definite.

The principle which it was thought would be most con- clusive was, not to form a judgment by the effect produced on the rock, but to endeavour, if possible, to obtain a charge of powder that should in each case just blow out, or sensibly

Quarrying An0 Blasting Bocks. 39

affect, the tamping; and a comparison of the charges to pro* duce that effect would afford a strong proof of l£e relative value of the different systems ; thus, —

If it should be shown (as will be found in the following Table of experiments) that | of an ounce of powder would blow out the sand tamping which filled a hole of 1 inch dia- meter and 2 feet deep, while 3 ounces in a similar hole would not disturb a well-rammed clay tamping, it afforded a perfect confirmation of General Pasley's statement, that the sand was good for nothing, as far as the use of it on that scale went.

The experiments detailed in the following Tables were made in granite rock, and» as far as could be judged, where it was firm, and without fissures.

The charges were of ordinary merchants' blasting powder, procured from the contractors.

The sand was sharp or gritty, quite dry, and simply poured in over the powder, with a little wad of hay intervening. It was from the sea-shore, and of different qualities.

The finest was a clean running sand, fine enough nearly for an hour- glass, and weighed . . . .65 lbs. per cube foot.

The second quality, a middling gritty sand, and weighed • . .93 lbs. „

The third, very coarse, or rather very fine sea shingle, the particles being from the size of a pin's head to that of a pea, and weighed . . 98 lbs. „

The clay had been dried at the fire of a smith's forge, and was well rammed down in the usual manner.

40

Quabbyim^ And Bla8Iino Rocks.

EafperimenU to try the Comparative Value of Sand and Clay

for Tamping.

F Sand, fine. M Sand, middling. C Sand, coarse.

Number

Depth

Diame- Charge

Descrip- tion of

of expe-

of

terof

of

Effect and Remarks.

riments.

hole.

hole.

powder.

tamping

No.

feet.

inches.

lbs.

oz.

1

2

2

Clay.

4 inch of top of tamping removed — ^rock fractured.

• 2

2

2

do.

Tamping remained — rock star- fractured.

3

2

2

do.

8i inches of tamping removed — rock fractured.

4

2

2

do.

Tamping remained — ^rock frac- tured.

5

2

3

do.

Portions of tamping adhered to sides of the hole— a mass of rock blown off.

6

2

3

do.

Tamping all remained — rock fractured.

7

2

3

do.

If inch of tamping removed — rock fractured.

8

2

3

do.

Tamping remained entire — ^rock fractured.

9

2

4

do.

5i inches of tamping removed — rock fractured.

10

2

4

do.

2 inches of tamping removed — rock star-fractured.

11

2

2

Sand.

Tamping entirely blown out — rock uninjured.

12

2

1

do.

do. do.

13

2

1

do.

do. do.

14

2

Oj

do.

do. do.

15

2

04

do.

do. do.

16

2

Oi

do.

do. do.

This was repeated three times with the same effect.

N.B.— By the ordinary miners* rule of allowing ^ depth of hole for the charge, one of 2 feet deep by 1 inch diameter

«

would require d| ounces. 1 foot 8 inches of top of tamping

17

4

u

6

Clay.

removed — ^rock fractured.

18

4

14

6

Sand.

Tamping blown clean out — no

fracture. N.B.— In hole 4 feet by IJ inch,

J of depth will contain 15

ounces of powder.

19

6

2

8

MSand

Tamping blown out — ^no frac- ture.

Quabbtino And Blasting Books.

4t

Number of expe- riments.

No. 20

21

22

23

24

25 26

27

28

29 30 St

32

33 34

35

36

37

38

39

40 41

Depth

of hole.

Diame- ter of hole.

feet.

inches.

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

6

2

9

2

9

2

9

2

9

2

Charge

of powder.

lbs. oz. 8

10

10

10

12

12 12

14

14

1.

1 1

1 4

1 8 1 8

1 8

1 8

1 8

6

8 8 10

Degcrip-

tion of

tamping

CSand

Clay.

Sand.

Mdo.

Clay.

Sand. Mdo.

Clay.

Sand.

Clay. Sand. Cdo.

Cdo.

C do.

Cdo.

Cdo. Cdo.

Clay.

Efliect and Remarks.

MSand

Mdo. Cdo. Cdo.

4 feet 7 inches of tamping blown out, below which was a hard crust of about 4 inches thick, and in the cavity below there remained 8 or 9 inches of the sand, mixed with burnt pow- der—no fracture in the rock.

Tamping unmoved — rock unin- jured.

1 inch of top of sand removed — rock fractured.

Tamping blown out — no frac- ture in rocL

2 inches of tamping removed- rock fractured.

2 feet 4 inches of sand removed.

Tamping all blown out — no fracture.

1 inch removed — ^rock fractured.

7 inches removed — rock frac- tured.

Tamping unmoved — rock frac- tured thoroughly.

Tamping blown out — rock frac- tured thoroughly.

Tamping unmoved — rock lifted — the explosion probably es- caped through the joints.

Tamping blown out — ^rock star- fractured.

Blown out — rock slightly cracked.

Tamping blown out — rock shaken, joints opened.

Tamping blown out — no frac- ture.

4 feet 1 inch blown out, then 3 inches of loose sand, and be- low that a hard crust— no frac- ture of rock.

Tamping unmoved — rock cracked.

N. B. — In hole 6 feet by 2 inches, j^ of depth will contain 2 lbs. 8 ounces of powder.

7 feet 10 inches blown out — ^no fracture in rock.

8 feet 64 inches do. do. 7 feet 4 inches do. do. 7 feet H inch. do. do.

42

QUABBYINa AUD BIASTINQ BOCKS.

Number

Depth

Charge

Descrip-

1

of expe-

of

terof

of

'

tion of

Effect and Remarks.

riments.

hole.

hole.

powder.

tamping

No.

feet.

inches.

lbs.

oz.

42

9

2

12

MSand

Tamping blown out — no fracture.

43

9

2

12

Cdo.

7 feet blown out — no fracture —

'

a hard substance 1 foot 3

inches above bottom of hole ; then a cavitr of 2 or 3 inches, and under it sand mixed with

burnt powder; the crust re-

quh^ considerable labour to

pierce with a 2-inch chum

jumper, worked by 2 men.

44

9

2

14

Cdo.

6 feet 10| inches blown out — no

fracture— similar hard crust to

preceding No.

45

9

2

3

Clay.

Tamping unmoved — rock very

slightly cracked. N. B. ~| of hole9feetby 2 inches

will contain 3f lbs. of powder.

46

9

21

1

CSand

3 feet 1 1 inches blown out — no fraeture — similar hard crust found.

47

9

24

1

Mdo.

Blown out, except a small crust

of about \ inch thick. 5 feet 9 inches blown out— rock

48

9

2i

1

8

Cdo.

cracked.

49

9

2i

2

Cdo.

Tamping unmoved.

50

9

2i

3

Cdo.

Tamping unmoved— the explo- sion found vent by a side joint near the charge— making an extensive fracture.

51

9

24

3

Clay.

Tamping unmoved — rock fract'.

52

9

24

3

8

CSand

5 feet lO inches blown out — no fracture.

53

9

24

4

Clay.

Tamping unmoved— rock fract<*.

54

9

34

4

CSand

3 feet 2 inches blown out — no fracture — the hard crust 5 feet 7 inches from top of hole was some inches thick.

55

9

24

4

8

CSand

Blown all out — rock slightly fractured.

56

9

24

5

Cdo.

Blown all out — rock fractured.

57

9

24

5

Clay.

Tamping unmoved— rock frac- tured.

58

9

24

6

do.

Tamping unmoved — ^rock shaken —explosion escaped through side joints.

N. B. i of depth of hole 9 feet by 2| inches would contain 5 lbs. 14 oz., or nearly Gibs.

.

I of powder.

QUABBYINa AHD BLASTING BOCKS. 4S

In the same paper of the Franklin Institute above referred to, it is stated that the sand was sometimes poured in loose, and sometimes carefully packed.

The packing was performed by means of a small sharp stick, which was worked up and down as the sand was slowly poured in.

It is stated, that

*' This method was found to be the best, and is the one always used at Fort Adams, in charging drill holes for sand blasting.

" Sand that was packed presented a much greater resist- ance than that which was poured in loose."

In order to try the value of thus packing the sand, it was ascertained how much was added to the mass by this mode of condensation; for this purpose we used a tin tube of 24 inches kmg by 2^ inches diameter at mouth.

2-^g> do. do. at bottom.

When filled with the different qualities of sand, the weights were respectively—

Fine, Middfing. Coarse,

oz. oz. oz.

Poured in loose . . 65 76 80 Packed by process above

described ... 74 83^ 84

Many trials in blasting were made with tamping of sand thus packed.

In holes 2 feet deep by 1 inch diameter, each of the three qualities of sand was tried with a |-ounce and a ^-ounce charge, and in the whole of them the sand was all blown out.

44

QUABBTIMa AND BLASTINO fiOCES.

Experiment on Tamping with Packed Sand. F Sand; fine. M Sand, middling. C Sand, coarse.

Number

Depth

Diame-

Charge

Descrip- tion of

of expe-

Olf

ter of

of

Eiftct and Remarks.

riments.

hole.

hole.

powder.

tamping

No.

feet.

inches.

lbs. oz.

59

4

n

7

CSand

Tamping blown out.

60

4

n

7

C do.

Tamping remained — ^rock frac- tured.

61

4

n

6

M do.

2 feet 6^ inches removed— rock fractured.

62

4

u

6

Mdo.

I foot 5^ inches removed — rock fractured.

63

4

n

6

C do.

Tamping blown out — but a slight crust adhered to the sides of the hole.

64

4

H

5

Mdo.

Tamping blown out

65

4

n

5

C do.

Tamping removed *- except a hard crust about 12 inches above bottom of hole.

66

4

n

5

C do.

do. do.

67

4

n

4

M do. 3 inches of tamping only le-

mained.

68

4

u

4

P do.

Tamping blown quite out.

69

6

2

7

F do.

■> * •=»

70

—

6

—«.

In all these, the tamping blown " out.

71

^—

—

5

— .

72

— .

^—

4

__

73

3

All blowfi out but li inch.

74

— .

12

Mdo.

1

75

.^^

._«

11

1

76

10

I In all these, the tamping blown ^ out

77

—

— .

9

78

—

8

m-^

79

_-

7

—

J

80

—

U 10

Mdo.

About 1 foot of sand remained — rock fractured.

81

—

1

C do.

Tried twice — ^in both cases the tamping blown out

82

—

—

15

Blown out, except a hard crust 17^ inches from bottom.

83

"

15

2 feet removed — a hard crust, took 2 men 40 minutes to bore through.

84

—

14

—

16 inches remained — ^hard crust formed.

85

13

Blown out, all but hard crust

86

13

3 feet 6i inches blown out- hard crust 12 or 14 inches thick, bored through with much labour.

87

—

—

12

5 feet 4^ inches blown out

QTrABBT:iNG AKD BLASTING ROCKS. 45

The quality of the sand has not been always noted in these or the former trials ; but all three kinds were employed. The very fine, contrary to the received opinion that it is the best, universally failed : the very coarse, in the larger explosions, was, for a few inches in thickness, generally vitrified or cemented together into a very hard crust. Oh trial with an acid, it was found that there were some particles of limestone mixed with this sand, the sudden burning of which might perhaps have assisted in producing this effect.

In all the descriptions of sand, indeed, this cementing process took place at times, more or less, and all of them contained particles of lime.

These last experiments were made at a different period from the former trials of sand, and probably with some variety in the quality of the powder and material, which must account for the apparent inferiority of the packed sand; whereas the packed must be the best, although in too small a degree to remedy the inherent defects in any tamping of sand.

In fact, it is impossible to reduce these kinds of experi* ments to any very close results in detail^ although by numerous trials we may come to general results that may be well relied on.

The conclusion come to from all these experiments, not- withstanding some discrepancies that will be observed, is, that sand of any description, and however applied, is, when used by itself for small blasts, perfectly worthless, and quite inferior to clay tamping for larger explosions, at least so far as for holes 9 feet deep by S^ inches in diameter.

The cause of the sand tamping not presenting the same resistance to the explosion of powder in a blasting hole that it does to the mechanical pressure through tubes, is, no doubt, that the explosion penetrates among the particles, and loosens and separates them, instead of wedging them together as when pressed. The same action will be observed in a subsequent part to produce an extraordinary effect on sand or other loose material when used with iron cones.

No examination was made in any of these or preceding experiments of the quality of the powder, excepting those expressly for that object. It was in all cases the ordinary merchants' blasting powder; nor was any account taken of weather, or other such circumstances as might cause dis- crepancies in trials made at different periods.

46 Quabbyikg And Blasting Books.

The only other materials for tampisg, requiring much notice, are

Broken brick, and

Broken stone, or quarry rubbish.

I. Broken brick is a good material for tamping, and gives considerable resistance, though not so much as clay: vide Nos. 116, 117, 118, in Table. It will not strike fire with iron, and it is to be procured in most situations.

II. Broken stone is of two qualities. Some quarrymen are in the habit of using a rotten kind of stone that is found in most stone countries; not being brittle, it rams into a very firm mass, and is not subject to strike fire ; but being stone at all, gives an opportunity for careless workmen to apply the harder quality instead, or, at any rate, to mix pieces of the latter with it, by which the operation is subject to the con- tingencies of the use of the hard material.

The ordinary material used for tamping is the broken stone and rubbish of the quarry itself, unless notoriously subject to strike fire.

This, by experiment with the blue limestone or granite of the neighbourhood of Dublin, was found to be inferior to clay as a resisting medium. Vide experiment No. 119.

It is also more liable to cut the safety fuse, or to derange the needle hole; but, above all, it is never, in any rock, entirely free from some danger of giving fire, and causing accidents : this is quite enough to occasion it to be rejected wherever it is possible to procure a substitute.

Quaseying Akd Blasting Bocks.

47

Eiq)enment8 with Tamping of Clay, Broken Brick, and

Broken Stone, C Contractor's Powder. G Government Powder.

^1

Holes.

Charge

and descrip- tion of powder.

Os

1

Tamping.

Results and OiMervationt.

No.

Depth.

Dia^ in.

ft.

in.

88

3

2

2oi. C.

' Ctay 4 to

16 in. Do. 17 in.

All blown out.

89

3

2

i>

A small quantity left.

90

3

2

tt

Do. 18 in.

All blown out.

91

2

2

»

Do. 19 in.

7 inches of tamping removed.

1

92

2

2

2oz. G.

Do. 19 in.

7^ inches removed.

93

3

2

2oz.C.

Do. 20 in.

5^ inches removed.

94

2

2

2oz. G.

Do. 20 in.

8.^ inches removed.

1

95

3

2

2oz. C.

Do. 24 in.

3 inches removed.

96

2

2

2

2oz.G.

Do. 24 in.

6 inches removed.

1

97

2 10

2

doz.C.

Do. 329 in.

Tamping undisturbed— rock well

'■

cracked— line of least resist-

ance 19 inches in a favourable

position, near a salient angle.

98

3

2

2

3oz. G.

Do.37fin.

Tamping blown out — rock, to all appearance, not affected — line of least resistance 2 feet, in an

unfavourable position, near a

re-entemg angle *.

99

4

H

2

2|oz.

Do. 4 ft.

16 inches removed — the clay in this case was very dry, and in

*

C.

powder, and considered to be less efficient than when caked.

100

3

2

4oz. C.

Do. 24 in.

Tamping not disturbed — rock lifted.

101

I

7

2

1 oz. C.

Do. 10 in.

All blown out

102

1

2i

2

loz.C.

Do. 12 in.

About 3 inches of top blown out, and a considerable por-

108

i»

tion round ftise hole.

to

1

2oz.C.

Do.5&6in.

All blown out.

105

106

3

1

20Z.C.

Do. 7 in.

1^ inch removed.

107

3

1

2oz.G.

Do. 7 in.

All blown out— tried twice.

108

2

9i

1

2oz.G.

Do< 8 in.

f inch removed— rock slightly affected.

109

3

1

1

2oz. G.

Do. 8 in.

2^ inches removed.

110

4

3

2oz.C.

Do. 14 in.

All blown out

Hi

3

n

3

2oz.C.

Do. 18 in.

All blown out

112

2

3

2oz. C.

Do. 20 in.

Very little removed, except on Bide of fuse hole.

113

3

m

3

2oz. C.

Do. 22 in.

13 inches removed.

* The effect on the tamping in this experiment (No. 98) is so different from all the others, with even superior charges, (vide Nos. 100, and 114 to 129,) that there was pro- bably some misapprehensi<m In preparing or recording the experiment.

48

Quabbting And Blasting Bocks.

H

Holes.

Charge

and descrip- tion of powder.

Ptc *

«^ •. m ^^^^ A»

Os 11

No.

Depth.

Dia->. in.

Tamping.

Besults and Obaerrations. «

ft.

in.

114

4

Oi

3

4oz. C.

Clay 26 in.

17^ inches removed.

115

4

Oi

3

4oz. C.

Do. 30 in.

22 inches removed.

116

3

2

2

4oz. C.

Do. 24 in.

Tamping undisturbed — rock slightly cracked.

117

3

2

2

4oz. C.

Do. 22 in.

3 inches of top of tamping re- moved — the remainder undis- turbed.

118

3

2

2

4oz. C.

Do. 21 in.

4 inches of tamping removed — rock burst

119

3

2

2

4oz. C.

Do. 20 in.

1 inch removed — rock burst

120

2

2

4oz. C.

Do. 18 in.

6 inches removed— rock burst

121

2

3

4oz.C.

Do. 20 in.

Rock burst — enlarged upper part of fuse hole.

122

2

3

4oz.C.

Do. 18 in.

8 inches removed — ^rock burst

123

16

4

35 lbs. C.

Do. 9 ft.

The charge occupied 7 feet — the rock was separated across the hole, at the outer end of which 4 inches of the tamping was found firmly adhering to the side of the half hole in the solid rock.

124

7

2

2

2 lbs. 8oz. C.

Do.5ft.2in.

The powder occupied 2 feet — the rock was separated so as to cut the hole longitudinally in two— the tamping was found adhering firmly to 15 inches of the upper end of the half hole.

125

Ii

3

19 lbs.

12 oz.

C.

Do. 4 ft.

The powder occupied 7 feet out 11— the ftu;e of the rock was blown down along the line of the hole, excepting the upper 2 feet 6 inches, which re-

mained, and in which the

tamping continued firmly

fixed after the explosion.

Fig. 18, p. 49.

126

2

2

2oz. C.

Broken brick, quite dry, 18 in.

All blown out

127

2

2

2oz.C.

Do. 23 in.

All blown out

128

2

2

2oz. G.

Broken

brick,

damped,

23 m.

All blown out, except a slight incrustation on sides near Uie bottom.

129

2

2

2oz.C.

Broken

granite

stone, 23 in.

All blown out — the stone was nearly in a state of disin- tegration.

IKB. i9

But few trials were made Fig. 19.

witli broken brick; the object waa merely to confirm the opinion that it possessed no decided advantage, in point of resistanc*, orer clay : if any- thing, it is believed to be some- what inferior, and requires a little moistore, which is a slight disadvantage ; and it is more liable to have particles of stone, or bard material that might strike fire, mixed up witii it.

The broken stone was tried once or twice besides the in- stance recorded, and in all showed an inferiority to the ctfly ; the use of it being always attended with more or- less of danger, it was not thought advisable even to exp^menPrnach with it.

It m\] be perceived that in holes of ii inches diameter, Q ounces of powder will blow out about 18 inches of clay, and not more.

In holes of 1 inch diameter, 2 ounces wiU not blow out above 7 inches.

In holes of 3 inches diameter, 3 ounces will not blow ont above 19 or 30 inches.

This compftrisonr however, is not quite conclusive enough to found a theory on, as the position of so small a quantity as a ounces spread on the surface of a 3-inch hole gives it a dis- advantage, i^ereas in a 1-inch hole it lies very compact.

Increase of chaises does not produce the increased effect

rn good tamping that might be expected. It has been im (Nos. 90, 91, Table of Experiments,) that in a 2-inch hole S ounces of powder will just blow out 18 inches of the tamping; in No. 100, and from 116 to 123, it will be found that 4 onnees, that is, double the charge, had scarcely, if at all, more effect, so I^ as can be judged under the different circumstances.

When, however, the rock is opened by the explosion, the effect on a lamping of clay or other tough material is greatly reduced: see Nos. 133 and 124, and particularly No. 126, for a, remarkable instance of this; also Nos. 9T and 98, for the difierence in effect on the tamping caused by the rock yielding, or not, to the explosion. It would appear that the

60 QUABBTUffO AN9 BIiASTINa BOCKS.

action upon the rock in opening it is much more rapid than on the tamping; even where me rock is separated across the line of the hole itself, the tamping is usually found adhering to one or both sides.

This is a very favourable circumstance in blasting.

It would be interesting to follow up the experiments of the effect of varying charges, with varying depths and dia« meters, upon one uniform description of clay or other good tamping ; it would seem probable that after a certain point, which may be perhaps about 34 inches in a 2-feet hole, the charges to remove increasing depths of such tamping must be increased in a much greater proportion even than as the cubes of those depths : it is very difficult, however, to make such experiments, on account of the bursting of the rock with increasing charges, by which the effect on the tamping is reduced; it could only be done by holes in re-entering angles, very closely bound by projecting masses.

After having tried the value of the ordinary modes of tamping with broken stone, sand, brick, and clay, it becomes wordiy of consideration whether additional resistance might not be obtained by some mechanical application of a different nature, tending to save time, labour, and chances of accident.

Any such contrivance, to be practically of general service, must be very simple in construction and application, and obtained at an expense not disproportionate to the advantages gained by its use.

The one that naturally suggests itself is some kind of plug or wedge, fixed in the loaded hole in a manner to increase the resistance.

If such a plug could be contrived to give, with sand, or loose small broken stone, or quarry rubbish, equal resis^ ance to the same depth of good clay tamping, a very great advantage would be obtained in rapidity* of the tamping, and in security &om accidents.

Many trials were made for this purpose.

The first was with an iron plug two or three inches long, and very slightly coned, the larger end being of somewhat greater diameter than the hole.

It is well known that such plugs, when driven into a hole in rock, and not having perhaps half an inch of contact, will raise from the ground the weight of many tons, showing a

* Substantial tamping is usually executed at the rate of from 6 to 12 inches per minute; 9 inches per minute may therefore be calculated upon as a medium for holes of almost any size.

ouAUCCDio AND Buamra books. 61

degree of tenacity that it was expected would be very po«er- fiil agaiitat the explosion from within ; but whan tried o»«r the sand, although evidently affording much increased oppo- Bition, they were still in all cases driven out with sharp explosionB, by smaller quantities of powder than would have removed good clay tamping. Plugs of wood were tried with a similar result Ifod plugs, of a form slightly curved in a barrel stu^, and ^ut 3 inches long, were also tried, and with better effect: irtien tightl; driven into the top of the bole they took firm hold, and over loose sand, when properly fitted, f^peared to give more resistance than equal depths of clay (vide Nos. 130, 131, 132 of Tables); they had a groove along the side for the fuse to pass through (fig. 14), and a strong eye to which

J^. 14.

a string could be &stoned with some object attached, to enable it to be seen and found if the plug was forced into the lir.

A few of them were made for it-inch holes, that is, airing in diameter from a httle less to a little more than 3 inches ; so that from the set it was easy by trial to find one that would fit with a proper degree of tightness.

The objections to the use of snch plugs would he — ex- pense; occasional losses; when blown out, some danger of billing on the by-standers ; a degree of difficulty in removing^^ them when not blown out, or the rock cracked precisely across the mouth of the hole; and want of simplicity by requiring an additional implement ; — in this case, too, there s 3

6!t aOABBYIKO AMD BLMTIHO BOCSS.

ia the chance of the workmen carolagslj applying ench aa would not fit well, by which they would be rendered of little or no service.

Pins formed of cylindrical pieces of iron, 6 inches long, whereof two sides were taken off, each of diem of the thick- ness at top of about a quarter of the diameter of the cylinder, and tapenng to nothing at tiie bottom, so as to form two wedges, were then tried over sand at the upper edge of the hole ; and although the pin was driven up af^ainst these wedges, and much effect produced, Btill they were not equal to the clay.

A cone placed immediately -TV- 15.

on the cba^e of powder, and filled over with stAne broken to pieces of about half an inch cube (fig. 15), it was consi- dered would give very power- ful effects. Such a cone at the end of a rod of iron, and having only 18 inches of broken stone over it, at Chat- ham, where the idea origin- ated, was proved to support a weight of IS tons. A similar trial was made subsequently at Kingstown, and it supported a weight of 10 tons without showing any signs of yielding,

and even with fine sand, instead of stone, over it; and although the base of the cone was only 1} inch in a bole of Sg inches in diameter, it sustained the same weight perfectly.

Still, notwithstanding this great power, when opposed to the gradual application of a force from above, it was found to give way to the explosion of the powder from below (see Nos. 133 to 145).

It would seem that the explosion penetrates round the sides of the cones, however small the windage (and they cannot be made to fit very tight, on account of the irregular size and shape of the holes), and by the fuse hole, and acts directly on the broken stone or sand above, so as to prevent them from operating as a wedge.

Some of the objections to the barret-shaped plugs apply to these cones also : it would be aU«uded with great labour, to

Qdarbying And Biabtiho Books. &3

extract them if not disengaged by the explosion; and it would be Tery difficult t« apply them in holes horizontal, or nearly so, unjeas they were vety shallow.

The last contnTance tried, and which, as tax it haa gone, has given a greater degree of resistance than any other mode of tamping, has been dte ^plication of iron cones, with long inm arrows applied as wedges (fig. 16).

Fig. 16.

The cones may be from 3 to 6 inches long, with a groove for the fuse, and an eye at the top.

The arrows, from SI inches to 3 feet 6 inches long, made of ^inch round iron, with a long fine point at one end, and turned to a handle at the other.

The arrows are proposed to be of this shape, aa perhaps the cheapeet that could be made.

These cones were inserted at from 6 inches to 3 feet below the edge of the hole: for their effects, see Nos. 146 to 1S3 of the following Tables.

The arrows should not be less than J inch thick (see No. 163), DOT more than J ; nor fewer in number than 3 for a 2-inch hole, or 6 for a 3-inch (see Nos. 162, and 161, 162).

The cone is let down over the sand, clay, or rubbish, and the arrows are fixed to their position by a alight blow or two with a hammer or stone.

The objections to this implement are in some respects

54 Quabryino And Blajstxno Bocsb.

similar to the others ; namely, expense, chance of bccasionai losses when blown out or of falling on people's heads ; the almost impossibility, frequently, of removing them when not blown out, without breaking open the rock ; and want of sim- plicity in reqnirii^ so many additional implements.

The wear and tear of the arrows would be considerable, as they are usually thoroughly flattened near their lower end, and sometimes broken by the explosion.

One remarkable circumstance occurred repeatedly in the trials with these cones and arrows.

With sand laid over the charge of powder, and under the cones, the latter were firmly wedged, while the sand (some- times in considerable quantity) was blown out entirely, or nearly so, by the small opening between the base of the cone and the side of the hole, the cones not being particularly loose, or more so than was necessary to go down freely (see Nos. 146, 149, experiments).

Even clay to the depth of 6 inches was removed in the same manner from under the cone (No. 156).

Broken stone could not escape in a similar way, but the explosions through it were observed also to find a vent round the sides of thB cones.

From 8 to 12 inches of clay tamping over the sand pre- vented this effect.

In all cases the powder was poured in by a copper tube to the bottom of the hole, and a very thin covering of one or two folds of paper was the only wadding used.

The rock was not affected, so far as could be perceived, unless where otherwise mentioned.

Clay, and broken brick tamping, were in all cases firmly rammed down. ■

Sand and gravel in all cases poured in loose.

Broken stone, when employed by itself, was well rammed ; and when used with any kind of plugs or cones, it was poured in loose.

Where portions of the tampiog were removed, it was con- sidered to have been occasioned by the escape of the explosion up the fuse hole, or round the cones, and not by the general concussion.

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QtrASBTIIiG AHD BLAflTING BOCKS. 59

The coiielasions which T think may be reasonably drawn from the foregoing experiments and observations on tamping, are,

1. That clay dried to a certain extent is, all things con* ddered, the best material that can be nsed for tamping.

2. That hroken brick, tempered with a little moisture during the opemtion, is the next best material.

' 3. That some kinds of rotten stone are as good as either, but that it is not so easy to be sure of always having the proper kind, and the use of it is very likely to lead to an occasional substitution or mixture of stone of other quality, such as is decidedly objectionable.

4. That sand, or any other matter poured in loose, is entirely inefficient.

5. That the stone-dust and chippings of the excavation itself (excepting the rotten kind above mentioned) afiford less resistance than clay, and being always more or less attended vnth risk of aocidents by untimely explosion, should never be employed.

6. That of the mechaiiical contrivances by means of plugs or wedges, the most effective of those referred to are, the cone with arrows, and the barrel-shaped plug ; both of which, par- ticularly the former, give a great increase of resistance ; but that all such contrivances, leading to increased expense, requiring extra arrangements, and some attention to a proper application, such as cannot always be depended upon, are none of them applicable to ordinary purposes, but might be very useful under circumstances where every blast is under great difficulties, ot attended with much expense; for instance, under water, or in carrying on shafts, galleries, &c., through -very Imrd rocks ; in such cases the additional cost and labour of employing these means would perhaps be well repaid by the improved effect of each explosion.

In the case of blasting in shafts and confined driftways, where the openings made by the explosion must necessarily be across the line of the hole, ono great difficulty, namely, that of disengaging the cone or plug after the firing, does not occur.

In very confined situations, like the bottom of small shafts, where the greatest possible effect is required from the shal- lowest holes ; the effects from deep holes being counteracted by the infinite resistance of the contiguous masses, these means of increasing the resistance of the tamping might be very useful.

60 QTJABKnNG.AND BLASHNO BOOKS.

The comparative strength of different kinds of tamping will vary in a small degree in different places ; that which is most commonly used, will, in each locality, give relatively, no doubt, better effects ; thus where broken brick or broken stone are commonly employed, they will perhaps on trial be found to give somewhat better results, as compared with day, than are noted in these Tables, which were drawn up where the clay was in habitual use, and the others were only tried for experiment ; but it is apprehended that, although they may vary in degree, in no case would the difference be so great as to alter the relative order in which they stand.

Tunnelling.

By far the most difficult, expensive, and dilatory blasting operations, are those connected with sinking shafts and driving glories in rock.

The disadyaatages under which such work proceeds, arise from —

1. Want of space in which to work to most effect.

a. Want of light

3. Want of pure air.

4. Penetration of water into the works, sometimes in lai^e quantities.

5. The necessity for securing the parts excavated, on every side, from loose fragments, or other portions that might give way.

6. The inconvenient communication for men and imple- ments, for removing the material, &c., to and from the work during the operation.

These peculiarities are such as to justify and even to require the most perfect arrangements and contrivances to be made use of; some that might be considered, for ordinary blasting, as leading to unnecessary refinement and cost.

The easiest tunnels or galleries to open, are those that can be worked from the ends, without requiring any shaft ; and more particularly those worked on an ascending inclination, by which any water met with has a natural drainage away.

Sometimes it may be so well circumstanced, as to rise from both ends, and have a summit in the interior.

The disadvantage of blasting in a re-entering angle, sur- rounded on all sides by great resistance, has been adverted to: this would be the case nearly through the whole progress of a tunnel, if the face were all to be taken out together, and

QUABBTIMQ ABD BLABTIHa BOOKS' 61

therefore the fblltmiiig, it ia conceiyed, would be a better order of proceeding, and has partially been acted npon in some instances.

Gonunence by a gal- lery or driftway a. Pig- 17- (fig. 17), at the apex of the roof*, as small as can conTeniently be worked in ; viz., about 6 feet high by 8 feet wide. Thia will be carried on neoessarily in the most disadvan- tageouB way for the e^t of the powder, as prerioosty ex- plained.

The next portion to work out will be b b ; and in that some ad- vantage will be obtained from the first opening a, to apply the powder to more effect.

The great niass o will be then removed almost as &Tonrably aa in an open qoany, having a face towards that part of the Bame portion c, that has been previously removea, to which the lines of least resistance can be directed.

Thus A will throughout be kept well in advance of B, and b in advance of c.

It is probable that each, vrithout chet^ing the progress of the part preceding, may be made to keep pace with it ; and if BO, the whole tannel may he worked out in nearly the same time as would be required for a driftway.

The advantage of beginning at the roof is,

1. The scaffolding and ladders for forking from, become unneceBsary.

a. The roof or arch is easily got at, and made sound and secure in the first instance.

3. The drainage is facilitated as the work proceeds, as will be explained.

In tunnels of very great length, the operation would be far t4Xi long by working ttiem only from one or even from both

t^ QVAXOTTHO AKD BIASTIIIO BOCKS.

ends : it becomes necessary then to sink shafte to intennediate points, from the bottom of which the tunnel is carried on in each direction until the whole shall be connected.

This of course will add very greatly to the difficulty and expense :

1. By the additional labour of excavating the shafts..

2. By the necessity for passing all the workmen, imple* ments, tools, and the materials from the excavation, up or down the shaft, as the case may be.

3. By the limited space below, particularly as subject to the interruptions occasioned by the explosicms, from which, it is more difficult to obtain refuge.

4. By the probable necessity for increased artifidal means of ventilation.

5. And principally, by the machinery and labour requisite to keep each distinct shaft, and the galleries connected with it, free from water.

The expenses will be increased in proportion to the number of shafts ; and the number of shafts will be regulated by the time to which the execution of the tunnel is limited.

Thus, if the nature of the rock and other circumstances are such, that the engineer cannot be sure of penetrating faster, at each head of driving, the gallery, than 3 yards per week, if the tunnel is to be 2 miles long, and the period for its being opened three years from the commencement ; on these data 468 yards would be the amount that would be opened during three years in each head of working, requiring consequently between 7 and 8 heads for the whole, or three shafts, and the two ends. This, however, would be to suppose that the work com- menees at once from the bottom of each shaft: the time necessary for sinking the shafts, however, must be considered, which will consequently increase the necessary number of them.

A good record of the actual result of working tunnels, with a minute detail of all particulars, is very much wanted as a guide for future operations.

Many circumstances will have influence upon the dimen- sions to be given to tunnels ; if for a railway, — ^the width of the locomotives and carriages, the height of the former, &c.

Certain dimensions may be deemed fixed : for a railway, for instance, the height of the vertical side walls, suppose 10 feet; the space between the two tracks, and between each of them and the walls, suppose 16 feet in all; besides the width of the track of this space, it might be better to diminish that in the

«UABBm<a AXS BLASTISO BOOKVl 68

middle, and to increoee those on the Bides, euppMe 4 feet tor the first, iind 6 feet for each of the ethers, because —

1. The side spaces vould be more useful for gas or otfaet pipes, or for lampe, or for drains, or for tools or matenEds during repairs.

3. It la the readiest and meet natural position for anj person to seek for refuge, should an engine oi carri^je pass while he may be in the tunnel.

The roof should be Fig. IB.

as flat as the rock will admit to be secure, provided there bs suffi- cient height for the eiwine up to a i, (fig. IB I) over each track- way.

Some rocks will bear being cut to an al- most straight horizon- tal roof; this will be particularly the case j where the strata are vertical, or nearly so :

others require to be high and pointed ; when even that form shall be insufficient, tiie very troublesome and costly exp&- dient of lining with briek or masonry must be resorted to.

It baa been sometimes proposed to construct a double gallery for a tuimel ; one for the traffic in one direction, and the other for that in the opposite : the assimied advantages are —

I. That a small roof may be more easily secured than a larger one.

S. That one line can be opened first, and the second worked out by degrees, and at leisure, without interrupting the traffic in me first.

8. That the cross traffic cannot at an; time interfere, and that persons who may be accidentally in a gallery while an engine or carriage is about to pass, will find secure refuge in the other, or in the connecting passages.

i. That the subsequent repairs, &c., will be quite safe from any interference with the traffic, which would then be con- fined to the line not under repair.

In chalk, a material that is easily woiked and shaped, and in rocks like it, and in which a large roof may be of doubtful

64

(WrABBTmO AND BIASTTV0 BOCKS.

Stability, while a small one might be considered secure, this system would be most applicable ; but I should think it ob- jectionable in hard rocks requiring to be blasted.

A single tunnel of 28 feet wide will afiPord as much useful accommodation as two of 18 feet wide each.

Suppose the width of trackway to be 6 feet; then, in either case, there would be a space of 6 feet between each trackway and the wall : but as it is proposed aboye to allow but 4 feet between the two trackways, it may be considered a more fair comparison to calculate each of the double galleries as only 16 feet wide.

The comparison of the Fig, 19.

relative labour of opening either may be exhibited thus, bringing the two double gal- leries (which would be seve- ral feet asunder in practice) close together for the con- sideration of the question (fig. 19).

The excavation will in quantity be probably about Uie same, allowing for the connecting passages between the two smaller ones ; but the single will be much easier to work out, because the space to work upon will be larger.

In the trimming work, which, after the first opening or driftway, is the most troublesome, the advantage is greatly in favour of the large gallery ; as in the one case there is the amount of trimming the lines f, l, e, and d, l, e, besides the connecting passages, to compare with i, b, e, which they much exceed.

The single gallery will also require but one driftway ; the double, two, — ^a point of great importance as regards labour and expense.

The single also gives additional space and height at the roof, where it is very useful as a receptacle for the vapours of steam and smoke.

It may be mentioned here, that the time and expense con- sumed in working out a shaft or gallery will be by no means increased in the direct proportion of its size.

One of reduced dimensions would take very nearly the same time in excavating as a larger (unless the difference be excessive), and the expense per cube yard will decrease

Ib

QUASfiYIHd ^KS BU8TIH0 BOCKS. 05

with the extent of opening, — the first or driftway of a few feet in either case being bj for the moBt costly *.

Where a shaft or gallery ia full large, there will be less occa- sion to be very particular in trimming the sides, by which much time and expense will be saved.

With regard to the floor of a gallery, no partionlar nicety is required, except to take care to excavate enough : if it should be more, it is of no consequence, as any hollows con be filled np without inconvenience, whereas in sides or roof any excess of rock removed may be troublesome to remedy.

The only asanmed advantage of the double gallery worthy of mention, to compensate for the above-stat«d points of inferiority, is that of the capability of opening them in suc- cession, the second, during die operation, not interfering with the first ; bat though it has an advantage in that respect, still it ia apprehended diat the difficulty of doubling the opening of a single gallery, one trackway being previously made good, would not be great.

Should it for any rea-

son be judged inexpe- ^'S- 20- _ _

dient to open a double line at once, the mode irill be to open the driftway 1 (fig. 20), and then one of the sides 3, and then 3 on the same side, leaving the other portion 4 for subsequent completion.

The half tunnel 1, 2, 3, will be more easy to open than one of the double galleries, on ac- cotint of the leu extmt

of nice trimming, Ac, and the other half 4 will be fer easier than die second small gallery.

The only inconvenience of this proposed mode will be, the danger of incommodii^ the first line of railway by the mate- rials Szom the subsequent excavation ; but it is apprehended that with moderate precautions this need not be the case.

The work will be gradually performed, the blasts not large;

(bund in the coA ^the tunosl of Drenodrobur, p^ 73.

66 qXTABBYINO AND BLASTIKO ROOKfif.

they naay be always fired immediately after the passing of a train, and the line cleared of any little rubbish before the next shall arrive, and a proper system of signals established, by which' every train at its entry may be assured that the line is clear.

In the single tunnel, the lower end of the shafts will be in the middle, and form part of it ; whereas in the double, how* ever arranged, the shafts cannot be so conveniently placed with reference to both galleries.

In sinking shafts, the work is much more disadvantageous than even in the galleries, on account of-<-*

1. The more limited space.

2. The more constrained position of the workmen.

8. The danger of any thing, even small articles, fiediing down upon them.

4. The difficulty of applying any holes for blasting, but such as are vertical, or nearly so.

5. The immediate vicinity of the receptacle for the drain- age water, from which it wUl be almost impossible to keep dear.

It will be found more advantageous probably to sink shafts rather long and narrow (the length crossing the direction of the tunnel at right angles), than circular or square ; for in- stance, 16 feet by 9 feet may be better dimensions to give a shaft than 12 feet each way, provided always that the width is ample for working the buckets up and down. By this arrangement it will be easier to apply transverse bearers across the top for machinery ; the space for the workmen will be more convenient ; the pipes for drawing off the water, for ventilation, &c., will be more out of the way at one end, while the buckets for drawing men and materials, &o.f up and down, may be at the other.

The upper surface edge of each shaft must be thoroughly

. lined, jsihd secured froip the possibility of any thing falling

down; the buckets and windlass of perfect description and

arrangement to prevent such accidents, or the striking against

each other in meeting, &c.

It is in blasting at the bottom of shafts that the shields described in another part might, it is conceived, be more use- fully applied than in any other situation. The holes will be vertical, the blasts small, the shield always dose at hand, and

^UABRYISO AKD BLUTnTQ ZOOXB. 6T

the great labonr and loss of time saved of remaking the woi^- men to the top of the shaft at each blasts

When the shaft is Biink to the depth of the drifiaay at Ihe roof of the gtJleries, those dnfcmays roxj be U once com- menced to nve time ; and the remainder of the ehaft sunk while the gsllery work ia going on.

Effects Of Btrita.

Tn stratified rocks, the direction of the Btrata in tannelling will be of much importance.

The most &vo arable woold be yertical, and at Fig.i\ — (LoagitudlitBl Section.) right angles with the di- rection of the line of tun- nel, because when the drift A jfii^. SI) is carried to sufficient extent, the boles for the subsequent blasts can be bored down the joints, and the enploaion made to act in the most favourable manner.

The Bame principle may be adopted where the atnita may be inclined upwards from the miners, as at b (fig. 22), but it wUl be

.Fi;. 02. — (LongiMdinal Section.)

DO QnARBETKQ AND BLABTIKQ BOCKS.

more diEScult to work mith advantage from the other end of the Kfllery o; as, to follow the eame principle, the rock will be always overhanging the workmen.

If the strata be in horizontal beds, it wilt he worked upon by horizontal boring after the roof is entirely cleared out

A most un&vourable direction is when the work ia proceed- ing in the same line with vertical strata, which will conse- quently always present their edges in front. Fig- 3S.

In that case an open- ing should be carried down from top to bot- tom, either at one aide at D (fig. 33), or in any other part, and then the holes bored down the strata as at a, or hori- zontally as at b; the whole roof, however, and opening d, will be worked to mucn disadvantage.

An adequate drain will be necessary through the whole length of any tunnel.

A veiy &vourable inclination for a gallery, as respects drainage, would be about 16 feet in a mile (I in 330). *

The drain will be lai^er or smaller acconling to me quan- tity of water which it may have to discharge, bat at 1 in 33U the Ml will be sufficiently considerable to render a very large drain probably unnecessary.

In working the ascending galleries, either from the end or from a shaft, it will he quite easy to proceed so that there shall be always a natural drainage, at eveiy period, to the receptacles from whence it will run ofi, or be pumped out, as the case may be.

* Whether for ortGnary road or railway, the iodide in a hinnel ihauld be eaeyi as it nould be pecullaily iacodTenient io that paiticulitr part of a Une to idcur the risk of a stoppage id ucending, or of so acddeot in de-

QUABBYIKa AKD BUkSTING BOCKS. 69

But in each descending gallery some little arrangement mast be made to assist it.

When the descending meets the ascending gallery, the whole of the drainage will be carried off by the latter ; till then, the following arrangement will be better than carrying pipes to the end of the gallery, as must be done if the inclination be steep.

Suppose the descending gallery to be 440 yards in length before it is to meet the other; this, at 16 feet to a mile, will give a perpendicular difference of level of 4 feet : as the gal- lery will be from 24 to 30 feet high, it is manifest that the &r greater portion may have a regular natural drainage out, the same as an ascending gallery; but by sinking a small well- hole at the bottom of the shaft, of 5 or 6 feet deep, from whence the pump may draw the water out, a drain may be cut to it from the very end of such descending gallery, as it progresses, that will carry off the water naturally &om its very floor.

That drain will form part of the regular longitudinal drain that must be made at all events, and the only additional labour vnll be in excavating the well in each shaft, which also might at any rate be desirable.

When the tunnel or gallery is to be horizontal, as it must be for a canal, the drainage vdll be as described for the descending gallery.

In deep sinkings, drainage is sometimes effected, or rather more usually assisted, by means of Artesian wells or bore- holes sunk from lower levels of the surface groimd, dovm to the lines of strata that shall descend from the works. Where the joints shall not be too close, and the distance not too great, the water will be drawn from the works by this self-acting drainage down to the level of the top of the Arte- sian bore-hole ; or, practically, to nearly that level.

Ventilation.

The difl&culty of working galleries to any extent under ground is occasionally very great, for want of ventilation, or from the presence of foul air.

The remedies are, either to force fresh air to the end of the work, or to draw the foul air off from thence, when the fresh air will rush into the vacuum : the latter is esteemed to be the more easily effected.

In either case there must be an air-tight tube from the

w

(KFASBIINO ANP BLASTOre BOOKS..

fresh air to the part where the workmen are engaged ; and the great difficulty must be to establish such a tube perfecdj firm and perfectly air-tight.

In operations on a small scale, such as military miners are engaged in» a small and light tubing is used, and the air forced in by a pair of smith's bellows^ or others of about equal power; but to work a gallery of some hundred yards long from the bottom of deep shafts, will require tulmig more Sub- stantial and of larger dimensions, with a continued force ap- plied for exhausting the foul air; or fresh air has frequently been introduced by a £Eui-wheel.

Fig. 24.

Quabbtxko And Bla8Tino Books. ' 71

In a recent number of the Annales des Foots et Chanss^es of France, there is an account of a simple contrivance which enabled the working of a shaft of 5 feet diameter, and 220 feet deep, to be continued after it had been interrupted by the constant collection of carbonic acid gas ; all the ordinary measures by bellows, &c., having proved quite ineffectual.

A large tub a (fig. 24) was firmly placed on balks on a level wi& the top of the shaft, and mled with water to the level o, G.

An air-tight pipe from the bottom of the shaft was brought through the tub a, and had its upper edge a very few inches above the water ; it had a valve h on the top.

A smaller tub b, reversed, was suspended within a, by the cords KK, which were made &st to the ends of the levers 1 1.

B had a very short pipe at top, with a valve d.

The tub B being allowed to descend by its own weight, the air within it was expelled through the opening d ; when again reused by pulling the handles attached to the ropes l l, the air was diawn up through the opening h, from the end of the descending tube, and by continuing this reciprocating action, a circulation was created at the very bottom of the shaft.

No dimensions are given; but it is coigectured that the lower tub a would be about 4 feet by 3 feet 6 inches, and the upper one b, about 3 feet by 3 feet

It was found capable of drawing off 4 cubic yards of air per minute.

No additional men were employed to work it ; those at the top of the shaft, who got out the materials from the ex cavation, were only required to work this pump for about 5 minutes every hour, to keep the air perfectly good at the bottom.

It is in fact an air-exhausting pump of large power and simple construction : if found useful, and required for regular service, it might no doubt be improved, and made more com- pact, portable, and easy of application.

Instead of using a pump or manual labour for drawing the air from the ends of galleries, the upper ends of the tubes are sometimes made to communicate with a fire kept constantly burning, to which the tubes furnish exclusively the requisite air.

Improved ventilation is said to be obtained by double galleries or driftways, with occasional air-holes connecting them.

The advantage in this respect can hardly be equal to the

72 ' QUAHBTINO iiND BLASTING BOCKS.

cost of carrying on the double opening, if not necessary for other objects.

Cost.

No kind of work can be more variable in its cost than tunnelling, or driving galleries : so much will depend upon tlie quality of the rock, the depth at which the gallery is under ground, the &cility of communication by more or less of con- fined galleries, shafts, &c., to and from^the actual work, — tlie amount of necessary ventilation, and the quantity of water to be drawn ofif, — that the expense may vary from 23. to £2, and much more, per cube yard.

Where the rate is very heavy, it will probably be good economy to adopt the most refined improvements that -will forward that portion of the operation which peculiarly leads to the extra expense.

The following is the result of the cost of working out the road tunnel of Drenodrohur, between Kenmare and Grlen- gariff, during 1836 and 1837, in the county of Kerry, under many favourable circumstances.

The piercing of this tunnel, which was 582 feet in length, through the summit ridge of the mountain, saved an ascent, of which the perpendicular height was from 60 to 80 feet, which, reduced from a constant rise of 1000 feet on each side, was of much value.

The rock was stratified, varying in character from a granular to a compact silicious, and to a common clay slate, intersected by veins of quartz. It was all hard, some of it exceedingly so. The strata in one direction were nearly vertical to the horizon, excepting occasional veins of a few feet in thickness, which were more inclined ; and in the other direction, nearly perpendicular to the line of the tunnel.

The rise in the tunnel was from both ends, and at the rate of 1 in 100, forming a summit in the middle, which was conse- quently nearly 3 feet higher than the entrance.

The passage, as commenced, was meant to be 18 feet wide and 18 feet high; but subsequently, to save expense, the width of the roof or chord of the arch was reduced to from 15 to 17 feet, and the part below the arch to 12 feet.

The arch stood perfectly without any support, although cut very fiat, and with a rise or versed sine of only 2 feet. The cost of the different portions was as follows : — The roof or arch was first cut out, and contained sectional

QUABBYINO AND BLASTINa BOCKS.

73

areas at different parts of about 96 and 90 feet, comprising an excavation of about 2012 cube yards in the aggregate, and cost j£6555 16s. 8d,, being at the rate of about 6«. 6d. per cube yard.

The body of the gallery under the arch contained sectional areas of about 204 and 144 feet, comprising an excavation of about 3493 cube yards, and cost ^599 Is, 11(2., being at the rate of about 3«. 6\d. per cube yard.

A small shaft, 6 feet by 4 feet, was opened to the depth of 33 feet, containing about 29^ cube yards, and cost £32 2«. 10(2., being at the rate of £1 Is, 10 ^d, per cube yard*.

The average cost of tunnel alone per cube yard is, Qyi. „ „ „ „ and shaft . . . 4^, Sd,

The material from the excavation was deposited in hollows near the entrance at each end.

The total cost of tunnel and shaft £1287 Is. 6(2., exclusive of some miners* cottages built, and a few such contingencies.

Labour

>» • Iron . .

Steel . .

Gunpowder

Safety fuse

Heads Of Expense.

Miners and labourers Smiths (including coals) 13,109 lbs. at 1-7(2. per lb.

321 lbs. at Is, per lb. 7946 lbs. at Is. per lb. 1745 coils, of 8 yards each, at Is.

£ 8. d.

. 620 9 8

. 73 3 3

. 92 16 6

. 16 1

. 397 6

. 87 6

£1287 1 6

At the railway tunnel at Liverpool, the excavation of the rock is stated to have cost 4s. per cube yard ; the material was a sandstone, and, as it required to be lined nearly throughout with brick-wall and arch, was not probably very hard.

It would form a most useful guide to engineers, if record were kept, and made public, of all the particulars of the actual experience in tunnelling and driving galleries, and sinking shafts : it might be kept without difficulty, and be made to afford very useful checks on the works during the operation.

X F. B.

* This shaft proved eventually of little or no use, and had better have been omitted.

E

Appendix.

In the following Memorandum, Major-Gen. Sir John Bur- goyne describes the mode in use at Marseilles for enlarging the inner end of the hole by means of the action of acid upon the calcareous rocks of that district.

The process for blasting calcareous rocks at Marseilles is extremely simple ; it is merely to form a chamber or magazine at the bottom of the drift by means of dilute acid, so as to admit of a larger charge of powder being employed for the blast than is available in the ordinary mode of proceeding, the rock being of a calcareous nature. The apparatus was somewhat rude, but it appeared to answer its purpose very eifectually. The rock was pierced in the usucd way, by a 2 J inch jumper, to the depth of 6 to 7 feet, generally in a slanting direction, according to the form and mass of the rock to be detached. They then introduced a copper pipe, the size of the bore, in the form sketched on the margin, and pressed the end a, which is open, down to the bottom of the hole, the orifice round the outside of the pipe at b being closed up tight with clay, so that no air could escape ; and the bent neck of the pipe c, which is open, hanging downwards, with reference to tiie slope of the bore. Through the copper

5ipe at D was introduced a small leaden pipe, e, of about inch diameter, formed with a funnel, /, at the top, and this passed down through the copper pipe to within about an inch of the bottom, the upper ori£ce of the copper tube round the leaden one at g being filled up with a packing of hemp.

Matters being thus adjusted, dilute nitric acid was poured through the funnel and leaden pipe, and, on arriving at the bottom, it produced effervescence, and at the end of a few minutes the frothy substance of the dissolved rock began to run out through the orifice of the bent tube at c. So long as they poured in the dilute acid at /this action continued, and,

whenever they considered from the quantity of substance delivered through the pipe that the intemnl chamber had become of sufficient magnitude to admit the quantity of gunpowder

required, the pipes were withdrawn ; the hole very soon became dry enough, from the veiy action of the acid upon the limestone, to permit the chamber being chained without damage to the powder, and the blast was given in the usual way.

The time occupied would of course vary according to the size of chamber required, llie foreman ef the works informed me that he had succeeded in forming a chamber capable of holding 26 kilos, of powder (about 65 lbs. English) in the space of 4 hours ; he showed an unwillingness to give me the proportions of acid that he used, or the nature of it, and I did not therefore press my questions, being satisfied by the vapour that it was nitric acid, and the strength of the mixture must in all cases vary according to the greater or less proportion of calcareous matter existent in the rock to be acted upon. This may at all times be determined in a few minutes hy experiment upon pieces of the stone, with acids of different degrees of strength.

They were blasting very large masses from

the foot of the hill, onwhich the Fort of Notre

Dame de la Gardp stands, on the south side

of the town, for the purpose, in the first

:- place, of obtaining sites for building, and at

. the same time making use of the dibris for

, forming the new port which is in progress,

.' and the foreman assured me that this new

' process had operated a very lai^e saving to

1- the MM. Lerm, Freres, who are the parties

that have brought it into action. i lu March, 1845, a patent was granted to e William Joseph Conrad Marif, Baron de i Liebhaber, of Paris, for " Improvements in ] blasting rocks and other mineral substances ; for mining and other purposes, and in ap- paratus to be used in such works." The in- ventor's mode of enlarging the inner end of

76 QtTARRTINa AND BLASTINa BOOKS.

the hole was described to consist in dissolving a portion of the stone by means of muriatic or other acid, diluted with about three times its weight of water. A tube is inserted in the hole and externally sealed round at the lower end with some composition which shall prevent the froth or vapours from the acid passing between the outside of the tube and the inside of the hole bored in the rock. Within this tube there is a smaller tube, through which the acid passed into the hole. These tubes are bent over at the top, and terminate in a vessel containing the acid, and which vessel receives the froth that passes up between the pipes. The inner tube is bent upward at the lower end so as to prevent the froth passing through the stone. When the hole is sufficiently enlarged, the contents of the hole are removed by a siphon or pump before drying and charging with the powder.

In addition to the important facts given by Gen. Burgoyne, the following, regarding some operations in blastiug in the Jumna and at Delhi, conducted by Lieut. Tremenheere, may be quoted as useful and interesting. For the purpose of blasting in order to improve the navigation of the Jumna, the jumpers used were 6 feet long, and 2J inches in diameter ; the blasts 5 feet deep, and 4 feet from each other. The rate of boring varied from 2 J to 5 feet per day's work for 2 men. A double-headed jumper was used, to render the hole com- pletely circular for the reception of the canister, about 2^ feet in length, and 2 inches in diameter, and filled two-thirds with powder and the rest with sand. The small tube reaching to the surface of the water contained quick match with a piece of slow match at the extremity. The canister, well greased, was placed in the hole without any additional tamping.

At Delhi, the blasting was in dry rock, and, economy of powder being of more importance than economy of time, tamping was resorted to. For this a stiff red clay, slightly moistened, was employed, and the tamping bar was of wood, the priming wire of copper. Any dampness which might exist in the bore was obviated by a tube of coarse paper, greased on the outside. Fine mealed powder was used as priming, and a piece of port-fire for ignition. If the firing did not succeed, a fresh priming hole was bored in the tamping, or the mine abandoned. In large irregular masses of rock, the depth of the bore, or the intervals between the blasts, will generally represent the line of least resistance; and the following results were obtained in the rock at Delhi, which is hard quartz. The line of least resistance not exceeding 1 foot, a charge of 2 oz. is sufficient; the line not exceeding 4

Quabbying And Blasting Bocks. 77

feet, and the rock not being highly crystalline, 3 oz. per foot will be sufficient. The charges mil vary with the tenacity of the rock, but the following may be a general guide : — the line of least resistance being 1, 2, 3, 4, 5, 6 feet, the charge will be 4, 8, 14, 20, 26, 36 ounces. On comparing the charges used at Delhi, where stiff clay was used as tamping, with those in the Jumna, where sand was used, the following table is the result : —

Line of least resistance.

With

clay tamping.

With sand.

2 feet .

•

. •

8

26-8 oz.

22 »»

•

* •

10

33-5 „

8 „ .

•

« •

12

40-2 „

4 „ .

•

• •

20

53-6 „

The charges in the l£ist column are to those in the second as 3 to 1, nearly; they are not, however, given as the least required, but are those actually used*.

In the neighbourhood of Plymouth, the limestone, with which that district abounds, is raised in solid masses, of from 8 to 10 tons' weight: it is used most extensively for building, and for lime manure. About 13 cubic feet weigh a ton. It is of a light blue or gray colour, generally free from metallic veins, but with some indications of manganese and ironstone, round pieces of the latter being found in clay beds, intermixed with the rock, and a vein of ironstone 4 inches thick at the surface of the rock, and dipping towards the south, has been opened.

In the blasting of this stone, if a deep hole is required, a 2* inch jumper or bit is used for about 4 feet, and a 1^-inch for the next 4 feet by one man; then two men are employed with a l|-inch to the depth of 14 feet, a If-inch to the depth of 21 feet. A constant supply of water is required during the boring. The hole being well dried, about one- third is filled with powder, say 15 lbs. ; a needle is introduced as far as possible without driving it ; the hole is tamped with dry clay to the top, and then covered with a little wet clay to prevent any of the loose particles falling in when the needle is withdrawn. A reed filled with powder and split at the top, to prevent its falling to the bottom of the hole, is inserted, and a stone laid upon it; the powder being ignited by a piece of touch paper and a train, the reed flies to the bottom of the hole, and ignites the main load. The rock is generally

* Report of Papers, Inst Civ. Engineers.

78 Quabbting Amd Blasting Bocks.

crax^ked and loosened to a considerable extent, if not thrown ; in that case the needle is driven through the tamping, and such a fresh charge is run through the needle-hole as may be requisite. From 6 to 8 tons of rock are generally blajsted with 1 cwt. of powder. In July last, however, it was reported that with one charge of 1 cwt. of powder, in a hole 18 feet deep, no less than 1000 tons of the limestpme rock, destined for the Plymouth Breakwater, were detadied from their bed. We cannot answer for the entire truth of this report ; but it is well known that, since the Breakwater Quarries were opened in 1811, a great augmentation has been effected in the produce of the blasting there carried on.

In blasting the white limestone of the Antrim coast, in the north of Ireland, it was found that one ounce of powder would rend 14-12 cubic feet of the stone, when in blocks; but the same quantity rent only 11*76 cubic feet of loose whinstone blocks. The specific gravity of the white limestone is nearly 2*76, of the whinstone or basalt about 3*20. The limestone is similar to the chalk of England, in the flints which it con- tains ; but it is exceedingly indurated. The induration may be estimated from the. fact that two men will bore one foot in depth in half an hour, with jumpers from If to 2 inches in diameter.

The following account of the method pursued in getting the valuable granites of Scotland is written by a gentleman of extensive practical knowledge of the subject.

The granite quarries of Aberdeen and Peterhead, in the north of Scotland, are comparatively inexhaustible, and the granite which they yield of excellent quality. The manner of extracting the rock in these quarries is by boring, and blasting it with gunpowder. In this process the quarry-men use the ordinary *' jumpers," having a piece of steel welded to one end, and made with an edge similar to that of a stone- cutter's chisel, but much more obtuse. They are also made of different lengths — the long ones to follow the short, as the boring proceeds. Three men are employed in this depart- ment of the work — one sitting on the rock and turning the "jumper" round, while the other two strike alternately with hammers, each of which is about 12 lbs. weight. These bores are sometimes from 12 to 16, and often 18 feet deep, by about 2^ inches in diameter; and, when charged and fired, they generally loosen a very great quantity of rock, but seldom do much more than merely move it. " Bulling" is then had recourse to, and this consists of filling all the per-

Quabrying And Biasting Rocks. 79

pendicular cracks or fissures, caused by the former operation, with gunpowder, and firing it ; by which means the rock is shifted several inches from its bed, and often thrown some yards forward. The next process is to cut up the rock into the required scantlings, and this is done in the following manner : — ^A number of holes are cut in a straight line, about 3 inches long, 2 deep, and 3 inches apart, each tapering towards the bottom, into which iron wedges are inserted, and struck with a heavy iron hammer, beginning at one end of the row and striking them from end to end untU the block gives way.

Cutting with " Plug and Feather " is also had recourse to, when the block intended to be split is very deep and sup- posed to be beyond the power of the ordinary wedges. In this case a row of circular holes, about 1^ inch in diameter, 5 or 6 inches deep, and 6 inches apart, are bored with a "jumper," into each of these are put two "feathers" at opposite sides. (The " feathers," when in position, are merely inverted wedges, having circular backs, so as to fit to the curvature of the holes, the opposite sides being plain, to receive the wedges.) Between these " feathers" long wedges are then introduced, and driven, as in the former case, until the block is split asunder.

In the Seventh Volume of the Professional Papers of the Corps of Eoyal Engineers*, Capt. Nelson, R.E., has re- corded some interesting and useful memoranda on the quar- rying of the Plymouth limestone ; from which paper some facts may be well quoted. This limestone is described as fine-grained and hard, abounding in organic remains, and varying in colour from light to dark gray. The tools used in these quarries consist of — the "jumper," or **bit," from 8 to 30 feet in length, and from 1 to 2| inches in width ; — the " pitching bar," from 6 to 8 feet long ;— the " tamping bar," which is i inch diameter for IJ inch bit; — the "needle," which is from 3 to 13 feet in length;— and the " ripping" or " crow bar," from 6 to 14 feet long, and from 2^ to 3 inches square at the lower end. In addition to these the " feather and tearers" consist of a wedge about 6 inches long, 1 or IJ inch square at one end and ^ inch square at the other end, and two thin wedges having one flat fece and the other seg- mental; so that the central "feather" with two "tearers," one on each side, serve to fill pretty well a round hole in the stone. The quarry-carts are short and very stoutly built,

* Weale, 1845.

80 Quabbtiko And Bla8Tino Boceb.

lined with strips 2^ X ^ inch flat iron; they carry from 1^ to 1} tons — they are 4 feet long, 8 feet 6 inches wide at the hind end, and 3 feet 4 inches in front ; the sides ahout 1 foot 6 inches high» and the front much higher; they cost about £15 each, and, with repairs, will last nine years. The navi- gator-barrows, which are of the common pattern with wooden wheel, cost lOs. Qd. In the quarry, where they are used all day, and loaded and worked quietly, they are entirely of wood; but at the wharf, where the work is shorter and sharper, a body of plate iron is used on a wooden carriage. Iron carriages for the barrows would be more economical, bat too heavy for the quarry-men. Iron wheels are considered too destructive to the planks. The barrows last from three to five months, accordmg to the work, and without repairs. The planks, which are of yellow pine, and in the quarry- generally about 25 feet by 14 inches by 2^ inches, hooped and bolted, cost 4^. per superficial foot. At the wharf the planks used are longer, broader, and thicker ; they last about six months. The "jumpers" cost 6d. per lb. For the re- moval of heavy stones the " devil cart " is used ; this consists of a pair of large and strong wheels with a stout and well- braced axle, to which a long central pole is fixed ; the front and lower end of which is carried upon a small wheel or roller. To this cart the heavy stones are slung by double chains, one of which is attached to the hinder side of the axle, and the other to the pole as near to the axle as may be necessary, according to the dimensions of the stone carried. The quarry screw-jack is an implement of great power, re- sembling the ordinary tool of that name, hut having a more extensive series of gearing within ; the winch is on a pinion of four teeth working a wheel of fourteen ; on this is another pinion of four teeth, working a wheel of eighteen, on which is a three-teethed pinion or triple stud engaged with the vertical ratchet

Capt. Nelson^s memoranda refer to three quarries in the neighbourhood of Plymouth, in the two first of which the limestone is chiefly raised in blocks of from ^ to 1 cwt., either to be burned on the spot for lime, or shipped for diflerent places in the neighbourhood for that purpose. The stone is likewise wrought for curb-stones and paving slabs, but cannot be got in masses large enough for wharf ashlar. In the third quarry the stone is raised in the largest blocks with heavy charges, and used for breakwaters and wharf ashlar. The largest block known to have been raised in this quarry weighed about 200 tons ; and so variable are

QUABBTING AND BLASTDia BOOKS. 81

the effects of blasting, that, on one occasion, upwards of 1000 tons were detached by a charge of 100 lbs. of powder in a 30 feet hole. It is usuallj considered that, well stratified as the rock in tins quany is, where the mass to be raised is not jammed at the sides, and where the beds dip to the front of the quarry, a quarter of a pound of powder per ton will dis- lodge the block sufficiently.

In quarry No. 1, one man raises 5 tons per day, besides loading and unloading the cart, and removing the rubbish produced 50 yards. Wages (in 1839?) 15a. per week, on piece work. In jumping, 16 feet, in four 4-feet holes, is considered a good day's work. Powder used, about 4 lbs. for 16 tons ; one-fourth of the hole filled with the charge.

In quarry No. 2, one man in one day (10 hours net time) will put down 20 feet with 1^-inch bit, or 1 5 feet with 2-inch bit ; depth of the charge from one-third to one-half that of the hole ; half a pound of powder allowed per cubic yard of solid rock. A man will turn out and break up for. rubble stone 4 tons, or 56 cubic feet per day; or 6 tons without breaking. When thus broken into pieces of from ^ to f cwt. each, and delivered at the kiln (close to the quarry), he will break it up for burning at one loaid of 16 tons, or 224 cubic feet per day.

In quarry No. 3, 20 feet of 1 J to l^inch bit is reckoned a good day's work, although one man puts down 30 feet, which is very unusual ; in deep holes, one man is employed for the first 6 feet, two for the next 10 ; and, after 16 feet, three men, provided the hole is not more than 10® or 12° out of the perpendicular ; if it is, even five or six men are put on after the first 15 feet. In such holes, it is usual to com- mence with a 2^-inch bit, and end with about 1 f inch. In a 30 feet hole, 2^ inch in diameter, 25 lbs. of powder are used for the first charge. If this does not succeed, it vdll, at all events, probably disturb the beds beneath sufficiently to allow space for the repetition of the blast, perhaps three or four times over, increasing somewhat every time before the final charge is introduced ; as the block, if not well detached on all sides first, will be destroyed by the premature application of the full charge.

Slate Quabbying.

In order to understand the peculiar methods adopted in slate quarrying, it is necessary to refer to the distinguishing geological features of the slate formation. Slate, besides being divided by fissures which form beds and joints to the

E 3

8^ Quabbting And Blasting Bocks.

masses, as is the case with all stratified materials, is divisible into laminsB or plates of any required thickness, the direction of which laminae is commonly vertical, or nearly so, but always oblique to, and never coincident with, either the beds or joints. This peculiarity of structure affords the means of splitting the slate and adapting it so suitably to the extensive purposes for which it is employed in Great Britain, and, at the same time, determines the most convenient manner of quarrying to be by detaching the masses of slate vertically from the face of a trench or gullet. The cutting of this gullet into the side of the slate mountain is, therefore, the first operation in the working of the quarry. As the trench proceeds, and the height of the surface above becomes greater than convenient (say about 40 feet), a second trench is commenced above the other, and similarly carried onward into the mountain until the height above reaches a similar quantity, when a tliird trench is commenced, and so on. In the great slate quarries of Bangor*, sixteen of these stages are in progress together; the lower ones being gradually widened, by the getting of the slates, as the upper ones are advanced. In the upper part of the quarry, the slates are removed with crow-bars ; but the slates become harder as they are lower from the surface, and require the use of gun- powder to detach the main masses. The miners engaged in drilling the holes for the powder are suspended by ropes from the upper parts of the rock, and are liable to many and severe accidents. After the slates are detached by powder or otherwise, they consume considerable labour in splitting them with wedges and mallets into marketable sizes, and reducing them to the several sizes required for roofing and other pur- poses. The means of communication between the several stages or levels (each of which in the Bangor quarry is about 40 feet high, or nearly 640 feet from bottom to top) are pro- vided by self-acting inclined planes, of great extent, laid from each stage to the contiguous stages. On these planes rails are laid to facilitate the motion of the trucks in which the

* These quarries are about six miles south-east of Bangor, and are worked in the mountain called in Welsh YJBron, a name signifying a breast or pap^ and commonly given to any hill the contour of which has a flowing outline, free from abruptness. This mountain Y Bron is on the side of a deep valley, through which the river Ogwen flows towards Lavan Sands, where it falls into the sea nearly opposite Beaumaris. An interesting paper on these quarries, to which we are indebted in preparing this notice,

is contained in the Quarterly Papers on Engineering, vol. iii. part 5

( Weak, 1845.)

Quabbting And Blasting Bocks. 83

slate is conveyed. At the head of each plane, a drum and break-wheel are fixed to regulate the velocity of the descent of the loaded trucks towards the level below. From the quarry at Bangor the slates are conveyed upon a railway to die shipping-port, a distance of about seven miles. On the several stages long ranges of sheds are erected for the men employed in cutting and shaping the slates. The slates for roofing are merely split to the required thickness with long iron wedges, and then trimmed with the cutting knife, by being placed on a fixed steel edge.

The dykes of greenstone, with which slate rocks are fre- quently traversed, are found to injure the slate, and destroy the cleavage of its structure for a considerable breadth. These dykes are usually removed by blasting, and form a very expensive impediment to the operations of the slate- miner.

At the Bangor quarries, about 1000 men are commonly employed, and the profits are understood to amount to about £80,000 per annum.

Some of the slate quarries of France are worked by sub- terranean galleries. In those of Rimogne the main gallery is about 400 feet long, with several lateral galleries, 200 feet in length, on each side of the main gallery. These galleries are about 60 feet high, and contain about 40 feet in height of good slate, the remainder consisting of quartz, or being injured by contact with volcanic substances.

At Angers, in France, are other slate quarries, worked in open cuttings, and which afford blocks, of which most of the houses of mat town are built. In the German States there are several slate quarries: at Eisleben, in Saxony; at II- menau; Mansfield, in Thuringia; and at Pappenheim, in Franconia. Switzerland is said to possess no slate, except in the valley of Semst, in the Canton of Glaris. Italy has only one quarry, that at Lavagna, in Genoa, the slate from which is used for lining the cisterns in which olive oil is kept *.

* (Papers on Engineering, vol. iii. part 5.) The application of slate here stated in the text is a good proof of the close texture and compara- tive impermeability of slate. M. Vialet states that he is able to double the natural hardness of this material by baking it in a brick kiln till it assumes a red colour. Subject to the severe test of Brard's process (boiling in sulphate of soda), slate is found to betray no symptoms of decomposition.

84 Quabbtikg And Blasting Bocks.

Firing Mines By Voltaic Electricity.

The removal of a large mass of the chalk cliffs near Dover for the works of the South-Eastem Eailway Company, by a grand blasting operation effected by three mines, simulta- neously fired by electrical communication, was a work of such surpassing magnitude, and so completely successful in its results, that a brief account of the anungements made and effects produced may be suitably introduced in an Appendix to the valuable treatise of Sir J. F. Burgoyne. We have at the same time the greater pleasure and greater facility in doing this, because the operations have been so well described by the able officer under whose experience they were con- ducted*, and from whose description the following notice has been abridged.

The Bound Down Cliff is situated 2 miles W. of Dover. Its summit is about 380 feet above high-water mark, and 70 feet above that of the Shakspeare Cliff, which is f of a mile nearer to the town. It is composed of a compact chalk, principally without flints, forming the lower bed of the chalk formation. The dip inclines from W. to E. about 40 feet in a mile. The base jutted out to seaward consider- ably beyond the general line of cliff to the westward, under and along which (from the Abbott's Cliff Tunnel towards Folkestone) a distance of 2 miles of the South-Eastem Bail- way is passed on an open embankment, defended by a sub- stantial retaining wall of concrete. The Shakspeare Tunnel (which forms the portion of the same line nearest to Dover) had been for some time completed, and its mouth or entrance from Folkstone is about 400 feet eastward of the central part of the base of Round Down. This intervening point, of about 300 feet in length, was therefore to be passed either by a tunnel or an open cutting : the former had been commenced, and the preliminary driftway formed on the upper level, when heavy slips occurring on either side, which partially extended to the cliff in (j^uestion, materially impaired its stability : the idea of tunnelling was therefore abandoned, and it was deter- mined to remove this point by blasting, and to continue the open railway and sea wall up to the mouth of the Shakspeare Tunnel, For this purpose the principle adopted was to

* Account of the Demolition and Removal by Blasting of a portion of the Round Down Cliff, near Dover, in January, 1843. By Lieut Hut- chinson, R.E. Prof. Papers of Royal Engineers, vol. vi. p. 188. (Weale.)

QUABBYINa AMD BLASITNa B0CE8. 85

employ large charges, placed a little above the intended level of the railway, which, by blowing out the base of the cliff in their front, would cause the downM of the superin- cumbent mass. The result fully justified the adoption of this method.

The experience gained in the many and extensive mining operations on this line of railway led to the adoption of a charge in lbs., bearing the proportion of ^^ of the cube of the line of least resistance in feet, corresponding with the rule laid down by Sir J. F. Bui^oyne, and which had been found sufficient for the works at Dover for blasts with charges vary- ing from 500 to 1300 lbs. This calculation was therefore adopted in the present instance, and, as the length of face to be removed was great (300 feet), three charges were used, one in the centre at the back of the salient point, the others at the distance of 70 feet on either side. From careful measurements the lines of least resistance were found to be^

Centre ... 73 feet to face of cliff. East and west . . 56 ditto ditto.

By calculation the quantity of powder required for the centre chamber was found to be 6750 lbs., which was increased to 7500, to provide against contingencies. For each of the two end chambers an allowance of 5500 lbs. was made, and thus the total quantity of powder became 7500 + 5500 -f 5500 = 18,500 lbs., or about 8J tons. The preliminary driftway already mentioned was used for excavating to the chambers, being about 4 feet wide and 5 feet 6 inches high ; but, being cut on the upper level of the intended tunnel, it became necessary to sink shafts a depth of 17 feet to reach the lower level of the chambers 3 feet above that of the railway. These shafts were formed as truncated cones, 5 feet diameter at bottom, and 3 feet at top, thus affording additional security for the retention of the tamping. At the bottom of these shafts, galleries 5 feet 6 inches high were cut at right angles to the driftway, and continued to the points determined for the chambers. These branches also were made of a dove- tailed form, 2 feet wide at the shaft, and 4 feet 6 inches at the other extremity, to assist in securing the tamping. The chambers were excavated at right angles to the galleries, and of the following dimensions, viz. : —

Centre chamber . 13 ft. by 5 ft. 6 in. high, by 4 ft. 6 in. Two ends of do. . 10 ft. by 5 ft 6 in. high, by 4 ft.

86 Quarrying And Blasting Rocks.

The voltaic batteries consisted of fiftj-four of Daniell*s cylin- ders, being eighteen for each mine. These cylinders were made of sheet copper, 32 oz. to the superficial foot, 1 foot 10 inches long, and 3| inches diameter, placed in sets of six each, each set in a deal box 1 foot 4 inches by 1 foot, by

1 foot 9 inches high, with a lid 4 inches deep. The zinc rods were 1 foot 8 inches long, and ^ inch diameter. These batteries differ from the common plate-battery also in em- ploying two liquids separated by a partition of animal mem- brane, or plaster of Paris. The liquid into which the zinc rod is plunged is sulphuric acid diluted with eight times its quantity of water. The liquid on the outside of the partition is a saturated solution of sulphate of copper.

Besides the eighteen Darnell's cylinders, two plate-bat- teries were applied for each mine, in order to guard against the injury which it appeared DanielFs apparatus was liable to by the low temperature of the season. In these plate batteries the solution was weaker, being only 1 of the acid to 12 water. The plate-batteries were contained in boxes 3 feet

2 inches by 12 inches and 8 inches deep, of 1 inch deal, and each divided into 20 cells 1^ inch wide, by partitions of f inch deal, the cells being coated with a waterproof com position of spirits of wine and sealing-wax. The 20 pairs of plates forming the series, each composed of a zinc plate J inch thick, in a rectangular case of copper 10 inches long, Ij inch wide, and 8 inches deep, without top or bottom, were united by stout copper wire attached to the zinc plate of one pair and the copper plate of the adjoining pair.

For the purpose of firing, it was determined to use three sets of wires and three separate batteries. The total length of wire required was thus 6000 feet, being 2000 for each mine, and J inch diameter. The wires were coated with a composition of pitch 8 to bees*- wax 1, and tallow 1, and covered with a coarse cotton tape, bound round while the composition was hot. The two wires thus prepared were in- sulated by being laid one on each side of a 1^ inch rope, and overlaid by a stout packthread turned once round each wire at every coil. The whole was then bound over with 2 yam- spun yam, and finally coated with the same composition of pitch, wax, and tallow. One man with a labourer prepared this wire at the rate of 6 feet per hour.

The cartridges or bursting charges were made 9 inches long and 2 inches in diameter, the top and bottom being

J

Qt7Abrying And Blasting Bocks. 87

secured by cork bungs. The priming wires, -^^ of an inch in diameter, projected 1 foot 6 inches beyond the top. They were passed through a slip of wood If inch square and I inch thick, inserted at the centre of the tube, and their ends clenched on a circular plate If inches diameter, lying over the lower cork bung. The platinum wire was fixed half- way between the two. The powder, which was of the finest sporting quality, was poured in from the top. The upper bung, being in halves, one-half was removed for this purpose, and refined when the tube was filled: the top and bottom were then coated with a waterproof composition. Two of these cartridges, after being tested by the galvanometer, were attached to each of the conducting wires, the wires being per- fectly insulated, and covered with spun yam. The caitridges were extended to a distance of 3 feet apart, and buried in the centre tier of loose powder in the box. The wires were then carried from the chambers along grooves cut in the sides of the galleries, shafts, and driftway, and covered with wooden troughs.

For the tamping, a dry wall was built in chalk across the end of each chamber, and the galleries and shafts were after- wards filled in with the same material, which was extended in the driftway to 10 feet on each side of the top of the shafts. The tamping occupied about twenty hours with four men to each mine.

For containing the charges of powder, the deal cases were constructed within the chambers of the following dimen- sions : —

Boxes.—Centre 11 ft. by 4 ft. 3 in. by 3 ft. 6 in. Ends 10 ft. by 2 ft. 8 in. by 3 ft, 3 in.

The powder was deposited in the boxes, in bags holding 50 lbs. each; the tiers above the centre were placed with their mouths downwards, those below it with their mouths upwards.

The circuit being completed at each battery by pre-arranged words of command, the mines were fired simultaneously on the 26th January, 1843, at 2*20 p.m. The ignition was fol- lowed by a deep hollow sound, and the effect was described to resemble the appearance of the fall, or rather flowing, of lava from the side of a mountain, assuming a gently imdu- lating wave-like motion, as the mass slid along the bottom and into the sea. The mass fell exactly as had been desired, and the quantity removed was estimated at more than

88 Stones Used In Building.

400,000 cubic yards, being a parallel mass or slice from the inclined face of the cliff, and averaging 380 feet in height by 80 feet in thickness, and 360 feet in length of face. The operation thus successfully conducted and completed, without the slightest accident, saved about 7000L to the South- Eastem Eailway Company, and reflects the highest credit upon Lieut. Hutchinson, Messrs. Cubitt, Wright, and Hodges, and all other parties concerned.

Part Ii.

Stones Used In Building.

To the architect and the engineer, alike, is a knowledge of the materials which he has to employ, or to deal with, of supreme importance. And, were it worth while to inquire the rank which each class of materials occupies in the scale of professional consideration, we should start upon the fSact that those substances which, for their substantial properties and enduring character, are selected as the foundations and the exposed external parts of our buildings and structures, claim our first and most attentive examination. Frequently, in- deed, local circumstances will define the limits within which the selection must be made ; but there are few, if there are any, cases in which the designer is altogether denied the privilege of selection ; while in many instances an acquaint- ance with the materials at his disposal will open a wide field for the exercise of his judgment in aiming at current eco- nomy and permanent preservation.

In the few pages left to us in the present volume, we pro- pose to follow up the account given of the methods of getting or quarrying stones, &c. by describing the several properties of the leading classes of those materials which fit them for the purposes of construction, and which should lead to the adoption of one or other of them, according to the service they may be required for.

Without attempting to observe the classification laid down by geologists, we propose to treat of stones under the four general divisions of Granites^ Slates, Limestones, and Sand- stones, including under each of these general heads such con- stituents or subordinate combinations of each as may appear essential to be noticed in this rudimentary outline of a really extensive and highly important department of practical science.

Stones Used In Buildin0. 89

Obanite.

This rock, which appears to have originally been a fased mass, and subsequently to have undergone the process of crystallization, is of a granular structure, that is, consisting of separate grains of different substances, united, apparently, without the aid of any intermediate matter or cement. These substances are quartz, felspar, and mica, each of these being a compound. The infinite variety of proportions in which these several constituent elements are united in the mass, occasions the great diversities of colour and appearance of the several kinds of granite, and also affects in a much more important manner the enduring characteristics of this va- luable material. Thus its colour varies from light gray to a dark tint closely approaching black, and is to be found of all shades of red, and many green. Of the constituents of gra- nite, quartz is a substance of a glassy appearance, and of a gray colour, and is composed of a metallic base aUicium and oxygen: felspar is also a crystalline substance, but com- monly opaque, of a yellowish or pink colour, composed of silicious and aluminous matter, with a small proportion of Hme and potash; mica, a glittering substance, principally consists of clay and flint, with a little magnesia and oxide of iron. Instead of the mica, another substance, called horn- blende, is found in some granites : hornblende is a dark crys- talline substance, composed of flint, alumina, and magnesia, besides a large proportion of the black oxide of iron. Gra- nites in which hornblende exists are sometimes called Syenite, having been first found in the island of Syene, in Egypt. A similar rock is found in Scotiand, in Aberdeen, and in the Isle of Arran.

Granite is found in mountain-chains, and usually in rugged outlines, in nearly all parts of Europe. In the Pyrenees it is found in masses of piles or columns. In Germany it forms the material of those famed scenes of supernatural tradition, the Brocken and the Hartz Mountains. Granite forms the bold ridges of Switzerland and the Savoy. In England, this valuable rock occurs in Devonshire and Corn- wall, also in North Wales, Anglesea, the Malvern Hills in Worcestershire, Chamwood Forest in Leicestershire, and in Cumberland and Westmorland. Granite rises near the foot of Skiddaw in Cumberland, and there are masses of it on the banks of Ulswater. It is found in the mountains of Armagh and Wicklow in Ireland; and Mr. Bakewell supposes

90 STOllES USED IN BUILDINa.

that the same formation of this rock, which occurs on the western side of England, is continued under the Irish Chan- nel, or, if interrupted, it rises a^ain in the Isle of Man, and in the counties of Dublin and Wicklow in Ireland. Granite blocks are found in the beds of some of the rivers in the north-west parts of Yorkshire, and in clay pits in Cheshire and Lancashire, at great distances from any quarries where the stone is obtainable. Most of the granite met with in Chamwood Forest is of the kind called Sienitey and already described. A continuation of the same description of rock appears upon the surface, near Bedworth, in Warwickshire.

In the granite of Cornwall the felspar is usually white, but in the Scotch granite it is commonly red. Among the cele- brated works of which granite forms the material, may be named the monuments of Ancient Egypt and of Thebes, the celebrated block used as a pedestal for the statue of Peter the Great in St. Petersburgh, the columns in the church of the Casan in the same city ; and in England the columns in the King's Library in the Museum, and the bridges of London, &c., &c.

Although all granites are similar in structure, the differ- ence in the proportions of its constituent substances occasions great difference in its enduring and useful properties. Some varieties are exceedingly friable, and liable to decomposition, while others, including that known as Sienite, suffer but imperceptibly from moisture and the atmosphere. Some remarks upon the properties of a Sienite, the "'Hearm Gra- nite'' of Guernsey, published in the first volume of the Trans- actions of the Institution of Civil Engineers, may be here usefully quoted : —

"The Herm granite, as compared with Peterhead, and Moorstone from Devon or Cornwall, is a highly crystallized intermixture of felspar, quartz, and hornblende, with a small quantity of black mica, the first of these ingredients hard and sometimes transparent in a greater degree than that found in other British granites, — the contact of the other substances perfect. It resists the effect of exposure to air, and does not easily disintegrate from the mass when mica does not prevail ; but, as this last is usually scarce in Guern- sey granites, the mass is not deteriorated by its presence as in flie Brittany granites, where it abounds, decomposes, stains, and pervades the felspar, and finally destroys the adhesion of the component parts : — vide the interior columns of St. Peter's Port church (Guernsey), which is built of it,

STONES USED IN BUnJ)ING. 91

for an instance. The quartz is in a smaller quantity, and somewhat darker than the felspar in colour ; the grains are not large, but uniformly mixed with the other ingredients. The hornblende, which appears to supply the place of mica, is hard and crystallized in small prisms, rarely accompanied by chlorite; its dark colour gives the grayish tone to this granite, or when abundant forms the blue granite of the Yale parish. This substance is essentially superior to mica in the formation and durability of granites for strength and re- sistance; consequently its presence occasions more labour in working or facing the block, and its specific gravity is in- creased. The mica is inferior in quantity to the hornblende, and usually dispersed in small flakes in the mass;— it may, with chlorite, be considered rare."

"The compact nature of a close-grained granite, such as the Vale and Herm stone, having the felspar highly crystal- lized and free from stained cracks, seems well calculated to resist the effect of air and water. When the exterior bruised sur£ax;e of a block has been blown off, it is better disposed to resist decay; — if the surface blocks of the island are now examined after the lapse of ages, it will be found to have resisted the gradual disintegration of time in a superior degree, when compared with large grained or porphyritic granite ; when exposed to water and air, there is no change beyond the polish resulting from friction of the elements. Among the symptoms of decay, disintegration prevails gene- rally among granites, usually commencing with the decom- position of the mica; its exfoliating deranges the cohesion of the grains, and it may be considered then to be the more fre- quent mode of decay."

*' The churches of the Vale and St. Sampson (Guernsey), although much of the materials are French and Aldemey, bear many proofs of the above remarks : these erections date A.D. 1100 — 1150. The ancient buildings of decided Herm and Vale stone must be sought for among the old houses in the northern parishes of Guernsey, where they not only encounter the effect of air and water (rain), but the sea air and burning rays of the sun. Disintegration alone appears going on by slow degrees, but in no case affecting the interior of the stone, and so gradual and general as not to deface the building materially; indeed, the oldest proofs taken from door-posts, lintels, and arches, have scarcely lost their original sharpness or sculpture. The pier of St. Peter's Port and bridge of St. Sampson's may also be mentioned.

n

STONES USED IN BTTILDINa.

'* The shore rocks in like manner do not show any material change of surface by wearing ; where the force of the tide is strongest, a slight smoothness alone may be observed on the exterior, and in many instances each substance possesses this polish without being levelled down to a face,"

" Vale stone on the northern point of Guernsey produces a finer grained Sienite than Herm, more hornblende in it, and specific gravity greater. The Herm is somewhat larger grained, but equally good for every erection where durability is the chief point. The Cat-avrroque stone in the western part of Guernsey must be considered of a different structure to the above : it is a fair and good stone, and appears to last well ; its schistose texture must ally it to the gneiss series. In colour it is much the same as the blue granites, the felspar is brilliant and the hornblende prisms are well defined ; there is more chlorite in it, and it is easier to work."

From the same volume, the following interesting results of experiments upon the relative wear of seven different kinds of granite and one whinstone are extracted, as peculiarly yalu- able in the choice of materials which will be exposed to simi- larly destructive forces.

" Table showing the result of Experiments made under the direction of Mr. Walker^ on the Wear of different Stones in the Tramway on the Comm^cial Hood, London^ from 27t/^ March, 1830, to 24tA August, 1831, being a period of seven- teen months*

Nameof ttone.

Guernsey

Herm

Budle

Peterhead (blue).

Heytor

Aberdeen (red) .

Dartmoor

Aberdeen (blue).

Suf.

area in

feet*

4-734 5-250 6336 3-484 4*313 5-375 4-500 4-823

Original weight.

cwt. qn.

7 1

7 3

9

4 1

6

7 2 6 2 6 2

Ibt. 12-75 24-25 50-75

7-50 15-25 11-50 25-00 16-00

Lou of

weight

hy wear.

Lon

per 8up.

fbot

Relative lowes.

lbs.

lbs.

4-50

0-951

1-000

5-50

1048

1-102

7-75

1-223

1-286

6-25

1-795

1-887

8-25

1-915

2-014

11-50

2-139

2-249

12-50

2-778

2-921

14-75

3-058

3-216

** The Commercial Road stoneway, on which these experi- ments were made, consists of two parallel lines of rectangular tramstones, 18 inches wide by a foot deep, and jointed to each other endwise, for the wheels to travel on, vrith a common street pavement between for the horses. The tramstones

Stones Used In Building. 03

subjected to experiment were laid in the gateway of the Limehouse turnpike, so as of necessity to be exposed to all the heavy traffic from the East and West India Docks. A similar set of experiments had previously been made in the same place, but for a shorter period (little more than four months), with, however, not very diflferent results, as the fol- lowing figures, corresponding with the column of ^^ relative losses,'' in the foregoing table will show.

"Guernsey . .1000 Peterhead (blue) 1-716 Budle . . . 1-040 Aberdeen (red) . 2-413 Herm . . .1-166 Aberdeen (blue) 2-821

All the above stones are granites except the Budle, which is a species of whin from Northumberland, and they were all new pieces in each series of experiments."

The relative hardness, or resistance to crushing, of the several kinds of granite in common use, is exhibited in the following Table of Experiments made with an hydrostatic press on specimens of the sizes stated in the Table.

These experiments were made with a 12-inch press, the pump one inch diameter, and the lever 10 to 1; — the me- chanical advantage therefore 144 x 10 = 1440 to 1. The weights on the lever were added by 7 lbs. at a time ; — each addition therefore equivalent to 1440 x 7 = 10,080 lbs. or 4^ tons.

In consequence of the smallness of the specimens, the press was filled with blocks to the required height, and with these the surplus effect of the lever was 4^ lbs. at 10 to 1 , which strictly should be added to the pressure ; but, as the friction of the apparatus is equal to the effect of the lever, it is dispensed with in the calciilation.

The column containing the pressure per square inch re- quired to produce a fracture gives the true value of the stone, as the weight that does so would possibly completely destroy the stone if allowed to remedn on for a length of time. It should also be observed that, from the exceedingly short time allowed for the experiments, the results are pro- bably too high.

94

Stones Used In Building.

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STONES USED IN BUILDINa. 95

The method pursued in quarrying the Peterhead granite has been already described at page 78.

Some experiments upon the granites of Ireland were re- ported to the Geological Society of Dublin, in January, 1844. These experiments were instituted to show (among other results) the weight of water which the stones would imbibe when immersed in water. The size of the stones immersed was 14 inches long and 3 inches square. They were placed on their ends in 16 inches of water, and were uniformly im- mersed for 88 hours, having been brought to a dry state before immersion by being kept some time in a room at the ordinary temperature of domestic apartments. They were carefully weighed before and after the immersion. The average weight of several specimens of the stones was 170 lbs. per cubic foot ; the maximum being 176, and the minimum 143 lbs. The Newry and Kingston granites absorbed a quarter of a pound of water to the cubic foot; the Carlow, from 1^ to 2 lbs. ; and the Glenties, from Donegal (between granite and gneiss), 4 lbs.

Serpentine and Porphyry are sometimes classed as varieties of granite; but more properly as distinct rocks of the same primary character as granite. Serpentine is a valuable mate- rial for the ornamental purposes of architecture, being dis- tinguished by its variety and richness of colours ; these are generally light and dark green of various shades, intermixed in spots or clouds, resembling the spots on the skins of ser- pents (whence its name). Some varieties of this rock have also a red colour; others are found having an intermixture of crystalline white marble, and these are known as verde an- tiqtte, highly valued for sculpture of ornamental character. Some kinds of serpentine are crystalline, and are called schiUer spar or diaUage, In some of these rocks, magnesia exists in the proportion of 48 per cent.

Serpentine is found in Cornwall with a micaceous rock overlying the granite, and forms part of the promontory called the Lizard Point; it also occurs in the same county, near Liskeard. It is not met vdth elsewhere in England ; but in Anglesea beautiful varieties of the red and green- coloured are found in beds of considerable thickness, asso- ciated with the common slate rocks of the district. The mixture of serpentine with talc or steatite becomes soft, and forms the substance called potstone, which resists fire, and is used in Switzerland, Lombardy, and Egypt, for culinary and other purposes.

06 Stones Used In Building.

Siate.

In treatmg of slate as a material of common utilitj to tbe builder, it will be scarcely necessary to do more tban enume- rate the several varieties which are known under the general term slate, but distinguished one from another, and from the slate of general utility, by a peculiar prefix. Thus, the geo- logist recognises mica slate, talcous slate, flinty slate, and common, or clay slate. Of these, the last only is a material of extended use in the arts of building and construction. Of the others, the first, or mica slate, is a compound of quartz and mica, with sometimes a little felspar. The several varieties of this rock are dependent on the proportion of mica contained in each, and on the comparative fineness or coarseness of the constituent particles. If the felspar abound, the compound passes into a form of rock known as gneiss; and if the mica exist in only small proportion, the material as- sumes the form of quartz rock. The talcous slates are dis- tinguished by their green colour, and contain a large propor- tion of ma^esia. One variety of this kind of slat6 contains particles of quartz, and is sometimes used for hones, under the name of whetstone slate. The third variety on our list, flinty slate, contains a larger proportion of flinty or silicious matter, and assimilates to the scaly structure of flint Pos- sessing the silicious earth, but not the scaly kind of forma- tion, Uiis slate passes into a rock known as homstone by us, and as petro-sUex by the French. If it contains felspar in crystals, it is distinguished as homstone porphyry. All of these varieties of slate are found alternating with each other ' in the same rocks in North Wales, and in the Chamwood Forest, Leicestershire. The common or clay slate abounds in the most rocky districts, and is found lying upon granite, gneiss, or mica slate. The several varieties of character — from the extreme crystalline to the extreme earthy — ^are found occupying positions in regular order, from the primary towards the transition rocks. Clay slate, as its name implies, consists chiefly of clay in an indurated condition, and occa- sionally containing particles of mica and quartz; and, in some of the coarser kinds, grains of felspar and other frag- ments of the primary rocks. In the extreme admixture of these foreign substances, clay-slate approaches the nature of the rock Imown as greywacke. The beds of clay-slate are invariably stratified, the thickness of the strata, however, varying from a fraction of an inch to many feet. Its laminar

STOKES USED IN BTJILDlNa. 97

texture admits of a ready separation into thin plates, and thus endows it with a supreme value for roofing and other pur- poses, in which great density and comparative impermeability are required to coexist with a minimum thickness and weight. In our preceding pages, we have quoted a highly interesting description of the method pursued in quarrying this invalu- able material. We may here add that, besides the immense quarries which are' worked, as there described, at Bangor, in North Wales, slate is also procured from the counties of Westmoreland, York, Leicester, Cornwall, and Devon, and that Scotland is supplied with this useful material from Bala- hulish and Easdale.

In Ireland slate quarries are worked to a considerable ex- tent at EUlaloe, Valentia, and in Wicklow County; the slates from the latter of which are said to resemble those from Bangor in quality and extreme tenacity, and can be raised in blocks 30 feet long, 4 or 5 feet wide, and from 6 to 12 inches in thickness. The weight of slates varies from 174 to 179 lbs. per cubic foot ; the average weight of several specimens being 177 lbs. When immersed in water in the manner already described for granite (page 95), the clay-roofing slate absorbed less than a quarter of a pound of water; while a softer quality of clay slate, from the neighbourhood of Bantry, absorbed nearly 2 lbs.

Sandstones.

These rocks, belonging, geologically, to various positions in the order of the strata of which the exterior of the earth is composed, and sometimes alternating with the variety of limestones, are widely distributed, or ratlier frequently met with, superficially, in exploring the surfax^e of our island.

The vast accumulation of beds, known as forming the Silurian System, and of which sandstone is the principal member, is found to extend, with some interruptions, from Carmarthenshire and Radnorshire, in the west, to Dudley in Staffordshire, in the central part of England. At the western boundaries of this system the sandstone is known as Llandillo flagstones ; it occurs also at Caer-Caradock in Shropshire, and is tiiere and elsewhere known as Caradock sandstone. Some varieties of this stone are found to contain a large proportion of lime, occasionally in the form of shells, and are hence sometimes called shelly limestones and sandy limestones.

Sandstones are principally silicious, and possess various degrees of induration. The chemical analysis of several

F

98 St0Nb8 Used In Buildzno.

specimens of sandstone from four quarries, tIz., Graigleith, in Edinburghshire ; — ^Darlej Dale, in Derbyshire ; Heddon, in Northumberland, and Kenton, in the same county, gives their average constituents thus :—

Silica 95-725

Carbonate of lime . . . 1-065 Iron alumina . . . . .2*15 Water and loss 1-06

100.000

The average weight of these four kinds of stone was found to be 142 lbs. 7 oz. per cubic foot. Adopting the same high authority from which these analyses are derived, viz., the scientific Commission appointed to visit quarries and examine the qualities of stones to be used in building the New Houses of Parliament, the composition of these four kinds of sand- stone appears to be as follows: — Craigleith: Fine quartz grains with a silicious cement, slightly calcareous ; occasional plates of mica ; colour, whitish gray. — Darky Dale : Quartz grains of moderate size and decomposed feldspar, with an argillo-silicious cement ; ferruginous spots, and plates of mica; colour, light ferruginous brown. — Heddon: Coarse quartz grains, and decomposed feldspar, with an argillo- silicious cement ; ferruginous spots ; colour, light brown ochre. --Kenton: Fine quartz grains with an argillo-Silicious and ferruginous cement; mica in planes of beds; colour, light ferruginous brown.

From the nature of the composition of sandstones, (of which the above four are described as average specimens,) it results that their resistance against, or yielding to, the decomposing effects to which they are subjected, depends to a great extent, if not wholly, upon the nature of the cementing substance by which the grains are united ; these latter being comparatiTely indestructible. From the nature of their formation, sand- stones are usually laminated, and more especially so when mica is present, the plates of which are generally arranged in planes parallel to their beds. Stones of tibis description should be carefully placed in constructions, so that these planes of lamination may be horizontal, for if placed verti(»lly, the action of decomposition will occur hi flakes, according to the thickness of the laminse. Indeed the best way of using all descriptions of stone is in the same position which they had in the quarry, but this becomes a really imperative rule with those of laminated structure. Uniformity of colour is a

Stones Used In Buildikg. 09

tolerably correct criterion of uniformity of structure, and this constitutes, other circumstances being equal, one of the prac- tical excellencies of building stones. The great injury occa- sioned to these materials by &eir absorption of moisture, leads properly to a preference for such stones as resist its introduc- tion» for all above-ground purposes. Those which imbibe and retain moisture are especially liable to disruption by frost if exposed. The simplest method of ascertaining the disposition of a stone to imbibe moisture is to immerse it for a lengthened period in water, and to compare the weight of it before and after such immersion.

A method recently introduced of determining the suscepti- bility of a stone to injury by frost, is to dip tibe stone in a solution of some salt, and then suspend it for several days over the solution, repeating the process several times, so as to allow the salt to ciystallize on the surface of the stone. If the stone can resist frost the solution will remain free from sand or fragments of stone, but if otherwise, the edges of the stone will be found deposited in the vessel beneath.

As examples of the durability of sandstone in buildings, the following may be instanced : — ^Ecclestone Abbey, built in the thirteenth century, near Barnard Castle, Durham, in which the minute ornaments and mouldings remain still in excellent condition. The circular keep of Barnard Castle (14th century), is also in fine preservation. Tintern Abbey (13th century), built of red and gray sandstones of the vicinity, is for the most part in perfect condition. Whitby Abbey (13th century), is built of stone similar to that in the vicinity, and is generally in good con4ition, excepting ^e west front, which is very much decomposed. The stone used is of two colours, brown and white, of which the latter is uniformly in the best pre- servation. The enrichments on the east front are all in good condition. Of Eipon Cathedral, the west front, the tran- septs and tower, were built in the 12th and 13th centuries of a coarse sandstone of the vicinity, and remain in very fair condition. Eivaulx Abbey, built in the 13th century, of a sandstone one mile from the ruins, is generally in excellent condition. The west front is slightly decomposed, but the south front is remarkably perfect, even to the preservation of the original tool-marks.

Experiments upon several sandstones to ascertain the force required to crush them, performed with the hydrostatic press, as already described of the specimens of granite (page 93) gave the following results —

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Stones Used In Building.

101

Limestones.

The class of limestones, including the magnesian limestones and the oolites, is one of extreme importance in the building arts, comprehending some of the most advantageous materials of construction, and combining great comparative durability with peculiar feusilities for working, in which thej surpass the sand- stones ; as those do the rocks of a primary and unstratified character. Of the limestones and the oolites, the principal material is carbonate of lime. The magnesian limestones contain a quantity of carbonate of magnesia, in some cases nearly equal to that of the carbonate of lime. The analyses of four varieties of oolites and three limestones are given below. The oolites were from Ancaster in Lincolnshire; from Bath; from Portland, Dorsetshire; and from Ketton in Rutlandshire. The three Mmestones were from Bamack, Northamptonshire ; Ohilmark, Wiltshire, and Ham Hill in Somersetshire.

Oolites.

Ancaster.

Portland.

Silica .... Carbonate of lime . Carbonate of Magnesia . Iron Alumina Water and loss

• • . .

93 59

290

•80

2-71

94-52 2-50 1-20 1-78

1*20

95-16

1-20

•50

1-94

. • . .

92-17

4-10

•90

283

Bamack.

Silica . . . , Carbonate of lime . Carbonate of magnesia • Iron Alumina Water and loss

....

93*4 3-8 13 1-5

10-4

79-0

3-7

20

4-2

4-7 79-3 62 8 3 2-5

All of these stones contain a slight trace of bitumen in their composition. The weights of the several kinds are as follow: — Of the oolites, the Ancaster stone 139 lbs. 4 oz. per cubic foot. — Bath, 123 lbs. — Portland, top bed, 135 lbs., best or lower bed, 147 lbs., mean, say 141 lbs. — Ketton, 128 lbs.

102

8T0NBS USED IN BtJILDZNa.

5oz. Of the three limestones, the weights axe, Bamack, 136 lbs. 12 oz.— Chilmark, 163 lbs. 7 oz. ; and Ham Hill, 141 lbs. 12 oz. The composition of these stones is described as follows: — First, Oolites. — Ancaster: fine oolitic grains, cemented by compact and often crystalline carbonate of lime ; colour, cream. — Bath : chiefly carbonate of lime in moderately fine oolitic grains, with fragments of shells. The weather bed of the quarry is generally used for plinths, strings, cornices, &c, ; the com grit for dressings ; the scallet, which is the finest in grain, is used for ashlar. Eight quarries are opened on the Box escarpment, many of them of great antiquity. The colour is that of cream. — Portland : oolitic carbonate of lime, with fragments of shells; colour, whitish brown. — Ketton : oolitic grains of moderate size, slightly cemented by carbonate of lime; colour, dark cream. Secondly, Lime- stones. — Bamack: carbonate of lime, compact and oolitic, with shells, often in fragments ; coarsely laminated in planes of beds ; colour, light whitish brown. This stone is used for troughs and cisterns, and is perfectly impervious. — Chilmark : carbonate of lime, with a moderate proportion of silica, and occasional grains of silicate of iron ; colour, light greenish brown. — Ham HUl : compact carbonate of lime with shells, chiefly in fragments, coarsely laminated in planes or beds ; colour, deep ferruginous brown.

Of four varieties of magnesian limestone, the following are the analyses : —

MAGNXSIAir LIMKBT0NK8.

Bolsover.

Huddlestone.

Roach Abbey.

Park Nook.

Silica

Carbonate of Lime . . Carbonate of Magnesia . Iron Alumina .... Water and Loss . . .

3-6

51 1

40*2

1-8

3*3

2-53

5419

41-37

•30

1-61-

• •

•8 57-5 39-4

•7 1*6

55-7

41-6

•4

2-3

The weights of these limestones were as follows : — Bolsover, 151 lbs. 11 oz. per cubic foot; Huddlestone, 137 lbs. 13 oz.; Boach Abbey, 139 lbs. 2oz. ; and Park Nook, 137 lbs. 8 oz. The composition of them is as follows : — Bolsover: chiefly car- bonate of lime and carbonate of magnesia, semi-crystalline ;

Stones Used Ik Building. 103

colour, light yellowish brown. — HudMestone: similar com- ponent parts ; colour, whitish cream. — Roach Abbey : chiefly carbonate of lime and carbonate of magnesia, with occasional dendritic spots of iron or manganese; semi-crystalline; colour, whitish cream. — Park Nook : similar constitution, and of cream colour. Sinks and tanks are made of this stone, but the water wastes in them.

The following structures of magnesian limestones may be distinguished: — Southwell Church, Nottinghamshire, built in the 10th century, and now in perfect condition. Konings- burgh Castle in Yorkshire (Norman), built of coarse-grained and semi-crystallinis. magnesian limestone, from the adjacent hill, is in excellent preservation. The mortar has in many parts disappeared, but the edges of the joints remain per- fect. The church at Hemingborough, in Yorkshire (15 th century), is in a very perfect state. It is built of a white crys- talline magnesian limestone, resembling that from Huddle- stone. The entire building is in a perfect state ; even the spire, where no traces of decay are apparent.

It is remarked that magnesian limestone appears capable of resisting decomposing action in proportion as its structure is crystalline, and the late Professor Daniell gave it as his opinion, based upon experiments, that '* the nearer the mag- nesian limestones approach to equivalent proportions of car- bonate of lime and carbonate of magnesia, the more crystal- line and better they are in every respect."

Among the buildings constructed of oolitic and other lime- stones, the following are deserving of notice : — Byland Abbey, Yorkshire, of the 12th century, built partly of a silicious grit (principally in the interior), and partly (chiefly in the ex- terior) of a compact oolite, from the Wass quarries in the vicinity. The west front, which is of the oolite, is in perfect condition, even in the dog's-tooth and other florid decorations of the doorways, &c. This building is generally covered with lichens.

Bath. — Abbey Church {167 Q\ built in an oolite from the vi- cinity. The tower is in fair condition, the body of the church in the upper part of the south and west sides much decom- posed. The lower parts (formerly in contact with buildings) are in a more perfect state : the relief in the west front of Jacob's ladder are in parts nearly effaced. — Queen's Square^ north side, and the obelisk in the centre, built about 110 years since, of an oolite with shells, in fair condition.

104 BTONXS trSSD IK BUILDING.

OkeuSy built about 1760, of an oolite in the vioimty, gene- rally in fair condition, except those portions which haye a west and southern aspect, where the most exposed parts are decomposed. — Orescent, built about 60 years since, of an oolite of the vicinity, generally in fair condition, excepting a few places where the stone appears to be of an inferior quality.

Oxford. — Cathedral (Norman, 12th century), chiefly of a shelly oolite, similar to that of Taynton. Norman work in good condition; the later work much decomposed. — Merkm CoUege Chapel (13th century), of a shelly oolite, resem- bling Taynton stone, in good condition generally. — New Col- lege Cloisters (14th century), of a shelly oolite (Taynton) in a good condition. The whole of the colleges, churches, and o^er public buildings of Oxford, erected within the last three centuries, are of an oolitic limestone from Headington, about 1| mile from the University, and are all, more or less, in a deplorable state of decomposition. The plinths, string- courses, and such portions of the buildings as are much ex- posed to the action of the atmosphere, are mostly of a shelly oolite from Taynton, 16 miles from the University, and are universally in good condition.

Saint PauVs Cathedral, London, Finished about 1700. Built of Portland oolite, from the grove quarries on the East Cliff. The building generally in good condition, especially the north and east fronts. The carvings of flowers, &c., are throughout nearly as perfect as when executed. On the south and west fronts large portions of the stone exhibit their natural colour, occasioned by slight decomposition of the surfieu^e. The stone in the drum of the dome, and in the cu- pola above it, appears not so well selected as the rest, yet shows scarcely any decay in tiiose parts.

Westminster Abbey (16th century). Built of several varie- ties of stone, similar to Gatton or Eeigate, much decomposed, and of Caen stone, generally in bad condition. A consider- able portion of the exterior, especially on the north side, has been restored at various periods; nevertheless, abundant symptoms of decay are apparent. The cloisters built of se- veral kinds of stone, are in a very mouldering condition, ex- cept where they have been recently restored with Bath and Portland stones. The west towers erected in the be^ning of the IBth century, with a shelly variety of Portland oolite, exhibit scarcely any appearance of decay; Henry the

Stokes Used In Building. 105

Seventh's chapel, restored about thirty years since, mth Goombe Down Bath stone, is already in a state of decomposi- tion*.

In Spofforth Castle is a striking example of an unequal decomposition of the magnesian limestone and a sandstone ; the former used in the decorated parts, and the latter in ash- lar and plain facings. Although the magnesian limestone has been equally exposed with the sandstone, it has remained as perfect as when erected, while the sandstone has suffered considerably. In Chepstow Castle, and in Bristol Cathedral, similar contrasted effects are visible upon the magnesian limestones and sandstones employed.

The late Professor Dauiell gives the following valuable summary of the results of his experiments upon the stones we have referred to. ''If the stones be divided into classes, according to their chemical composition, it will be found that in all stones of the same class there exists, generally, a close relation between their various physical qualities; — thus it will be observed that the specimen which has the greatest specific gravity possesses the greatest cohesive strength, ab- sorbs the least quantity of water, and disintegrates the least by the process which imitates the effects of weather. A com- parison of all the experiments shows this to be the general rule, though it is liable to individual exceptions. But this will not enable us to compare stones of different classes to- gether. The sandstones absorb the least water, but they dis- integrate more than the magnesian limestones, which, con- sidering their compactness, absorb a great quantity. The heaviest and most cohesive of the sandstones are the Craig- leith and the Park Spring. Among the magnesian lime- stones that from Bolsover is the heaviest, strongest, and ab- sorbs the least water. Among the oolites, the Eetton Kag is greatly distinguished from all the rest by its great cohesive strength and high specific gravity."

For durability, for crystalline character, combined with a close approach to the equivalent proportions of carbonate of lime and carbonate of magnesia ; for uniformity of structure ; for facility and economy in conversion ; and for advantage of colour, the Commissioners declared their preference for the magnesian limestone of Bolsover and its neighbourhood, and, taking into account the extended range and careful precision of their observations, and the skilful manner in which their

* Report of Comminionen.

106 STONBS tlBED IN BUILDINQ.

experiments were designed and conducted, it will be generall j admitted that the opinions thus formed and presented to us are excellent guides for our selection of stone in all arcMtec- tural constructions, and deserve our most careful considera- tion, if they do not claim our immediate concurrence.

G. Woodfall and Son, Printen, Angel Court* Skinner Street, London.

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