SPONS'

DICTIONARY OF ENGINEERING

DIVISION VIII.

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SPONS'

DICTIONARY OF ENGINEERING,

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€M, Porotal, lltilitog, mìa alatoti;

WITH TECHNICAL TEEMS

IN FRENCH, GERMAN, ITALIAN, AND SPANISH.

EDITED BY

BYRNE AND SPON.

DIVISION VIII.

LONDON;

Ë. & F. N. SPON, 48, CHARING CROSS.

New York ;- 446, BROOME STREET.

18 74.

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JUL 2 3 1958

IX)NDON : PRINTED 15Y WILLIAM CLOWES AND SONS, STAMFORD STREET AND CHARING CROSS.

PREFACE.

Previous to the publication of the present work, the want of a book of reference on Civil and Mechanical Engineering had long been experienced by the Engineer. A great deal of information of a useful kind had been recorded in the various Scientific Journals and Transactions of Engineering Societies, but it was given in a form not available for ready reference. The work so much needed is supplied, we trust, in this Dictionary of Engineering, written mainly by practical Engineers well acquainted with special branches of their profession, and whose names will be found in the List of Contributors.

Use has also been made of a large number of works devoted to Civil, Mechanical, Military, and Naval Engineering, and of the published writings of eminent Engineers.

Many subjects which ought perhaps to have a place in a complete work have been omitted, in the desire to confine the number of pages to something near the limit announced at the commencement ; but we may be allowed to add that no other work on Engineering has been published which contains such a variety and amount of information on the same class of subjects in a collective form.

From the commencement of the work until August, 1872, the editorial department was conducted by Mr. Oliver Byrne, assisted by Mr. Ernest Spon ; at that period Mr. Byrne ceased to be Editor, and the work has been completed under the direction of Mr. E. Spon.

Our thanks are specially due to G\ Gr. André, Esq., CE., for the careful attention bestowed on the subjects entrusted to him; and we also return our sincere thanks to the kind friends who have assisted in the compilation and revision of the various articles.

E. & F. N. SPON.

LIST OF CONTRIBUTORS.

-OO^i

Adriani, Dr.

Andre, Geo. G., Civil Engineer, M.S.E.

Anstruther, Major-General P.

Ardagli, J. C, E.E.

At wool, Josiah.

Beck, W. H., Mechanical Engineer.

Bower, George, Gas Engineer.

Burgh, N. P., Marine Engineer, M.I.M.E.,

Assoc. Inst. C.E. Byrne, Oliver.

Cargill, Thos., B.A., A.I.C.E , M.S.E. Colburn, Zerah, C.E. Coles, Capt. Cowper, P. Conti, Lt.-Col., Boyal Italian Engineers. Dawnay, Archibald D., C.E. Denison, Sir W., K.C.B., Col. K.E. Don, Thos., Millwright. Dunn, Thos., Mechanical Engineer. Eckhold, C.

Edson, M. B., of New York. Guthrie, C. T. Hall, Henry, F.R.G.S., late War Dept,

Surveyor.

Hann, E., Mining Engineer. Hart, J. H. E., Civil Engineer, M.I.C.E. Hurst, J. T., C.E. Jauralcle, C.E., Madrid. Jeffcock, Parkin, Mining Engineer. Kaulbach, E. Lindner, Rudolph. Moncrieff, Capt. C. C. Scott, B.E. Müller, Moritz. Napier, B. D. Beid, W. F.

Richards, John, of Philadelphia, Mecha- nical Engineer. Selwyn, Capt. Jaspar H., R.N. Smith, Major-General M. W., C.B. Soames, Peter, M.I.M.E., A.I.C.E. Spence, Peter, F.C.S. Spencer, A. Spon, Ernest. Stevenson, Graham.

Tweddell, R. H., Mechanical Engineer. Wilson, Robert.

Among the able Authors from whose writings valuable information has been selected, the following may be mentioned ;

Addenbrooke, George. Allan, Alex. Anderson, Dr. John. Armstrong, Sir William. Atkinson, J. J.

Baker, W. Proctor. Beardmore, N. Bell, I. Lowthian.

Benson, Martin. Bloxam, C. L. Box, Thomas. Briggs, Robert. Brown, Henry T. Browne, W. R. Burgoyne, Major-Gen. Sir

John H. Burnell, G. R.

Carr, Thomas. Chapman, Ernest T. Clark, Latimer. Clift, J. E. ' Cochrane, Charles. Cochrane, W. Conrad, Chevalier. Coulthard, Hiram C. Cowper, E. A.

( ™i )

Craig, W. G.

*ö>

Culley, E. S.

Daglish, G. H.

Darcy, M.

D'Aubuisson de Voisins,

J. F. Dieudonné, C. Douglass, James N. Dru, M.

Eichhorn, Jacob. Elliot, George.

Fairbairn, Sir William. Fernie, John. Forsyth, W. Fothergill, B. Fowler, John. Francis, J. B.

Gale, James M. Gaudard, Jules. Greenwood, Thomas. Greig, David. Grubb, Thomas. Grubhard, A.

Hague, James D. Halsted, Admiral E.

Pelle w. Hamilton, Colonel, B.E. Harrison, T. E. Henderson, D. M. Henderson, James. Hewitt, Abram S. Hick, John. Higgin, George. Holley, Alex. L.

Imray, John. Inglis, William.

Jenkin, Fleeming. Joly, M.

King, Clarence. Kingsbury, W. F. Kirkaldy, David. Kirkwood, James P. Kirtley, William. Knight, Cameron.

Low, George. Lyall, Sir Charles.

Mallet, Bobert. Martin, Henry. Menalaus, William. Miller, Daniel. Morin, General A.

Naquet, A. Neville, John. Newland, J. Newton, A. Noble, Captain. Nystiom, John W.

Ott, A.

Overman, Frederick.

Paget, Arthur. Paul, Dr. B. H. Peclet, E. Percy, Dr. John. Périsse, Sylvain. Phillips, John Arthur. Piatt, John. Poncelet, J. Y. Porter, C. G. Prony, E. de.

Eamsbottom, John. Eankine, W. J. M.

Eaymond, E. W. Eeid, P. S. Eoebling, J. A. Eose, H. Eoy, Edmond.

Sabine, E. Samuelson, Alex. Samuelson, Bernhard. Sang, E. Scott, G. L. Scott Eussell, John. Scratchley, P. H. Shelley, Charles P. B. Slate, Archibald. Smith, Thomas. Sonnet, H.

Sopwith, Thomas, jun. Stanley, F. W. Stoney, B. B. Swindell, J. G. Symons, G. J.

Thornycroft, Thomas. Tinmouth, Nicholas. Towne, H. E. Truran, William.

Unwin, W. Cawthorn.

Yuillemin, L.

Waller, W. Wanklyn, Dr. Williams, Charles Wye. Williams, J. B. Wood, Nicholas.

PUMP. 2689

pipes would create a partial vacuum in that part of its motor cylinder ; but then the atmosphere pressing on the surface of the water in the cistern would at once opea the valve and admit as much water from the cistern as required to restore the necessary equilibrium. Other appliances for signalling a defect and instantly remedying it have been provided ; but we shall not describe them here.

By this system, the force developed by the motor may be transmitted to the pump without any other loas than that due to the friction of the water, which for a depth of a thousand feet will usually be less than 2 per cent, of the total force required to raise the water. It is applicable to water as well as to steam power, and the pumps being double-acting, no portion of the power of the water-wheel is lost. The pressure-pipes are fixed parallel to each other against the sides of the shaft, or upon the floor of a level, so that the space occupied by them is practically nothing. When used in the place of flat rods, that is, when carried horizontally from the engine-house or water- wheel to the shaft, they may be laid underground so as not to obstruct surface operations. One great advantage possessed by this system is the facility it affords for changing the direction. Provided sharp angles are avoided, the pressure-pipes may be carried along in all manner of direc- tions, as occasion and locality may require, without any appreciable loss of power.

Pumps for Surface-draining. The requirements of surface-draining, and the conditions under which a pump applied to that purpose has to work, are altogether different from those which we have been considering. In mines a comparatively small quantity of water has to be lifted to a great height, and the motor is, in most cases, necessarily situate a long distance from the pump. For surface work, such, for example, as draining a marsh, a large quantity of water is required to be lifted to a small height, and the motor may be placed close to the machinery to be driven. Generally the motor will be steam ; for it is rarely possible to obtain water-power in a convenient situation. In Holland wind is frequently employed for this purpose, but the variable character of this motor renders it unsuitable for pumping operations. It may, however, often be used as an auxiliary with great advantage. The kind of pump best suited for surface drainage is, in general, the centrifugal pump. The nature of this pump renders it peculiarly well adapted for this kind of work. It is exceedingly simple in construction, is easily erected, and requires no massive foun- dations. The absence of valves is a great advantage, as small pieces of wood, weeds, and other small floating substances, may be passed without choking the pump. An experiment was made some time ago with one of Appold's 12-in. pumps by throwing in all at once about half a gallon of nut-galls when working at full speed. They all passed through without one being broken. Also when the height of lift is small, a very large quantity of water may be raised a minute by a centri- fugal pump, a condition usually imposed by the nature of the work, and which this pump is there- fore capable of fulfilling. We have described and illustrated some of the best models under Hydraulic Machines, and hence it will be unnecessary to do more than refer to them here. In many cases, Murray's chain-pump may be applied to the purpose of surface drainage with advan- tage, especially when the area to be drained is small. It will be for the engineer to determine which of these kinds is the more suitable to the requirements of the case under his consideration.

Pumps for Water-supply. The requirements of this case are a large quantity of water to be raised to a considerable height, and a steady, continuous supply, requirements wThich neither the centrifugal nor the chain pump is capable of satisfactorily fulfilling. Reciprocating pumps are exclusively used for this purpose. Whether, however, the lifting or the forcing variety is the more suitable seems still to be an open question, judging from the want of uniformity in the practice of engineers. We have shown that whenever a considerable height of lift and a continuous working are conditions to be fulfilled, the force-pump possesses great advantages over the lift ; and it is satis- factory to see that the former variety is gradually coming into favour. No particular construction can be recommended for this case, as a great deal must depend on local circumstances. For a small supply an arrangement of Hayward Tyler and Co.'s Universal pump has been found to work very satisfactorily. It has been used at the Slough Water-works, and also, as an auxiliary, at the Tottenham Water-works.

Pumps for Raising particular Liquids. We have spoken of the corrosive properties of mine water, and the necessity of lining the working barrel and other working parts with brass, to enable them to withstand the corrosive action. This precaution is, however, insufficient in many cases where liquids of a particular nature have to be raised. Thus in chemical works pumps are required to raise strong acids and various other substances which would speedily destroy the working parts if constructed of ordinary materials. In paper-mills they are needed to raise the paper-pulp and bleachers ; in breweries, for raising the hot wort ; in gasworks, for pumping ammoniacal liquor and tar ; in tan-yards, for pumping tan liquor ; and also in town drainage works, for raising the sewage. The only kind of pumps suitable for these operations are the reciprocating kind, and of these the forcing variety is the best adapted for sewage, and, generally, the lifting variety for the other purposes mentioned. The fittings of pumps to be applied to any of these purposes should be of gun-metal. Cast-iron clacks are frequently used for pumping ammonia water ; but geuerally gun-metal should be adopted. In chemical works it is often necessary to employ india-rubber instead of metal for the valves. In Fig. 6420 we illustrate a pump specially designed for these purposes, having india-rubber valves and a glass cylinder. The design and construction of this pump, which is known as Perreaux's, are excellent. The working barrel A is made from the best plate glass bored out by machinery and polished. The bucket-valve B and the foot-valve C, shown in section in Figs. 6421, 6422, are of india-rubber, and the elasticity of the material is relied upon to close them. We are not aware of any experiments made to ascertain the amount of slip through these valves, but the principles we laid down in the former part of this article would lead us to expect very little. The mode of fixing these valves is so clearly shown in the figures that description is unnecessary ; we cannot, however, refrain from expressing our admiration of the very excellent nature of this mode, which is alike creditable to the designer and the constructor. The glass barrels are mounted in cast-iron suction-pipe and rising-main, with wrought-iron stretcher-

8 i

2690

PUMP.

rods and nuts, as shown in Fig. 6420. The valves may be mounted in brass, lead, or gun-metal, as required.

6420.

6421.

W^

rfti¿

rTSr

6422.

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A

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In raising hot liquids, such as the wort in breweries, suction cannot be employed by reason of the impossibility of creating a vacuum in consequence of the evolution of steam from the heated liquid. In such cases, therefore, the pump must be placed on a sufficiently low level to allow the liquid to enter by the force of its own gravity. When it is required to raise liquids of such a consistency as to be incapable of a rapid flow, as tar, for example, the motion of the pump should be slow, and the height of the suction should be reduced as much as possible. In such cases, the pipes and working barrel should never be of small diameter, and the valves should have a higher lift than is requisite for water. Also all contractions of the passages and changes of direction should be avoided, as they greatly impede the flow of thick liquids. These remarks apply, though in a less degree, to town sewage.

Pumps for Emptying Docks. The requirements of this case are similar to those of surface drainage, and therefore the same pumps may be applied to this purpose. It should be remarked, however, that the nature of the chain-pump renders it peculiarly suitable to the work of emptying a dock.

Contractors' Pumps. The chief purposes to which a contractor's pump is applied, are the removal of water from cuttings and other excavations, and the emptying of coffer-dams. The nature of the work, and the conditions under which it has to be executed, are such that a pump which is to be applied to these purposes must be simple in construction, capable of bearing rough usage, easily repaired when out of order, of such a nature that it may be readily erected in any locality, and as readily removed when circumstances require it, capable of raising a considerable quantity of water to a small height, and netd but little attention. The whole of these require- ments are fulfilled by the chain-pump, and accordingly we find this pump generally adopted. Of reciprocating pumps, Hayward Tyler and Co.'s Universal pump fulfils the above requirements, with the exception, perhaps, of that one which requires it to be capable of easy repair. This pump has been used on several engineering works recently, and appears to have given entire satisfaction. One advantage possessed by this pump is, that it may take its steam from a portable engine that is employed for other purposes, such, for instance, as sawing.

Bilge-pumps. Bilge-pumps are the pumps used on board ships to remove the bilge-water, that is, the water which lies upon the bilge or bottom of the vessel. In their simplest form they consist of a pump having a staff or rod 7 or 8 ft. long, with a bar of wood to which the leather is nailed, and which serves instead of a box. This staff is worked by men who pull it up and down with a rope fastened to the middle of it. Bilge-pumps as now used in all but the smallest vessels, have all the improvements that of late years have been effected in this kind of machinery. Usually they are

PUMP.

2691

force-pumps, and in steam-ships they are worked by the engine. In such cases they are capable of raising a large quantity of water at a stroke. As they differ in no essential particular from the pumps we have already described, it will not be necessary to describe them here. Among the best designed and constructed of this class of pumps are those manufactured by "Watt and Co. Cen- trifugal pumps have been successfully applied to this purpose.

Pumps for Supplying Hydraulic Machinery. The purpose of this class of pumps is to force water into a receiver against the pressure exerted by a heavy weight, or by the elasticity of the opposing substance. The former case is that of Armstrong's accumulator, into which the water is forced by the engine against the pressure often equal to 1500 ft. of water exerted by the loaded ram, the latter that of Brahma's press, into which the water is forced against the pressure due to the elasticity of the substance compressed. The only kind of pump applicable to this case is the reciprocating, and of these only the forcing variety. There is nothing particular to note in pumps applied to these purposes, beyond the necessity of adapting their details to the work they have to perform. The chief requirement is that their several parts shall possess sufficient strength to with- stand the pressure to which they will be subjected.

Feed-pumps. These belong to the same class of pumps as the preceding. They are required to force water into a boiler against the pressure of the steam, and hence are subject to the same con- ditions as those for supplying hydraulic machinery. A certain degree of modification in the case of feed-pumps is due to the fact that they usually work against a lower pressure than the latter ; but essentially the conditions are identical. The same kind and variety of pumps will therefore be requisite in this case. Feed-pumps have been fully treated of under Details of Engines, and we must refer the reader to that article for complete information on this subject.

Air-pumps. Air-pumps are employed either to exhaust the air contained in a given space, or to compress the air contained in that space. The latter are of the nature of the forcing pumps employed for liquids ; the former resemble the lifting pump. We have described and illustrated both kinds under Air-pump, Diving, and Details of Engines ; in the latter of these articles the air-pump, as applied to steam-engines, being fully discussed. Kecently, however, the compressing air pump has been applied to the setting of large iron columns in deep water, by expelling the water and mud from the bottom by means of compressed air instead of pumping it out of the top. The engineer of the new graving dock at Hog Island, Bombay Harbour, conceived the idea of setting the large columns, 6 ft. in diameter and 70 ft. in length, required for this work, in this way. To do this, however, an air-pump of great power and large volume was requisite. Such a pump was designed and supplied by Barnett and Foster, of London, and its use was attended with remarkable success. Fig. 6423 is a side elevation, and Fig. 6424 a section through one of the

B 6424- A

6423.

- A

r

ÍL—C

-|S7 -

cylinders of this large treble pump. These cylinders are 9 in. in diameter and 18 in. in length, the throw of the crank being 9 in., and the diameter of the latter 5 in. The leathering of the piston is on the principle adopted in hydraulic pumps, that is, it is so arranged that the pressine from within helps to tighten it. This arrangement is shown at C, Fig. 6424. The diameter of the inlet-valve B is in., and that of the outlet-valve A 2 in. There is a copper cooling cistern around the outside of the pumps. This cistern is a cylinder of larger diameter than the pump-cylinder, the annular space between the two being filled with water to prevent the latter from becoming heated, and so to preserve the air within the pump from being rarefied. The three pump- cylinders are connected at the top, as shown in Fig. 6423. and hence the stream of air is continuous. On the top of each cylinder there is a lubricating cup.

The mode of applying this pump to the setting of the columns was as follows ; The several pieces were bolted together above water in a massive framework, and lowered to receive a fresh one till the first touched the bottom. The hood was then fitted into the top, and the interior of the

8 T 2

2692 QUAKRYING.

column put into communication with the air-pump. The water contained in the column was thus forced down and out at the bottom, the time required to clear out the whole of the contents being less than half an hour. Such was the force of the pressure developed, that the whole column would frequently lift fully 18 in., letting the mud out at the bottom. When cleared, the columns were entered, and filled up to a height of 5 or 6 ft. with hard cement, thus converting them into a solid mass at bottom. When it is added that the power requisite to work the air-pump was only 6-horse, the superiority of this mode of emptying columns over that usually adopted of pumping the water out of the top will be readily acknowledged.

PUPPET. Fe., Poupée; Ger., Docke; Ital., Toppo; Span., Soporte de mandril.

The upright support of a mandrel in a lathe is termed the puppet or poppet. See Hand-Tools. Machine Tools.

PYROMETER. Fr., Pyromètre; Ger., Pyrometer; Ital., Pirometro; Span., Piròmetro.

A pyrometer is any instrument used for measuring degrees of heat above those indicated by the mercurial thermometer, and constructed usually on the principle of registering or measuring, by means of multiplying levers and a scale, the change in length of some expansible substance, as a metallic rod, when exposed to the heat, to be measured.

QUARRYING. Fr., Exploitation des carrières, Détacher le roc, les pierres; Ger., Gestein abtreiben; Ital., Cavare; Span., Cantería.

An excavation made for the purpose of obtaining stone is called a quarry. When the object sought is a metal or coal, the excavation is called a mine. A quarry is usually worked open to surface, and is never carried to a great depth ; a mine, on the contrary, is rarely worked to surface, and the depth to which it is sunk is in all cases considerable. Quarrying differs little from mining in principle beyond what follows, through the latter being essentially an underground operation.

Quarries are of two kinds, determined by the use to which the excavated material is to be applied ; and the mode of carrying out the work of excavation differs in detail in each of these kinds. When the stone is required for building purposes, it is requisite to extract it in that form from which the designs of the builder can be most readily obtained, and at the same time to avoid waste by breaking the stone in an undesirable manner. This necessitates a certain mode of operating, and some care and skill in conducting the operations. But when the shape and size of the pieces of stone extracted are immaterial, as, for instance, in the cases of chalk for lime, stone tor road construction and maintenance, or in cuttings through rock for a line of railway, the expe- ditious removal of the stone is the main object to be kept in view.

In quarrying for any of the above purposes, as, indeed, in all operations, a great object is to produce the greatest results with the available means. And to effect this object, it is necessary to study closely the formation of the rocks in which the excavation is to be made, so as to be able to take advantage of the natural divisions, and by that means to greatly lessen the labour of the quarryman. It must be borne in mind that all rocks belong to one or other of two great classes, namely, the stratified and the unstratified. The former are sedimentary rocks, occurring in parallel beds or strata, and include a large class of most valuable building materials, such as the magnesian lime, sand, and free stone, millstone grit, Yorkshire landings, and other well-known stone. Unstra- tified or igneous rocks, which include greenstone or whinstone, granite, and porphyry, have no distinct bedding, that is, they do not lie in separate layers. Roofing slate is a stratified rock, but it splits into thinner laminae in the direction of its cleavage than in that of its bedding, the former being often at right angles to the latter. Some igneous rocks, as granite, have also a natural cleavage, though not stratified. Advantage must be taken of all these peculiarities in order to carry out quarrying operations in an efficient and economical manner.

When the excavation is in stratified rock and the stone is required for building purposes, hand labour is generally preferred to blasting, especially when large blocks for columns, obelisks, tomb- stones, and similar objects are required. Such blocks are obtained from the more valuable parts of sandstone deposits, technically known as liver-rock; these are the thicker and more consolidated strata. Pieces of limited thickness, as flagstones, are obtained from the thinner beds termed bed-rocks. In quarrying by these means from stratified rocks, a sufficient surface of the rock is first laid bare parallel to the bed of deposit. This portion has then to be disconnected from the general mass by cutting through the stratum or layer, so that it may be removed by sliding upon its bed. To effect the operation, the quarryman, having previously marked out on the exposed surface the size and shape of the stone required, makes a number of small holes with a pick along the line drawn. The distance of these holes apart will depend upon the facility with which the rock can be cleaved. Wrought-iron steel-tipped wedges are then inserted in the holes and struck in succession with heavy hammers until the openings made by them extend from one to the other and also down through the stratum. The block is then free to slide upon its bed, and is removed from its original position by means of iron bars and levers. When the stratum is too thick to be divided in this way, and the stone is of a nature to yield readily to the cutting tool, which is usually a pointed hammer called a pick-hammer, the holes above referred to are sunk deeper, in the form of the letter y, and the wedges inserted in the bottom. Another mode, when the rocks are easily cleaved, is to insert another row of wedges parallel to the natural cleavage. By striking these simultaneously with the others a block is procured of less thickness than the stratum.

When the blocks have been removed from their natural position, they have still to be quarried into shape according to the purpose for which each piece is best suited. Thus, in a building-stone quarry, after the stones of unusual size and quality have been selected for the purposes mentioned above, the larger pieces are roughly formed into ashlar, window-sills, lintels, rybats, corners, steps, and the like, by means of picks, hammers of various kinds, and wedges. The small irregular-shaped pieces are called rubble, and are used for the commonest kind of building. Slates are split up into the requisite thickness by means of a broad chisel and mallet.

The methods we have described apply chiefly to quarries opened for the sole purpose of procuring building stone. But it behoves the engineer who has to execute an excavation in stratified rocks to

QUARRYING. 2693

consider whether the material removed may not be advantageously employed in the construction of his works, and if such be the case, whether he may not profitably adopt these methods in preference to others which, though more expeditious, spoil a large proportion of the stone.

When the rock is uustratified, or when the stratum is too thick to be disrupted by the wedge without great labour, recourse is had to the action of explosive agents. The explosives most frequently used for this purpose are gun-cotton, dynamite, and gunpowder. Dynamite is now often employed, and always with considerable success. The dangerous character of gun-cotton has hitherto prevented its adoption for ordinary operations, while the comparatively safe character and convenient form of gunpowder have commended it to the confidence of workmen, and hence, for quarrying operations, this . explosive is -generally employed. We shall therefore, in treating of blasting for stone, consider these operations as carried out by the aid of gunpowder alone.

The system of blasting employed in quarrying is that known as the small-shot system, which consists in boring holes from 1 to 3 in. diameter in the rock to be disrupted to receive the charge. The position of these holes is a matter of the highest importance, from the point of view of pro- ducing the greatest effects with the available means, and to determine them properly requires a complete knowledge of the nature of the forces developed by an explosive agent. This knowledge is rarely possessed by quarrymen. Indeed, such is the ignorance of this subject displayed by quarrymen generally, that when the proportioning and placing the charges are left to their judgment, a large expenditure of labour and material will produce very inadequate results. In all cases it is far more economical to entrust these duties to one who thoroughly understands the subject. The following principles should govern all operations of this nature ;

The explosion of gunpowder, by the expansion of the gases suddenly evolved, develops an enormous force, and this force, due to the pressure of a fluid, is exerted equally in all directions. Consequently, the surrounding mass subjected to this force will yield, if it yield at all, in its weakest part, that is, in the part which offers least resistance. The line along which the mass yields, or line of rupture, is called the line of least resistance, and is the distance traversed by the gases before reaching the surface. When the surrounding mass is uniformly resisting, the line of least resistance will be a straight line, and will be the shortest distance from the centre of the charge to the surface. Such, however, is rarely the case, and the line of rupture will therefore in most instances be an irregular line, and often much longer than that from thè centre direct to the surface. Hence in all blasting operations there will be two things to determine, the line of least resistance and the quantity of powder requisite to overcome the resistance along that line. For it is obvious that all excess of powder is waste ; and, moreover, as the force developed by this excess must be expended upon something, it will probably be employed in doing mischief by shattering stones which it would be desirable to preserve whole. Charges of powder of uniform strength produce effects varying with their weight, that is, a double charge will move a double mass. And as homogeneous masses vary as the cube of any similar line within them, the general rule is esta- blished that charges of powder to produce similar results are to each other as the cubes of the lines of least resistance. Hence when the charge requisite to produce a given effect in a particular substance has been determined by experiment, that necessary to produce a like effect in a given mass of the same substance may be readily determined. As the substances to be acted upon are various and differ in tenacity in different localities, and as, moreover, the quality of powder varies greatly, it will be necessary, in undertaking quarrying operations, to make experiments in order to determine the constant which should be employed in calculating the charges of powder. In practice, the line of least resistance is taken as the shortest distance from the centre of the charge to the surface of the rock, unless the existence of natural divisions shows it to lie in some other direction ; and, generally, the charge requisite to overcome the resistance will vary from -^ to -^ of the cube of the line, the latter being taken in feet and the former in pounds. Thus, suppose the material to be blasted is chalk and the line of least resistance 4 ft. The cube of 4 is 64, and taking the proportion for chalk as ^q, we have f^ = 2^- lbs. as the charge necessary to produce disruption.

In commencing quarrying operations, the first thing is to find an exposed surface behind which the charge may be placed so as to force it outwards. A vertical surface presents fewer difficulties than any other, both because the resistance in such a case is usually less, and because the proper placing of the charge may be more readily effected. When the blasting is in stratified rock, the position of the charge will frequently be determined by the natural divisions and fissures ; for if these are not duly taken into consideration, the quarryman will have the mortification of finding, after his shot has been fired, that the elastic gases have found an easier vent through one of these flaws, and that consequently no useful effect has been produced. The Hue of least resistance, in this case, will generally be perpendicular to the beds of the strata, so that the hole for the charge may be driven parallel to the strata and in such a position as not to touch the planes which separate them. This hole should never be driven in the direction of the line of least resistance, and when practicable should be at right angles to it.

The instruments employed in boring the holes for the shot are iron rods having a -wedge-shaped piece of steel welded to their lower ends and brought to an edge so as to cut into the rock. These are worked either by striking them on the head with a hammer, or by jumping them up and down and allowing them to penetrate by their own weight. When used in the former manner they are called borers or drills ; in the latter case they are termed jumpers. Recently power jumpers worked by compressed air, and drills actuated in the same manner, have been very successfully employed. Holes may be made by these instruments in almost any direction ; but when hand labour only is available, the vertical can be most advantageously worked.

The speed with which holes may be sunk varies of course with the hardness of the rock and the diameter of the hole. At Holyhead the average work done by three men in hard quartz reck with l£-in. drills was 14 in. an hour ; one man holding the drill, and two striking. In granite of good quality, it has been ascertained by experience that three men are able to sink with a 3-in.

2694

QUARRYING.

6426.

6425.

mm.

jumper 4 ft. in a day ; with a 2¿-in. jumper, 5 ft. ; with a 2|-in., 6 ft. ; with a 2-in., 8 ft. ; and with a If -in., 12 ft. A strong man with a 1-in. jumper will bore 8 ft. in a day. The weight of the hammers used with drills is a matter deserving attention ; for if too heavy they fatigue the men, and consequently fewer blows are given and the effect produced lessened ; while, on the other haud, if too light, the strength of the workman is not fully employed. The usual weight is from 5 to 7 lbs.

As the labour of boring a shot-hole in a given kind of rock is dependent on the diameter, it is obviously desirable to make the hole as small as possible, due regard being had to the size of the charge ; for it must be borne in mind in determining the diameter of the boring that the charge should not occupy a great length in it. Various expedients have been resorted to for the purpose of enlarging the hole at the bottom so as to form a chamber for the powder. If this could be easily effected, such a mode of placing the charge would be highly advantageous, as a very small bore- hole would be sufficient, and the difficulties of tamping much lessened. One of these expedients is to place a small charge at the bottom of the bore and to fire it after being properly tamped. The charge being insufficient to cause fracture, the parts in immediate contact with it are compressed and crushed to dust, and the cavity is thereby enlarged. The proper charge may then be inserted in the chamber thus formed by boring through the lamping. Another method, applicable chiefly to calcareous rock, has been tried with satisfactory results at Marseilles. When the bore-hole has been sunk to the required depth, a copper pipe, Fig. 6425, of a diameter to fit the bore loosely, is introduced, the end A reaching to the bottom of the hole, which is closed up tight at B with clay so that no air may escape. The pipe is provided with a bent neck C. A small leaden pipe about | in. in diameter, with a funnel / at the top, is introduced into the copper pipe at D and passed down to within about an inch of the bottom. The annular space between the leaden and copper pipes at g is filled with a packing of hemp. Dilute nitric acid is then poured through the funnel and leaden pipe. The acid dis- solves the calcareous rock at the bottom, causing an effervescence, and a substance containing the dissolved lime is forced out of the orifice C. This process is continued until from the quantity of acid consumed it is judged that the chamber is sufficiently enlarged. Other acids, such as muriatic or sulphuric, will produce the same eflects, but the result of the chemical solution will of course depend upon the nature of the stone.

After the shot-hole has been bored, it is cleaned out and dried with a wisp of hay, and the powder poured down ; or, when the hole is not vertical, pushed in with a wooden rammer. The quantity of powder should _ always be determined by weight. One pound, when loosely poured out, will occupy about 30 cub. in., and 1 cub. ft. weighs 57 lbs. A hole 1 in. in diameter will therefore contain '414 oz. for every inch of depth. Hence to find the weight of powder to an inch of depth in any given hole, we have only to multiply •414 oz. by the square of the diameter of the hole in inches, and we are enabled to determine either the length of hole for a given charge, or the charge in a given space. It is important to use strong powder in blast- ing operations, because, as a smaller quantity will be sufficient, it will occupy less space, and thereby save labour in boring.

When the line of least resistance has been decided upon, care must be taken that it remains the line of least resistance; for if the space in the bore-hole is not properly filled, the elastic gases may find an easier vent in that direction than in any other. The materials employed to fill this space are, when so applied, called tamping, and they consist of the chips and dust of the quarry, sand, well-dried clay, or broken brick or stones. Various opinions are held concerning the relative value of these materials as tamping. Sand offers very great resistance from the friction of the particles amongst themselves and against the sides of the bore-hole ; it may be easily applied by pouring it in, and is always readily obtain- able. Clay, if thoroughly baked, offers a somewhat greater resistance than sand, and, where readily procurable, may be advantageously employed. Broken stone is much inferior to either of these substances in resisting power. The favour in which it is held by quarrymen, and the frequent use they make of it as tamping, must be attributed to the fact of its being always ready to hand, rather than to any excellent results obtained from its use.

To lessen the danger of the tamping being blown out, plugs or cones of metal of different akapes are sometimes inserted in the hole. The best forms of plug are shown in Figs. 6426, 6427 ; Fig. 6426 is a metal cone wedged in on the tamping with arrows, and Fig. 6427 is a barrel-shaped plug. These mechanical contrivances are employed only in particular circumstances, such as blasting in a shaft ; but their efficacy may well be doubted.

RAILWAY ENGINEERING. 2695

In determining the most economic method of obtaining a given quantity of stone from a quarry of any particular description of rock, it is necessary to ascertain, first, the speed with which the bore-holes may be sunk; second, the effects of certain agents, such as small charges or acids, in enlarging the chamber at the bottom ; third, the constant from which the charge is to be calculated ; and, fourth, the height of face that can be obtained in the quarry. The latter is a very important question economically, for it is obvious, since the charge is placed behind the face, that the higher that face is, the larger will be the mass of rock dislodged. When the face is low, the charge has the same mass to act upon as when the face is high ; but in the latter case, a much larger mass is dislodged by its own weight. After these data have been determined, the size of the block required must be considered, and a large charge, or a succession of small charges, applied accord- ingly. In some quarries large charges are always preferred on account of the less frequent necessity of clearing the quarry of the workmen. To fire the charge a Bickford's fuze is generally employed ; this fuze is inexpensive, very certain in its effects, not easily injured by tamping, and is unaffected by damp.

In excavating rock for a railway cutting, a gullet or small cutting is first carried throughout the work, and it is of the highest importance that this gullet should be carried down to the full depth of the cutting. The gullet is then widened by blasting down the faces. The economy of these operations depends in a very high degree upon the skill with which the charges are applied. There is a case on record in which a railway cutting through hard rock was carried down by blast- ing to a depth of 2 or 3 ft. less than was required of the contractor. To remove these 2 or 3 ft. by band labour, cost about a guinea a cubic yard, whereas the rest of the cutting averaged only 3s. 6d. Had the gullet been taken out to the required depth in the first instance, and the charges placed lower, the same quantity of powder would have been sufficient to complete the work.

In quarrying, as in mining, much of the cost is incurred for the removal of water from the workings. A set of pumps and a steam-engine, or a water-wheel where water-power