a term used by the engineer and miner to denote the application of the explosive force of gunpowder in opening or rending rocks, indurated clay, consolidated earth, and the walls of buildings. In quarrying sandstone, consisting of regular layers, the work is performed chiefly by means of the pick, the wedge, the hammer, and the pinch or lever; but for many kinds of limestone, and for greenstone and basalt, blasting is always resorted to. Most of the primary and transition rocks, and nearly all of the trap or igneous rocks, such as basalt, greenstone, porphyry, amygdaloid, &c., called primitive, could scarcely be torn asunder by any other means.

At what period blasting with gunpowder was first resorted to as a power in mechanics, is uncertain. Gunpowder was applied to military engines in 1312, but there is reason to believe that its application to the peaceful arts is of a much later date. It may seem strange at this day to propose the expansive or explosive force of gunpowder as a new mechanical power; but when the lever and the wedge become inefficacious for the purposes of the artificer, he must naturally attach a high value, and be disposed to apply an elevated term, to that instrument or means by which he is enabled, in a very simple manner, to effect his purpose, and overcome the greatest obstructions to his operations.

This agent is no less simple in its application than it is powerful in its effects. It is considered as the result of the sudden extrication of a permanently elastic fluid by the ignition of the gunpowder, the extricated gas occupying about 472 times more space than the grains of the powder. Some authors are of opinion that the powder contains only atmospheric air in a state of great condensation, and that, when this fluid is set at liberty, being at the same time highly rarefied by the heat, from the inflammation of the powder, it produces the wonderful effects already mentioned. By others, it is supposed that the air contained in the nitre of gunpowder is about 236 times denser than atmospheric air, and that, when exploded, it produces an effect proportioned to its condensation; the elastic fluid expanding with a velocity which has been calculated at the rate of about 10,000 feet per second; and its pressure or force, when thus expanding, having been estimated as equal to a thousand atmospheres, or as a thousand times greater than the atmospheric pressure upon a base of the same extent. If we apply this product to the pressure of the atmosphere, or at the rate of 143 pounds to the square inch, we shall find that the elastic fluid of gunpowder, at the moment of explosion, exerts a force equivalent to 6½ tons upon the square inch of surface exposed to its force. Count Rumford, indeed, estimated this force at 10,000 atmospheres; but we have rather followed the calculations of Hutton, whose opportunities of experiment, connected with the military college of Woolwich, were unquestionably great.

In Europe, the art of mining was long chiefly confined to Sweden and Germany; but since the disappearance of our thickly wooded forests, and the universal introduction of pit-coal for fuel, and of cast-iron in the arts, Great Britain has made rapid strides towards perfection in the art of mining; and now rivals her Continental neighbours. Here we may allude to the coalworks of Northumberland and Durham, of Cumberland, and the western counties of England and Wales. We may also notice the great extent of similar works in the south-eastern and south-western districts of Scotland. Much of this kind of work is done with the pick and shovel; but without the aid of the expansive force of gunpowder these operations must have been of very limited extent. Other works of no less magnitude than those of coal-mines have been executed in Great Britain, almost wholly by the force of gunpowder. To illustrate more fully the use of gunpowder in mining operations, we may mention the extensive works in tunnelling for railways, and for preserving the level of canals, instead of forming locks, or following a circuitous line of navigation. The bold attempt of blasting rocks under such circumstances was, in this country, reserved for Brindley, the engineer upon the Duke of Bridgewater's canals, who in 1776 completed the first navigable tunnel, at Harecastle in Staffordshire, upwards of a mile in length. Since that period the art of blasting has been extensively practised in a great variety of works, and carried to a wonderful degree of perfection.

When a perforation is to be made in a rock for the purpose of blasting with gunpowder, the nature of the rock, and the inclination or dip of the strata, determine the calibre, and the depth and direction of the bore or recipient for the gunpowder. According to circumstances, the diameter of the hole varies from half an inch to two and a half inches, the depth from a few inches to many feet; and the direction varies to all angles from the perpendicular to the horizontal. The implements for the performance of this operation are extremely simple; and the whole operation of boring and blasting rocks is so easily performed, that, in the space of a few weeks, an intelligent labourer may become an expert quarryman. The chisel, or jumper as it is technically called, varies in its length and other dimensions according to the work to be performed, and its edge is more or less pointed to suit the hardness or tenacity of the rock to be bored. If the cylindrical hole to be drilled is of small diameter and of no great depth, as often happens, the operation of boring is performed by a single person; with one hand he manages the chisel or jumper, which he keeps continually turning, and with the other he strikes the jumper with a hammer of six or eight pounds weight. But when the hole is of larger dimensions, and of a depth exceeding a foot, it generally becomes the business of one man, in a sitting posture, to hold and direct the jumper, to keep it constantly turning, to supply the hole with water, and occasionally to clean it out, while two, and even three men, with hammers of ten or twelve pounds weight, strike successive blows upon the jumper, until the rock is perforated to the desired depth.

To prevent annoyance to the quarrymen from the squirting up of the water, a small rope of straw or hemp is simply twisted round the jumper, and kept resting on the orifice of the hole. When the perforation is to be made to a greater depth than about thirty inches, a chisel or jumper is used, varying in length from six to eight feet, pointed at both ends, and having a bulbous part in the middle for the convenience of holding it. It thus becomes a kind of double jumper, and is used without a hammer, with either end put into the hole at pleasure. When a bore of considerable depth is to be made, after the hole has been perforated a few inches with the common jumper, the quarrymen lay it aside, and, collecting round the long jumper, lay hold of it by the bulbous part, lifting and letting it drop into the hole by its own gravity. In this manner, a hole to the depth of five feet and upwards is perforated by the workmen with ease and with great expedition. A very ingenious and expeditious method, borrowed from the Chinese, is by means of a jumper of very considerable length and weight, suspended and worked by a rope passed over a wheel; and which thus acquires, by the twisting and untwisting of the rope, the requisite rotatory motion. The jumper is hollow, and is so contrived as to receive and retain the debris, by means of valves opening inwards. When the boring is completed, the debris and moisture are carefully cleaned out, and the charge of powder is put into the hole. In practice, there was formerly no very precise rule for the quantity of the charge, this being regulated at the discretion of the quarryman, according to the tenacity and mass of the rock to be removed; and these circumstances having been previously considered in the dimensions of the bore, it is customary to fill the hole in the proportion of about one-half with gunpowder.

Of late the experiments and observations of Sir John Burgoyne and others, which were conducted more exactly than those of former years, seem to have fully established the propriety of proportioning the charges to the cubes of the lines of least resistance, which is the law that theory would assign for rocks of uniform consistence and cohesion. The line of least resistance is the distance between the bore and the open side of the rock, measured in the direction in which the resistance to the explosion is least. In the chalk excavations on the South-Eastern railway, where the blasts were on the largest scale of any work hitherto executed, the charge in pounds for that kind of work was found in practice to be in the proportion of $\frac{3}{4}$ of the cube of the line of least resistance in feet. To assist in calculating the charges, it may be useful to remark that 1 lb. of loosely poured powder occupies about 30 cubic inches, so that a cubic foot will weigh about 57½ lb.

After the charge has been introduced, which should be done by means of a copper tube extending down to the bottom of the bore, a long iron, called the pricker, is inserted amongst the powder, to be afterwards withdrawn when the priming powder is introduced. While this rod remains, the process of ramming or stemming the hole is performed by forcing burnt clay, fragments of pounded brick, stone, or any other substance less liable than another to produce sparks of fire on being struck with iron. After a stratum of such matter has been pressed down upon the powder, the hole is filled up with pounded stone or earthy matters of any kind, forced down with an iron punch or rammer of such dimensions that it nearly fills the hole, but having a groove in it to receive the pricker. The rammer being flat at the end which enters the hole, the fragments of stone are pounded by it round the pricker, which must be occasionally turned to prevent it from becoming too firmly fixed to be withdrawn. This wadding or matter laid immediately over the powder is forced down gently at first, lest it should explode prematurely; but as the hole is more and more filled up, the quarryman strikes down the stemmer with more violence, and consolidates the wadding as much as possible, with a view to produce a greater effect by the shot. In this operation consists the chief danger attending the process of blasting; for it must be obvious, that unless the utmost care be taken in forcing down the first portions of the wadding above the powder, there is great danger of such a collision taking place between the stemmer and the pricker, or between either of these and the rock or sides of the hole, as may elicit a spark of fire, and produce an explosion. From this cause, indeed, the most dreadful accidents have sometimes happened to quarrymen. It is necessary, as before noticed, frequently to turn the pricker during the process of stemming the shot; and it has been known that, by the friction produced in the mere act of turning it unguardedly, the shot has been fired. Blasting.

To prevent accident in this way, copper prickers, or, to save expense, prickers composed partly of copper and partly of iron, have been introduced. The copper pricker is certainly much less hazardous; but notwithstanding that this fact is self-evident, and has been clearly established in quarries where copper and iron prickers have been used at the same time, yet, from the greater expense of the copper, and its being more liable to twist and break, it is not yet in universal use.

The hole being now fully charged with the powder and wadding, the pricker is drawn out; and the small tubular space which it leaves is sometimes wholly filled with powder. But with a view to save that expensive article, it is common to insert wheaten or eaten straws filled with powder. These straw tubes may be joined so as to reach any necessary depth, the lower straw always terminating in the root part, where a natural obstruction occurs, or it is artificially stopped with clay. The lower part of the priming straw is pared very thin, so as to insure the inflammation of the charge of powder in the hole. A slow match, consisting generally of soft paper, prepared by dipping it into a solution of saltpetre, is then carefully applied to the priming powder. When this match is touched with fire, the quarriers give the alarm to all around to retire to a sufficient distance, so as to avoid accident from the expected explosion. This commonly takes place in about a minute. The priming first explodes, attended only with flame; then the rock opens with a sharp report, and fragments of stone are shot into the air in all directions, from amidst a cloud of smoke.

When blasting is carried on in confined situations, where the workmen cannot get speedily out of the reach of the shot, or where adjoining houses, &c., may be in danger of being injured, it is common to load or cover up the rock to be blasted with a quantity of furze or brushwood, loaded with stones or chains to prevent the fragments being driven to a distance.

It was long supposed that the more firmly the shot was rammed home, by means of a punch or hammer, the more powerful would be the effect of the explosion. This, we know, was long the conviction of military engineers, and was also a principle invariably adopted by miners, to the great personal hazard of the artificer. It has however been, we think, sufficiently established that a wadding or tamping of loose sand, or of any earthy matter in a dry state, answers all the purposes of the firmest ramming or wadding. Now, as it is in the operation of ramming that accidents most commonly befall the quarryman,—accidents which the use of the copper-pricker cannot altogether prevent,—it is surprising that the use of sand is not universal.

It may be noticed, that in several works this method is adopted, particularly at Lord Elgin's extensive mining operations at Charlestown in Fifeshire, where much attention is paid to the security and comfort of the artificer, as well as to everything interesting to science. The practice of using loose sand instead of pounded stone rammed with force, has been in use at these works for many years,—it is believed since about 1810. The writer of this article has also had considerable opportunities of trying the accuracy of these statements, as to the efficiency of sand, at the extensive quarrying operations which became necessary in cutting down a part of the Caltonhill, to form the new approach to the city of Edinburgh, where upwards of 100,000 cubic yards of rocky matter were removed, and gunpowder to the value of nearly L1,000 sterling was expended, chiefly in blasting rock, consisting of whinstone or greenstone, much traversed by calcareous spar. The holes at this work were bored of various dimensions, both as to calibre and depth, and also at all the angles of inclination, from the perpendicular to the horizontal. Trials were here made with holes from three to seven or eight feet in depth, and from an inch to two and a half inches in diameter; and it was invariably found, that when the powder was tamped with sand, the effect in tearing or blasting the rock was as great as when the more common method of ramming with pounded stone was adopted. In the judgment of the contractors, the fragments of rock had a greater tendency to fly to a distance when sand only was employed; but there was as great a bulk of the rock raised by the shot wadded with sand as by that which was rammed in the usual way; and in practice it was found that the shots with sand were not more liable to fail, or blow without doing execution, than those which were rammed. It is a fact perhaps as curious and interesting as any connected with the subject, that in both ways the shots fail, and at times blow out, without producing any effect, or being occasioned by any apparent cause.

When sand is used immediately above the powder, both the pricker and the rammer are wholly unnecessary: the primed straw being inserted into the powder, the sand is poured into the hole, and the shot is ready for the match. But a difficulty occurs in the use of sand, which, though easily surmounted, it may be proper to notice. When the explosion happens to be horizontal, or at more than an angle of 45° from the perpendicular, the priming straw is apt to be injured in filling the hole with sand, an evil to which the pricker is not liable; but this is easily got over by inserting the priming straw into a small cylindrical tube of sheet-iron or copper, while the sand is gently pressed into the hole; and the small tube, which is open at both ends, is afterwards withdrawn. By this means the operation of the horizontal shot is rendered not less sure, and is attended with no greater expense, and little more trouble, than when the bore is perpendicular.

It is proper to observe, however, that although hard stemming of broken stones with punches or hammers is generally disapproved of, there is still some diversity of opinion among writers on the subject as to the use of sand tamping. General Pauley and some other experimenters contend for the superiority of clay over sand in every case, and especially for short bores.

It has been supposed by some that a more complete inflammation of the powder would take place if it were ignited at the bottom of the hole; but it has been found, from experience, that gunpowder is even more fully inflamed by der applying the fire near the top; for, in firing ordnance, considerable quantities of the unflamed grains of the powder have been collected, by placing a piece of cloth at a distance from the gun, and allowing the shot to pass through it.

Quick-lime, suddenly slackened, has been suggested as a mode of rendering rocks; but this process would in practice quick-lime be found very defective. In some situations where the explosive effects of gunpowder could not be applied with safety, as in the interior of a building, or for such like purposes, this mode may be resorted to with good effect.

Blasting with gunpowder under water is necessarily performed in various operations of the engineer, particularly in under the excavation of the foundations of piers, and in deepening water, the entrances of harbours. This used to be done by inserting the charge of powder into the perforated rock by means of a case or cartridge made of tin-plate. The lower part is made to fit the bore in the rock as nearly as may be; and from this a small pipe of the same metal, with the priming powder, is carried to the surface of the water. Here wading is unnecessary, the pressure of the water upon the tin case superseding the necessity of any; and the explosive effects are generally greater, in proportion to the charge, than those in the open air. The use of tin tubes in submarine blasting has now been wholly abandoned, since the introduction of Beckford's patent fuse, which may with strict propriety be called one of the greatest modern improvements in blasting. The fuse is alike applicable to the removal of rock thirty feet under water, as to all situations where the rock is spongy or full of springs. The charge is contained in water-proof bags, and the fuse, which may be described... Bleaching, as a perforated water-tight rope or hose, is attached to the shot-bag; and the inflammable composition in the fuse is thus kept in contact with the charge. The fuse itself is of length sufficient to reach the inside of the diving-bell, or, where that is not used, it must be of length to come above the water. It burns at the rate of from two to three feet per minute. When the fuse is used above water in damp quarries, the shot-bags may, for economy, be made of strong brown paper twice oiled, instead of tarred canvas. It may here be observed, that explosions under water have in some instances been proposed as a mode of attack in marine warfare; and it is presumed that explosions at considerable depths might occasion such an impression on the water, and so disturb the equilibrium of the atmospheric pressure, as to be capable of sinking large ships or floating batteries.

The mode of firing the charge by galvanism is a modern improvement of very great importance, and has the advantage of being equally applicable to submarine and to ordinary blasting. All that is necessary is to make a small interruption in the conducting wire in contact with the charge. In passing the electric current, a spark is produced at the interruption sufficient to fire the charge. It is instantaneous, and enables the operator to fire simultaneously any number of charges, according to the effect desired to be produced. The application of galvanic firing to submarine charges was first put into practice by General Pasley, in 1839, on the wreck of the Royal George at Spithead. It was also used in the same year, at the Skerryvore rock, by Mr Alan Stevenson. The simultaneous firing of several charges was extensively employed by Mr William Cubitt in the blasting near Dover in 1843. Three charges of 18,000 lb. of gunpowder were simultaneously fired by this means. Roundown Cliff, about 400 feet high, was thrown down, with comparatively little explosion, and covered the beach with 400,000 cubic yards of chalk rock; producing a saving of £7,000 to the South-Eastern Railway Company in this part of their works. This method of blasting is now extensively employed in various parts of the country.

Gun-cotton has also been employed in blasting, especially on the Manchester and Huddersfield railway in Standedge tunnel, and on the works in the Stour Valley near Birmingham. It has been stated that gun-cotton produces a much greater effect, weight for weight, than gunpowder, in the proportion of 3 to 1. This seems an exaggeration; but the disruptive effect really seems to be greater from gun-cotton; and as it gives no smoke, in confined situations the workmen are enabled sooner to resume their work.

It may also be mentioned, that an instrument called the Blasting Screw has been applied with considerable success to the rending or splitting of large trees and logs of timber. It consists of a screw which is wrought into an auger-hole, bored in the centre of the timber; here the charge of powder is inserted, and the orifice of the hole in the log is then shut up or closed with the screw, when a match or piece of cord prepared with saltpetre is introduced into a small hole left in the screw for this purpose, by which the powder is ignited. The application of this screw to the purposes of blasting is not very obviously necessary, because, from what we have seen, it would appear that the anger-hole, being charged with powder and sand, would answer every purpose. One great objection to the process of blasting applied to the rending of timber is, the irregular and uncertain direction of the fracture, by which great waste is sometimes occasioned. It may, however, be necessary to resort to this mode of breaking up large trees, when cut down and left in inaccessible situations, where a great force of men and of implements cannot easily be procured or applied.

See Treatise of Artillery, by John Muller; Hutton's Mathematical Dictionary; Robins's New Principles of Gunnery, by Dr Hutton; Nicholson's Journal, vols. xii. and xiii.; Papers of Corps of Roy. Eng., vols. iv. and vi.; Rudimentary Treatise on Blasting and Quarrying Stone, by Sir J. Burgoyne, Lond. 1849; Stevenson's Skerryvore Lighthouse, Edin.1848; Pasley's Memoranda on Blasting; London Electric Soc. Trans., 1839. The reader is also referred to Voltaic Electricity for later methods of Blasting. (t.s.) (t.s.)