BLASTING is 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 old 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; recourse being seldom had to the more violent and irregular effects of gunpowder. But for many kinds of limestone, and for greenstone and basalt, blasting is always resorted to; and some of the rocks called primitive, such as granite, gneiss, and sienite, 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 1330, 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 mechanicalpower; but when the lever and the wedge become ineffectual to the purposes of the artificer, he must naturally attach a high value, and be disposed to give 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. One could almost, therefore, wish it dignified with such a title as the explosive power.

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 the 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 14^ pounds to the square inch, we shall find that the elastic fluid of gunpowder, at the moment of explosion, exerts a force equivalent to 6⅜ tons upon the square inch of surface exposed to its force, and that with a velocity which even the imagination can hardly follow. 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, have been unquestionably great.

The progress of quarrying and blasting rocks has of late years made great advancement in this country. 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 to improvement 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 the like works in the south-eastern and south-western dis-triets[7:4:676] 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 a 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, particularly in canal and road-works. To illustrate more fully the use of gunpowder in mining operations, we may mention the extensive works in tunnelling, for preserving the level of canals through mountainous districts of country, 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 Mr Brindley, engineer upon the Duke of Bridgewater’s canals. In 1776 this celebrated engineer completed the first navigable tunnel, at Hareeastle in Staffordshire, which is upwards of one mile in length. Sinee that period, many other works of a similar nature, and even of much greater extent, have been executed in various parts of Europe. By the art of blasting, immense exeavations have been made upon the great canal in Sweden. In France a tunnel of about seven miles in length has lately been completed; and in our own country, at Sapperton, on the canal joining the rivers Severn and Thames, and at Marsden-hill, there is a tunnel upwards of three miles in length, forced entirely through rock by means of gunpowder. We may also instance the great national work of the Caledonian Canal. In all of these works, in road-making, and many others intimately connected with the prosperity of commerce, the extension of the arts, our domestie comfort, and national importance, it is most evident that, but for the simple process of applying the expansive force of gunpowder, we must have been deprived of innumerable advantages and accommodation.

When a perforation or hole is to be made in a rock for the purpose of blasting with gunpowder, the prudent quarrier considers the nature of the rock, and the inclination or dip of the strata, and from these determines the calibre, and the depth and direction of the bore or recipient for the gunpowder. Aeeording 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 the angles from the perpendicular to the horizontal. The implements for the performance of this operation are rude, and so extremely simple and familiar as hardly to require description; 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 quarrier. The tools are few in number, and, as we have just said, simple in their construction. 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 tenaeity of the rock to be bored. If the eylindrical hole to be drilled is of small diameter and of no great depth, or the work fixed to a confined position, 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 whole 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. 1o prevent annoyance to the quarriers 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 perforations are to be made to a greater depth than about thirty inches it is now common to use a chisel or jumper, varying in length from six to eight feet, pointed at both ends, 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 quarriers lay it and their hammers aside, and collect round the long jumper, in a standing posture, and lay hold of it by the bulbous part, lifting and letting it drop into the hole by its own gravity; in this manner, by the successive strokes or falling of the long jumper, a hole to the depth of five feet and upwards is perforated, with much ease to the workmen, and with wonderful expedition. When the boring of the hole is completed, the débrìs and moisture are then carefully cleaned out, and a proper charge of powder is put into it. In practice, there is no very preeise rule for the charge or quantity of gunpowder, this being regulated at the discretion of the quarrier, 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 it in the proportion of about one half with gunpowder.

The charge being introduced into the cylindrical hole bored or drilled in the rock, 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 layer or stratum of such matter has been pressed down upon the powder, the remaining depth of the hole is filled 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 prieker; the rammer being flat at the end which enters the hole, the fragments of stone are pounded by it round the prieker, which must be occasionally turned to prevent it from being too firmly fixed, and thereby prevented from being drawn. This wadding or matter, laid immediately over the powder, is gently forced down at first, to prevent, as much as possible, the danger of premature explosion; but as the hole is more and more filled up, the quarrier strikes down the stemmer with more violence and less care, 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 with gunpowder; for it must be obvious, that unless the utmost care be taken in foreing 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 prieker, or between either of these and the rock or sides of the hole, as may elicit a spark of fire, and produce an unintentional explosion. From this cause, indeed, the most unfortunate and distressing accidents have sometimes happened to quarriers. A ease occurred under the notice of the writerorthis article, from which an experienced workman lost the sight of both his eyes, and had his legs and arms much shattered. It is necessary, as before noticed, frequently to turn the prieker during the process of stemming th shot, in order to prevent its being so bound by the wadding as to prevent its being withdrawn; and it has been known that, by the friction produced in the mere act o turning it unguardedly, the shot has been fired off. 1 ¢ [7:4:677]prevent accident in this way, copper prickers, or, to save expense, prickers composed partly of copper and partly of iron, have been introduced, instead of those formed wholly of iron. The copper pricker is certainly much less liable to accident; 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 has by no means come into general 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 now common to insert wheaten or oaten straws filled with powder. Thèse straw tubes may be joined so as to reach any necessary depth, the lower straw always terminating i∙n the root part, where a natural obstruction occurs, or it is artificially stopped with clay, to prevent the powder from being lost. The lower part of the priming straw is pared quite thin, so as to insure the inflammation of the charge of powder in the hole. This being done, a slow match, consisting generally of a bit of soft paper, prepared by dipping it into a solution of saltpetre, is 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; a short interval of suspense commonly ensues; the eyes of the byestanders being anxiously directed towards the spot; the rock is instantly seen to open, when a sharp report, or a detonating noise, takes place, and numerous fragments of stone are observed to spring into the air, and fly about in all directions, from amidst a cloud of smoke. The quarrier then returns with alacrity to the scene of his operations. When blasting with gunpowder is carried on in coal-pits or in sinking wells, where the workmen cannot get speedily out of the reach of the shot, or in any situation where adjoining houses, &c. may be in danger of being injured, it is common to load or cover up part of the rock to be blasted with a quantity of furze or brushwood, to prevent the fragments of blasted rock from being driven to a distance.

The simplicity of this operation, so important to our means of quarrying or prying into the bowels of the earth, is perhaps one cause of so little attention having been paid to it by persons of science; while the personal risk attending it may have also operated in some measure to prevent particular inquiries regarding it. It was an extremely natural conclusion for the quarrier to suppose, that the more firmly the shot was rammed home, 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. In many places this notion still prevails, and we cannot enough lament the force and stubbornness of custom in this instance, as it has been fully established that a wadding 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 quarrier, and which the use of the copper pricker cannot altogether prevent, it is not a little surprising that the use of sand does not become universal.

To the common-labourer, indeed, it naturally seems somewhat paradoxical to say, that particles of loose sand can produce an effect equal to stemming a shot with an iron punch and hammer; but those who are better informed should insist on the use of sand, whereby the person of the quarrier would be much less exposed, and much time and trouble would be saved. It may be noticed, that in several works this is observed, particularly at Lord Elgin’s extensive mining operations at Charlestown in Scotland, where much attention is paid to the security and comfort of the artificer, as well as to every thing interesting to science. The practice of using loose sand instead of pounded stone rammed with force, has been in use at these works for several years,—it is believed since about the year 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 matters were removed, and gunpowder to the value of nearly L.1000 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 wadded with sand, the effect in tearing or blasting the rock was as great as when the more commonly followed 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. Reasoning from the simultaneous effects of the sudden extrication of the elastic fluid of gunpowder, whether a wadding of loose sand or of firmly pounded stone be employed, trial was made of gunpowder without any wadding; but the effect produced by this method was rather to shake or rend the upper part, near the orifice of the hole or surface of the rock, than at the bottom of the hole. This fact, however, favours the conclusion that the explosive force of gunpowder is in proportion to the surface upon which it acts; and that the effect is so instantaneous, that it seems a matter not essentially connected with the operation, in what manner the wadding is effected, provided that the atmospheric air is not in immediate contact with the powder; as otherwise the fluid appears to divide, and its effects to be lost in space, without being applied chiefly at the bottom of the hole, where the greatest execution is wished to be done.

It may be noticed, that although the use of sand for blasting in mining operations is by no means general, yet so much of this practice has obtained, that the quarrier is now only at pains to ram an inch or two of the lower wadding firmly home; the upper parts are done loosely, with little attention either to the stuff employed, or to the ramming of it; and he merely consolidates it in such a manner that the broken particles shall not fall into the charge amongst the powder when he withdraws the pricker. This is, to a certain extent, a saving of time; but unfortunately the quarrier still undergoes much personal risk, the chief danger being in ramming at first, or in the turning or withdrawing of the pricker, where the wadding is firm. When sand is used immediately above the powder, both [7:4:678]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 in this place. When the hole or perforation in the rock 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 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 by experience that this is not essential. It even appears from experiment, that gunpowder is more fully inflamed by applying the fire near the top, for, in firing ordnance, considerable quantities of the uninflamed 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 slacked, has been suggested as a ’ ∙ mode of rending rocks; but this process would in practice 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 the excavation of the foundations of piers, and in deepening the entrances of harbours. This is performed 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; from this a small pipe of the same metal is carried to the surface of the water, with the priming powder. Here wadding is unnecessary, the pressure off 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. 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 iïŉpression on the water, and so disturb the equilibrium of the atmospheric pressure, as to be capable of sinking large ships or floating batteries.

It may also be mentioned, that a new instrument, called the Blasting Screw, has been lately 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 auger-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 J⅛- thematical Dictionary; Robins’s New Principles of Gunnery, corrected and enlarged by Dr Hutton; and Nicholson’s Journal, vols. xii. and xiii.