When a perforation or hole is to be made in al 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. Ac cording to circumstances, the diameter of the hole varies from half an inch to 21- inches, the depth from a few inches to many feet, and the direction walks to all the angles from the perpendicular to the hori zontal. The implements for the performance of this operation are rude, and so extremely simple and fa miliar, 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 quer rier. The tools are few in number, and, as just said, are simple in their construction. The chisel, or jumper, as it is technically called, varies in its length and othex dimensions according to the work to be performed, and 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 die. meter 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 constantly turning, and with the other he strikes the jumper with a hammer of 6 or 8 lb. weight. But when the hole is of larger dimensions and of a depth exceeding a foot, it generally be: comes the business of one man, in a sitting posture, to hold and direct the jumper,—to keep it constantly tuming,—to supply the hole with water, and oc casionally to clean it out; while two and even three men, with hammers of 10 or 12 lb. weight, strike successive blows upon the jumper, until the rock is perforated to the desired depth. To 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 SO inches, it is now common to use a chisel or jumper, varying in length from 6 to 8 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 consi derable 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 pos ture, and lay hold of it by the bulbous part, lifting and letting it drop into the hole by its own gra vity; 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 debris and moisture are then carefully cleaned out, and a prop% charge of powder is put into it. In practice, there is no very precise 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 for cing 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 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 pre vent it from being too firmly fixed, and thereby pre vented 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 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 uninten tioned explosion. From this cause, indeed, the most unfortunate and distressing accidents have sometimes happened to quarriers. A recent case occurred un der the notice of the writer of this article, from which an experienced workman lost the sight of both eyes, and had his legs and arms much shattered. It is necessary, as before noticed, frequently to turn _ the pricker during the process of stemming the shot, in order to prevent its being so bound by the wad ding as to prevent its being withdrawn ; and it has• been known that, by the friction produced in the mere act of turning it unguardedly, the shot has been fired off. To prevent accident in this way, copper prickers, or, to save expence, prickers com posed 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 quar ries where copper and iron prickers have been used at the *me time, yet, from the greater ea pence of the copper, and its being more liable to twist and break, it has by no means come into ge neral use.
The hole being now fully charged with the pow der and wadding, the pricker is drawn out. 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. These straw tubes may be joined so as to reach any neces sary depth ; the lower straw always terminating in 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 in sure the inflammation of the charge of powder in the hole. This being done, a slow match, consist ing generally of a bit of soft paper, prepared by dip ping it into a solution of saltpetre, is carefully ap plied 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 to wards 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 Observ ed to spring into the air, and Sy about in all direc tions, from amidst a cloud of smoke. The guarder then returns with alacrity to the scene of his opera- • Lions. 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 i 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 frag ments of blasted rock from being driven to a dis tance.