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 oper ated, in some measure, to prevent particular in.. quiries regarding it. It was an extremely natural conclusion for the quarrier to suppose, that the inure 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 En gineers ; and was also a principle invariably adopted by miners, to the great personal hazard of the arti ficer. In many places, this notion still prevails, and we cannot enough lament the force, and stubborn ness 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 com monly 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 stem ming 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 Charles town 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 ram med with force, has been in use at these works for se veral 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 state ments, as to the ejiciency of sand, at the extensive quarrying operations which lately became necessary in cutting down a part of the Caltonhill, in forming 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 near ly L.1000 Sterling, was expended, chiefly. in blast ing 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 horizon tal, Trials were here made with holes from three to seven or eight feet in depth, and of a diameter from an inch to two and a half inches in dia meter ; when it was invariably found, that when the powder was wadded with sand, the effect in tear ing 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 em ployed; 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 occa sioned by any apparent cause. Reasoning from the simultaneous effects of the sudden extrication of the elastic fluid of gunpowder, whether a wading 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 conclu sion that the explosive force of gunpowder is in pro portion 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 ap plied 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; 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. In so far, this is a saving of time ; but unfortunately he still undergoes much personal risk, the chief danger be ing in ramming at first, or in the turning or with drawing of the pricker, where the wadding is firm. When sand is used immediately above the powder, both the pricker and the rammer are wholly unne cessary ; the primed draw being inserted into the powder, the sand is poured' into the hole, and the shot is ready for the match. 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 perpendi cular, the priming straw is apt to be injured is 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 ; 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 more expence, and little more trouble, than when the bore is perpendi cular.