BLASTING or ROCKS, is an operation of great importance in the formation of roads, or in the breaking up of uncultivated ground.
The process of blasting rocks, or stones, in boring a cylindrical hole, about 10 or 12 inches deep, in the rock, by means of a chisel for that pur pose. The lower part of this hole is filled with gunpowder. The upper part of the hole is then filled up with fragments of stone, firmly rammed together ; a hole being left through these materials, by the insertion of an iron rod, which is turned round during the operation of ramming. This hole is next filled with powder, and a match is applied to it in such a manner, that the operator has time to run out of the reach of the fragments of the rock.
This process, which is both tedious and dangerous, is now abandoned for one which is more simple and ef fectual, and, which consists merely in introducing a straw, filled with gunpowder, among the powder at the bottom of the cylindrical hole in the rock, and fil ling the rest of the cylindrical hole with loose sand. By applying a match to the gunpowder in the straw, an explosion takes place ; and, instead of the loose sand being driven out • of the cylindrical hole, as might naturally be expected, the rock is completely -shivered in pieces. Mr Jessop tried the experiment with great success on some of the hard rocks at Fortwilliam, and also on the lime works at Bristol% Mr Farey mentions his having witnessed, near ' Aylesbury, a method of blasting large rocks without gunpowder. fhe rock was undermined for about a yard in length, and half a yard in depth, and a small faggot of brushwood, furze, or a bundle of straw, was introduced into the cavity. As soon as it was set on fire, the expansive force of the air, confined in the stone, burst it into innumerable fragments.
Mr Headrick proposes to blast rocks by introdu cing the purest quicklime into the cylindrical hole, instead of gunpowder. By suddenly slaking the lime, he conceives, that the expansive force would rend the stone in pieces. See Nicholson's Journal, vol. x. p. 230.; vol. xi. p. 211. Communications to the Board of Agriculture, vol. ii. Philosophical Magazine, vol. xx. p. 208. (o) is the art by which those manufac tures which have vegetable substances for their raw material, are freed from the colouring matter with which such substances are naturally combined, or accidentally stained ; and the pure vegetable fibre, deprived of these coloured matters, is left to reflect the different rays of light in due proportion, so as to appear white.
Besides the spoils of animals, mankind, to supply their natural want of covering, have, in all countries, had recourse to vegetable substances, preferring those whose fibres excelled in strength, durability, and pliancy ; and experience having proved, that flax and cotton were well adapted to such purposes, these substances have been very generally adopted, and formed into such cloths as the skill and industry pf the wearers could execute.
It would soon be observed, that the action of wa ter, together with that of the sun and air, rendered those rude cloths whiter than they were at their first formation ; and, since the first step towards refine ment is to add beauty to utility, as the state of so ciety improved, a desire to give them a pure and spotless white would naturally arise. The idea of white raiment being the emblem of innocence and peace, which seems to have been very early enter tained, would make every means for facilitating the removal of natural or adventitious stains more ear nestly studied.
Accident would probably discover, that a certain degree of putrid fermentation carried off colouring matters from vegetable fibres. Hence the practice of macerating cloth in water, mixed with putrid urine, and the dung of domestic animals, which has been continued to our days.
From the earliest accounts we have of India, E gypt, and Syria, it appears, that these enlightened nations knew the efficacy of natron, (the nitre of scripture,) an impure mineral alkali found in these countries, for combining with and carrying off the colouring matters with which cloth is stained ; and it is still found in great abundance by the present in habitants, and used for the same purpose. We are also informed by Pliny, (lib. xviii. c. 51.) that the ancient Gauls were acquainted with the use of a lixi vium, extracted from the ashes of burnt vegetables as a detergent, and knew how to combine this lixi vium with animal oil to form soap.