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 gun powder. 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 gra nite, 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 expan sive or explosive force of gunpowder as a new me chanical power; but when the lever and the wedge become ineffectual to the purposes of the artificer, he must naturally attach a high value, and be dis posed 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 dignifiedswith 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 consider ed as the result of the sudden extrication of a per manently elastic „fluid by the ignition of the gun powder, the extricated gas occupying perhaps 1000 times more space than the grains of the pow der. Some authors are of opinion, that the pow der 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 ra. rifled 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 a bout 244 times denser than atmospheric air, 'and that, when exploded, it produces an effect propor tioned to its condensation ; the elastic fluid expand ing with a velocity which has been calculated at the rate of about 10,000 feet per second ; and its pres sure or force, when thus expanding, having been es timated as equal to a thousand atmospheres, or as a thousand times greater than the atmospheric pres sure upon a base of the same extent. If we apply this product to the pressure of the atmosphere, or at the rate of 141 pounds to the square inch, we shall find that the elastic fluid of gunpowder, at the mo ment of explosion, exerts a force equiialent to 6i tons upon the square inch of surface exposed to its force ; and that with a velocity which even the ima gination 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 unques ' tionably 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, 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 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 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, particular!, 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 pre serving 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 cir cumstances, was, in this country, reserved for Mr Brindley, Engineer upon the Duke of Bridge water's canals. In 1776, this celebrated Engineer completed the first navigable tunnel, at Hare castle in Staffordshire, which is upwards of one mile in length. Since that period, many other works of a similar nature, and even of much greater ex tent, have been executed in various parts of Europe. By the art of blasting, immense excavations have been made upon the Great Canal in Sweden. In France, a tunnel of about seven miles in length has lately been made ; and, in our own country, at Sap perton, on the canal joining the rivers Severn and Thames, and at Marsdenhill, there is a tunnel, up wards of three miles in length, forced entirely through rock, by the use 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 domestic comfort, and national importance, it is meet evident, that, but for the simple process of applying the expansive force • of gunpowder, we must have been deprived of innumerable advantages and accommodations.