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Blasting

fig, hole, charge and needle

BLASTING. An operation resorted to in mines and quarries for the pur pose of detaching large masses of earth or stones. The implements employed, (which are few and simple,) are shown in the engraving. Fig. 1. The sledge hammer, or mallet. Fig. 2. The borer, or chisel. Fig. 3. The wedges. Fig. 4. The scraper. Fig. 5. The claying bar. Fig. 8. The needle. Fig. 7. The tamping bar. Fig. 8. The shovel. Fig. 9. The fusee inserted in the charge. To perform the operation of blasting, two men only are requisite. The miner's judgment directs him to the fittest place for the charge, and a hole is bored or cut in the rock, in the following manner, to receive it. Theborer, or chisel, Fig. 2, is held by one man, whilst the other man strikes it with the hammer or mallet; the man holding the chisel turning it at every blow, so as to cross the previous cut, by which means the atone is chipped away by degrees. The boring, or cutting, is occasionally suspended to clear out the hole, which is done by the scraper, Fig. 4. When the perforation is of the required depth, (which varies from one to three feet, the diameter being about an inch and a halt) if the hole be wet, some tough dry clay is introduced, and the claying bar, Fig. 5, is driven in with great violence, by which means the clay is forced into all the crevices, absorb ing the moisture, and preventing the entrance of more; on withdrawing the claying-bar, the hole is left dry, and of a smooth uniform surface, which adapts it for receiving the charge. This consists of gunpowder alone, or mixed with

some quicklime, (which it is said increases the force of the explosion); it is inclosed in paper as a common cartridge, to fit the bore ; but in very wet situa tions, a tin case is sometimes used to contain it. The charge being now intro duced, and thrust to the bottom of the hole by means of a thin tapering copper rod called the needle, Fig. 6, which is also driven down with the charge. The next operation is to exclude as much of the air as possible, by reducing the size of the vent; for this purpose, the tamping bar, lig. 7, is employed in ramming round the needle some yielding yet compact substance, so that when the needle is withdrawn, a very small vent or touch-hole remains. Into this perforation is dropped a ft:see, or rush, charged with powder, on the top of which is fixed a snuft," as it is called, or some other contrivance, so adjusted as to burn a suffi cient time to permit the man who fires it to retreat to a proper distance. Pre vious to firing, it is usual to give notice to all perms in the immediate neighbourhood, by blowing a horn or ringing a be4 that they may have the opportunity of retiring to some place of security.