ON THE LIMESTONE, THE LIME CEMENT, AND THE METHOD OF BLASTING, IN THE NEIGHBOURHOOD OF PLYMOUTH
Minutes of the Proceedings of the Institution of Civil Engineers
Mr. Bethell's attention was directed to this subject in 1834, ~i~i when engaged in experiments with his new diving-dresses. It is Blasts hy frequently necessary to blow off the upper decks of a wreck, so as to get at the cargo ; but great difficulty has arisen in igniting the powder. A fuze of cotton steeped in spirits of wine and gunpowder and enclosed in a caoutchouc tube was at first used; this, however, being uncertain and expensive, the idea occurred of trying galvanism. I t is well known
... I t is well known that when two ends of copper wires leading from the poles of the battery are connected by a piece of platinum, or iron wire, the latter becomes red-hot. T o apply this method, the top of the tin canister which contains the charge is titted with two copper wires, about 6 inches long, passing through a piece of cork, and connected at their lower ends by a piece of platinum or iron wire. The canister being charged, the platinum or iron wire is pushed down into the middle of the charge, and the top of the canister cemented on with putty. The wires are well coated with a non-conducting medium, as a mixture of resin, wax, and tallow, or caoutchouc, excepting at their lower end where they are connected by the platinum, and at the upper where they are to be connected with the two long copper wires which proceed to the battery. These connecting wires, covered with cotton thread, are coated with the caoutchouc varnish, and then tied together so as to form one rope; the diver having connected the wires of this rope wit,h the wires of the canister, and uncoiled a sufficient length of rope, descends and deposits the canister in the wreck or hole prepared for the blast, and returns to the surface. The other ends of the wire are then dipped in the mercury cups of the galvanic battery, and the platinum wire becoming instantly red-hot, the charge is exploded. There is not more than about six inches of the wire rope lost at each discharge. The security, certainty, and convenience, of this plan are evident. I n quarries, any number of charges could be fired at the same instant, or in rapid succession ; and this method possesses incalculable advantages over every other for the military engineer, since any number of mines could be exploded at the precise moment that is desired. On the Limestone, the Lime Cement, and method of Blasting, in the neighbourhood of Plymouth.