Compressed Air Work And Diving 1909

FUSES. loi out. Before putting the fuse into the detonator, the end should be cut clean in an oblique direction. In caisson and tiinnelling in compressecl air, electric detonators are used exclusively. These are of two kinds, high tension and low tension. Both are very similar in appearance, consisting of small copper tubes fillecl with fulminate of mercury and chlorate of potash, and closed by a cement ping. I he high-tension detonator is fired by a spark passing between the terminals. The low-tension by a small wire connecting them which gets red hot. The high-tension fuse must be connected up in parallel when there are two or more charges to be fired at the same time. Low- tension fuses are connected up in series. The low-tension fuse is the one in most general use. Low-tension fuses, if coverecl with an iron pot or pipe, can be tested with a galvanometer, but this must not be done with high-tension fuses. When putting in the detonator, a hole is made in the top with a pointeel stick, and the detonator pushed right into the cartridge until it is completely buriecl. The cartridge should be gently squeezed to just above the detonator, i.e., at the end at which it has been put in, and the paper should then be tied rouncl the wires in the same way as described for the safety fuse. In the States another method of putting in the detonator is used. A hole is made at the side of the cartridge, and the detonator put in until quite buriecl. The wires are then o'iven a <F> turn rouncl the cartridge at the point of insertion, and then carried to the other end and tied there. The advantages of this method are that it is a good cleal quicker than the other, and that a cushion of explosives is formed at each end, which protects the detonator from the tamping rod. Experts in this country do not view