Page:Popular Science Monthly Volume 28.djvu/459

Rh in Fig. 8, are 24 inches long by 2$1/4$ inches in diameter, and are provided at their forward ends with a fulminate primer which is inserted after they are tilled. This primer is shown in half size in Fig. 9, and consists of a fulminate exploder similar to that shown in Fig. 7, in a copper tube containing an ounce of No. 1 dynamite. The



cartridges are secured in the holes by the wire springs shown at their lower ends; and the dynamite cartridge is also wedged in with wooden wedges. Fig. 10 shows the mine-exploder, the position of which in the mine is illustrated in Fig. 12. It consists of a brass cylinder, eight inches long by two in diameter, filled with dynamite. Inclosed within the dynamite is a fuse, shown half size in Fig. 10, the wires from which pass through a divided cork in the mouth of the brass cylinder. It consists of a copper tube nearly filled with 30 grains of fulminate of mercury. Fitting in the open end of this tube is a second tube containing sulphur, through which pass the two conducting-wires, they being held firmly in place by the sulphur. The inner ends of the wires are united by a small platinum wire. The ends of the wires are then surrounded with fulminate, and the two parts of the tube arc put together, that containing the wires slipping within the other. The entire fuse is then covered with gutta-percha. The passage of an electric current through the wires heats the platinum bridge to redness, and causes an explosion of the fulminate.