EAST RIVER AND HELL GATE IMPROVEMENT. 445 



sented in Fig. 8, are 24 inches long by '^\ inches in diameter, and 

 are provided at their forward ends with a fulminate primer which 

 is inserted after they are filled. 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 



Fig. 11. FiQ. 8. Fig. 10. 

 Cabtkidqes and Mine-Explodeb. 



Fig. 12. 



Arrangement op the Charges in the Mines. 



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 con- 

 taining 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 arc then 

 surrounded with fulminate, and the two parts of the tube are put to- 

 gether, that containing the wires slipping within the other. The entire 

 fuse is then covered with gutta-percha. The passage of an electric cur- 

 rent through the wires heats the platinum bridge to redness, and causes 

 an explosion of the fulminate. 



