EXPLOSIVES. 9-5 



an electric shot firer. Low tension electric detonator fuses are 

 used ; these are packed in cases of 1000, and have wires at- 

 tached 48, 54, 60, 72in. and upwards in length, 

 according to the depth of the hole. A broad red 

 line is made at one end of the cartridge, where there 

 is an excess of paper; this end is opened, a hole 

 is made in the explosive by means of a pencil, or small 

 pointed stick, deep and large enough to completely bury the 

 detonator when lightly pushed in ; the loose paper is then 

 tied over the detonator-fuse-wires with a piece of twine to 

 prevent withdrawal of the detonator from the explosive. A 

 good plan is to reverse the cartridge, bend the wire round, and 

 give it a half hitch round the cartridge. The half hitch pre- 

 vents the detonator from being pulled out accidentally, and the 

 wire is led up the side of the hole, at the same time the de- 

 tonator is protected between two cartridges, and there is less 

 danger of a premature explosion due to careless stemming. 



Fig. 32. Galvanometer, with Testing Battery. 



The tamping should be damp clay, the first two or three pieces 

 being pressed gently home, and the remainder rammed fairly 

 hard with a wooden rod, as this is less likely to damage the 

 wires than one tipped with copper. The electric fuses should 

 be stored in a dry place, and care should be taken not to kink 

 or twist the fuse wires in such a way as to cut the insula- 

 tion and render the fuse useless, this being especially import- 

 ant in wet ground. So as to prevent miss-fires, each fuse 

 should be tested before being used. This is done by placing 

 the fuse in an iron pot or pipe for protection in case of 

 accidental explosion; it is then connected to a galvanometer 

 (Fig. 32) by pressing the bared end of the fuse wires on to 

 the knife edge terminals of the galvanometer with the fingers, 

 care being taken that the ends of the wires do not touch each 

 other. If the needle moves, the fuse is good, but if it remains 



