90 COALFIELDS AND COLLIF.'RIIOS OK ATSTKALfA. 



stationary, the fuse is defective, and must be discarded. Each 

 fuse must be tested separately, and the galvanometer must 

 stand ou a firm basis, so that it does not get shaken, when in 

 use. The ends of Ihe fuse and cable wires should be bright 

 and clean; they are twisted toother in such a way that they 

 are in close contact, and cannot be drawn apart when pulled 

 about. To ensure continuity of insulation, and obviate risk 

 of loss of current, which is very important in simultaneous- 

 shot-firing, and in wet ground, the joint may be covered with 

 prepared rubber taping-, or some similar substance. Generally 

 when shooting down coal only one shot is fired at a time, so as 

 to reduce the amount of dust made. In cases where several 

 shots are fired at the time, the fuses are connected up in series 

 (Fig. 33). There are different types of exploders which are 

 practically small hand dynamos. The connection between the 



Fig. 33. Holes Connected in Series. 



cable and the exploder is not made till everything is ready for 

 firing. As soon as the shots are fired, the cables should be dis- 

 connected, from the exploder, and freed from any rubbish that 

 may have fallen 011 them, after which they are coiled up out 

 of the way. In case of a miss-fire, the tamping and charge 

 must not be drawn, but another hole must be drilled parallel 

 with, and at least a foot away from it. Before firing, the fuse 

 of the miss-shot should be attached by means of a piece of 

 string to some object, such as a prop, or the cable, which can 

 be readily found later. Immediately after firing, the shot- 

 firer must search the coal or stone with his hands only, for the 

 detonator, so as to avoid the risk of filling it out with the 

 broken material. The construction of a low 7 tension fuse is 

 shown in Fig. 34. The thin iridium-platinum wire is made red 

 hot when the current passes through it, and this fires the 

 priming. Low tension fuses are cheaper, safer, and less likely 

 to deteriorate than high tension fuses, and have a further ad- 

 vantage, inasmuch as they can be readily tested without being 



