ELECTRICITY FOR BLASTING 



197 





mends for this operation, a cement composed of one part of bees'-wax and two parts of 

 resin ; the tube is then filled with powder by its other extremity, which is likewise 

 stopped with a cork, which is cemented in the same manner. Fig. 780 indicates the 

 manner in which the cartridge is placed in the hole, after having care- ,.,-Q 



fully expelled all dust and moisture ; care must be taken that the car- ^ 

 tridge is situated in the middle of the charge of powder that is intro- 

 duced into the hole. Above the powder is placed a plug of straw 

 or tow, so as to allow between it and the powder a small space filled 

 with air ; and above the plug is poured dry sand, until the hole is 

 filled with it. The two ends of the copper- wires that come out of the 

 cartridge are made to communicate with the poles of the pile, by 

 means of conductors of sufficient length, that one may be protected 

 from all dangers arising from the explosion of the mine. 



M. Kuhmkorff, and after him M. Verdu, have successfully tried to 

 substitute the induction-spark for the incandescence of a wire, in order 

 to bring about the ignition of the powder. This process, besides the 

 considerable economy that it presents since instead of from fifteen 

 to twenty Bunsen's pairs, necessary for causing the ignition of the 

 wire, it requires but a single one for producing the induction-spark 

 possesses the advantages of being less susceptible of derangement. 

 Only it was necessary to contrive a plan to bring about the ignition 

 of the powder ; in fact, it happens that when by the effect of the 

 length of the conductors that abut upon the mine, the circuit pre- 

 sents too great a resistance, the induction-spark is able to pass 

 through the powder without inflaming it. M. Kuhmkorff has con- 

 ceived the happy idea of seeking for a medium, which, more easily 

 inflammable by the spark, may bring about the ignition of the powder 

 in all possible conditions. He found it in Statham's fuzes, which are 

 prepared by taking two ends of copper-wire covered with ordinary 

 gutta-percha; they are twisted (fig. 781), and the ends are bent so 

 as to make them enter into an envelope of vulcanised (sulphured) 

 gutta-percha, which has been cut and drawn off from a copper-wire 

 that had been for a long time covered with it. Upon this envelope 

 a sloping cut a, b, is formed; and after having maintained the ex- 

 tremities of the copper-wires at about the eighth of an inch from 

 each other, their points are covered with fulminate of mercury, in 

 order to render the ignition of the powder more easy. The cut is 

 filled with powder, and the whole is wrapped round with a piece of caoutchouc tube c, d, 

 or else it is placed in a cartridge filled with powder. 



779 



In the Statham fuzes, it is the sulphide (sulphuret) of copper adhering to the wire, 

 produced by the action of the vulcanised gutta-percha which is removed from the 

 copper-wire that it covered, which by being inflamed under the action of the induction- 



