Nitro- Glycerine. 



103 



tricity, the 8 in. post will be blown to splinters, with a 

 force, says Prof. Abel, almost, if not quite equal, to that ex- 

 erted by an explosion of nitro-glycerine. The senses are 

 unable to measure these velocities of explosion, and yet, 

 the effective force of a blasting material is, ceteris paribus, in 

 direct proportion to the rapidity of conversion of the solid or fluid 

 into a given quantity of gaseous matter. 



The exploders which I introduced for blasting at the 

 Hoosac tunnel consist essentially of a priming compound 

 capable of being fired by the electric spark, surmounted by 

 a cap containing fifteen grains of fulminate mercury. The 

 two points (terminals) of the conducting and return 

 wires, are so arranged as to have the priming compound 

 secured between them. On the spark passing, the priming 

 explodes, firing the fulminate, whose powerful explosion 

 again fires the nitro-glycerine. On this fuse priming much 

 depends, for if out of twenty cartridges, two or three should 

 fail to explode, there is impatience among the miners at 

 delay, and indeed, as has sometimes happened, a charged 

 cartridge may be found amongst the shattered rock. 



Failure to secure a safe priming has led some manufac- 

 turers to make this priming according to a patent of Jacob 

 Dowse, by mixing fulminate of mercury still moist with 

 precipitated copper, thus forming a fulminate of copper, 

 which is so sensitive to electricity that in a room where 

 machinery is running, or a boiler throwing out steam, the 

 electricity set free is sufficient to discharge them. Espe- 

 cially during a thunder storm is this spontaneous explosion 

 likely to occur. 



To hit the intermediate point, of always firing by means 

 of a spark of electricity, and never to fire by the free, ra- 

 diant or induced electricity of the atmosphere, was a long, 

 tedious and indeed many months' occupation. It was 

 finally attained by using sulphide copper, phosphide cop- 

 per with 35 per cent of chlorate potash, and was the discovery 



