THE HISTOET OP EXPLOSIVE AGENTS. 
499 
violent action of the fulminate being, in these instances, developed by the confinement 
of the portions first ignited in a weak envelope, which consists partly or entirely of the 
surrounding or superincumbent fulminate (see p. 491)*. 
6. It need perhaps scarcely be stated that the degree of proximity of the detonating 
charge to the gun-cotton, which is essential for the explosion of the latter, is regulated 
by the violence of the detonation produced. 0‘ 32 grm. (5 grains) of fulminate enclosed 
in a metal cap must be placed in close contact with (i. e. closely surrounded by) the un- 
confined gun-cotton, in order to effect its explosion, while l - 3 grm. (20 grains), similarly 
confined, will produce the same result if placed at least 0-5 inch distant from the surface 
of the compressed gun-cotton. 
The foregoing facts appear to point to the mechanical action of a detonation as being 
the real cause of the violent explosion of freely exposed gun-cotton or nitroglycerine. 
At any rate they appear to indicate decisively that such explosion is not a result of the 
direct application of the heat developed by the explosion of the detonating materials. 
If it were so, then the detonating mixture described as percussion-cap composition, and 
other explosive mixtures, the ignition of which is attended by much greater development 
of heat than is obtained by the ignition of pure mercuric fulminate, should explode 
freely exposed gun-cotton more readily than the latter does ; the readiness with which 
the gun-cotton is exploded should be solely proportionate to the amount of fulminate 
employed ; and gun-cotton should be more readily exploded in the loose and open con- 
dition than in the compact and highly compressed form ; for the latter presents it in 
the condition least favourable, and the former that most favourable to ready and rapid 
ignition by heat. Again, the actual temperature required for the explosion of nitrogly- 
cerine is very considerably higher than the exploding temperature of gun-cotton ; the 
former may be heated to a temperature of 193° C. (380° F.) for some time without ex- 
ploding, while the latter inflames at a temperature of 150° C., yet a much smaller charge 
(not more than 0-2 of the amount) of fulminate suffices for the explosion of unconfined 
nitroglycerine than it needed for the detonation of gun-cotton f. On the other hand, a 
quantity of confined percussion-cap composition which, if it were pure mercuric fulmi- 
nate, would be altogether inadequate for the detonation of gun-cotton, suffices for the 
detonation of nitroglycerine. 
Although the foregoing facts appear to afford indisputable evidence that the direct 
application of heat, from an exploding charge of detonating powder, is not concerned 
in developing the violent action of gun-cotton or nitroglycerine, an attempt has been 
made to devise some experiments in which the detonation of either of those substances 
by the agency described should be accomplished in such a manner as to interpose an 
effectual barrier between the material to be exploded and the heated gases or flame 
* 3-24 grms. (50 grains) of the fulminate heaped upon the gun-cotton-surface as in the ahoye experiments, 
but inflamed at the top of the heap, failed to explode or even to inflame the gun-cotton. 
f About 3-24 grms. (50 grains) of chloride of nitrogen, confined by water, are required for the detonation of 
gun-cotton, whereas 0T grm. (1-5 grain) of the chloride, similarly confined, suffices to detonate nitroglycerine. 
3x2 
