THE HISTOET OE EXPLOSIVE AGENTS. 
497 
confined charge of gunpowder, or of a detonating substance, while other modes of ex- 
plosion by the application of heat or flame, which liaye been described by M. Nobel, 
only develope explosion under special conditions, points to a decided difference between 
the action of the two modes of ignition, and appears to indicate that it is not simply the 
heat developed by the chemical change of the gunpowder or detonating powder which 
determines the explosion of the nitroglycerine. 
An experimental investigation of this subject has left no doubt on my mind that the 
explosion of nitroglycerine through the agency of a small detonation is due, at any rate 
in part, to the mechanical effect of that detonation, and that this effect may operate in 
exploding the nitroglycerine quite independently of any direct action of the heat disen- 
gaged by the gunpowder or other detonating charge. 
I was led to examine into this question by an interesting and important observation 
recently made by my Assistant, Mr. E. O. Brown, in connexion with gun-cotton. The 
fact that the violent explosion of this substance cannot be developed except when it is 
confined in receptacles of some strength has been up to the present time accepted as 
indisputable. It occurred, however, to Mr. Brown that as gun-cotton is analogous in its 
nature and operation as an explosive agent to nitroglycerine, differing principally from 
that substance in the rapidity and consequent violence of its explosion, it might also, 
like nitroglycerine, be susceptible of violent explosion when unconfined, by being ignited 
through the agency of detonation. This proved to be the case ; for upon exploding 
a small charge of detonating powder in contact with, or in the immediate vicinity to, 
compressed gun-cotton freely exposed to air, instead of the latter being simply inflamed 
and then burning gradually, as would be the case if it were brought into contact with 
flame or any sufficient source of heat, it explodes with great violence, exerting a destruc- 
tive action equal to that of nitroglycerine, and decidedly greater than that produced by 
gun-cotton when exploded under the conditions hitherto believed to be those most 
favourable to the full development of its explosive force. The explosion of a small 
mass of compressed gun-cotton in this manner suffices to determine the similarly violent 
and apparently simultaneous explosion of small detached masses of the same material, 
which may indeed be placed at distances of 05 to 1 inch from the original source of 
the explosion or from each other. Thus, rows of detached masses of gun-cotton, placed 
on the ground and extending 4 or 5 feet, have been exploded with most destructive 
results, by the firing of a small detonating tube in contact with the piece of compressed 
gun-cotton which formed one extremity of the row or train, the explosion of the entire 
quantity being apparently instantaneous and equally violent throughout. 
In the first experiments instituted with the view of ascertaining the conditions to 
be fulfilled for ensuring the development of the violent action, or for accomplishing 
the detonation of gun-cotton, when perfectly unconfined, the following points were 
observed : — 
1. If a confined charge of mercuric fulminate be placed in contact with, or buried in 
gun-cotton which is in the form of wool or spun yarn, its explosion does not develope the 
violent action of the gun-cotton, as would be the case if the latter were in the form of 
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