THE HISTORY OF EXPLOSIVE \GENTS. 
495 
M. Nobel has described various devices for effecting this so-called initiative explosion 
of some portion of a nitroglycerine charge, of which evidently the most successful are 
the explosion of a small confined charge of gunpowder, or of a large purcussion-cap, 
when immersed in or placed immediately over the nitroglycerine. M. Nobel, however, 
classes these two modes of ignition in which an explosion or detonation is applied as the 
exploding agency together with various others in which the simple application of a high 
temperature to some portions of the nitroglycerine is proposed as the means of explo- 
until it was entirely deprived of explosive properties. A larger quantity enclosed in a sealed tube was exposed 
for four days to a temperature of 100° C. without exploding. At the expiration of that period the liquid had 
assumed a brownish colour, hut this gradually disappeared altogether after the tube had cooled down ; and when 
the latter was opened after the lapse of some days, there was no pressure of gas, nor did the liquid exhibit 
the slightest acidity. In this instance the decomposition, probably resulting in the liberation of the nitrogen- 
oxides, was established by the continued exposure to 100°, and would doubtless, as in the case of the electric ex- 
periments, have gradually increased if the application of heat had been continued until the internal develop- 
ment of heat had resulted in explosion. 
The difference in the behaviour of nitroglycerine and gun-cotton, when exposed to the influence of a source 
of heat (apart from the difference in the heat required for their explosion), is evidently due principally to the 
difference in their physical condition. "When a heated body is applied to nitroglycerine, the liquid nature of 
the latter leads to the distribution through its mass of the heat applied, with rapidity sufficient to render the 
ignition of the but slightly volatile liquid a matter of difficulty, even by the application of a very highly heated 
body, such as a red-hot wire or rod, or a piece of burning wood • and when the liquid is actually inflamed it 
burns at first non-explosively, because the increase in temperature of the body of liquid (or of that part pre- 
sented by the burning surface) which is necessary for developing its sudden decomposition or explosion, takes; 
place only gradually. But if by establishment of a slow decomposition throughout or in some portion of the 
nitroglycerine, a tendency to disruption of the constituent molecules is developed, the disturbance of chemical 
equilibrium favours the action of any impulse from without, such as the direct application of heat, so that the 
violent explosion or sudden decomposition of the mass is determined by applying heat to an extent which would, 
under normal conditions, be quite inadequate to bring about such a result. 
In the case of the solid and badly conducting substance gun-cotton, when a source of heat just sufficient for 
its ignition is applied to any portion, the heat is not diminished by distribution through the mass, hence the 
particles of gun-cotton contiguous to the source of heat are inflamed almost immediately. If the gun-cotton 
be in a loose or porous condition (e. g. in the form of wool or of loosely wound thread), the entire mass will in- 
flame with such rapidity as to produce a species of explosion, on account of the rapid penetration to the sur- 
rounding particles of the heat resulting from the first ignition ; but if it be in a compact (compressed) mass, in 
which the contiguity of particles more nearly approaches that of the particles in the liquid nitroglycerine, the 
gun-cotton proceeds to burn gradually from the exterior towards the centre of the mass. 
If gun-cotton be exposed to a source of heat insufficient for its ignition, the heat will gradually accumulate in 
those parts most contiguous to the source, spreading with comparative tardiness through the mass. A twofold 
result will then be obtained ; heat eventually accumulates to an extent sufficient to establish chemical change 
in the mass, which becomes greatest near the source of heat, so that, if the application of the latter be not inter- 
rupted, the temperature requisite for ignition will be speedily attained in those portions : the result will, how- 
ever, be no longer the simple inflaming of the gun-cotton with more or less rapidity, but an explosion will ensue, 
as in the case of nitroglycerine, the violence being proportionate to the heat which has accumulated, and to the 
extent to which a disturbance of chemical equilibrium has been established. 
Frequent confirmations of this view have been obtained in the course of my investigations on the effects of heat 
upon gun-cotton. The violence of explosion of samples of gun-cotton confined in flasks with not very narrow 
