THE ROYAL ARTILLERY INSTITUTION. 
129 
bottom of the vessel, ceased to burn almost immediately. Of a piece of gun¬ 
cotton weighing 2*17 grs,, there remained unchanged 1*80 gr.; the quantity 
burned amounted therefore to 037 gr., and corresponded closely to the 
quantity which was completely burned in the preceding experiments. (The 
depression of the mercurial column in this experiment, by the gases generated 
from the gun-cotton, amounted to 0*2 in.) 
A piece of the twist, l^in. long, was placed across the wire, and 
supported by a plate of plaster of Paris, fixed immediately beneath it. The 
current was established to an extent just sufficient to heat the wire to the 
point of ignition of the gun-cotton, and then interrupted.. The twist 
burned slowly in both directions until about a quarter of an inch was 
consumed on either side of the wire, when the combustion ceased. The 
same result was obtained in repetitions of the experiment, the wire being at 
once raised to a red heat, and thus maintained until the gun-cotton ceased 
to burn. But upon increasing the battery-power, doubling the thickness 
of the wire, and maintaining the heat, while a similar piece of twist was 
burning in both directions, the slow combustion continued until the entire 
quantity was transformed into gas. The same result was obtained by 
repeating this experiment with similar and larger quantities of gun-cotton, 
placed in the same position as before with reference to the wire. 
In the next experiment, the mass of cotton exposed at one time to heat 
was increased by doubling a piece of the twist (4 in. long) and laying it 
thus doubled across the wire, as before. The current was allowed to pass 
until the wire was heated just sufficiently to ignite the gun-cotton, and then 
interrupted. In this case the slow combustion proceeded throughout the 
entire mass of the cotton. The permanent depression of mercury in this 
experiment was 0’6 in. It was particularly noticed on this occasion, that, 
as the decomposition of the gun-cotton crept slowly along the mass, the 
burning portions or extremities of twist were surrounded by a beautiful green 
light, more like a phosphorescence than a flame, and in form something 
similar to the brush of an electric discharge. 
Eight inches of the twist were laid fourfold over the wire, which was 
heated just sufficiently to ignite the cotton. The decomposition proceeded, 
as before, gradually throughout the mass of the gun-cotton, but became 
somewhat more rapid towards the end, when the green glow, observed at 
first, was superseded by a pale yellowish lambent flame, very different in 
appearance from the flame which accompanies the combustion of gun-cotton 
under ordinary conditions. The permanent depression of the column of 
mercury in this experiment was 1*2 in. 
The various modifications in the nature and extent of combustion which 
gun-cotton may be made to undergo, as demonstrated by the above 
experiments, when exposed to heat in highly rarefied atmospheres under 
variously modified conditions, are evidently due to the same causes which 
affect the rate of combustion of fuzes uuder different atmospheric pressures, 
and which have already been pointed out by Erankland* in his interesting 
paper on the influence of atmospheric pressure upon some of the phenomena 
of combustion. The heat furnished by an incandescent or melting platinum 
wire is greatly in excess of that required to induce perfect combustion in 
* Vide Vol. III. p. 14, 
