THE ROYAL ARTILLERY INSTITUTION. 
131 
In the description of the two experiments last referred to above, I have 
stated that some peculiar phenomena were observed to attend the imperfect 
kind of combustion induced in the gun-cotton in rarefied atmospheres. 
In order to examine these phenomena more closely, 1 instituted a series of 
experiments, in a darkened room, with equal quantities of gun-cotton in. 
of twist= 0*3 gr.) placed always in the same position, across the platinum 
wire, the only varying element in the experiment being the pressure of the 
atmosphere in the vessel, which was gradually increased. The following 
were the results observed :— 
Experiment I. Pressure= 0*62 in. The wire was heated just sufficiently 
to ignite the material; the current was then interrupted. The gun-cotton 
burned very slowly in both directions, emitting only the small green phos¬ 
phorescent flame, or brush, already described. 
Experiment II. Pressure = 1 in. In addition to the green glow which 
surrounded the burning ends, a very faint yellowish flame was observed 
hovering over the gun-cotton. 
Experiment III. Pressure 1*5 in. The cotton burned a little faster, 
and the faint yellowish flame was of a more decided character; indeed two 
separate flames were observed, each following up the green light as the 
cotton burned in the two directions. 
Experiment IY. Pressure=2 in. The results were the same as in 
the preceding experiment, excepting that the yellowish flames became more 
marked. 
Experiment Y. Pressure =2*5 in. The same phenomena, the cotton 
burning considerably faster. 
Experiment YI. Pressure =3 in. The same phenomena, the yellow 
flames increasing in size. 
Experiment YII. Pressure=4 in. The rapidity of combustion of the 
cotton increased again considerably; the other phenomena observed were as 
before. 
Experiment YIII. Pressure =6 in. The pale yellow flame had in¬ 
creased in size considerably, no longer forming a tongue, as in the preceding 
experiments, but completely enveloping the burning ends of the gun-cotton. 
The green glow, though much reduced, was still observed immediately round 
the burning surfaces. 
Experiment IX. Pressure = 8 in. The green glow was only just per¬ 
ceptible in this instance, and the cotton burned very rapidly, almost with the 
ordinary flash; but the flame was still of a pale yellow. In the preceding 
experiments clouds of white vapour were observed after the decomposition of 
the gun-cotton; in this and the following experiments this white vapour was 
produced in much smaller proportion. 
Experiments X. to XY. inclusive. Pressure=10, 12, 14, 18, 20, 
24 in. The phenomena observed in these experiments did not differ in any 
important degree from those of Experiment IX. 
