132 
MINUTES OF PROCEEDINGS OF 
Experiment XVI. The same pressure (24 in.) was employed as in the 
last experiment, but the piece of gun-cotton-twist was laid double across the 
wire. In this instance the gun-cotton burned with a bright yellow flash, 
as in open air. 
Experiment XVII. Pressure=26in. The gun-cotton was laid singly 
over the wire, as in all experiments but the last. It burned with a flash of 
bright light, as in open air. 
It appears from these experiments that gun-cotton, when ignited in small 
quantities in rarefied atmospheres, may exhibit, during its combustion, three 
distinct luminous phenomena. In the most highly rarefied atmospheres, the 
only indication of combustion is a beautiful green glow or phosphorescence 
which surrounds the extremity of the gun-cotton as it is slowly transformed 
into gases or vapours. When the pressure of the atmosphere is increased to 
one inch (with the proportion of gun-cotton indicated), a faint yellow flame 
appears at a short distance from the point of decomposition; and as the 
pressure is increased this pale yellow flame increases in size, and eventually 
appears quite to obliterate the green light. Lastljq when the pressure of 
the atmosphere and consequently proportion of the oxygen in the confined 
space is considerable, the cotton burns with the ordinary bright yellow flame. 
There can be no doubt that this final result is due to the almost instantaneous 
secondary combustion, in the air supplied, of the inflammable gases evolved 
by the explosion of the gun-cotton. It was thought that the pale yellow 
flame described might also be due to a combustion (in the air still contained 
in the vessel) of portions of the gases resulting from the decomposition of 
the gun-cotton; but a series of experiments, in which nitrogen, instead of 
air, constituted the rarefied atmosphere, showed that this could not be the 
case. The results obtained in these experiments corresponded closely to 
those above described, as far as relates to the production of the green glow 
and of the pale yellow flame. With rarefied atmospheres of nitrogen ranging 
down to one inch of pressure, the green flame was alone obtained; and the 
pale yellow flame, accompanying the green, became very marked at a pressure 
of 3 in., as in the experiments with air. 
It would seem probable from these results, that the mixture of gaseous 
products obtained by the peculiar change which heat effects in gun-cotton 
in highly rarefied atmospheres, contains not only combustible bodies, such 
as carbonic oxide, but also a small proportion of oxidizing gas (possibly 
protoxide of nitrogen, or even ox}^gen), and that when the pressure of the 
atmosphere is sufficiently great this mixture, which has self-combustible 
properties, retains sufficient heat as it escapes, to burn, more or less com¬ 
pletely, according to the degree of rarefaction of the atmosphere. 
A series of experiments instituted with gun-cotton in highly rarefied 
atmospheres of oxygen, showed that the additional proportion of this gas 
thus introduced into the apparatus, beyond that which would have been 
contained in it with the employment of air of the same rarefaction, affected 
in a very important manner the behaviour of the explosion under the 
influence of heat. If eight or ten grains of gun-cotton are placed round the 
platinum wire, and the pressure of the atmosphere of oxygen in the vessel 
be reduced to four or three (in inches of mercury), the cotton explodes 
instantaneously, with an intensely bright flash, when the wire is heated. In 
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