THE ROYAL ARTILLERY INSTITUTION. 
133 
a series of experiments made under gradually diminished pressures, oxygen 
being used instead of air, it was found that the gun-cotton exploded 
instantaneously, with a bright flash, until the pressure was reduced to T2 in.; 
from this pressure to that of 0*8 in. it still burned with a flash, but not 
instantaneously; and at pressures below 0*8in. it no longer burned with 
a bright flash, but exhibited the comparatively slow combustion, ac¬ 
companied by the pale yellow flame, which has been spoken of as observed 
■when gun-cotton was ignited in air rarefied to pressures ranging from lin. 
to 24 in. 
The interesting phenomena exhibited by gun-cotton in highly rarefied 
atmospheres, induced me to make some experiments of a corresponding 
nature with gunpowder. The same apparatus was used as in the preceding 
experiments, but a small glass cup was fixed immediately beneath the 
platinum wire, so that, by bending the latter in the centre, it was made to 
dip into the cup, and could be covered by grains of gunpowder. 
Two grains' weight of small grain gunpowder were heaped over the wire, 
and the pressure of air in the apparatus was reduced to 0’65 in. The wire 
being heated to redness, three or four grains, in immediate proximity to it, 
fused in a short time and appeared to boil, evolving yellowish vapours, no 
doubt of sulphur. After the heat had been continued for eight or ten 
seconds, those particular grains deflagrated, and the remainder of the powder 
was scattered by the slight explosion, without being ignited. No appreciable 
depression of the mercurial column occurred during the evolution of the 
yellowish vapours; the permanent depression, after the deflagration, was 
only 0T5in. 
The experiment was repeated wfith small-grain gunpowder, amounting to 
four grains, and the same phenomena were observed, with this difference, 
.that a second slight deflagration followed shortly after the first, probably in 
consequence of a grain or two of the powder falling back into the cup. 
A single piece of gunpowder, weighing 14 grns., so shaped as to remain 
in good contact with the wire, was placed over the latter, being supported 
by the cup. The pressure of air in the apparatus w r as, as before, equal to 
0‘65 inch of mercury. There was no perceptible effect for a short time 
after the wire was first heated to redness; vapours of sulphur were then 
given off, and slight scintillations were occasionally observed; after a time 
the wire became deeply buried in the superincumbent mass of gunpowder, 
which fused, and appeared to boil, where it was in actual contact with the 
source of heat. After the lapse of three minutes from the commencement 
of the experiment, the powder deflagrated. The permanent depression of 
the mercury column amounted to 1*35 inch. 
The experiment was repeated with a similar piece of powder, weighing 
16 grns.; the same phenomena were observed; and five minutes elapsed 
between the first heating of the wire and the deflagration of the powder. 
The experiments were continued with fine-grained gunpow r der, and under 
pressures gradually increased, in successive experiments, from 0*7 to 3 in 
inches of mercury. The same weight of gunpowder (4 grns.) was used in 
all the experiments. In those made under a pressure of 1 in., the results 
observed w r ere similar to those obtained in the first experiments; single 
grains of gunpowder were successively deflagrated, burning very slowly, and 
scattering but never igniting contiguous grains of powder. Eventually, 
