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MINUTES OF PROCEEDINGS OF 
series of experiments, under variously modified conditions, was instituted, of 
which the following are the most important. 
It was found in numerous experiments, made with proportions of gun¬ 
cotton varying from one to two grains, in the form of a loose twist laid 
double, that in highly rarefied atmospheres (the pressure being varied 
from 1 to 8 in inches of mercury) the gun-cotton, when ignited by means 
of the platinum wire, burned very slowly, presenting by daylight an appear¬ 
ance as if it smouldered, with little or no flame attending the combustion. 
1 was at first led by these results to conjecture that this peculiar kind of 
combustion of the gun-cotton was determined solely by its ignition in 
atmospheres rarefied beyond a certain limit; and I was induced, in con¬ 
sequence, to institute a number of experiments with the view of ascertaining 
what was the most highly rarefied atmosphere in which gun-cotton would 
burn as in the open air—with a flash, accompanied by a body of bright 
flame. In order to ensure uniformity in the degree of heat applied to the 
cotton in these experiments, the platinum wire employed was sufficiently 
thin to be instantaneously melted on the passage of the voltaic current. 
About fifty different experiments were made with equal quantities of gun¬ 
cotton (0*2 grain), placed always in the same position, so that the platinum 
wire rested upon the material. A tolerably definite limit of the degree of 
rarefaction was arrived at, within which the gun-cotton was exploded 
instantaneously, as in the open air. When the pressure of air in the 
apparatus was reduced to 8*2 in inches of mercury, the gun-cotton still 
exploded with a flash, but not quite instantaneously; on reducing the 
pressure to 8 in., the cotton underwent the slow kind of combustion in the 
majority of cases; on a few occasions it exploded with a flash of flame. The 
same occurred in a succession of experiments, until the pressure was reduced 
gradually to 7*7 in., when instances of the rapid explosion of gun-cotton 
were no longer obtained. 
Although these results were moderately definite when the conditions of 
the experiments were as nearly as possible uniform, it was found that they 
could be altered by slight modifications of any one particular condition 
(such as the quantity of gun-cotton, its mechanical condition, its position 
with reference to the source of heat, the quantity of heat applied, and the 
duration of its application). In illustration of this, the following results 
may .be quoted. 
If the gun-cotton was wrapped round, instead of being simply placed 
across the wire, its instantaneous combustion was effected in atmospheres 
considerably more rarefied than with the above experiments. 
In employing a small piece of gun-cotton (0*8 of an inch long and 
weighing 0*3 to 0*4 of a grain) loosely twisted, laid across the wire, or upon 
a support immediately beneath the latter so that the wire rested upon it, 
the slow combustion established in it by the heated wire, under greatly 
diminished atmospheric pressure (amounting to 0*6 inch in this and the 
following ex 2 )eriments), proceeded uniformly towards each end of the piece 
of twist, until the whole was transformed into gas. But if a piece of the 
same twist, of considerably greater length (say 4 in. long and weighing about 
2 grs.), was exposed to heat in an atmosphere of the same rarefaction, the 
gun-cotton being laid over the wire and hanging down on either side, it was 
cut through by the passage of the current, and the two pieces, falling to the 
