134 
MINUTES OE PROCEEDINGS OF 
after the lapse of from ten to twenty seconds, 3 or 4 grns. were deflagrated 
at once, the remainder of the powder being thereby projected from the cup. 
At a pressure of 1*5 in., the same phenomena were observed, but the 
successive deflagrations of fused grains of powder followed more quickly 
upon each other, and the final ignition of several together occurred in about 
ten seconds after the wire was first heated. At a pressure of 2 in., at first 
only one or two of the fused grains were ignited, singly; and several were 
deflagrated together after the lapse of five seconds. A larger quantity of 
the powder was burned, but a portion was projected from the cup as in 
preceding experiments. At a pressure of 3 in., no grains were ignited 
singly; the combustion of the powder was effected after an interval of about 
four seconds, and the greater portion was burned; the combustion, though 
it had gradually become more similar to that of gunpowder in open air, was 
still very slow. 
Experiments made with gunpowder in highly rarefied atmospheres of 
nitrogen furnished results quite similar to those described ; nor was any 
important difference in the character of the phenomena observed when 
oxygen was substituted for air, except that the scintillations and defla¬ 
grations of the powder-grains w r ere in some instances somewhat more 
brilliant. 
The above experiments show that, when gunpowder is in contact with 
an incandescent wire in a highly rarefied atmosphere, the heat is, in the 
first instance, abstracted to so great an extent by the volatilization of the 
sulphur, that the particles of powder cannot be raised to the temperature 
necessary for their ignition, until at any rate the greater part of that 
element has been expelled from the mixture, in consequence of which the 
portions first acted upon by heat will have become less explosive in their 
character, and require, therefore, a higher temperature for their ignition than 
in their original condition. The effect of the continued application of heat 
to the powder thus changed is, to fuse the saltpetre and to establish chemical 
action between it and the charcoal, which, however, only gradually and 
occasionally becomes so energetic as to be accompanied by deflagration, 
because the gas disengaged by the oxidation of the charcoal continues to 
convey away much of the heat applied, in escaping into the rarefied space. 
Eor the same reason, the grains of unaltered powder which are in actual 
contact with the deflagrating particles are not ignited by the heat resulting 
from the combustion, but are simply scattered by the rush of escaping 
gases, at any rate until the pressure in the vessel has been so far increased 
by their generation as to diminish the rapidity and extent of their expansion 
at the moment of their escape. The disengagement, first of sulphur-vapour 
and then of gaseous products of chemical change, unattended by phenomena 
of combustion, when gunpowder is maintained in contact with a red-hot 
wire in very highly rarefied atmospheres, are results quite in harmony 
with the observations made by Mitchell, Erankland, and Dufour, with 
regard to the retarding influence of diminished atmospheric pressure upon 
the combustion of fuzes. The phenomena described are most strikingly 
exhibited by operating upon single masses of gunpowder, of some size, in the 
manner directed above, when the application of the red-hot wire may be con¬ 
tinued from three to five minutes (the gases disengaged during that period 
depressing the column of mercury from 0*5 to 0*7 inch) before the mass is 
