312 



Mr. Abel on the Combustion of 



[April 31, 



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 che- 

 mical 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 appUed, in escaping into the rarefied space. 

 For 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 expan- 

 sion 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 har- 

 mony with the observations made by Mitchell, Frankland, and Dufour, with 

 regard to the retarding influence of diminished atmospheric pressure upon 

 the combustion of fuses. 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 

 ignited. There is no doubt that the products of decomposition of the gun- 

 powder, obtained under these circumstances, differ greatly from those which 

 result from its explosion in confined spaces or in the open air under ordi- 

 nary atmospheric conditions. In all the experiments conducted in the 

 most highly rarefied atmospheres (at pressures of 0*5 to 1*5 in inches of 

 mercury), the contents of the vessel, after the final deflagration of the 

 powder, always possessed a very peculiar odour, similar to that of horse- 

 radish, due to the production of some sulphur-compound ; nitrous acid 

 was also very generally observed among the products. It is readily con- 

 ceivable that the chemical action established between the constituents of 

 gunpowder, under the circumstances described, must be of a very imperfect 

 or partial character, the conditions under which it is established being un- 

 favourable to its energetic development. 



In describing the phenomena which accompany the ignition of gun- 

 cotton in atmospheres of different rarefaction, I have pointed out that, at 

 pressures varying from one to twenty-four in inches of mercury, a pale 

 yellow flame was observed, which increased in size with the pressure of the 

 atmosphere ; and that a flame of precisely the same character was pro- 

 duced in rarefied atmospheres of nitrogen. The experiments instituted in 

 nitrogen show that the explosion of loose tufts of gun-cotton in atmo- 

 spheres of that gas, even at normal pressures, was always attended with a 

 pale yellow flash of flame, quite different from the bright flash produced by 

 igniting gun-cotton in air. The same result was observed in atmosplieres 



