204 



Mr. Abel on the Combustion of 



[April 21, 



II. " On some Phenomena exhibited by Gun-cotton and Gunpowder 

 under special conditions of Exposure to Heat.''^ By F. A. Abel, 

 F.H.S. Received March 29, 1864. 



The experiments upon which I have been engaged for some time past, in 

 connexion with the manufacture and properties of gun-cotton, have brought 

 under my notice some interesting points in the behaviour of both gun- 

 cotton and gunpowder, when exposed to high temperatures, under parti- 

 cular conditions. I believe that these phenomena have not been previously 

 observed, at any rate to their full extent, and I therefore venture to lay 

 before the Royal Society a brief account of them. 



Being anxious to possess some rapid method of testing the uniformity 

 of products obtained by carrying out General von Lenk's system of manu- 

 facture of gun-cotton, I instituted experiments for the purpose of ascer- 

 taining whether, by igniting equal weights of gun-cotton of the same com- 

 position, by voltaic agency, within a partially exhausted vessel connected 

 with a barometric tube, I could rely upon obtaining a uniform depression 

 of the mercurial column, in different experiments made in atmospheres of 

 uniform rarefaction, and whether slight differences in the composition of 

 the gun-cotton would be indicated, with sufficient accuracy, by a corre- 

 sponding difference in the volume of gas disengaged, or in the depression 

 of the mercury. I found that, provided the mechanical condition of the 

 gun-cotton, and its position with reference to the source of heat, were in 

 all instances the same, the indications furnished by these experiments were 

 sufficiently accurate for practical purposes. Each experiment was made 

 with fifteen grains of gun-cotton, which were wrapped compactly round the 

 platinum wire ; the apparatus was exhausted until the column of mercury 

 was raised to a height varying from 29 inches to 29*5 inches. The flash 

 which accompanied the deflagration of the gun-cotton was apparently 

 similar to that observed upon its ignition in open air ; but it was noticed 

 that an interval of time always occurred between the first application of 

 heat (or incandescence of the wire) and the flashing of the gun-cotton, and 

 that during this interval there was a very perceptible fall of the column of 

 mercury. On several occasions, when the gun-cotton, in the form of 

 " roving," or loosely twisted strand, was only laid over the wire, so that it 

 hung down on either side, the red-hot wire simply cut it into two pieces, 

 which fell to the bottom of the exhausted vessel, without continuing to 

 burn. As these results appeared to indicate that the effects of heat upon 

 gun-cotton, in a highly rarefied atmosphere, differed importantly from 

 those observed under ordinary circumstances, or in a very imperfect va- 

 cuum, a 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 



