1864.] 



Gun-cotton and Gunpoioder. 



211 



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 grains ; 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 gunpowder, and under 

 pressures gradually increased, in successive experiments, from '07 to 3 in 

 inches of mercury. The same weight of gunpowder (4 grains) was used in 

 all the experiments. In those made under a pressure of 1 inch, the results 

 observed were 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, 

 after the lapse of from ten to twenty seconds, 3 or 4 grains were defla- 

 grated at once, the remainder of the powder being thereby projected from 

 the cup. At a pressure of 1*5 inch, 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 

 inches, 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 inches, 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 deflagra- 

 tions of the powder-grains were in some instances somewhat more bril- 

 liant. 



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 sul- 

 phur, that the particles of powder cannot be raised to the temperature 

 necessary for their ignition, until at any rate the greater part of that ele- 

 ment has been expelled from the mixture, in consequence of which the por- 

 tions first acted upon by heat will have become less explosive in their cha- 

 racter, and require, therefore, a higher temperature for their ignition than 



R 2 



