1864.] 



Gun-cotton and Gunpowder. 



209 



ordinary flash ; but the flame was still of a pale yellow. In the preceding 

 experiments clouds of white vapour were observed after the decomposition 

 of the gun-cotton ; in this and the following experiments this white vapour 

 was produced in much smaller proportion. 



Expts. X. to XV. inclusive.— Vressme= 10, 12, 14, 18, 20, 24 inches. 

 The phenomena observed in these experiments did not differ in any im- 

 portant degree from those of Experiment IX. 



Exj). XVI. — The same pressure (24 inches) was employed as in the last 

 experiment, but the piece of gun-cotton-twist was laid double across the 

 wire. In this instance the gun-cotton burned with a bright yellow flash, 

 as in open air. 



Exj). XVII. — Pressure=26 inches. The gun-cotton was laid singly 

 over the wire, as in all experiments but the last. It burned with a flash o 

 bright light, as in open air. 



It appears from these experiments that gun-cotton, when ignited in small 

 quantities in rarefied atmospheres, may exhibit, during its combustion, three 

 distinct luminous phenomena. In the most highly rarefied atmospheres, the 

 only indication of combustion is a beautiful green glow or phosphorescence 

 which surrounds the extremity of the gun-cotton as it is slowly transformed 

 into gases or vapours. When the pressure of the atmosphere is increased to 

 one inch (with the proportion of gun-cotton indicated), a faint yellow flame 

 appears at a short distance from the point of decomposition ; and as the 

 pressure is increased this pale yellow flame increases in size, and eventually 

 appears quite to obliterate the green light. Lastly, when the pressure of 

 the atmosphere and consequently proportion of the oxygen in the con- 

 fined space is considerable, the cotton burns with the ordinary bright yellow 

 flame. There can be no doubt that this final result is due to the almost in- 

 stantaneous secondary combustion, in the air supplied, of the inflammable 

 gases evolved by the explosion of the gun-cotton. It was thought that the 

 pale yellow flame described might also be due to a combustion (in the air 

 still contained in the vessel) of portions of the gases resulting from the de- 

 composition of the gun-cotton ; but a series of experiments, in which 

 nitrogen, instead of air, constituted the rarefied atmosphere, showed that 

 this could not be the case. The results obtained in these experiments cor- 

 responded closely to those above described, as far as relates to the produc- 

 tion of the green glow and of the pale yellow flame. With rarefied atmo- 

 spheres of nitrogen ranging down to one inch of pressure, the green flame 

 was alone obtained; and the pale yellow flame, accompanying the green, 

 became very marked at a pressure of 3 inches, as in the experiments with 

 air. 



It would seem probable from these results, that the mixture of gaseous 

 products obtained by the peculiar change which heat efl'ects in gun-cotton 

 in highly rarefied atmospheres, contains not only combustible bodies, such 

 as carbonic oxide, but also a small proportion of oxidizing gas (possibly 

 protoxide of nitrogen, or even oxygen), and that when the pressure of the 



VOL. XIII. , R 



