214 



Mr. Abel on the Combustion of 



[April 21, 



burns slowly along the tube, with a very small sharp tongue of pale flame, 

 a jet of flame is obtained at the mouth of the tube, by the burning of 

 the gas evolved by the decomposition of the gun-cotton. Sometimes, and 

 especially when wider tubes are employed, the slow combustion will pro- 

 ceed only for a short distance, and then, in consequence of the ignition of 

 a mixture of the combustible gases and air within the tube, the gun-cotton 

 will explode with great violence, the tube being completely pulverized, 

 and portions of unburnt cotton scattered by the explosion. If still wider 

 tubes are employed, the cotton will flash into flame almost instantaneously 

 throughout the tube directly the flame reaches the opening : in these cases 

 the explosion is not violent ; sometimes the tube escapes fracture, and at 

 others is broken in a few places, or torn open longitudinally, a slit being 

 produced in the tube directly over the gun-cotton. By using narrow tubes 

 and gradually shortening the tube through which the gun-cotton was 

 passed, pieces of the twist being allowed to project at both ends, it was 

 found, upon inflaming the material which projected on one side, that the 

 slow form of combustion, induced in it as soon as it burned into the tube, 

 was maintained by that portion which burned in the open air on the other 

 side, when the combustion had proceeded through the tube. Eventually, 

 by the employment of a screen of wood or card-board containing a perfo- 

 ration of the same diameter as that of the gun-cotton-twist, through which 

 the latter was partially drawn, the alteration of the combustion of the 

 material from the ordinary to the slow kind was found to be invariably 

 efi^ected. On the one side of the screen, the gun-cotton burned with the 

 ordinary flame and rapidity, until the combustion extended to the perfo- 

 ration, when the flame was cut off and the material on the opposite side of 

 the screen burned only slowly, emitting the small-pointed tongue of pale 

 yellow flame. 



These results indicate that if, even for the briefest space of time, the 

 gases resulting from the first action of heat on gun-cotton upon its ignition 

 in open air are impeded from completely enveloping the burning extremity 

 of the gun-cotton-twist, their ignition is prevented ; and as it is the com- 

 paratively high temperature produced by their combustion which effects 

 the rapid and more complete combustion of the gun-cotton, the momentary 

 extinction of the gases, and the continuous abstraction of heat by them as 

 they escape from the point of combustion, render it impossible for the 

 gun-cotton to continue to burn otherwise than in the slow and imperfect 

 manner, undergoing a transformation similar in character to destructive 

 distillation. 



These facts appear to be fully established by the following additional 

 experimental results : — 



1 . If, instead of employing in the above experiments a moderately com- 

 pact gun-cotton-twist, one of more open structure is used, it becomes diflSi- 

 cult or even impossible to efi'ect the described change in the nature of the 

 combustion, by the means described, because the gases do not simply burn 



