1864.] 



Gun-cotton and Gunpowder, 



207 



have already been pointed out by Frankland in his interesting paper on the 

 influence of atmospheric pressure upon some of the phenomena of combus- 

 tion. The heat furnished by an incandescent or melting platinum wire is 

 greatly in excess of that required to induce perfect combustion in gun- 

 cotton which is]actually in contact with, or in close proximity to it ; and the 

 heat resulting from this combustion, which is contained in the products of 

 the change, will suffice to cause the transformation of the explosion to pro- 

 ceed from particle to particle. But if the pressure of the atmosphere in 

 which the gun-cotton is submitted to the action of heat be reduced, the 

 gases resulting from the combustion of the particles nearest to the source of 

 heat will have a tendency, proportionate to the degree of rarefaction of the 

 air, to pass away into space, and thus to convey away from proximity to the 

 cotton, more or less rapidly and completely, the heat necessary to carry on 

 the combustion established in the first particles. Thus, when the heated 

 wire is enveloped in a considerable body of gun-cotton, the ignition of the 

 entire mass is apparently not instantaneous, if attempted in a highly rarefied 

 atmosphere, because the products of the combustion first established in the 

 centre of the mass of gun-cotton escape rapidly into space, conveying away 

 from the point of combustion the heat essential for its full maintenance ; 

 the gun-cotton therefore undergoes at first an imperfect form of combus- 

 tion, or a kind of metamorphosis different from the normal result of the 

 action ©f heat upon this material. But the effects of the gradual generation 

 of heated gases from the interior of the mass of cotton are, to impart some 

 of their heat to the material through which they have to escape, as well as 

 gradually to increase the pressure of the atmosphere in the vessel, and thus 

 to diminish the rapidity of their escape ; hence a condition of things is in 

 time arrived at when the remainder of the gun-cotton undergoes the ordi- 

 nary metamorphosis, a result which is accelerated by maintaining the 

 original source of heat. If, however, the gun-cotton be employed in a 

 compact form (in the form of twist or thread), and placed only in contact 

 with the source of heat at one point, the heat will be so effectually conveyed 

 away by the escaping gases, that the material will undergo even what may 

 be termed the secondary combustion or metamorphosis for a limited pe- 

 riod only ; so that, if a sufficient length of gun-cotton be employed, it will 

 after a short time cease to burn, even imperfectly, because the heat essen- 

 tial for the maintenance of any chemical activity is soon completely abs- 

 tracted by the escaping gases. These results may obviously be modified in 

 various ways, as shown in the experiments described : thus, by increasing 

 and maintaining the source of heat independent of the burning cotton, the 

 slow combustion may be maintained through a much greater length of the 

 material until the pressure of the atmosphere is increased, by the products 

 disengaged, to an extent sufficient to admit of a more rapid and perfect 

 metamorphosis being established in the remainder of the material ; or the 

 same result may be attained, independently of the continued application of 

 external heat, by employing a thicker mass of cotton, or by using the 



