EFFECTS OF SLOW AND RAPID DECOMPOSITION. 7 



number of observations, that each mode of decomposition of a 

 given substance commences at a certain temperature, and in 

 a given time a limited weight of substance is decomposed. 



Special stress is laid upon the singular property which 

 ammonium nitrate possesses of undergoing several distinct 

 modes of decomposition, according to the rapidity of heating 

 and the temperature to which the substance is raised. Of these 

 decompositions, some take place with liberation of heat, others 

 with absorption of heat. 



5. A similar property is possessed by most bodies which liberate 

 heat during decomposition, and especially by explosive bodies, 

 properly so called. It is particularly manifested in proportion 

 to the difference of the local conditions developed by progressive 

 heating in a mass which is not instantaneously decomposed. 



On the other hand, the sudden explosion of detonating sub- 

 stances, when they consist of a definite compound such as gun- 

 cotton, nitroglycerin, mercury fulminate, etc., and when the 

 explosion is readily brought about, the reaction being uniformly 

 distributed throughout the entire mass, appears likely, generally 

 speaking, to give rise to simple and stable products. The 

 extreme conditions of temperature and molecular vibration 

 which accompany the phenomena hardly allow of its being 

 otherwise in a molecularly homogeneous mass. 



This is, in fact, what has been verified during the explosion 

 of gun-cotton, as studied by Sarrau and Vieille. 



If previous observers have noticed more complicated decom- 

 positions, it is because the conditions have been such that 

 the mass underwent partial coolings, and was decomposed at 

 certain points by distillation rather than by true explosion. 



From researches made in conjunction with Vieille on the 

 explosion of mercury fulminate, it has been established that this 

 substance is also decomposed in the most simple manner into 

 carbonic oxide, nitrogen, and mercury. With gunpowder the 

 diversity of local conditions of combustion cannot, under any 

 circumstances, be avoided, because a mechanical mixture of 

 three pulverised bodies can never attain the same degree of 

 homogeneousness as a true chemical combination. 



6. However, each of the products of the explosion is none the 

 less formed according to a regular law"; all result, in short from 

 a small number of definite transformations occurring at various 

 points of the mixture, and the diversity of which is the conse- 

 quence of the variety of the local conditions. 



If the products remained in contact for a sufficient time, they 

 would undergo reciprocal actions, which would bring them to 

 the state corresponding to the maximum heat liberated (at the 

 temperature and under the same conditions of the experiment) ; 

 but the sudden cooling which they experience prevents this 

 state from being realised. 



