EFFECTS OF DISSOCIATION, 529 



tion of the explosive substance and by the composition of 

 the products of explosion. These are further denned, a priori, 

 in the case of a total combustion, that is to say, when the 

 substance contains a sufficient quantity of oxygen. This is the 

 case with nitroglycerin and nitromannite, where carbon and 

 hydrogen are entirely transformable into water and carbonic 

 acid. 



If, on the other hand, oxygen be deficient, the products vary 

 with the conditions, and several reactions are often produced 

 simultaneously, as is the case with ammonium nitrate, with 

 gun-cotton, and also with service powder. This last, for 

 instance, does not only produce carbonic acid, potassium sul- 

 phate, and carbonate, the results of a complete explosion, but 

 also carbonic oxide and potassium sulphide, due to an imperfect 

 reaction. 



In both cases it must be borne in mind that the products 

 developed at the moment of the explosion, and at the high 

 temperature of such explosion, are not necessarily the same as 

 the products observed after cooling. A part of the water, for 

 instance, may be found decomposed into oxygen and hydrogen, 

 a part of the carbonic acid into oxygen and carbonic oxide. 

 Such are the effects of dissociation; it tends to diminish the 

 pressure of the system at the moment of the explosion, owing to 

 the lesser amount of heat developed, but heat is regenerated, 

 even during the process of cooling ; and it is this which 

 moderates the expansion and brings the total amount of work 

 to the same value as if dissociation had not taken place. 



4. The liberated heat is calculated from our knowledge of the 

 products of the reaction, either under constant pressure or under 

 constant volume ; it is calculated, that is, if the reaction is not 

 accompanied by any mechanical work. Otherwise, there is a 

 transformation of a part of this heat into work. Now, it is 

 precisely this transformation which it is proposed to effect by 

 the use of explosive substances. It never takes place except 

 fractionally, as we see in all transformations of this kind in 

 mechanics. The fraction available in principle amounts almost 

 to one-half in ordinary gunpowder; in practice we have not 

 obtained more than one-third. This figure defines the maximum 

 results which have been observed for this substance, constantly 

 employed in artillery. 



5. The volume of gases also results from chemical reaction ; 

 it is easily found from the equation which expresses this re- 

 action. It may be calculated either at a temperature of 0, and 

 under normal pressure, or at any temperature or pressure. It 

 should be observed that in making this calculation it is neces- 

 sary to add to the permanent gases the volume of the bodies, 

 such as water or mercury, which are susceptible of acquiring 

 the gaseous stage at the explosive temperature. Water, in fact, 



2 M 



