CHANGE IN CONSTITUTION OP SULPHUR "AND CAEBON. 505 



view of the heat liberated and the volume of gases produced by 

 a given weight of nitre, we obtain the following table 



15. Equation (5) would be that liberating the maximum 

 heat, if this maximum still subsisted at the temperature of 

 combustion, in spite of the variation in the specific heats. 

 Hence it seems that this reaction should take place to the 

 exclusion of the others. In any case it should be so with the 

 integral transformation of the oxygen by the carbon changed 

 into carbonic acid in accordance with equations (2) and (5). 



16. But these preponderating productions are checked by 

 the following circumstances : 



(1) Dissociation, which does not allow either the whole of 

 the potassium sulphate or the whole of the carbonic acid to be 

 formed at the high temperature developed by the combustion. 



(2) The change in the constitution of the sulphur at this high 

 temperature (see p. 27), a change which tends to increase in 

 an imperfectly known but certainly considerable proportion the 

 heat of formation of the compounds of this element. This fact 

 may play a specially important part in the way of increasing 

 the thermal importance of the polysulphides. 



(3) The change in the constitution of the carbon at a high 

 temperature ; this element existing in the gaseous state, at least 

 for an instant, in the flames, and the heat of formation of carbonic 

 oxide being then increased so as to become equal to, or perhaps 

 higher than, that of carbonic acid for the same weight of oxygen. 1 



Owing to these circumstances the thermal maximum calcu- 



1 " Annales de Chimie et de Physique," 4 s serie, torn, xviii. pp. 162 and 

 175, 176 ; 1869. " Revue Scientifique/' Novembre, 1882, pp. 677-680. 



