CHAPTER IV. 



PRESSURE OF GASES. 



1. VOLUME OF GASES. 



THE volume of gases formed and their temperature determine 

 the pressure developed when the explosive substance is decom- 

 posed in a constant volume. M. Berthelot proceeds to show 

 how these various data are obtained, and gives the usual 

 formulae found in text-books. 



2. TEMPERATURE. 



1. The temperature developed by an explosive substance 

 can be directly measured, in principle at least. But, as a 

 matter of fact, this measurement, which is exclusively that 

 of very high temperatures, presents extreme difficulties, and 

 there is hardly any known case in which they have been com- 

 pletely surmounted. All that is known is, that the explosion 

 of powder develops a temperature higher than that required for 

 the fusion of platinum, that is to say, than 1775. 



2. The theoretical calculation of the temperature can be per- 

 formed in the following manner. 



The temperature, T, developed in any reaction, such as an 

 explosion, is calculated by dividing the quantity of heat dis- 

 engaged, Q, by the mean specific heat of the products, c, esti- 

 mated between T and the surrounding temperature. 



This expression is exact, provided the true specific heat be 

 introduced into it, as well as the quantity of heat corresponding 

 to the formation of the products which really exist at the 

 temperature and under the conditions of the explosion. 



3. Theory further shows that the heat disengaged, and, conse- 

 quently, the temperature produced, are independent of the size 



