GENERAL DATA. 373 



therefrom the exact volume of the products at the tempera- 

 ture of explosion. Unfortunately these are data which are bu't 

 little known, and we generally content ourselves with the 

 densities in the cold for solids and liquids, and the densities 

 calculated according to Mariotte's and Gay-Lussac's laws for 



(2) These data are necessary to calculate a priori, according 

 to the same laws, the theoretical pressure which the explosive 

 would develop when detonating in its own volume (p. 30). 



(3) They would be equally useful for calculating the theoretical 

 pressure under any density of charge (p. 30), that is to say, the 

 real volume occupied by the gases at the moment of explosion ; 

 but for this purpose the real density of solid, liquid, and 

 gaseous products should be known exactly. 



7. The pressures developed must be measured directly (p. 20). 



(1) Under various densities of charge. 



(2) A curve is deduced therefrom which permits us to esti- 

 mate according to the experiments themselves, the real pressure 

 developed under a density equal to the unit, viz. the specific 

 pressure (p. 30) as well as, 



(3) The maximum pressure developed by the explosive. It 

 is that of a body detonating in its own volume (p. 30). 



If we admit that there exists a proportion between the 

 pressures and high densities of charge (p. 30), the specific 

 pressure, namely the pressure developed under a density, equal 

 to the unit, will characterise the force of the explosive. 



The effective measurements thus obtained for the real 

 pressures should be compared with the theoretical pressures 

 calculated, as has been said, with the aid of Mariotte's and 

 Gay-Lussac's laws. In this calculation the volume occupied 

 by the solid or liquid products must be taken into account. 



(4) A more certain datum, and one that is more easily calcu- 

 lated a priori and verified experimentally, is the permanent 

 pressure exercised by the gases of explosion reduced to in 

 a determinate and sufficiently resisting capacity (p. 32). It is 

 often limited by the liquefaction of the products, such as car- 

 bonic acid. 



(5) As a term of comparison, the characteristic product, if not 

 absolute at least relative, can be given, namely, the product of 

 the heat liberated multiplied by the reduced volume of the 

 gases and divided by the specific heat of the bodies formed 

 (p. 32). This product gives essentially in theory the same 

 relations between the various explosive substances as the theo- 

 retical pressure. 



8. The initial work which determines the reaction seems 

 to be summed up in a knowledge of the following data : 



(1) The temperature of incipient reaction, a temperature which 

 must be measured directly. 



