372 GENEKAL DATA. 



but capable of assuming the gaseous state at the temperature 

 of explosion. Much discussion often arises on this head. 



(4) The knowledge of the state of dissociation of the products 

 at the moment of explosion and during the period of cooling 

 (p. 8). 



In fact, up to the present this datum is known with precision 

 for scarcely any compound body, and our ignorance in this 

 respect is one of the principal causes of the divergence observed 

 between the practical results and the data of theoretical calcula- 

 tion. 



(5) The knowledge of the weight of oxygen actually employed 

 in the explosive reaction. 



(6) The knowledge of the weight of oxygen required for total 

 combustion is deduced from the preceding. 



4. The heats of formation of the components and products 

 comprise : 



(1) The knowledge of the heats of formation of these various 

 bodies from their elements ; quantities given in the thermo- 

 chemical tables (p. 125 and following). 



(2) Their heat of total combustion by free oxygen, or ly the 

 oxidising compounds (nitrates, chlorates, oxides, etc.). 



(3) The knowledge 'of the heat of vaporisation of bodies 

 actually liquid or solid, but capable of assuming the gaseous 

 state in the conditions of the explosion (p. 140). 



(4) The heat liberated by the explosive transformation is also 

 deduced from the foregoing data, which are supposed to be 

 known. On the other hand, it may be measured directly and 

 employed in the inverse calculation of these same data. 



5. The specific heats of the components and products are 

 generally known by the tables for the ordinary temperature 

 (pp. 141-143). For high temperatures, such as are developed 

 during the explosion, our knowledge on this point is very im- 

 perfect. 



From the mean specific heat of the products is deduced the 

 temperature developed during the explosion. The calculation is 

 made according to the knowledge of the quantities of heat 

 (pp. 11 and 19) ; but the accuracy of the result is subordinated 

 to the knowledge of the dissociation and that of the specific 

 heats (see p. 18). 



Processes of direct measurement for the temperatures would 

 be preferable ; but hitherto it has not been possible to try them 

 with any probability, except in one single case, namely with 

 black powder. 



6. The densities of the components and products may be 

 measured at the ordinary temperature (p. 144). 



(1) The molecular volumes are obtained from them. A 

 knowledge should be added of the co-efficients of expansion of 

 the various solid, liquid, or gaseous bodies, so as to deduce 



