114 GENERAL PRINCIPLES OF THERMO-CHEMISTRY. 



BOOK II. 



THERMO-CHEMISTRY OF EXPLOSIVE COMPOUNDS. 



CHAPTEK I. 



GENERAL PRINCIPLES OF THERMO-CHEMISTRY. 



THERMO-CHEMISTRY is based on the following three fundamental 

 principles : 



(1) MOLECULAR WORK. This furnishes the measure of chemical 

 affinity. 



(2) THE CALORIFIC EQUIVALENCE OF CHEMICAL TRANSFORMA- 

 TIONS. The heat disengaged in a definite chemical transformation 

 remains constant, like the sum of the weights of the elements. 



(3) MAXIMUM WORK, The forecast of chemical phenomena is, 

 in virtue of this principle, brought to the purely physical and 

 mechanical notion of the maximum work accomplished by the 

 molecular reactions. 



FIRST PRINCIPLE MOLECULAR WORK. 



1. The quantity of heat liberated in any reaction measures the 

 sum of chemical and physical work accomplished in this reaction. 



Now the heat liberated in chemical action may be attributed to 

 loss of energy, to changes of movement, and, lastly, to the relative 

 changes which take place at the moment when the different mole- 

 cules fly 'towards one another in order to form new compounds. 



It follows from this principle that the heat liberated in a re- 

 action is precisely equal to the amount of work which would 

 have to be accomplished to restore the bodies to their primitive 

 state. This work is at once chemical (changes of composition) 

 and physical (changes of condition) ; the former alone can serve 

 as measure of the affinities. We further see that the heat 

 liberated in one and the same combination varies with the 

 changes of state (solid, liquid, gaseous, or dissolved), with the 

 external pressure, with the temperature, etc. Hence the neces- 

 sity of defining all these conditions for each of the bodies 

 experimented upon. 



2. In general the heat of molecular combination which expresses 



