SYSTEMS COMPOSED OF MOLECULES. 207 



entropy, if the masses of fluid were different. It is evident, 

 therefore, that it is equilibrium with respect to generic phases, 

 and not with respect to specific, with which we have to do in 

 the evaluation of entropy, and therefore, that we must use 

 the average of H or of 7; gen , and not that of 77, as the equiva- 

 lent of entropy, except in the thermodynamics of bodies in 

 which the number of molecules of the various kinds is 

 constant. 



