J. P. Cooke, Jr.—Berthelot's Thermo- Chemistry. 263 
chemism. Not only, however, is it, at present, impossible to 
eliminate from our results the effects of physical changes ; but, 
moreover, when we study the details of the chemical processes 
the water becomes saturated with zinc sulphate, although a 
large excess, both of sulphuric acid and of zinc, may be present. 
But, after making all allowances for the potency of physical 
conditions, it would undoubtedly appear from the present 
standpoint of Chemistry that there must be certain differences 
of qualities inherent in the atoms, which correspond to differ- 
ences of chemical affinity and which are important factors in 
determining chemical changes, and it is certainly legitimate to 
seek to measure what we may call the relative potential of the 
atoms when in a state of indefinite expansion. It is obvious, 
however, from Berthelot’s discussion of the subject, that we 
to the theory which is accepted by the great majority of chem- 
. 
Substances when in the state of gas, and uses throughout his 
