196 Dr. W. C. M°C. Lewis on the 



Now /3»\ /d£\ ,^\ _ _ 



The assumption is the same as in the first relation. 



(c) In the Dutch edition of the ' Continuity of the liquid 

 and gaseous states ' of van der Waals the following expression 

 occurs : 



K2 _ C (l + qp 

 vft 



where C = the volume of a given mass of vapour, 

 v =the volume of the same mass of liquid. 

 u =the coefficient of gaseous expansion, 

 ft =the compressibility of the liquid. 

 This equation does not appear in the German edition nor 

 in the English translation, its removal being probably due 

 to the author. The relation is based on van der Waals' 

 equation, and further it is assumed in its deduction that the 



term -g- for the liquid state is negligible compared with 



the term -, j^- r In connexion with its application chiefly 



to elementary substances (solid as well as liquid), cf Traube, 

 Verhandlung d. deutsch. pliysik. Gesellschaft, 1909. 



(d) In the Zeitsclir. filr pliys. Chemie, xl. p. 176> 1902, 

 T. W. Richards writes the equation 



av 



where C is the thermal capacity (say per gram molecule). 

 Richards obtained this by considering that the heat which 

 had to be added to a small volume element dv to raise the 

 temperature dt, namely Gdt, was equivalent to the internal 

 work done YLdv. He applies this to elementary substances, 

 obtaining exceedingly large numerical values. The assump- 

 tions made are, first that K is independent of temperature, 

 and second that it is practically independent of volume, which 

 is far from the truth. 



(e) Traube (Zeitsclir. fur anorganische Chemie, xxxiv. 

 p. 416, 1903) takes up Richards' expression and shows that 

 it yields values which are pretty exactly three times the 



