134 Dr. Thomas Ewan on 



Substitute this value of k in equation 2, and it becomes 



and finally equation (i), gives 



1o V = St 



which value substituted in 5 gives 



r m T '-F cT/T -F\ 2 „ cZQT-Fl 



In the following table the vapour pressures of some 

 copper chloride solutions calculated from their freezing 

 points, by means of equation (5), are compared with those 

 found. The determinations used were made by Mr. 

 Ormandy and myself* 



Concentration 

 in grams. CuCl 2 

 to 1 gr. water. 



T -F 



dQ 



dTv (Thomsen) 



p. cal. 



p, found. 



Diff. 



•05 



'I 



'2 



i"9°5 



4*12 



9* 6 3 



'22 



78 



2.48 



15-086 

 14788 

 14*104 



i5'°33 

 14706 



!4-o35 



•053 

 •082 

 •069 



The differences are rather larger than the error in the 



measurements of the vapour pressures, but may be due to 



some extent to errors in the freezing points. 



Equation (5) also shows that v. Babo's law, according to 



v 

 which — is independent of temperature is only true when 



Po 



dw 



Q — will evidently decrease with rising temperature 



V 



when — is positive, and vice versa. This conclusion has 

 already been reached by Dieterici,f though in a different way. 



* Chem. Soc. Journ., 1892, p. 769. 

 t Wied. Ann., 45, p. 207, 1892. 



