CHEMICAL THEORY OF SOLUTIONS. PAET I. 



35 





= o'n = const. 



ri,')\, are all positive numbers greater or less than unity; 



but they can not all be greater or less than unity, because 

 this would lead to incompatibilities. For example, in a binary 

 system 





and 



\-C\ _ \-i\C\" 



l-C'/ 



l-C\' 



= r. 



.(A) 

 •(B) 



Hence if i\ be greater than unity then r-2 must be less than 

 unity. These two equations (A) and (B) determine the values 

 of Ci and C^'. In other words, the composition of the two 

 phases must have fixed values, which is in accordance with the 

 phase rule. 



For a ternary system we have 



C\" 



a 



2 



a" 



r.,. 



1-0/' -0^'^ 



from which we get 



a" = ^'' ^ + ''' '"' c\" 



i\ — ro '/\ —r<, 





9', — r, 



.(22) 



The former of these two equations represents the solubility 

 curves with respect to the composition of the solid phase, and 



