CHEMICAL THEORY OF SOLT'TIOXS. PAKT I. 23 



and some other simple cases Avliicli will be mentioned further on. 

 In the case of ideal solutions it is quite easy to establish general 

 quantitative relations and these may serve as the norm in the 

 investigation of actual cases. Even with the ideal solutions there 

 are so many problems that the discussion must be restricted 

 to the more important ones. The influence of pressure has not 

 been taken into consideration because it is in general quite 

 insignificant. 



(a) Isothermal delations. 



Equation (3) demonstrates the applicability of the law of 

 mass action to ideal solutions of any composition. It is indeed 

 very inconvenient to use the idea of spatial concentration in the 

 case of concentrated solutions and this must be replaced by that 

 of molar fraction. Guldbeeg and Waage reached the conclusion 

 that the active mass of a pure solid substance is constant at a 

 constant temperature. From this standpoint the relations of 

 solubility at a constant temperature can be readily surveyed and 

 described. 



When the solid phase has the composition (Si., So,,^ 



the composition of the solution which is in equilibrium with the 

 solid must satisfy the following equation : 



c;'^c:^ = K (14) 



Vi, V2, are the so called molecular coefficients or exchange 



numbers (Helm). K is a function of temperature and pressure. 

 But as the influence of the latter is generally very slight K may 

 be considered to be constant when the temperature is constant. 

 Equation (14) which represents the law of mass action in 



