CHEMICAL THEOEY OF SOLUTIONS. PART I. 



27 



Fig. 7. 



having the form shown in 

 Fig. 8. 



It must be remembered 

 that no compound exists in 

 the ideal solution itself, be- 

 cause the formation of a com- 



In a quaternary system 

 the surface of solubility has 

 the form represented by Fig. 

 7, B. When the molar frac- 

 tion of ©4 exceeds a certain 

 value, the product G"' C-i'- C^'^ 

 can no longer be equal to K, 

 but falls below it. Hence the 

 surface must have a maximum 

 point, for which the value of 

 •S^ is the maximum. This point 

 lies on the straight line con- 

 necting the points ©^ and r. 



When the solid is a quater- 

 nary compound, the surface of 

 solubility will be a closed one, 



