Ihermodynamical Theory of Ternary Mixtures. 959 



From equation (64) we see that the addition of C 2 to the 

 C phase always causes an increase of the concentration of 

 C 2 in the C * phase. From equation (63) we see that the 

 addition of C x may cause either an increase or a decrease of 

 the concentration of C 2 in the C * phase. 



The quantity S 2 * may be evaluated from a knowledge of 

 the therm odynamical properties of the solution of C 2 in 

 C * by means of formula3 which I have given previously "f. 

 Hence the quantities S 12 and S 22 may be evaluated from 

 partition equilibrium data and data relating to the solution 

 of C 2 in C *. 



If we regard equation (62) as determining s 2 as a function 

 of *!, 5 2 *, p, and 6, we have the equation 



~ds 2 _ _ S 21 (s u s 2 , p, 0) /gy, 



<^1 S 22 (Si, S 2 ,/>, 0)' 



which does not involve the properties of the solution of C 2 

 in C *. It will be seen that this equation is very similar 

 to equation (39) in the section dealing with Solubility 

 Influence. This similarity is due to the similarity of the 

 corresponding experimental processes. In both cases we 

 are investigating the manner in which s 1 and s 2 must vary 

 simultaneously so as to keep the potential of 2 constant, 

 — in one case equal to the potential of solid C 2 and in the 

 other equal to that of C 2 in a solution of C 2 in C * of a certain 

 concentration. 



We will next consider another two-phase liquid system. 

 Suppose that C and C, are two slightly miscible liquids, and 

 that C 2 is a substance soluble in C , but insoluble in C x . The 

 two-phase liquid system formed by these substances will 

 consist of a ternary mixture of C , C^ and C 2 , and (if we 

 neglect the very small amount of C 2 dissolved in the C\ 

 phase owing to the presence of C ) a binary mixture of G 1 

 and C . The effect of variations of pressure on such a system 

 has been investigated by Trouton J, the components being 

 water (C ), ether (C\), and sugar (C 2 ). As the theoretical 

 treatment by Trouton of his experimental results is erroneous, 

 we will consider the correct theory of the experiment. 



When ether is placed in contact with water, a certain 

 amount of water is absorbed by unit mass of ether. If ether 

 is placed in contact with an aqueous solution of sugar, less 

 water is absorbed by the ether. Trouton finds that if the 

 pressure on this latter system is increased more water is 

 absorbed by the ether, and that at a certain pressure the 



t Phil. Mag. xxv. p. 31 (1913). 



X Roy. Soc. Proc. lxxxvi. A. p. 149 (1912). 



