76 



arises at the reaction between the phases F, L and G, hy A V^ 

 (5) passes into: 



— a {rdw^ + 2sdxdy + tdy') = (x-ct) AV^ X ^^P - • • (6) 



Li 



Let us consider now in fig. 1 the pure solutions of F, thei-efore 

 the solutions of the line Ch. For j^oints between C ^w^ F x — «<C0, 

 for the other points x -«^0. Considering only the solutions of 

 the line Ch, we can consider the system F -\- L -\- G- as binary. 

 Imagining a 7*, ^'-diagram of this system, 77 is the^point of maximum- 

 temperature. From this it is apparent that A F^ is negative between 

 H and F, positive in the other points of the line Ch. From this it 



follows : 



(.r — «) A V^ is negative in points between C and /T, therefore for 

 the solutions of F rich in ^vater. 



{x — a) A T^i is positive in the other points of this line, therefore, 

 for the solutions of F poor in water. 



The same applies also when the point H is situated on the other 

 side of F. 



Let us take now a pure solution rich in water of F, for instance 

 solution c of the fig. 1 ; as the first term of (6) is positive and 

 (.^ — «) A Fj is negative,, it follows: dP is negative. This means that 

 the pressure is a maximum in c. 



When we take a pure solution poor in water of F, for instance 

 solution h of figure 1, (.« — «)^ ^^ is positive, therefore, the pressure 

 is a minimum in h. 



In accordance with the previous considerations, we find, there- 

 fore, that the pressure along the saturationcui've of a ternary com- 

 pound is a minimum for the pure solution j)Oor in water and a 

 maximum for the pure solution ricli in water. 



When the solid substance is a binary compound, as F' in fig. 1 

 or 3, we must equate « = 0. (Of course j:? = for the compound 

 F"). (2) and (3) pass now into : 



{xT + ys) dx -f (.fs 4- yt) dy = ~ C dP . . . . (7) 

 ■^sdx + iitdy =i — {A^C)dP, (8) 



From this we find : 



^^. {rt — s-") dx = [{xs + yt) {A + C) — ^C)] dP . . . (9) 



From this it is apparent that dP can never be zero or in other 

 words: on the saturationcurve of a binary hydrate never a point of 

 maximum- or of minimumpi-cssure can occur. 



In the terrainatingpoint of- a saturationcurve on BC a; :=()■, as 



