777 



intersection arise; tlie one disappears on BC by the coincidence of 

 e and r, tlie otlier on BA by the coincidence of d and s (tig. 1). 

 It is e^"ident that J/ is then the point of maximnm-pressure of the 

 satnrationcurve of B nnder its own vapoui'pressnre, the corresponding 

 vapourpoint M^ is situated of course on tlie line BM. 



One can understand the occurring diagram with the aid of fig. 5 ; 

 lierein we have to give an opposite direction to the arrows and we 

 have to replace the points of minimunipres&ure m and ni^ by the 

 points of maximumpressure M and M^ ; further the triangles Baa^ 

 and Bbb^ are to be drawn, in such a way that they turn their 

 sides solid — gas towards the line BMM^. 



We shall consider some points in another way now. In order to 

 find the conditions of equilibrium for the equilibrium B -\- L -\- G, 

 when the vapour consists of A and C only, we equate in the 

 relations (i) — (8) ii = 1 ; in the general values of ^ and C (II) 

 we put a ^ 0, ji = J and ?/i = 0. The condition for tlie occurrence 

 of a point of maximum- or of minimumpressure {dP=0) becomes then : 



..=z(l -y).v, ........ (19) 



This relation also follows from (9), when we put [3 = 1. This 

 means : the point of maximum- or of minimumpressure of the saturation- 

 curve of B under its own vapourpressure and the corresponding 

 vapourpoint are situated with point B on a straight line (fig. 5). 



In order to determine the change of pressure along a saturation- 

 curve under, its own vapourpressure in its ends on the sides .5C and 

 BA (tigs. 4 and 5) we put in (16) i3=zl. We then find 



7^1 =^(l-^)-^ (20) 



In this S and A Fj are determined by (13j and (15), when we 

 put herein /9=rl. Consequently >S is always positive. When we 

 apply (20) to the figures (4) and (5), tlien we see that the change 

 of pressure is in accordance with the position of the sides solid-gas 

 and solid-liquid of the threephasetriangles. 



Now we have treated the case that either the binary compound 

 F (figs. 2 and 3) or the component B (figs. 4 and 5) occurs as solid 

 phase. When F and B occur both as solid phases, then the two 

 saturationcurves under their own vapourpressure can either intersect 

 one another or not. We only consider the case, drawn in fig. p, that 

 the two curves intersect one another in a point; the vapour, being 

 in equilibrium with the liquid s, is represented by .s^ {.s-., or s\j. 



A similar case may occur for instance in the system Na2S04 -f- 

 water -]- alcohol, then curxc cs is the saturationcurve under its own 



