844 



Wlien liowever //, ij/ becomes greater than (//, — ï^) : (A/ — ■»/), while 

 it remains smaller than (F, — v) : {V — v), only AW,, can become 

 := and conseqnently only a point of maximnm pressnre occurs. 



In order that A T% may also become =0, V — f^ and 

 as Fj — V is ordinarily ten thousand times as great as V — v, y^ : y 

 mnst obtain a \'ery great value. As L W,, and A V,i may become 

 = 0, the P, 7^-curve has then a point of maximum pressure and of 

 maximnm tempeiatnre. Therefore we find : the P, J'-curve of the 

 binary equilibrium B -\- L -\- G is a curve ascending with the tem- 

 perature, when the solvent is less volatile or only a little more 

 volatile than the solid substance; it may show a point of maximum 

 pressure when the solvent is much more volatile than the solid sub- 

 stance; it may have, besides a point of maximum pressure, also a 

 point of maximum temperature, when the solvent is a thousand 

 times more volatile than the solid substance and this melts with 

 increase of volume. ^) 



Let us now consider the saturationcurves under (heir own vapour- 

 pressure of B. For this we take firstly the case sub 1. We now 

 choose the P and T in such a way, that the saturationcurve of B 

 is represented by r.v and the liquidcurve of the region LG by e d 

 in fig. 1. On decrease of pressure e d approaches to ?'.s'. We assume 

 that the first common point arises by the coincidence of r and s. 

 This point is represented in fig. 2 by //. In the same way as for 

 the case that the solid substance is a binary compound we can 

 prove, that e d and /• .v do not touch one another in h and that 

 although Pi, is the highest pressure, under which the system 

 p J^ L -\- G occurs, the point A is yet not a point of maximum 

 pressure of the saturationcurve under its own vapourpressure. The 

 vapour corresponding with li is indicated in fig. 2 by h^. 



Lowering the pressure still 

 more, the intersectingpoint of 

 e d and r s of fig. 1, shifts 

 within the triangle; in fig. 2 

 a similar intersecting point is 

 represented by a and the cor- 

 responding vapourpoint by a^. 

 From the manner in which the 

 three phase triangle arises, it 

 follows, that this must turn its 

 side solid-gas {Ba^) towards BC. 

 When on further decrease of piessure the curves ed and rs of 



Fig. 2. 



^) See also Ph. Kohnstamm; these communications 15, (1907). 



