171 



the coiTespoiidiiig vapourciirve .][,in^ is then, however, no more a 

 curve situated within the triangle ABC, but it becomes a straight 

 line, which is situated on one of the sides of the triangle. We shall 

 call this line the straight vapourline of the compound F. When A 

 and C are the two volatile components, then this straight vapourline 

 is situated on the side AC. As not a single liquid of curve i1/??i can 

 be in equilibrium with a vapour, which consists of pure A or of 

 pure C, the points A and C can never be situated on the straight 

 vapourline. From this follows: the straight vapourline of the ternary 

 compound F covers only partly the side AC and in such a way 

 that it covers neither A nor B. 



2. The solid substance is a binaiy compound^ of two volatile 

 components. We take a binary compound F of B and C (tig. 1) 

 so that B and C now represent the two volatile components and ^4 

 the non-volatile component. 



In order to deduce the saturationcurve under its own vapour- 

 pressure we may act again in the same way as we did before 

 for the general case. For this we take a detiniie temperature 7^ and 

 a pressure P in such a w^ay that no vapour can be formed and the 

 isotherm consists only of the saturationcurve of F. This is represented 

 in tig. i by pg. 



At decrease of F the region L — G occurs; such a region is 

 represented in tig. 1 by Cdee^ with the liquid-curve de and the 

 straight vapourline Ce^. The liquid e is in equilibrium with the 

 vapour dj, the liquid d with the vapour C and w^ith each liquid of 

 curve ed a definite vapour of the straight vapourline Ce^ is in 

 equilibrium. 



We may distinguish three cases with respect to the occurrence 

 of this region L — G. 



a. In the equilibrium L — G of the binary system BC a point of 

 maximum-pressure occurs. The heterogeneous region L — G arises in 

 a point of the side BC 



b. In the equilibrium L — G of the binary system BC a point of 

 minimum-pressure occurs; one heterogeneous region arises in B and 

 one in C, which come together at decrease of F in a point of BC. 



c. In the equilibrium L—G of the binary system BC neither a 

 point of maximum- nor a point of minimumpressure occurs; the 

 heterogeneous region arises in B or in C 



Here we consider only the last case and we assume in this case 

 that C is more volatile than B; after this the reader can easily 



