387 



\ \ 3 



4^ 



Fis. 1. 



of fig. 4 (VUT) ; we imagine the coiTesponding point N'i on the 



vaponr curve a/j^. We may 

 now distingiiisi) two cases, 

 according as the volume of 

 F+F' increases or decreas- 

 es on melting (congruent 

 or incongruent;. That there 

 may be agreement with our 

 previous derivations, we 

 shall assume that the vo- 

 lume increases. We see 

 from fig. 4'(Vni) that the 

 points N, S and D (and 

 consequently also the corresponding points N„ S^ and Dj must 

 then lie with respect to one another as in fig. 1. 



The liquid curve (tig. 1) has, therefore, its maximum temperature 

 at N, the vapour curve at JSf^. On the liquid curve, therefore, the 

 temperature decreases from jY, on the vapour curve from iV^ in 

 both directions. 



Let us now take a temper-ature 1\, lower than the maximum 

 temperature of sublimation 7/? ; the saturation- and vapour saturation 

 curves under their own vapour pressures (which are only partly 

 drawn in the figure) corresponding to this temperature T^, are indi- 

 cated by "1". In tig. 2 we find the complete diagram. From figs. 1 

 and 1 — 3 (VIII) it follows, (as is also drawn in fig. 2), that at 

 temperatures lower than the maximum point of sublimation, the two 

 liquid points and also the two vapour points of intersection are 

 situated in opposition with respect to FF'. 



We now take a temperature T^ between the maximum point of 

 sublimation Tn and the minimum meltingpoint 7^. The saturation 

 and vapour saturation curve under their own vapour pressures, 

 corresponding with this temperature 7\ and only partly drawn in 

 tlie figure, are indicated by "2". One of the liquid points of intersection 

 is situated between S and D, the corresponding vapour point of 

 intersection between S^ and D^. We hnd the complete diagram in 

 fig. 3. The points ƒ and g are situated in opposition, f\ and <j^ in 

 conjunction with respect to the line 7^7^''. The tigs. 2 and 3 differ from 

 one another only as regards the position of the point (/^ with respect 

 to the line FF'. When fig. 2 passes into fig. 3 the point g^ falls 

 on the line FF' ; this is the case at the maximum temperatm-e of 

 sublimation Tu; the points g and g^ of this transition figure agree 

 then with the points D and D^ of figure 1. 



25* 



