770 



then we see that this is impossible. Yet we can imagine a saturation- 

 curve with a point of maximum- and a point of minimumpressure. 



C 



Fig. 3. 



When we trace cnrve hn starting from n, we arrive first in the 

 point of maximum- afterwards in the point of minimumpressure. 

 We will refer to this later. 



7Y' <^ T. Now we take a temperature 7' a little above the minimum 

 meltingpoint Tf of the solid substance F. Then we must distinguish 

 two cases, according as the solid substance expands or contracts on 

 melting. We take the first case only. 



Then we find a diagram like tig. 4 (XI) ; herein, however, the 

 same as in figs. 2 and 3, we must imagine that the vapourcurve 

 h,a,n, is replaced by a straight vapourline 6J/, on side CA. We 

 will refer later to the possibility of the occurrence of a point of 

 maximum- and a point of minimumpressure. 



We can, however, also get curves of a form as curve hn and the 

 curves situated inside this in fig. 6 (XI); these curves show as well 

 a point of maximum- as a point of minimumpressure. 



When we draw the saturationcurves under their own vapour- 

 pressure for different temperatures, we can distinguish two principal 

 types; we can imagine those to be represented by figs. 5 (XI) and 

 6 (XI). At temperatures below Tf these curves are circumphased, 

 above 7V they are exphased. In tig. 5 (XI) they disappear in a point 

 H on side BC, in fig. 6 (XI) in a point R within the triangle. The 

 corresponding straight vapourlines disappear in fig. 5 (XI) at Th in 

 the point 6'; in figure 6 (XI) they disappear at I'r in a point R^, 

 the intersecting point of the line FR witii the .'ide CA. 



