( 166 ) 



the stable p-.r-ügure will contain the lefthand part of the former and 

 the righthand part of the latter p-,r-figure, which parls will meet 

 where a vapour phase coexists at the same time with a liquid phase 

 and with a mixed-crystal phase. 



As follows from the diagram the vapour branches of the two 

 p-x-Hgures intersect in g, so that g is a vapour which does not only 

 coexist with the liquid /, but also with the mixed-crystal phase /. 



So the three-phase-equilibrium G -f- L -f- F, which is non-variant 

 at constant temperature constitutes the transition between the series 

 of mixed-crystal phases af, and the series of liquid phases Id, which 

 can coexist at a series of pressures with vapour phases of different 

 concentration. 



We find the region of the liquid L above the line dl and the 

 region of the mixed crystals F above the line af. The two regions 

 are separated by a region of liquid -f- mixed crystals lying between 

 the lines la and fq. 



If we now draw some p-x- figures corresponding with different 

 temperatures in the same graphical representation beginning with the 

 triple point temperature of A, and ending with the triple- point tem- 

 perature of B, we get what is represented in fig. 3. 



Figure ab corresponds to the triple point temperature of A and a ;) b 3 

 to that of B, the p-.r-figures a x b x and a^b, referring to intermediate 

 temperatures. 



From this collection of p-x-ügares we see that when we join the 

 corresponding points of the different three-phase-pressure lines glf, 

 a three-phase-region is formed composed of two two-phase-regions, 

 first of the two-phase-region for the equilibria between vapour and 

 liquid, and secondly of a two-phase-region for the coexistence of 

 liquid and mixed crystals. 



If we think the p-.i'-diagrams corresponding with the different 

 temperatures placed in succession, the vapour-lines form a vapour- 

 sheet, the liquid-lines a liquid-sheet, and the mixed-crystal-lines a 

 mixed-crystal-sheet. 



The line bgg x a z indicates the intersection of the vapour-sheet of the 

 mixed-crystals l ) with the vapour-sheet of the liquid phases, the line 

 bll x a z that of the liquid sheet of the mixed-crystals with the liquid 

 sheet of the vapour phases, and bf/\a 3 the line along which the mixed- 

 crystal sheet of the liquid phases intersects the mixed-crystal sheet 

 of the vapour phases. 



2 ) By the vapour sheet of the mixed crystals we must understand here the 

 vapour sheet coexisting with the mixed-crystal sheet. 



