1150 



It follows amongst others from the formulas (52) — (54) that this 

 modificationciirve cannot go through the point F=F'; when we 

 put herein .v =(( and >/ =^ th it follows that 



H-ri^H-^^ri-n ^^^^ 



V — V V- — u' v' — V 



must be satisfied. 



This means that the curves F<J,F'(V and rlt of fig. 1 touch, one 

 another in one point. Now it is apparent that these curves may 

 intersect one another in one point. When viz. two of these curves 

 intersect one another, necessarily the third goes also through this 

 point of intersection; only very accidentally they can, however, 

 touch one another. In the same way we find that also the corre- 

 sponding vapourcurve cannot go through the point F = F' . From 

 (52) — (54) it follows that dP and dT become zero at the same time 

 and that this is the case when 



y^il^y^J (56) 



X — « x^ — u 



This means that the solid substance {F = F), the liquid and the 

 vapoui are situated on a straight line. It is evident that on each 

 closed modilicationcurve two such points u and iv occur and on the 

 corresponding vapourcurve tw^o corresponding points v^ and w^. 

 Pressure and temperature of the equilibrium F -^ F' -\- L,^ -\- Gu^, 

 are in accordance with point m of fig. 1, pressure and temperature 

 of the equilibrium F -\- F' -{- L,, f Ga-,, with the point w of fig. 1. 



From (54) it follows that the pressure can as well increase as 

 decrease at increase of temperature ; therefore we may distinguish 

 two cases. 



1) P- and 7-raaximum coincide and also P- and T-minimum. 



2) P-maximum and 7^-mininuim coincide and also P-minimum 

 and T-maximum. 



The case sub 1 occurs when the pressure increases at increase 

 of temperature; curve rh is then situated as in fig. 1. The case 

 sub 2 occurs when the pressure decreases at increase of temperature, 

 curve r h proceeds then in fig. 1 from r towards lower temperatures. 



Now we shall assume that F and consequently also P' is a binary 

 compound of B and C; to the P, P diagram again then fig. 1 applies, 

 in which now however the solutionpaths no longer touch the melting- 

 curve in F or F' . 



Tn the concentrationdiagrara the modificationcurveP4- F' -\- L -\- G 

 ends in two points on the side B C, the same applies to its corre- 

 sponding vapourcurve. 



