'M 



Bd _Bh_a 

 Ad A/c y 



Now it is perfectly clear that when the isotherm for the internal 

 liquid equilibrium passes exactly through the point L, or the point 

 of intersection of the two liquid isotherms, this implies that at the 

 considered temperature the solution saturate with respect to the 

 mixed crystal phases /I, and B^ is exactly in internal equilibrium. 

 Accordingly il follows immediately from tiiis, (hat also liie coexisting 

 solid phases will be in internal equilibrium in this case, and besides 

 that also the vapour coexisting with L will be in internal equili- 

 brium. The vapour (i lying in the point of intersection of tiie two 

 vapour isotherms will, therefore, in this case have to lie on the 

 equilibrium isotherm for the vapour. 



In this case, which [)resents itself at the transition temperature of 

 the two modifications, we get a coincidence of the points />„ and L, 

 G^ and G, A^ and A^, B^ 3-nd B^. Then coincide also the points e 

 and (/, g and /, which indicate the concentrations, the liquid phases, 

 and the vapour phases as far as the substances A and B are con- 

 cerned. 



To simplify the discussion we shall now denote the concentration 

 by small letters when the system is in internal equilibrium, capitals 

 being used wlien the system is not in internal equilibrium. 



The ratio of the concentration between .! and B will tlierefore 



be indicated bv - in the liquid L. and by — in the liquid £„. 



■ yt ' [IL 



In accordance with this the ratio between A and /:/ in the vapour 



A X 



G is then indicated by ^ , and that in the vapour G„ by — . 



Thus the ratio of concentration of A and B is denoted by — -' 



in the solid phase A., and that in the [ihase A, by = — , that in 



B, being given by ^ , and that in B„ by -- . 



For the temperature of the point of transition the following simple 

 equations hold : 



. . (2) ^ = ^ ... (4) 



. . (3) ^-1^ ... (5) 



