(5ft2) 



T,. Evidently in this case i/.t must be greater tlian '/j' ^^ 



4(^/Jr)'-9(^/Jr)H-^^/-'«'— 1= (y':x~-\y (4l/jr — 1), 

 and hence -t^Vi». •" agreement with wiiat has already been 

 found above. 



h. Maximum of vapour jin'ssuri'. As is known, this will occur at 

 higher temperatures, when at loiver temperatures in the case of a three 

 phase equilibrium the three phase pressure docs not lie between the 

 vapour pressures of the two components, but is greater than either. The 

 concentration x^ of the vapour lies then betimen the concentrations 

 X and x^ of the two liquid phases. On the side of the lower critical 

 temperature .^"3>.^', will always have to be satisfied. 



Let us now try to determine the condition for this. 



For equilibrium between the phase 1 and 3 we have evidently 

 when [la and fit represent the molecular potentials of the two components: 



(Ml = Ws ; (f*i)i = (f 6)3 , 

 or 



Ci-f i> + (l-.^0-^j +7?r%,f, =6'i-f i2 + (l-.0^J -^RTlo<ux, 



where il = | fdc — pr, and Ca and L\, are functions of the tem- 

 perature. 



Subtraction of the two equations yields : 



dfi 1— A-, öi> , 1— .r, 



\- RT log i — J^ RT loa ' , 



d.%\ ' A\ 0.», .Tj 



1- 



loij — 



1— .r, RT 



da;, d.v. 



as has been repeatedly derived before, inter alia by van der Waals. 

 Now we found before for— (I.e. p 649 tormula (3) and p. 050): 

 dii 2l/a / nA 



Hence we have for x = 0, when n = a^: 



