( 228 ) 

 Pk vk _ J_ ^ — P_ <o — L 



RTk "" c; ^' "" Pk ~~ vk ' 



may be easily transformed into : 



"f^ = - i- - fp/Zo - loq ^^ X log X + (l-.^■) loq (l-.i-) . (1) 



u 



if we put n a certain large number and neglect other temperature 

 functions. 



For convenience we may call j \^ dv as function of o the cun-'e of 



n 



reduced free energy for f. In llie construction of each given »|'-surface 

 occurs the group of curves of reduced if' that lie between the extreme 

 values of reduced temperature which occur on this surface. 



On the planes .c = and x := 1 of the i|'-model we can draw 

 the if^-curves of higher and lower temperature. In passing over to 

 a i|?-surface of higher temperature the t|'-curves (at least in the most 

 common case) are moved on the surface from the side of the 

 highest reduced temperature to that of the lowest, while the lineai- 

 dimensions in the two directions ip and v undergo a certain variation. 



§ 6. The x^-stirface for mixtures of methylchloride and carbon 

 dioxide at — 25° C. As an example of the application of the graphical 

 method and the empirical reduced equation of state w^e have now 

 chosen the prediction of the composition of the coexisting phases 

 and the coexistence pressure for mixtures of methylchloride and 

 carbon dioxide at — 25^ C. We were led to this choice by the 

 following considerations : 



1». we can derive the critical quantities from the experiments of 

 KuENEN '), they lie tolerably far from each other, are given in 

 Comm. N". 59/;, while for + ^"^ C. a model has been constructed 

 by Hartman; 



2». — 25° C. corresponds to the lowest reduced temperature for 

 methylchloride for which the empirical reduced equation of state has 

 been calculated ; 



