( 50 ) 



of the solvent in the two liquid phases (separated by a semiperme- 

 able membrane onlj passable by the solvent) are the same. Hence: 



f^ (Ö, i?o) = f* G^'' P) (1) 



But evidently we have the identity 





dp 



Pa 



Here -— ° = r. (for meaning of v^, see §1). So w^e have also: 

 dp 



p 



(i{0,p,) = n{0,p) — I v,dp. 



Pa 



If we now assume v^ to be independent of the pressure — which 

 KoHNSTAMM thinks perfectly permissible — we get: 



H (0, p,) =z fi (0, p) — v,{p — p„) . 



Substituting this in (1), we get at once: 



1 



^ = P — Po = — il^o — l^x)p , (2) 



by which the osmotic pressure is immediately brought into connection 

 with the difference of the molecular potentials of the pure solvent 

 and of that in the solution, both under the same pressure p. 



Kow we can in the usual way replace fi^ — iix by its value. We 

 find then, as has been frequently derived: 



- RT log (1 - .r) - --^^ + RT W-^ etc. 



in which the latter terms is often neglected, and a and r have the 

 known meaning. 



In this way the apparent deviation with regard to Vg has been 

 disproved. My statement, therefore, that in the numerator for Vg no 

 correction term need be applied (see Kohnstamm, p. 729), was by 

 no means "too absolute". 



3. When reading through Kohnstamm's paper, I was further 

 struck by the following in my opinion inaccurate assertions. 



On p. 739 it says: "It appears from the explanation convincingly, 

 that VAN Laar goes too far, when he states, that w^e cannot speak 

 of osmotic pressure in an isolated solution." 



I fully maintain this view. For in the kinetic explanation of 



