612 



Mr. L. Vegard : Contributions to 



that it changes while the temperature is maintained constant ; 

 but still the change of concentration can occur under two 

 different circumstances. 



Either, the pressure can he kept constant in the solution ; 



then we get the relation indicated by (^) • ^ r we can 



keep the .pressure on the solvent constant — in practice the 



more general case — and we get ( =-— ) . 

 & Vdc J P0 



"We can now prove that these two quantities must 



generally differ from each other. I£ equations (4a) and (Ab) 



are subtracted, 



l\-bc) p \-bcjJ-K-dn P °-dp p -dp' 



Let us now suppose that ^— has a finite value, which is 

 generally the case. The necessary and sufficient condition 



£or (SX being equal to (btX is 



s that 



Po 



~dpo 





(8) 



Generally, however, this equation is not fulfilled. To 

 prove this, let us suppose that we increase the pressure on 

 the two sides by just so much, that equilibrium is not disturbed. 



Fig. 4. 









ill 1 



1 II 













z> 













3 





< 



-1 

 



2 



< 



I 



n 



-* CO 



We increase the pressure without moving along the mem- 

 brane. Such a change of pressure can be carried out, for 

 instance, by means of the arrangement represented in fig. 4. 



