The Osmotic Pressure of Solutions. 131 



" thermique ; par consequent les lois exposees s'appliquent a des 

 " solutions tellement diluees que la chaleur de dilution devient 

 " negligeable." 



I have obtained the equations connecting osmotic 

 pressure, temperature, volume, and heat of dilution of a 

 solution, and on giving the value zero to the heat of dilution 

 the equations become identical with van't HofFs. 



Connection between Osmotic Pressure and Temperature. 



The osmotic pressure of a solution cannot be directly 

 measured with any great accuracy, but it can be calculated 

 from the vapour pressure of the solution or from its freezing 

 point. 



The relation between the osmotic pressure and the vapour 

 pressure of a solution was first given by van't HofT {loc. 

 cit.) and afterwards reproduced by other authors, first by 

 Gouy and Chaperon.* The form given by the latter is : — 



PK.^ = RTlog^ 



X p 



where P = the osmotic pressure at T. 



K is a coefficient which depends on the contraction which 

 takes place when the solution is diluted. 



M is the molecular weight of the solvent (as gas). 



A is the density of liquid solvent. 



p and/ the vapour pressures of the solvent and solution 

 respectively, and 



R the gas constant for 1 gram molecule. 

 The coefficient K is defined by Gouy and Chaperonf by 

 the following equation : — 



K= A / 1 _^As 

 A . V dwJ 



A being the density of the solution and w the quantity of 



* Ann. Chim. Phys. (6), XIII., p. 120. 1888. 

 t Ann. Chim. Phys. (6) XII., p. 384. 1887. 



