THE NEW THEORY OF SOLUTIONS. 419 



the solution at its absolute boiling-point T ± , by the method 

 which is employed in deducing (8) it may be shown that 

 \og e plp' = MX AT/2TT1 (10). Here it is assumed since 

 AT is small that A is the same at T as at Tj. AT is 

 thus connected with the vapour-pressures of the solvent and 

 solution. Now, equation (6) can give us at T 1 the relation 

 between vapour-pressure and osmotic pressure, hence from 

 (10) and (6) we have — 



P = -0819 PAAT/2T (11). 



It is thus possible to calculate the osmotic pressure of a 

 solution from the rise in the boiling-point. If we next intro- 

 duce into (11) the value of A derived from M'AT/^ = 

 *02T 2 /A we have — 



P = -0819 Tpo/100 W (12). 



If V be the volume of solution containing M' grams of dis- 

 solved substance V = 100 M'/pg, the densities of solvent 

 and solution being supposed to be the same, and the weight 

 of the dissolved substance being neglected. Consequently 

 (12) reduces to — 



PV = -0819 T. 



Observations on boiling-point like the direct observations 

 on vapour-pressure lead, therefore, to the result that osmotic 

 pressure obeys gaseous laws and is independent of the 

 nature of the solvent. 



J. W. Rodger. 

 ( To be continued. ) 



