24 J- SAKURAI: MODIFICATION OF BECKMAXN'S BOILING 



in his method which are capahle of improvement and simpKfication. 

 The object of the present paper is to describe a modification of the 

 method which renders it practicable in every laboratory and, at the 

 same time, able to yield results which are even more concordant than 

 those obtained by Beckmann. 



It may, however, not be out of place to first briefly refer to the 

 principle which underlies this method of determining molecular 

 weights. By the study of the lowering of vapour pressure of various 

 solvents by bodies dissolved in them, Raoult was ultimately led to 

 the following law : 



" The relative lowering of vapour pressure is proportional to the 

 ratio of the number of molecules of the dissolved substance to the total 

 number of molecules in the solution." 



Expressed in a formula, we have 



p N+n 



where p and p' are the vapour pressures of the solvent and of the 



solution, and N and n, the number of molecules of the solvent and of 



the dissolved body respectively. The constant c may be taken as 



equal to unity. If, then, G and g be the weights taken, and M and m 



the molecular weights, of the solvent and of the dissolved body, all 



expressed in grams, we have 



9 

 p—p' _ m 



P ^ _; ^ ' 



or vi=M.-4t~' — ^• 



(r p—p 



Hence, if M, G and g are known, the molecular weiglit of the dis- 

 solved substance, m, is given by determining p and 2_>', the vapour 

 pressures of the solvent and of the solution. 



Now, the diuiiuution of vapour j>ressure is proportional, on the 



