2 g J. SAKURAI: MODIFICATIOX OF BECKMAXX'S BOILING 



difference is called the mokcular elevation of boiling point. This con- 

 stant is ohtained expérimental 1 y by determinino; the rise of boiling 

 point of ÎI solvent, fo]l(3wing* the dissolution of a known weight of a, 

 substance of known molecular weight in a known ({uantity of the 

 solvent. Thus, for example, Beckmann (Zeitscli. phijsil'. Cheiu., 3, 

 603 [1889]) found that 4.740 grams of ethyl benzoate dissolved in 

 100 grams of ether raised the boiling point of the latter by 0.605°. 

 The weight of ethyl benzoate dissolved in one gram-molecule of ether 

 (74 grams) is, therefore, — — tää =3.5076 grams. The rise of boil- 

 ing point corresponding to the dissolution of one gram-molecule of 

 eth}^ benzoate (150 grams) in one gram-molecule of ether would 



then he 



0.66.5x1.50 ,,o i 

 8.5076 



Experiments with other sul)stances give nearly the same value for the 



molecular elevation of the boiling point of ether. 'J'he molecular 



weiglit of any dissolved substance is, then, obtained from tlie equation, 



A 

 where, in case of ether, 7>=28.4, f/= weight of tlie substance dis- 

 solved in 74 grams of ether, and A= the observed rise of boiling 

 point. 



In practice, it is more convenient to refer the constant B to 100 

 grams, instead of to the molecular weight, of the solvent ; the calcula- 

 tion is thus very much simplified. The formula then becomes 



A 



74 

 where, in case of ether, jB' = 28.4x^r7— -='21.0, and ^'=weight of the 



substance dissolved in 100 grams of the solvent. As the mean of 



several determinations, lîeckmann (he. rit.) o])tained the number, 20.9 



for the value of 2^. 



