M 



THE NEW THEORY OF SOLUTIONS. 



{Continued /ran/ vol. ii., p. 184.) 



CONCENTRATED SOLUTIONS. 



OLECULAR weights and concentration. - The 

 extensive measurements which have been made of 

 the molecular weights of dissolved substances are at one 

 in showing that, no matter what method is used or on what 

 property the method depends, the values obtained for the 

 molecular weight of the same substance when dissolved in 

 the same solvent vary with the concentration of the solutions 

 employed. The extent of this variation depends both on 

 the nature of the solvent and the dissolved substance, but 

 for the great majority of indifferent solutions the order of 

 magnitude of the variation is somewhat the same, and is 

 illustrated by the numbers given in the following table. 

 The data, determined by Beckmann, refer to the freezing- 

 points of solutions of alcohol in acetic acid, and show that, 

 as the concentration varies from '2 gr. to 14/2 gr. of alcohol 

 per 100 gr. of solvent, the molecular weight, calculated by 

 the ordinar) T freezing-point formula, varies between 47 and 

 58, the theoretical value being 46. 



Instead of expressing the concentration, as above, in 

 grams per a definite weight of solvent, it may be expressed, 

 as in the case of gases, in grams per a definite volume of 

 solution. With dilute solutions these two methods give 

 practically the same results, and the former, due to Raoult, 

 is almost exclusively used in laboratory methods of 

 determining molecular weights, since the latter, first used 



