MOLECULAR WEIGHT OF IODINE 235 



n. 



MI and Mo being the molecular weights of iodine and solvent 

 respectively. This is a working formula derived by Raoult 

 from an expression for the relation between the ratio of mole- 

 cules of solvent and substance dissolved on the one hand, and 

 the ratio between the tension of the pure solvent and the 

 depressed tension on the other, where the dissolved substance 

 itself has a comparatively insignificant tension. It is interest- 

 ing to note that the latter expression was reached independ- 

 ently and almost simultaneously by Planck. 1 



In the following tabulated statement of my observations, 

 the first two columns show the weights of the ingredients 

 of the solution originally introduced; the third gives the tem- 

 perature; the fourth, the depression of tension; the fifth, the 

 true tension of the solution; the sixth, the concentration as 

 calculated by formula I; finally, we have the molecular weight 

 as calculated by formula II. Before giving the results ob- 

 tained for iodine, I think it useful to give a summary of a 

 few test experiments made on the molecular weight of naph- 

 thalene, which not only proved the trustworthiness of the 

 method, but also showed that there is no specific difference 

 between ether and carbon bisulphide which could invalidate 

 the effect of the great difference of the molecular weights 

 found for iodine. 



1 Compare Raoult, Zeilschr. physik. Chem. 2, 372 (1889), and Planck, ibid. 2, 



408 (1888). , [EDITOR.] 



