THE MOLECULAR WEIGHT OF IODINE IN ITS 

 SOLUTIONS x 



IT is a matter of everyday observation that iodine has the 

 property of dissolving with different colors in different liquids; 

 in some it shows the reddish-brown hues of its solid and 

 liquid states; in others it acquires the violet color so charac- 

 teristic of its vapor. The inference seems very natural that 

 this diversity of color must depend on a different form of 

 aggregation of the iodine atoms within the solvent. Since 

 the molecules of solids and liquids appear to be more com- 

 plex than those of gases, we might suppose that the red solu- 

 tions contain more complex molecules of iodine than do the 

 violet ones. This is, in fact, the usual assumption; but apart 

 from certain qualitative indications, there has been no proof 

 of its truth; quantitative evidence has not yet been forthcom- 

 ing in support of the hypothesis. That I have been fortunate 

 in obtaining such, I owe to those new [806] means of investi- 

 gating the state of dissolved matter with which the happy 

 generalizations of Raoult, and the skillful mathematical de- 

 ductions of van't Hoff, have furnished us. I refer to the 

 phenomena of "osmotic pressure," which can be measured 

 by the depression of freezing-point and vapor tension which 

 liquids experience when mingled with a foreign substance. 

 By the advice of Professor Ostwald, I undertook to attack 

 the problem of the molecular weight of iodine in its solutions 

 by the vapor-tension method, and I now give the results of 

 the experiments carried out under his direction at the Chem- 

 ico-Physical Laboratory of Leipzig University. 



1 Reprinted from the Journal of the Chemical Society, 63, 805 (October, 1888). 



