TRANSACTIONS OF SECTION B. 691 



The fusing point being lower than those of iodine and sulphur would indicate 

 tliat some chemical action takes place when the elements are mixed together, but 

 its properties more resemble those of a non-metaUic alloy than of a definite chemical 

 compound. 



7. On Solutions of Iodine. By W. W. J. NicOL, D.8c. 



The question as to the composition of the iodine molecule in solution is one 

 which has from time to time attracted the attention of chemists. It is well known 

 that the colour of dilute solutions of iodine is dependent largely on the nature of 

 the solvent, and this difference of colour has been generally attributed to a greater 

 or less complexity of the iodine molecule. The well-known violet of iodine vapour 

 is characteristic of the solution of iodine in carbon disulphide, and from this it is 

 argued the molecule must be the same in both states, i.e., T,,. 



The methods employed for the determination of the molecular weight of iodine 

 in solution have been two : that dependent on the lowering of the freezing point 

 of the solvent — a method necessarily applicable to but few solutions —the other 

 relies on the alteration of the vapour pressure of the solvent, a method of general 

 applicability. The first of these has been employed by Gautier and Charpy, the 

 second by Loeb and Beckmaun. 



But these results are far from satisfactory, and the author has endeavoured lo 

 throw further light on this subject by a study of the molecular volume of iodine 

 in solution. His experiments are far from complete, but he wished to lay some of the 

 first results before the Section with the object of reserving his special method of 

 investigating the point. 



The method of experimenting is extremely simple: solutions of iodine in various 

 solvents are prepared of definite strength by direct weighing of both substances, the 

 specific gravity of the solutions is then determined at a definite temperature (20° C), 

 and thus the apparent volume of the iodine in solution can be calculated. 



The following are the results obtained : — 



Neglecting the three results with potassium iodide for the present we find on 

 dividing the atomic weight by the atomic volume that the densities of iodine in the 

 first five solvents are as follows : — 



Atomic Volume calculated 

 6-0 if^ = 21-1 



50 i^ = 31-7 



Ether. 



Rectified spirits 



Benzol 



Chloroform 



Carbon disulphide 



While solid iodine has a density of 5-0 and the atomic volume 25-4. 



50 



= 3'5 IP = 36-3 



The solutions in solutions of potassium iodide clearly belong to a difi^erent order; 

 there is evidently combination more or less complete between the potassium iodide 

 and the iodine. 



Before any definite conclusion can be arrived at the experiments must be 

 extended to include other solvents, and the behaviour of all the solvents with some 

 substance which does not alter its molecular constitution must be fully examined. 

 This the author intends to carry out at once. 



T Y 2 



