Van Name and Bos worth — Solution of Certain Metals. 207 



Akt. XXIV. — On the Rates of Solution of Certain Metals in 

 Dissolved Iodine, and their Relation to the Diffusion 

 Theory ; by K. G. Van Name and Rowland S. Bosworth. 



[Contribution from the Kent Chemical Laboratory of Yale Univ.— ccxxiii.] 



In a recent paper* it was shown that the metals mercury, 

 cadmium, zinc, copper, and silver, all dissolve at the same rate 

 in a solution of iodine in potassium iodide, a result which seems 

 to prove that the velocity of the reaction is determined by the 

 rate of diffusion of the iodine rather than the actual rate of 

 combination of the iodine with the metal. Moreover, it was 

 found that when the concentration of the potassium iodide is 

 changed, or when bromine or cupric bromide is substituted for 

 the iodine, the reaction velocity is altered in the direction which 

 would be expected from the rates of diffusion of the active 

 substances. 



The present investigation is an extension of the work of Van 

 Name and Edgar, intended to further test the applicability of 

 the Diffusion Theory to this type of reaction. It covers, (1), 

 a comparison of the rates of solution of several more metals in 

 iodine ; (2), a study of the effect of substituting other metallic 

 iodides for potassium iodide ; and (3), of the effect of varying 

 acidity. 



The method and apparatus employed were substantially the 

 same as those used and described by Van Name and Edgar, but 

 with several minor modifications which increased the regularity 

 and reproducibility of the results. Disks of the different 

 metals, of like size, were held in a fixed position in the iodine 

 solution with the plane of the disk vertical and close to the 

 path of the blades of a propeller-shaped glass stirrer revolving 

 at a known rate. The velocity of the reaction was measured 

 by removing samples of the liquid from time to time and titra- 

 ting with 0*02 normal thiosulphate. 



Two points in which the procedure differed from that of Van 

 Name and Edgar are worthy of mention; first, the special pre- 

 cautions, described below, which were employed to insure uni- 

 formity in the size of the metal disks, and second, the use of a 

 holder for the disks made entirely of platinum. The latter 

 eliminated a source of trouble and uncertainty present in the 

 earlier work owing to the occasional breakage of the glass 

 holder, since it was necessary, and by no means easy, to repair 

 the holder without appreciably altering its dimensions. This 

 new holder, which was identical in shape with the glass ones, 

 was constructed of stiff heavy platinum wire. To prevent 



* Van Name and Edgar, this Journal, xxix, 237, 1910. 



