224 Win Name and Bosworth — Solution of Certain Metals. 



iodine will probably prove to diffuse in cadmium iodide faster, 

 and in hydrogen iodide slower, than the above considerations 



have led us to expect. 



There is obviously nothing in the results of this investiga- 

 tion, as judged by the evidence at present available, which is 

 incompatible with the diffusion theory. On the other hand, 

 the results are in most respects in striking agreement with the 

 predictions of that theory. A study of the temperature coef- 

 ficient of the reaction between iodine and a metal has already 

 been begun. 



Summary. 



1. The rates of solution of cadmium, iron, nickel, and cobalt 

 in similar iodine solutions have been measured and found to 

 be equal. This result extends the list of metals, which by the 

 former article were shown to dissolve at the same rate, from 

 five to eight : viz. Hg, Cu, Ag, Zn, Cd, Fe, TSTi, and Co. 



2. Tin gives a higher velocity constant than the above 

 metals. This is what would be expected if the formation of the 

 stannic iodide took place in two stages, as is probably the case. 



3. Magnesium dissolves abnormally fast owing to the stirring 

 action of the bubbles of hydrogen set free from its surface. 



4. An increase in the acidity of the solution above 0"1 nor- 

 mal lowers the value of the velocity constant. 



5. The rates of solution of cadmium in the presence of eight 

 different iodides have been determined. Except in the cases 

 of cadmium iodide and of hydriodic acid the relative values of 

 the velocity constants roughly correspond with what would be 

 expected from the probable rates of diffusion of the correspond- 

 ing triiodides as estimated from the available data. Since the 

 diffusion coefficients of iodine in the different solutions are . 

 still unknown, it is not yet possible to base a satisfactory test 

 of the diffusion hypothesis upon these constants. 



6. The results as a whole support the validity of the diffu- 

 sion theory. 



