between Metals and Dissolved Halogens. 



245 



Table IV. 

 Cadmium and Iodine at 25°. 



c 



M 



V 



K 



c 



At 



V 



K 



1. 100 g. 



KI pei 



liter, r— 



:170 



2. 100 g 



KI per 



liter, r— 



:240. 



0-0364 

 0-0340 

 0-0318 

 0-0297 



5 

 5 

 5 

 5 



500 

 480 

 460 

 440 



6-36 



6-28 . 

 (5-95) 

 6-28 

 6-27 

 6-28 



0-0329 

 0-0301 

 0-0274 

 0-0249 



5 

 5 

 5 



500 

 480 

 460 

 440 



8 57 

 8-55 

 8-60 

 8-61 

 9-03 

 8-77 



0-0276 



420 



0-0214 



6 

 6 



420 



0255 

 0-0235 



5 



400 

 380 



0-0195 

 0-0170 



400 

 380 







Average 



6-29 







Average 



8-69 







Corrected 



6-36 















c 



At 



15 



K 









3. 200 g. 



KI per 



liter, r— 



240 









0-0387 



5 

 5 



5 



500 



9-52 

 956 

 9-41 

 9-52 

 9-60 

 9-74 











0-0350 

 0-0316 

 0-0283 



480 

 460 

 440 











0-0253 

 0-0224 

 0-0197 



5 

 5 



420 

 400 

 380 















Average 



9-56 







metal of high purity, obtained from Kahlbaum. Experiments 

 carried out in the same manner as those with cadmium and the 

 other metals gave low and rapidly diminishing values of the 

 constant. On examining the disk at the close of such an experi- 

 ment a whitish semi-transparent film could be seen on its sur- 

 face which proved to consist of zinc hydroxide, evidently 

 formed by hydrolysis of the zinc iodide. 



To obviate this difficulty the iodine solutions were made 

 1/100 normal with respect to sulphuric acid, after it had been 

 proved by trial that sulphuric acid of this strength had no 

 appreciable effect upon the very pure zinc of the disks. This 

 expedient proved effective and at once gave normal values of 

 the constant. 



According to Schukarew,* the reaction between zinc and 

 iodine is retarded by the presence of zinc iodide, but no figures 

 are given in support of the statement. As the reaction is non- 

 reversible such an effect would hardly be expected. To test 

 this point, ten grams of zinc iodide, prepared by direct action 

 of the two elements, was added at the outset to the solution in 

 experiment 4, which in other respects was carried out exactly 



* Zeitschr. phys. Chem.,viii, 81. 



