Certain Metals in Dissolved Iodine. 



215 



force, thus actually increasing* the rate of solution of the disk. 

 In view of these facts it seems reasonable to conclude that a 

 particle of carbon or of a more negative metal adhering to the 

 disk might have a similar effect, so that in many cases (not 

 necessarily in all) an impure metal would give a higher constant 

 than a pure one, as in the present instance. 



In comparing these results with those obtained with cad- 

 mium, only those experiments need be considered in which 

 the purest iron was used. Experiments 5, 6, 7, 8, and 9 carried 

 out at O02 normal acidity, give an average value of K of 6 - 74: ; 

 experiments 10 and 11, at Ol normal acidity, an average of 

 6*71, thus again proving that the rate of solution is independent 

 of the acidity when the latter is not too high. Since these 

 experiments were carried out before the readjustment of the 

 apparatus! they are to be compared with the value 6'72 for 





cadmium. The agreement is excellent, 













Table IV. 











KI 0'5 normal. 



H 2 S0 4 0-02 normal. Temperature 25°. r = 17( 



) 







Nickel. 









1. 



v - 580 



560 540 520 



500 



480 







St= 10 



10 15 10 



10 



10 







c = 20-03 17-85 



! 15-81 13-12 11-55 10-09 8-77 







K= 6-78 



6-70 6-71 6-61 



6-75 



6 - 72 Average, 



671 



2. 



At= 10 



10 10 10 



10 



10 







c = 19-84 17-6S 



i 15-69 13-84 12- 



17 10' 



59 9-18 







K= 6-64 



6-71 6-77 6-67 

 Cobalt (Impure). 



6-95 



6-86 Av. 



677 



3. 



Z= 6-24 



6-00 615 5-72 



5-83 



5-73 Av. 



595 



4. 



K= 6-47 



6-25 6-33 605 



Cobalt (Electrolytic) 



6-37 



6-18 Av. 



628 



5. 



Disk 38-76 x 0-075 



mm 











At= 10 



10 11 11 



10 



11 







c = 39-40 34-66 



1 30-38 26-26 22- 



59 19-64 10-70 







K= 739 



7-41 7-15 7-11 



6-99 



7-07 





K (corrected for stirring) av. 7'15 

 K, with further correction for size of disk, 6'90 

 i. Disk 38-64 x 0-068 mm 



At= 10 10 11 10 10 10 



c = 39-54 34-92 30-58 26-70 23-39 20-37 17-48 

 K= 7-19 7-43 6-65 688 6-90 7'34 



K (corrected for stirring) av. 7 '01 

 K, with further correction for size of disk, 6'83 



* A greater increase would be produced by the discharge of the much 

 more numerous I' ions, but as this would not directly affect the free iodine 

 concentration it would not appear in the results. 



f See page 211. 



