Certain Metals in Dissolved Iodine. 



223 



Table VII. 



Summary of Velocity Constants. 



A. 



Acidity N/500 N/50 N/10 N/4 N/3 N/2 9N/10 N/1 NH 4 C1 



N/40 

 Cadmium.... 6-79 686 6-86 .... 664 6-40 631 6-30 



Iron .... *6-88 *6-85 



Nickel *6-88 



Cobalt 6-87 .-- 



Tin .... *8-02 *7"48 *7"67 



Magnesium... ..., 8"73 10-29 



B. 



Cadmium Migration Viscosities of 



in presence velocity of chlorides in N/2 



of K cation. sol. at 25°. 



Potassium Iodide 6'86 K+ 64"9 0-987 



Cadmium Iodide 6'82 1/2 Cd+ + 47'4 1-063 



Sodium Iodide 6-56 Na+ 43-6 1-047 



Hydrogen Iodide 6-45 H+ 318- 1.034 



Barium Iodide 645 1/2 Ba+ + 55-1 1-057 



Lithium Iodide 6-41 Li+ 33"4 1067 



Magnesium Iodide 6-25 1/2 Mg+ + 45'9 1094 



Calcium Iodide 6.23 1/2 Ca+ + 51-5 1-076 



* Starred values have been multiplied by 6 - 86/6 - 72. 



expected to stand at the bottom of the list or near it ; the 

 other is the value for hydrogen iodide, which is surprisingly 

 low considering the high mobility of the hydrogen ion. It is 

 evidently this peculiarity in the behavior of hydriodic acid 

 which accounts for the observed effect of acidity in lowering 

 the velocity constant. 



Another factor besides the rate of diffusion, which would 

 affect the rate of solution of a metal, is the viscosity, an 

 increase in which would tend to increase the thickness of 

 the diffusion layer and thus retard the reaction. In the 

 absence of published data on the iodides, the viscosities of the 

 corresponding 0-5-normal chloride solutions at 25°, referred to 

 water at the same temperature as unity, are given for compari- 

 son in the last column of the table. f The order of increasing 

 viscosity is K, H, JSTa, Ba, Cd, Li, Ca, Mg, which is nearer the 

 order of the velocity constants than was the case with the 

 ionic velocities, and explains in part the unexpected values 

 observed with cadmium and hydrogen iodides. The inference 

 to be drawn from the two anomalous velocity constants is that 



f According to measurements by J. Wagner, Zeitschr. phys. Chem., v, 

 31, and by Beyher, Zeitschr. phys. Chem., ii, 744. 



