Van Name and Hill — Solution of Silver in Chromic Acid. 57 



Table II. 

 Silver (Sample B) in Chromic Acid. 



Keaction periods usually 10 minutes with 5 molar H 2 S0 4 , 



and 7 minutes with 0-25 molar H.SOj. 



H 2 SO, Average 



,(5-0 molar 1-72 1-74 1-57 1-68 



1 |0-25 molar 4-92 4-71 4-71 4-59 4-81 4-75 



~(5-0 molar 1-63 1-46 1-57 1-55 



-J0-25 molar 4-59 4-50 4-81 4-27 4-67 4-53 4-49 4-55 



o (0-25 molar 5-03 5-22 4-91 507 506 



^{5.0 molar 1-69 1-51 1-47 1-69 1-44 1-52 1-50 1-55 



f 50 molar 1-63 1-62 1-54 1-63 1-55 159 



4] 025 molar 4-36 4-69 4-61 4-82 4-94 4-89 4-76 4-80 4-73 



[5-0 molar 1-79 1-68 1-60 1-53 1-63 



f 0-25 molar 474 4-75 4-67 4-78 4-74 



5^ 50 molar 163 1-65 1-44 1-65 1-59 



[0-25 molar 4-50 4-20 4-38 4-57 4-41 



error were fully understood. The mean value of the 

 constant k is 4-70 for the weaker, and 1-60 for the 

 stronger acid. Combination of these results with those 

 formerly obtained for cadmium under like conditions, 

 gives for the ratio Cd : Ag the value 1-50 in the 0-25 molar 

 acid, and 1-67 in the 5 molar acid. This still constitutes 

 an exception to the empirical rule that the agreement 

 should be closer in the stronger acid, but the exception 

 is a much less conspicuous one than the former results 

 indicated. 



Considering these results from the standpoint of the 

 diffusion theory the most interesting and important fact 

 brought out is the proof of the existence in the case of 

 silver of such large differences in the rate of solution 

 depending upon the physical state of the metal. In the 

 light of that theory we can distinguish, as shown in 

 the former article, two classes of cases, those in which the 

 reaction velocity is determined entirely by the rate of 

 diffusion, and those in which the chemical stage of the 

 reaction also exerts its influence upon the observed 

 result. Differences in the physical state of the metal 

 could affect the reaction velocity in the former case only 

 in so far as they produced considerable variations in the 

 roughness of the surface, for theory and experience alike 

 go to show that slight variations would be without appre- 

 ciable effect. Moreover, such changes would account, in 

 general, only for an increasing reaction velocity, since it 

 is only in the rarest cases that the surface of the metal 

 would grow smoother as it dissolved, while the progres- 



