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



Art. II. — On the Rate of Solution of Silver in Chromic 

 Acid; by R. G. Van Name and D. U. Hill. 



(Contributions from the Kent Chemical Laboratory of Yale Univ. — ccxcvi.) 



In a recent study of the rates of solution of metals in 

 oxidizing solutions, the results of which have already 

 been published in this Journal, 1 it was found that when 

 two or more metals under like conditions dissolved at 

 different rates, these rates could be brought into closer 

 agreement by increasing the acidity. The only exception 

 to this empirical rule was observed in the case of silver 

 dissolving in a chromic acid solution containing sulphuric 

 acid. When the sulphuric acid was 0-25 molar the ratio 

 of the rate of solution of cadmium to that of silver was 

 found to be 1-64, while in the presence of 5 molar sul- 

 phuric acid this ratio was 2-19, a larger difference in the 

 stronger acid. A conspicuous feature of the experiments 

 with silver in the 5 molar sulphuric acid was the fact 

 that the initial velocity constant of the series was much 

 higher than the succeeding ones, as seen in the following 

 example : 2 



k = 1-53 1-26 1-20 1-18 1-21 1-23 1-25 



This was not the case in the 0-25 molar acid, though the 

 constants showed a slight tendency to decrease as the 

 experiment progressed. 



On account of these peculiarities the case seemed to 

 merit a further investigation, which has now been car- 

 ried out, with the results described below. For this work 

 no changes were made in the apparatus, experimental 

 conditions, or procedure described in the former article. 

 All experiments were at 25°. 



At the outset it seemed possible that the effects noted 

 might be due in part to the formation of an interfering 

 coating on the dissolving disk of metal, and as chlorine 

 might act in this manner great care was taken to have 

 the reagents used free from traces of chloride. Later, 

 however, it was found that the addition of small amounts 

 of hydrochloric acid (two or three drops) to the solution 

 at the beginning of the experiment had no measurable 

 effect upon the reaction velocity, since the silver ions 



1 Vol. xlii, 301, 1916. 



2 Table X, Exp. 18. 



