On the Separation of Cadmium in the Presence of Zinc. 433 



rized at a different angle of incidence — that corresponding to 

 the refractive index of water. It is chiefly reflected from 

 clouds, and is in no way to be confounded with that reaching 

 us from the clear sky. 



Peekskill, New York, 

 July 23, 1879. 



LII. On the Separation and Estimation of Cadmium in the 

 Presence of Zinc; with Remarks upon the Separation of 

 Copper, Cadmium, and Zinc. By Christopher Clarke 

 Hutchinson, Assoc. P.C.Sc.L* 



A SHORT time ago I conducted an investigation on the 

 influence of mass in chemical reactions, particularly di- 

 recting my attention to the influence which copper, cadmium, 

 and zinc exercise upon each other, and their mutual relations 

 during precipitation. The two latter metals seem to have 

 many points in common with each other, and show great 

 similarity in their behaviour towards most chemical reagents. 



The investigation necessitated an examination of the me- 

 thods in use for the separation and estimation of these metals. 

 Most of such processes proved very unsatisfactory ; I was 

 therefore obliged to make some experiments in order to deter- 

 mine the methods most reliable. In this paper I shall give 

 the results I obtained, and the methods found most accurate. 

 Standard solutions of the pure crystallized sulphates made 

 from the pure metals were used throughout. 



Separation of Cadmium and Zinc. — If an acid solution con- 

 taining both of these metals be treated with sulphuretted 

 -hydrogen, the cadmium should be precipitated as the sulphide, 

 while the zinc should remain in solution. The reaction, how- 

 ever, is not so complete as indicated ; and its behaviour is de- 

 pendent upon the amount of acid present in excess. If too 

 great an amount of acid be present, the cadmium will only be 

 imperfectly precipitated ; while, on the other hand, if the so- 

 lution be not sufficiently acid, a portion of the zinc undergoes 

 precipitation as sulphide with the cadmium. A method of 

 separation based upon this behaviour will only yield satisfac- 

 tory results when the relative quantity of each metal present 

 is approximately known, so that the quantity of acid can be 

 adjusted (whether the one or the other be present in a larger 

 quantity) so as not to prevent the total precipitation of cad- 

 mium or favour that of zinc. Even when very carefully con- 

 ducted, it is often found necessary to redissolve the sulphides 



* Communicated by the Author. 



