Mr Dootson, A Method of detecting Nickel, etc. 125 



A Method of detecting Nickel and Cobalt in the presence of 

 each other. By F. W. Dootson, M.A., Trinity Hall. 



[Bead 2 March 1903.] 



The process described by Rosenheim and Huldschinsky (Ber. 

 1901, 2050) for the quantitative separation of these metals, though 

 somewhat long and laborious, may be so modified as to render it 

 a rapid and easy qualitative test. 



Nickel and Cobalt are separated from other metals and 

 obtained as sulphides by the ordinary processes of analysis. These 

 sulphides are then dissolved in the least possible quantity of 

 hydrochloric acid, with the addition of a few drops of nitric acid, 

 and the solution diluted if necessary. A large excess of acid 

 materially diminishes the sensitiveness of the reaction, and should 

 be removed, either by evaporation or by partial neutralisation 

 with alkali. 



To the acid solution sufficient ether is added to form a layer 

 about half an inch in depth. Commercial ether is usually suffi- 

 ciently free from alcohol for the purpose. 



A dilute solution of ammonium or potassium thiocyanate (1 in 

 10) is then poured in, a little at a time, the test tube being vigor- 

 ously shaken after each addition, till the ethereal layer acquires a 

 distinct colour. The addition of large excess of thiocyanate, in 

 presence of cobalt, is liable to mask the colour due to the nickel 

 when only traces of the latter metal are present. 



With nickel alone, the ethereal layer varies in tint from a pale 

 pink to blood red according to the concentration of the solution. 

 If nickel is absent, and cobalt present, the ether is tinted blue, 

 and the colour is considerably deepened by the subsequent ad- 

 dition of methylated spirit. 



When both metals are present the pink colour due to the 

 nickel is the first to appear, and cobalt is detected by the cautious 

 addition of methylated spirit after the solution has stood suffi- 

 ciently long to allow the ether to separate completely. An intense 

 blue colour appears where the ethereal and aqueous layers meet. 



The mechanism of the process appears to be that double 

 thiocyanates of nickel or cobalt with potassium or ammonium 



