4 Taylor, Method of Separating- Cobalt and Nickel. 



excess. My first impression was that tlie soluble barium 

 or calcium salt formed when the acid is neutralised by the 

 carbonate must be the cause of the retardation, but 

 experiment showed that it was not. The cause of the 

 retardation is simply free carbonic acid. If, after adding 

 the carbonate to a solution of cobalt containing free acid, 

 the liquid is boiled (to expel the carbon dioxide) and 

 cooled again before adding the bromine water, there is no 

 retardation. Also, if carbon dioxide is bubbled through a 

 neutral solution of cobalt, or if such a solution is mixed 

 with ordinary soda-water, on adding the carbonate and 

 bromine water there is a retardation of the precipita- 

 tion of the cobalt similar to that observed when free acid 

 is present at the outset. 



This curious retarding action of free carbonic acid 

 appears additionally strange when it is borne in mind that 

 carbon dioxide is one of the products of the reaction 

 itself, and that immediately the reaction begins there 

 must be free carbonic acid present in the liquid. Plainly, 

 the retarding action of the free carbonic acid is very 

 slight unless there is a considerable amount of it in pro- 

 portion to the water, and in dilute solutions the amount 

 never becomes sufficient. In strong neutral solutions the 

 carbonic acid produced during the reaction has its effect, 

 and the precipitation of the cobalt takes much longer. At 

 present I am unable to suggest any reason why free 

 carbonic acid should exert this curious retarding effect.* 



With a dilute solution which is approximately neutral 

 the process of separation works rapidly and well. I have 

 tested it quantitatively with most satisfactory results. The 



* It is well known that manganese is precipitated b)' barium or calcium 

 carbonate under the same^ circumstances as cobalt, and I find that free 

 carbonic acid acts exactly as it does with cobalt, — the precipitation of the 

 manganese is very considerably retarded. 



