CYANIDE OF POTASSIUM, 
301 
so that the resulting precipitate be redissolved, the solution 
will contain free hydrocyanic acid, cyanide of potassium, 
cyanide of nickel, and cyanide of cobalt; this last changes by 
heat into cobalto-cyanide of potassium; if diluted sulphuric 
acid be then added in the cold, the results may be presented 
under three forms: 
Cobalt and nickel existing in the solution, in the proportion 
of two of the former to three of the latter, (proportions cor- 
responding to their atomic weights in the cobalto-cyanide of 
nickel,) the precipitate which forms is cobalto-cyanide of 
nickel, of a bluish white color. The liquid, after filtration, 
contains neither nickel or cobalt. 
The solution containing an amount of nickel less than that 
corresponding to the above proportions, (two cobalt, three 
nickel,) there remains in the liquor a certain quantity of co- 
balto-cyanide of potassium, and the precipitate is equally co- 
balto-cyanide of nickel. 
If there be more nickel in solution, the precipitate contains 
a mixture of cyanide of nickel, and cobalto-cyanide of 
nickel. 
In the first and second case, the precipitate formed by the 
addition of diluted sulphuric acid is boiled in the acid liquor, 
in a matrass, as long as any traces of the disengagement of 
hydrocyanic acid can be perceived, (or, what is better, eva- 
porated to dryness on a salt water bath,) and then slightly 
heated with carbonate or hydrate of potassa in excess; the 
cobalto-cyanide of nickel is then decomposed into pure carbo- 
nate or oxide of nickel, which may be washed on a filter, 
dried and weighed, and into an alkaline liquor which con- 
tains all the cobalt. On evaporating this latter to dryness, 
adding a little nitrate of potassa, heating the dry residue to 
redness, and washing with water, all the cobalt is obtained in 
the state of oxide. 
This process is applicable to all the analyses of cobalt mi- 
nerals, where this metal predominates. With the minerals 
of nickel, in which the cobalt is consequently in the lesser 
