Group II.: the alkaline earth metals Ca, Sr, Ba, and also Be (GI), Mg, Zn, Cd, divalent; Hg, monovalent and divalent.
This salt may be used for the separation of cobalt and nickel, since the latter metal does not form a similar double nitrite, but it is necessary that the alkaline earth metals should be absent, for in their presence nickel forms complex nitrites containing the alkaline earth metal and the alkali metal.
The citrates are a numerous class of salts, the most soluble of which are those of the alkaline metals; the citrates of the alkaline earth metals are insoluble.
Numerous methods have been devised for the separation of nickel and cobalt, the more important of which are: -the cobaltinitrite method by which the cobalt is precipitated in the presence of acetic acid by means of potassium nitrite (the alkaline earth metals must not be present); the cyanide method (J.