Compounds of Nickel

General Properties of Compounds of Nickel - Nickel usually behaves as a divalent element. Its salts when anhydrous are yellow in colour. They can usually be obtained in various stages of hydration, in which condition they are usually green, and frequently yield series of double salts, analogous in physical properties and in chemical constitution to many double salts obtainable with divalent iron. Like copper salts, those of nickel readily unite with ammonia. Like ferrous salts they absorb nitric oxide, but without change of colour.

Evidence has been obtained of the existence of highly unstable salts of trivalent nickel, but it has not been found possible to isolate them from their solutions.

Nickel salts are antiseptic; they arrest fermentation and the growth of plants. The carbonyl is intensely poisonous.

As has already been mentioned, nickel closely resembles cobalt in many of its properties, and for many purposes it is quite unnecessary to effect a complete separation of the metals. When, however, pure salts of either metal are required, several convenient methods are to hand for effecting the removal of the unwanted element. In order to remove small quantities of cobalt from nickel salts any of the methods suggested for the removal of nickel from cobalt salts may be utilised. Of these, Fischer's nitrite process is specially convenient.

Another method consists in adding ammonia to the impure bromide in aqueous solution, whereby nickel bromide hexammoniate, NiBr₂.6NH₃, separates out in beautiful violet crystals. Since cobalt does not yield a similar derivative under like conditions, a very pure salt of nickel may be obtained in this way. The hexammoniate of nickel chloride, namely, NiCl₂.6NH₃, may similarly be used.