IRON, COBALT, AND NICKEL 



It is interesting to note the relation of the cobaltous and nickelous 

 "hydroxides to ammonia ; aqueous ammonia dissolves the precipitate of 

 cobaltous and nickelous hydroxide. The blue ammoniacal solution of 

 nickel resembles the same solution of cupric oxide, but has a somewhat 

 reddish tint. It is characterised by the fact that it dissolves silk in 

 the same way as the ammoniacal cuptic oxide dissolves cellulose. Am- 

 monia likewise dissolves the precipitate of cobaltous hydroxide, forming 

 a brownish liquid, which becomes darker in air and finally assumes a 

 bright red hue, absorbing oxygen. The admixture of ammonium chloride 

 prevents the precipitation of cobalt salts by ammonia j when the am- 

 monia is added, a brown solution is obtained from which, as in the 

 case of the preceding solution, potassium hydroxide does not separate 

 the cobaltous oxide. Peculiar compounds are produced in this solution j 

 they are comparatively stable, containing ammonia ancl an excess of 

 oxygen ; they bear the name cobaltoamine and cobaltiamine salts. They 

 have been principally investigated by Oenth, Fremy, Jorgenson and 

 others. Genth found that when a cobalt salt, mixed with an excess of 

 ammonium chloride, is treated with ammonia and exposed to the air, 

 after a certain lapse of time, on adding hydrochloric acid and boiling, 

 a red powder is precipitated and the remaining solution contains an 

 orange salt. The study of these compounds led to the discovery of a 

 whole series of similar salts, some of which correspond with particular 

 higher degrees of oxidation of cobalt, which are described later. 35 



CoC 2 N 2 + 4KCN first forms CoK4C 6 N 6 , which salt with water, H 2 O, forms potassium 

 hydroxide, KHO, hydrogen, H, and the salt, K 3 CoC 6 N 6 . Here naturally the presence of 

 the acid is indispensable in consequence of its being required to combine with the alkali. 

 Prom aqueous solutions this salt crystallises in transparent, hexagonal prisms of a yellow 

 colour, easily soluble in water. The reactions of double decomposition, and even the 

 formation of the corresponding acid, are here completely the same as in the case of the 

 ferricyanide. If a nickelous salt be treated in precisely the same manner as that just 

 described for a salt of cobalt, decomposition will occur. 



33 The cobalt salts may be divided into at least the following classes, which repeat 

 themselves for Cr, Ir, Rh (we shall not stop to consider the latter, particularly as they 

 closely resemble the cobalt salts) : 



(a) Ammonium cobalt salts, which are simply direct compounds of ths cobaltous 

 Ipalts 0X2 with ammonia, similar to various other compounds of the salts of silver, 

 copper, and even calcium and magnesium, with ammonia. They are easily crystallised 

 from an ammoniacal solution, and have a pink colour. Thus, for instance, when 

 cobaltous chloride in solution is mixed with sufficient ammonia to redissolve the 

 precipitate first formed, octahedral crystals are deposited which have a composition 

 CoCl 2 ,H 3 O,6NHg. These salts are nothing else but combinations with ammonia of 

 crystallisation if it may be so termed likening them in this way to combinations with 

 water of crystallisation. This similarity is evident both from their composition and from 

 their capability of giving off ammonia at various temperatures. The most important 

 point to observe is that all these salts contain 6 molecules of ammonia to 1 atom of cobalt, 

 and this ammonia is held in fairly stable connection. Water decomposes these salts. (Nickel 

 behaves similarly without forming other compounds corresponding to the true cobaltic.) 



(6) The solutions of the above-mentioned salts are rendered turbid by the action of 



