AMMONIA-COBALT BASES. 21 



that the different salts, not only of Koseocobalt but of the other similar bases, may 

 give different oxides by decomposition. "We propose to examine this point more 

 fully hereafter. 



The hydrate above mentioned and analyzed is a very dark-brown powder, which • 

 dries to a black mass with a gummy lustre. The powder is dark brown. Oxalic 

 acid dissolves it to a green solution, without evolution of gas, but this is decom- 

 posed by heating. Chlorhydric acid also dissolves the oxide, with evolution of 

 chlorine and formation of the protochloride. 



We have already mentioned that the anhydrous magnetic oxide of cobalt is 

 sometimes obtained during the decomposition of the chloride of Koseocobalt by heat. 

 We are, however, not able to state precisely under what circumstances this occurs; 

 either water or the oxygen of the air must take part in the decomposition, since 

 the chloride contains no oxygen. The anhydrous oxide occurs in the form of 

 small steel-gray octahedra, which are very hard, and which can only be dissolved 

 by long heating with sulphuric acid, or by fusion with sulphate of potash. Nitric, 

 chlorhydric, and nitro-muriatic acids have no decided action upon them. 



1.6425 grs. of this oxide gave 1.2059 grs. of metallic cobalt = 73.41 per cent. 



1.6425 grs. ignited in hydrogen gave 0.48T9 grs. water = 25.91 per cent, oxygen. 



The formula Co 3 4 requires 



Eqs. Calculated. Found. 



Cobalt ... 3 88.5 73.44 73.41 



. 4 32.0 26.56 25.91 



120.5 100.00 99.32 



This oxide has recently been described by Schwarzenberg, who obtained it by 

 igniting chloride of cobalt with free access of air, until the chlorine is expelled. It 

 is, therefore, very probable that in the decomposition of chloride of Koseocobalt by 

 heat, the chloride of cobalt is first produced, and then decomposed in the manner 

 observed by Schwarzenberg. 



With respect to the black sulphide which is thrown down from solutions of the 

 ammonia-cobalt bases by sulphide of ammonium, it can scarcely be doubted that this 

 is the bisulphide, as Claudet's analyses lead directly to the formula CoS 2 , corrobo- 

 rating the results obtained by Dingier already alluded to. 



PTJRPTJREOCOBALT. 



The salts of Purpureocobalt are often found among the direct products of the 

 oxidation of ammoniacal solutions of cobalt. They are often formed from the salts 

 of Roseocobalt by heating or by boiling with strong acids, the cobalt passing, as we 

 conceive, from one modification to another. The salts of Purpureocobalt are also 

 formed in great abundance by the action of acids upon salts of Xanthocobalt, and 

 we are disposed to think that they may also occur, though rarely, among the pro-, 

 ducts of the decomposition of salts of Luteocobalt. 



The salts of Purpureocobalt are distinguished by a fine violet-red or purple color, 



