AMMONIA-COBALT BASES. 



15 



observed in the ammonia-cobalt compounds, and might easily lead to erroneous 

 conclusions. The nitrate of Eoseocobalt is readily prepared by decomposing a 

 solution of the chloride with nitrate of silver, but the solubility of the chloride of 

 silver in chloride of Roseocobait renders it somewhat difficult to obtain a pure salt 

 in this manner. Nitrate of copper also gives nitrate of Roseocobait with chloride 

 of copper, when mixed with an equivalent proportion of chloride of Roseocobait; 

 but the purification is difficult. Finally, a pure nitrate may be prepared by double 

 decomposition of nitrate of baryta and sulphate of Roseocobait. The anhydrous 

 nitrate of Roseocobait, when in large crystals, has a fine red color, which, accord- 

 ing to Chevreul's determination, as given by Fremy, is the first red -^. The 

 crystals are dichrous ; the ordinary image is clear rose red, the extraordinary 

 image bright red. According to Prof. Dana, this salt, like the sulphate, crystallizes 

 in forms belonging to the dimetric system. Figs. 4 and 6 represent some of the 

 more usual combinations, Fig. 5 is a very rare form, which was obtained only once. 



1 : 1 (over the base) = 82° 40'. 



Whence 

 : 1 (not observed) = 138° QO'.j 1 



i": 1.= 131° 40. 



Ammonia dissolves the nitrate with a fine purple red tint, and the salt usually 

 crystallizes unchanged from the solution, though sometimes the hydrous nitrate is 

 obtained. In cold water the nitrate is rather insoluble, though more soluble than 

 the sulphate. Hot water dissolves it rather more easily; but the solution, unless it 

 be acid, is quickly decomposed, and this effect is very speedily produced by boiling.. 

 The products of the decomposition in this case are a dark-brown oxide of cobalt, 

 and a solution containing the nitrate of Luteocobalt and nitrate of ammonia. 

 The quantity of Luteocobalt is small in comparison with that of the nitrate of 

 Roseocobait employed. 



When heated, the nitrate of Roseocobait explodes, though not with violence. 

 A black anhydrous oxide remains, which is probably Co 3 3 . The reaction in this 

 case is easily explained, if we remark that the oxygen in the nitric acid is exactly 

 sufficient to form water with the hydrogen of the ammonia. The simplest equa- 

 tion representing the reaction is 



5NH 3 .Co 2 03,3N0 5 =Co 2 3 +8N+15HO. 



In point of fact, however, the decomposition is less simple, as red vapors are 

 always evolved. 



When a current of NO^ is passed through a solution of nitrate of Roseocobait a 

 rapid absorption takes place, and after a short time crystals of nitrate of Xantho- 

 cobalt are deposited. 



