AMMONIA-COBALT BASES. 57 



in the case of tlie action of the gas upon the chloride and sulphate of Roseocobalt, 

 by the equations 



5NH 3 .Co 2 Cl 3 +3N0 4 +3HO=NO s .5NH 8 .Co a O s ,2NO e +3HCl, 

 5NH s .Co 2 3 ,3S03+3N0 4 +3HO=N0 2 .5NH 3 .Co 2 03,2N0 5 +3HO,S03. 



It will be seen from these equations that when neutral solutions of the salts of 

 Roseocobalt or Purpureocobalt are employed, chlorhydric and sulphuric acids are 

 set free. The influence of an excess of ammonia in facilitating the process is 

 thus easily understood. The nitrate of Xanthocobalt, being much less soluble in 

 cold water than the ammonia salts, is easily purified by re-crystallization. In 

 treating of the sulphate and chloride of Xanthocobalt, we have mentioned that 

 the nitrate of Xanthocobalt is often formed while preparing these salts directly. 

 As a mode of preparation, this method is not to be recommended, but it possesses 

 much theoretical interest. The equation which represents the action when the 

 nitrate of Xanthocobalt is formed directly by the action of NO x upon an ammo- 

 niacal solution of the sulphate of cobalt, is possibly the following 



2CoO,SO s +7NH3+N0 3 +3N0 4 +2HO=NO a .5NHs.Co 2 Os,2NO s +2NH 4 0,S0 3 +N0 2 . 



When the chloride of cobalt is employed instead of the sulphate, other products 

 are always formed simultaneously with the nitrate of Xanthocobalt, and the reaction 

 becomes therefore more complicated. 



The nitrate of Xanthocobalt crystallizes in small brilliant crystals, which, accord- 

 ing to Prof. Dana's measurement, belong to the dimetric system. The only form 

 observed as yet is an octahedron, the angle at the base being 100° 45' — 101° 15'. 



The salt is dichrous, the ordinary image being pale' orange, while the extraordi- 

 nary is bright orange-yellow. 



The salt has a clear brown-yellow color, and the mass of crystals is usually very 

 brilliant. It is quite soluble in hot, but rather insoluble in cold water ; the solu- 

 tion is readily decomposed by boiling, with evolution of ammonia and precipitation 

 of a heavy black powder. The dry salt is readily decomposed by heating, abun- 

 dance of red vapors being given off, while a black oxide remains. The nitrate is 

 completely decomposed by boiling with chlorhydric acid, red vapors mixed with 

 chlorine being given off, while there remains a solution of chloride of Purpureo- 

 cobalt, from which crystals of this salt are deposited on cooling. "When boiled 

 with nitric acid, a similar decomposition is produced, and crystals of nitrate of 

 Eoseocobalt are obtained in small quantity.. It is probable that nitrate of Pur- 

 pureocobalt is the first product of this reaction, and that this by boiling with 

 excess of acid, passes into the nitrate of Roseocobalt. As a general rule, the 

 quantity of nitrate of Roseocobalt produced is small, and the decomposition results 

 in the conversion of the nitrate of Xanthocobalt into the nitrates of cobalt and 

 ammonia. 



Nitric acid precipitates nitrate of Xanthocobalt from its solution without sensi- 

 ble decomposition in the cold. By long boiling acetic acid completely reduces 

 nitrate of Xanthocobalt, and a solution of cobalt is obtained which is free from 

 ammonia-cobalt bases. Oxalic acid also reduces the nitrate by boiling, oxalate 

 of cobalt being thrown down. 

 8 



