AMMONIA-COBALT BASES. 11 



With respect to this formula, it must be remarked that it is extremely difficult 

 to obtain this chloride perfectly free from chloride of Pnrpureocobalt, into which it 

 is so easily converted. The uncertainty, however, will concern only the number 

 of equivalents of water. The chloride of Eoseocobalt combines with the chlorides 

 of the electro-negative metals to form well defined salts. The platinum salt, which 

 we have not yet fully examined, appears to have the formula 

 5NH 3 .Co 3 Cl 3 +3PtCl 2 +8HO. 



A neutral solution of the chloride of Eoseocobalt is easily decomposed by boiling, 

 with evolution of ammonia, and precipitation of a black powder. This powder is 

 probably a hydrate of the magnetic oxide, Co 3 4 +a;HO, but we have deferred its 

 examination to the second part of our memoir. The reactions of the chloride of 

 Eoseocobalt are as follows : 



Terchloride of gold gives no precipitate at first, but after standing a lilac or 

 purple precipitate, which is probably merely the chloride of Eoseocobalt. 



Bichloride of platinum gives a pale orange red precipitate. 



Chloride of mercury gives a pale rose or flesh-colored flocky precipitate. 



Ferridcyanide of potassium gives beautiful orange-red oblique rhombic crystals. 



Cobaltidcyanide of potassium gives fine red crystals. 



Ferrocyanide of potassium gives a cinnamon, passing to a chocolate brown pre- 

 cipitate. 



Oxalate of ammonia gives a brick-red precipitate of small granular crystals. 



Neutral chromate of potash gives no precipitate. 



Bichromate of potash gives a dark brick-red precipitate. 



The following reactions, which were obtained with a solution of the hydrated 

 nitrate of Eoseocobalt may also be introduced in this place. 



Pyrophosphate of soda gives a dull rose-red precipitate soluble in an excess of 

 the precipitant to a clear red liquid, which in a few minutes solidifies to a mass of 

 fine rose-red needles. 



Picrate of ammonia gives a fine bright orange-red precipitate soluble in hot water. 



Iodide of potassium gives no precipitate either with the chloride or nitrate. 



The precipitate with chloi'ide of mercury is readily soluble in chlorhydric acid, 

 and the solution after standing gives beautiful small granular crystals of a brownish 

 red color. 



The reactions which are peculiar to the sulphate of Eoseocobalt will be described 

 when speaking of that salt. 



SULPHATE OF ROSEOCOBALT. 



An ammoniacal solution of sulphate of cobalt absorbs oxygen readily from the 

 air, becoming at first brown and then dark red. The time required for complete 

 oxidation varies remarkably. The process is sometimes complete in a few days, 

 but often requires many weeks. From the perfectly oxidized solution, suljohuric 

 acid cautiously added usually throws down the sulphate of Eoseocobalt as a bright 

 red crystalline powder, which, after washing with cold water, is readily purified by 

 solution and crystallization, a very small quantity of acid being added to prevent 

 decomposition. 



