658 PRINCIPLES OF CHEMISTRY 



solution of a cobalt salt be heated almost" to the boiling-point, and the 

 solution be then mixed with a boiling solution of an alkali hydroxide, 

 a pink precipitate of cobaltous hydroxide^ CoH 2 O 2 ,"wiil be formed. If 

 air be not completely excluded during the precipitation by boiling, the 

 precipitate will also contain brown cobaltic hydroxide formed by the 

 further oxidation of the cobaltous oxide. 34 Under similar circumstances 

 nickel salts form a green precipitate of nickelous hydroxide> the forma- 

 tion of which is not hindered by the presence of ammonium salts, butt 

 in that case only requires more alkali to completely separate the 

 nickel. The nickelous oxide obtained by heating the hydroxide, or 

 from the carbonate or nitrate, is a grey powder, easily soluble in acids 

 'and easily reduced, but the same substance may be obtained in the 

 crystalline form as an ordinary product from the ores ; it crystallises 

 in regular octahedra, with a metallic lustre, and is of a grey colour. 

 In this state the nickelous oxide almost resists the action of acids. 34 bls 

 soluble in water but scarcely soluble in ethyl and methyl alcohol. They decompose into 

 ..green oxide of nickel and potassium fluoride when heated in a current of air. The 

 analogous salt of cobalt crystallises in crimson flakes. 



If instead of potassium fluoride, CoCl 2 or NiCl a be fused with ammonium fluoride, 

 they also form double salts with the latter. This gives the possibility of obtaining 

 anhydrous fluorides NiP 2 and CoF^. Crystalline fluoride of nickel, obtained by 

 heating the amorphous powder formed by decomposing the double ammonium salt in 

 a stream of hydrofluoric acid, occurs in beautiful green prisms, sp. gr. 4'63, which are 

 insoluble in water, alcohol, and ether; sulphuric, hydrochloric, and nitric acids also have 

 no action upon them, even when heated ; ^NiF 3 is decomposed by steam, with the forma- 

 tion of black oxide, which retains the crystalline structure of the salt. Fluoride of 

 cobalt, obtained as a r6se-coloured powder by decomposing the double ammonium salt 

 with the aid of heat in a stream of hydrofluoric acid, fuses into a ruby-coloured mass 

 which bears distinct signs of a crystalline structure; sp. gr. 4'48. The molten saH 

 only Volatilises at about 1400, which forms a clear distinction between CoF 3 and the 

 volatile NiFjj/ Hydrochloric, sulphuric, and nitric acids act upon CoFg even in the oold, 

 although slowly, while when heated the reaction proceeds rapidly (Poulenc, 1892). 



w Hydrated suboxide of cobalt (de Schulten, 1889) is obtained in the following 

 manner. A solution of 10 grams of CoCl 2 6H 2 O in 60 c.c. of water is heated in a flask 

 with 250 grams of caustic potash and a stream of coal gas is passed through the solution. 

 When heated the hydrate of the suboxide of cobalt which separates out, dissolves in the 

 caustic potash and forms a dark blue solution. This solution is allowed to stand for 24 

 hours in an atmosphere of coal gas (in order to prevent oxidation). The crystalline mass 

 which separates out has a composition Co(OH) 2 , and to the naked eye appears as a violet 

 powder, which is seen to be crystalline under the microscope. The specific gravity of 

 this hydrate is 8'597 at 15. It does not undergo change in the air ; warm acetic acid 

 dissolves it, but it is insoluble in warm and cold solutions of ammonia and sal- 

 ammoniac. 



54 bis The following reaction may be added to those of the cobaltous and nickelous 

 salts : potassium cyanide forms a precipitate with cobalt salts which is soluble ify an 

 excess of the reagent and forms a green solution. On heating this and adding a certain 

 quantity of acid, a double. cobaZi cyanide is formed which corresponds with potassium 

 lerricyanide'. Its formation. is Accompanied with the evolution of hydrogen, and is 

 founded upon the property which cobalt has of oxidising in an alkaline solution, the de. 

 velopment of which has been^observed in such a considerable measure in the cobaltamino 

 euJts. The process which goes on here may be expressed by the following equation | 



