570 COBALT. 



Arseniate of cobalt, Co 3 , AsO 5 + 6HO, exists as a crystalline 

 mineral. It contains 6 HO, according to Bucholz. 



Peroxide of cobalt, Co 2 O 3 , has not the same importance as 

 the peroxide of iron, as it does not combine with acids. It is 

 formed when chlorine is transmitted through water in which 

 the hydrated protoxide is suspended, or when a salt of the prot- 

 oxide is precipitated by a solution of chloride of lime. In the 

 former case, water is decomposed by the chlorine, and hydro- 

 chloric acid produced, while the oxygen of the water peroxidises 

 the cobalt : Co 2 O 2 and HO and Cl = Co 2 O 3 and H Cl. The 

 peroxide of cobalt is precipitated as a black hydrate, contain- 

 ing 2 HO. This hydrate, when cautiously heated to 600 or 

 700 yields the black anhydrous oxide. When the peroxide of 

 cobalt is digested in hydrochloric acid, chlorine is evolved, and 

 the protochloride formed. Exposed to a low red heat, the 

 peroxide loses oxygen, and the compound oxide, Co O, Co 2 O 3 , 

 is produced, (Hess.) When the protoxide of cobalt is calcined 

 with a borax glass, at a moderate heat, it absorbs oxygen, and a 

 black mass is obtained, which mixed with manganic oxide, 

 serves as a black colour in enamel painting. A cobaltic acid, 

 Co O 2 , was supposed to be formed by the conjoint action of 

 oxygen and ammonia upon the protoxide, but the evidence of 

 its existence is insufficient. 



There exist three sulphurets of cobalt, a protosulphuret, 

 sesquisulphuret, and bisulphuret. 



Per cyanide or sesquicyanide of cobalt has not been ob- 

 tained in a separate state, but it exists in a class of double 

 cyanides, of which the radical is cobalti- cyanogen, Cy 6 Co 2 , ana- 

 logous to the ferricyanides. The cobalticyanide of potassium, 

 corresponding with the red prussiate of potash, is formed when 

 protoxide of cobalt or its carbonate is dissolved in caustic 

 potash, which has been treated with an excess of hydrocyanic 

 acid. It is an anhydrous salt, pale yellow and nearly colourless 

 when pure, of the same form as the ferricyanide of potassium. 

 Its solution does not affect the salts of iron, but forms a rose- 

 coloured precipitate with those of the protoxide of cobalt. 



A phosphuret of cobalt, Co 3 , P, was obtained by Rose, as a 

 grey powder, on passing hydrogen over the subphosphate of 

 cobalt ignited in a porcelain tube. It is also produced by 

 the action of phosphuretted hydrogen on the chloride of cobalt, 

 and may be looked upon as analogous in composition to the 

 former compound, H 3 P. 



