866 PRINCIPLES OF CHEMISTRY 



nickelous oxide. Cobaltic oxide, Co 2 O 3 , exhibits more stability thao 

 nickelic oxide, and shows feeble basic properties j thus it is dissolve^ 

 in acetic acid without the evolution of oxygen. 35 bls But ordinary acids, 

 especially on heating, evolve oxygen, forming a' solution of a cobaltous 

 salt. The presence of a cobaltic salt in a solution of a cobaltous salt 

 may be detected by the brown colour of the solution and the blacfc 

 precipitate formed by the addition of alkali, and also from the fact that 

 euch solutions evolve chlorine when heated with hydrochloric acid, 

 Cobaltic oxide may not only be prepared by the above-mentioned 

 methods, but also by heating cobalt nitrate, after which a steel-coloured 

 mass remains which retains traces of nitric acid, but when heated 

 further to incandescence evolves oxygen, leaving a compound of 

 cobaltic and cobaltous oxides, similar to magnetic ironstone. Cobalt 

 (but not nickel) undoubtedly forms besides Co 2 O 3 a dioxide. Co0 2 

 This is obtained 36 when the cobaltous oxide is oxidised by iodine or 

 peroxide of barium. 37 



55 bis Marshall (1891) obtained cobaltic sulphate, CoafSO^.lSHjjO, by the action of an 

 electric current upon a strong solution of CoSO 4 . 



56 rk 6 action of an alkaline hypoohlorite or hypobromite upon a boiling solution of 

 cobaltous salts, according to Sohroederer (18S9), produces oxides, whose composition 

 varies between Co^Og (Rose's compound) and Co 2 s , and also between Co 5 8 and 

 Co 12 O 19 . If caustic potash and then bromine be added to the liquid, only Co 2 3 is 

 formed. The action of alkaline hypochlorites or hypo-bromites, or of iodine, upon 

 cobaltio salts, gives a highly-coloured precipitate which has a different colour to the 

 hydrate of the oxide Co. 2 (OH)e. According to Carnot the precipitate produced by the 

 hypochlorites has a composition Co^O^, whilst that given by iodine in the presence of 

 an alkali contains a larger amount of oxygen. Fortuuann (1891) reinvestigated the 

 composition of the higher oxygen oxide obtained by iodine in the presence of alkali, and 

 found that the greenish precipitate (which disengages oxygen when heated to 100) 

 corresponds to the formula Co0 2 . The reaction must be expressed by the equation: 

 CoX 2 + 1 2 + 4KHO = Co0 2 +.2KX + 2KI + 2H 2 O. 



37 Prior to Fortmann, Rousseau (1889) endeavoured to solve the question as to 

 whether Co0 2 was able to combine, with bases. He succeeded in obtaining a barium 

 compound corresponding to jthia oxide. Fifteen grams of BaCl 2 or BaBr a are triturated 

 with 5-G grams of oxide of barium, and the mixture heated to redness in a closed 

 platinum crucible ; 1 gram of oxide of cobalt is then gradually added to the fused mass. 

 Bach addition of oxide is accompanied by a violent disengagement of oxygen. After a 

 short time, however, the mass fuses quietly, and a salt settles at the bottom of the 

 crucible, which, when freed from the .residue, appears as black hexagonal, very brilliant 

 crystals. In dissolving in water this substance evolves chlorine ; its composition corre* 

 sponds to the formula 2(Co0 2 )BaO. If the original mass be neated for a long time 

 (40 hours), the amount of dioxide in the resultant mass decseases. The author ob- 

 tained a neutral salt having the composition CoO a BaO (this compound =-Ba0 2 CoO) 

 by breaking up the mass a,s it agglomerates together, and bringing the pieces into 

 /contact with the more heated surface of the crucible. This salt is formed between th* 

 Somewhat narrow limits of temperature 1,000-1,100 ; above and below these limit* 

 compounds richer or poorer in Co0 2 are formed. The formation of Co0 2 by the action 

 of BaO 2 , and the easy decomposition, of Co0 2 with the evolution of oxygen, give reason 

 for thinking that it belongs *Q the class of peroxides (like Cr 2 O 7 , Ca0 2 , &c.) ; it is not yet 

 fenovra whether they give peroxide of hydrogen like the true peroxides. The fact that 



