Mixter — Formation of the Oxides of Cobalt and Nickel. 195 



73'4i per cent of cobalt. The cobalt was not quite pure, con- 

 taining a little silicon and iron. The ratio of oxygen con- 

 sumed to cobalt burned in experiments 3, 4, and 5 and the 

 ratio found in the analysis given is very nearly 1 to 1, proving 

 that the oxide is mostly CoO. Portions of oxide from the 

 combustion were tested for a higher oxide by treating with 

 hydrochloric acid. A small quantity of chlorine evolved indi- 

 cated that the oxide contained a little COgO^. Why then is 

 not the ratio of oxygen to cobalt greater than 1 to 1 instead of 

 slightly less? The presence of impurities accounts for it in 

 the portion analyzed, and the fact that the oxygen ratios found 

 in experiments 3, 4, and 5 are low, and also that the heat 

 effect calculated for one gram atom of cobalt burned is less 

 than found for one gram atom of oxygen takeii up, prove that 

 the cobalt used in the experiments was slightly oxidized. 

 Moreover, the formation of a small amount of CojO^ affects 

 the result but slightly since, as shown later, 3CoO-i-0 — CojO^-h 

 41,700"=. 



The result, therefore, based on the oxygen consumed should 

 be regarded as the better one. The average of the results is 

 57,179'' at constant volume and 57,460'= at constant pressure for 

 the heat effect of 16 grams of oxygen combining with cobalt 

 to form chiefly crystalline cobaltous oxide. Dulong* made one 

 determination of the heat of combustion of cobalt and found 

 that 1 liter of oxygen combining with cobalt gave a heat 

 effect of 5721'^. For 16 grams of oxygen the result is 64,000"=. 



Cobaltous oxide in a finely divided and amorphous form 

 oxidizes readily when heated in air to CojO,, and Foote and 

 Smithf have shown that the dissociation pressure of the latter 

 oxide is 10"" at 800°, the pressure rising rapidly with increas- 

 ing temperature. These facts explain the formation of CoO 

 when cobalt is burned in oxygen under pressure. The high 

 temperature accompanying the reaction dissociates any COjO^ 

 formed into CoO and O and the molten CoO falling upon the 

 cold bomb is quickly changed to a solid which a,3 it cools takes 

 up oxygen only on its surface. The following experiment 

 shows the slow rate of oxidation : 1'1424 gram of finely pul- 

 verized cobaltous oxide of same lot taken for the analysis on 

 p. 194 gained on heating to redness for 15 minutes in oxygen 

 0*0267, after 3 hours heating in air O'OOSO, and then gained 

 0"0035 gram when heated an hour in oxygen. The total gain 

 was 0*0332 gram ; the calculated gain for complete oxidation 

 to CO3O, being 0*0812 gram. 



2. Heat of reaction of cobalt with sodimn jperoxide. 

 Experiments 6 and 7. — Cobalt 4*000, sulphur 1*000, sodium 



*C. E., xii, 871, 1838. 



t J. Am. Chem. Soc, xxx, 1344. 



