Mixter — Formation of the Oxides of Cobalt and Nickel. 193 



Aet. 'X.YK.—The Heat of Formation of the Oxides of 

 Cobalt and Nickel ; and sixth paper on the Heat of Com- 

 binatio7i of Acidic Oxides with Sodium, Oxide j by W. G. 



MiXTEK. 



[Contributions from the Sheffield Chemical Laboratory of Yale University.] 



Cobalt. 



1. Heat of comhustion of cobalt — The cobalt and its oxides 

 used in the work were obtained from a cobalt carbonate of 

 unknown source. It was probably made by precipitation with 

 ammonium carbonate, as it contained ammonia. Metallic cobalt, 

 which was reduced by hydrogen at about 420° and kept at this 

 temperature for three hours and at a pressure of 65""" of 

 mercury and then left to cool, ignited spontaneously in the air. 

 When the reduction was made at incipient redness, then lower- 

 ing the temperature to 420° and reducing the pressure as 

 above stated, the oxidation was less rapid in air. The metal 

 reduced at 420° was dark grey and very bulky ; that reduced 

 at the higher temperature was lighter colored. Whether 

 oxidation of the cobalt at common temperature was due to the 

 finely divided state of the metal or to a content of hydrogen 

 was not determined. The metal used for the calorimetric 

 experiments was reduced at a cherry-red heat and cooled in 

 hydrogen at atmospheric pressure. It probably oxidized 

 slightly in the air. It was sifted through a 1/100 inch mesh. 

 The metliod of determining the heat of oxidation of cobalt 

 was as follows : The metal was spread over a flat, thin silver foil 

 or mica tray 7 to 8™ in diameter, which was fastened 3 to 6'''^ 

 above the bottom of the bomb. The bomb was exhausted and 

 then filled with dry oxygen at a pressure of 12 to 13 atmos- 

 pheres. In the upper half of the bomb was a fine iron wire 

 which was ignited by an electric current. The hot globule of 

 magnetic oxide falling on the cobalt ignited it. The tray, the 

 oxide formed and the unoxidized cobalt were all melted. The 

 oxide was found in the bottom of the bomb in the shape of a 

 black crystalline hollow lump about Z"™ wide and 2™ thick. The 

 unburned metal was in one or more globules at the bottom of 

 it. The observed weight of the solid contents of the lower 

 half of the bomb less the weight of the tray, metal taken and 

 FcjO^ from the iron wire, plus 4'4 per cent correction for 

 water and volatile matter in the mica, gave the weight of 

 oxygen taken up in the combustion. After weighing, the 

 lump above mentioned was broken and the globules of metallic 

 cobalt separated and weighed. To make sure that the oxide 

 was then free from particles of the metal it was pulverized and 



Am. Joue. Sci. — Fourth Series, Vol. XXX, No. 177. — September, 1910. 



