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This paper describes the results of measurements of the heat capacity of nickel oxide, NiO, from 68-298.1°K., making use of the calorimeter described in a previous publication.1 From these results the entropy has been evaluated at 298.1°K., and from published heats of formation and heat capacities at higher temperatures the complete thermodynamic properties of the oxide have been derived.Material.-The nickel oxide used was a c. p. Baker analyzed grade containing less than 0.2% of impurities. Microscopic examination (X1000) showed the material to be made up of transparent cubic crystals of uniform size. This is the only form of the pure oxide which has been reported. The powder was dried for several days at 100°, and a sample then showed no ignition loss on heating to bright redness in a platinum crucible. The total charge of nickel oxide used in these measurements was 151.085 g. (in vacuo) or 2.0229 moles. Frequent checks of the calorimeter resistance against the calibrated thermocouple during the heat capacity measurements showed no significant changes in the calibration.

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