The equilibrium oxygen pressure for the reaction was accurately measured over the temperature range 910°–1145°K. The following working equation for the oxygen pressure is valid over the experimental range. The following expressions, valid from 298°–1200°K, apply to the formation of one mole of The heat of formation and entropy of at 298.15°K were found to be −28,345 ± 400 cal/mole and 8.60 ± 0.3 eu, respectively.