Results Because aliphatic hydrazines are subject to oxidation on standing in air, samples awaiting combustion under an oxygen atmosphere are likely to be unstable. We therefore chose solution calorimetry to determine the AHH of azo-n-butane (ANB) using Turner's hydrogenation calorimeter.'Ethanol solutions of ANB were hydrogenated with a large excess of 10% Pd/C catalyst, but the heats obtained varied from-14.9 to-26.8 kcal/mol. It was ...