An effective oxidizing agent is required for the complete burning of refractory substances such as pyridine, pyrimidine, thiazole, and pteridine compounds. Generative force of oxygen of several metal oxides heated in the sample heater was examined and cobaltic oxide was found to be the most suitable in the point of oxygen generating velocity and temperature. It was thereby concluded that cobaltic oxide should preferably be used in place of the conventional cupric oxide powder for the complete burning, of refractory substances.