The reactions of MgO, CaO, SrO, BaO, ZnO, CdO, SnO, PbO, Pb3O4 and As2O3 With K2S2O7 were investigated using TG and DTA methods of thermal analysis. The exothermic peaks diagnostic of acid-base reactions were observed in the reactions of MgO, CaO, SrO, BaO, ZnO, CdO, SnO, PbO and Pb3O4 However, As2O3 showed an endothermic redox reaction in which As2O3 was oxidised to As2O5 and the pyrosulphate reacted to evolve SO2. In each metal oxide reaction the corresponding metal sulphate was produced. On the basis of acidimetric and TG results the stoichiometries are proposed for these reactions.