The formation of zinc ferrite by the direct addition of zinc and ferric oxides was studied at various temperatures between 580° and 660° C. During the first two or three hours of heating, the reaction obeys Tamman's logarithmic law on reactions between solid phases. An apparent equilibrium appears afterwards. At 580° C. the reaction takes place extremely slowly. It is found by thermal analysis that there is no evidence for the formation of a compound containing more zinc oxide than ZnFe2O4, at least not below 1,070° C. The solubility of zinc ferrite in normal and two‐normal sulfuric acid is studied. A mixture of 7.5 per cent sulfur dioxide in air, passed on zinc ferrite heated at 450° C., decomposes it slowly and liberates the zinc as zinc sulfate.