The results of the present investigation may be summarised as follows : We have ascertained, that in the artificial magnetite, the existence of magnetic transformation and break point of conductivity occurring when log σ is plotted against 1/T are due to an excess of oxygen in the crystal Moreover, the intensity of magnetization and conductivity increase with the concentration of oxygen in the crystal, may have been shown. Having concern about the diffusion of oxygen in the crystal, crystal of FeO・Fe_2O_3 will have perhaps vacant lattice point, for the ionic radius of oxygen is so large that oxygen atom can very seldom settle down interstitially into the lattice of FeO・Fe_2O_3. Comparing the conductivity of FeO・Fe_2O_3 with that of other semiconductors, it is similar to Cu_2O that the various values of activation energy can be expected with the increasing of oxygen concentration. We know, Cu_2O is a defect semiconductor, the current being carried by positive holes. In the case of FeO・Fe_2O_3, owing to the oxygen rich lattice, (3d)^ band of Fe^ or Fe^ ion loses electrons and forms the positive holes if Fe^ and Fe^ ions have higher energy than oxygen ions. The variation of activation energy and the existence of magnetic transformation will be illustrated if we assume the impurity level
