Magnetization per gram of an iron sphere &sgr; as a function of temperatureThas been studied between the ferromagnetic Curie temperatureTFCandTFC+30°K with applied magnetic fields between 180 and 1360 Oe. The temperatureTFC, appearing as an abrupt decrease in the &sgr; vsTcurves, occurs at 1044±2°K. Mass magnetic susceptibility of iron, above the ferromagnetic Curie temperature in small magnetic fields, is proportional to (T‐TFC)−4/3, which is the theoretical prediction for a Heisenberg three‐dimensional ferromagnet.