Hydrogen was electrolyzed into flat ring cathodes of magnetically soft iron in 0.5 N solutions of H2SO4or of KOH. The design of the electrolytic cell permitted magnetic testing at intervals. Magnetic hardening began after many hours provided the electrolytic current density was kept above a lower limit depending on the electrolyte. This hardening proceeded, at adequate current density, to an end point beyond which longer charging at any current density rarely produced any further changes in magnetic properties. Removal of hydrogen by storage in air at room temperature for 5 months, or by annealing at 400°C in vacuum for 17 hours, did not diminish the magnetic hardness produced during electrolysis. It is suggested that the iron is locally cold‐worked by non‐uniform distribution in it of hydrogen in excess of the solubility limit at room temperature, and that uniformly distributed hydrogen up to this limit has very little effect on the ferromagnetic properties.