An investigation of the permeation rate of electrolytic hydrogen through Armco iron single crystals and polycrystals by an electrochemical technique is described. The variation of the permeation rate with cathodic overpotential has been determined in alkaline , alkaline cyanide, acidic , acidic iodide, acidic napthalene, and acidic nitrile (valeronitrile, napthonitrile, benzonitrile) solutions. The potential‐permeation behavior as a function of temperature has been investigated in acid solutions. The permeation potential behavior in alkaline solutions indicate a coupled discharge recombination mechanism for hydrogen evolution at low overpotentials while at higher overpotentials the mechanism is slow discharge‐fast electrochemical. The effects of CN−, I−, and napthalene which increase permeation rate has been interpreted in terms of a lowering of the bond energy. Nitriles were found to decrease the permeation rate, and their effect on the permeation rate is interpreted in terms of their vertical adsorption on the electrode hindering the discharge process. The results indicate that hydrogen goes through an adsorbed intermediate state on discharge before entering the metal lattice. Grain boundaries play no part in the hydrogen evolution kinetics or in the entry of hydrogen to the metal.