An electrochemical technique has been developed with which the steadystate concentration of adsorbed hydrogen on an iron surface, 8, can be determined. By using values of e determined by electrochemical techniques, a method of evaluating the specific rate constant for hydrogen absorption into iron, kabs, has been developed. Values of ~ determined on a cathodically polarized iron surface in 0.0001N sodium hydroxide ~ 0.1M sodium sulfate were between 5 and 12% of the total monolayer coverage, over the currentdensity range 10-300 ~A/cm 2. This current-density range represents a hydrogen generation rate equivalent to a corrosion rate of 5-150 mils penetration per year. The variation of ~ with cathodic overpotential was in close agreement with theory; values of 5~/5 log10 ~ were 3.5 V/decade measured experimentally and 4.2 V/decade theoretically. Experimental values of 0 permit, for the first time, determination of the specific rate constant for the absorption reaction. * Electrochemical Society Active Member.

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