The diffusion of hydrogen through hydrogen‐purified carbonyl iron shows breaks in the log (rate)vs.1/Tcurve at 834, 909 (body‐centered→face‐centered phase change), 945, 1009, 1056, 1082 and 1103 deg. centigrade. These are average values for three samples of ``Mehl'' iron. The log (rate)vs.1/Tcurves at these temperatures are composed of arcs, the above points being ends of these arcs. These points fall on a line whose slope is 4085 deg. Kelvin. Thusbin the expression exp (—b/RT) is given as 18,680 cal./g atom for these points. The above temperatures belonging to the ends of the arcs can be fitted to a Balmer type formula, i.e.,T(°K) =C(1/32—1/n2), wheren= 6, 7, 8, ..., andC= 13,430±30 for the breaks starting withn= 7, whileC= 13,301 for the break withn= 6. This difference is presumably caused by then= 6 break being in the body‐centered phase, while all breaks starting withn= 7 are in the face‐centered phase.
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