Studies of rates of various transformations and reactions in iron alloys seem to indicate that certain elements have a definite influence on the rate of diffusion of carbon in $\gamma$-iron. In particular, cobalt shows a pronounced accelerating influence. By direct measurement of the rate of diffusion of carbon in iron-cobalt alloys this conclusion is confirmed and an increase in the diffusion coefficient established. An addition of 4 percent cobalt decteases the activation energy from 32,500 cal. down to 30,000 cal. corresponding to an almost twofold increase of the diffusion rate at 1 atomic percent carbon concentration. At higher carbon contents the accelerating influence of cobalt is smaller. This property of cobalt is unusual especially in view of the fact that both manganese and nickel are known to have practically no influence on the diffusion of carbon.

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