1. A prolonged cathodic polarization of the nickel electrode in dilute acid and in an atmosphere of hydrogen did not cause any increse, but rather a slight decrease in the initial value of the electromotive force of the cell, Ni | SiSO4 (0.05 M.) | KCl (0.1 N.), Hg2CL2| Hg. The effect of hydrogen produced in the metals of the iron group by cathodic polarization, i.e. of making the metals less noble as found by previous investigators, was not be repeated in the case of reduced nickel powder. The slight diminution in the initial value of the electromotive force is supposed that it may be the effect of a trace of the free acid which might have remained in the cell, owing to the difficulty of the replacing it. 2. The potentials of the nickel electrode in an atmosphere of nitrogen, and of nitrogen mixed with a little hydrogen were measured. As a result of these series of experiments the conclusion is reached that the occluded hydrogen in nickel has no effect upon the true electrode potential. But, it was observed that in the case of an electrode which has been once affected by oxygen, the effect of hydrogen is very remarkable, and. the electrode returns to its active state even at a low temperature. 3. For the measurement of the potential of nickel electrode, the complete exclusion of oxygen is the essential requirement.