In addition to single nickel crystals also nickel samples produced by dc and pr (pulse-reversal) plating were examined. As previously reported the true rate of dissolution of nickel in solutions containing oxygen was found to be as much as three times the electrochemical rate at the corrosion potential. When passivation was approached (spontaneously or by anodic polarization) the true rate of dissolution approached the rate of anodic reaction. During cathodic polarization there was still a significant rate of dissolution. The true rate of dissolution was determined by CMT measurements (Corrosion Measurements by Titration). Electrochemical measurements (EC) indicating the rate of electrochemical reactions were made simultaneously.