Abstract
It is shown that in evaluating the rates of anodic dissolution processes it is necessary to consider the influence of the positive and negative difference effects; otherwise ions going into solution with uncommon valency may be found. Scale fragments detached from an aluminum anode by the current passing through it could be seen. The hypothesis of valence change of ions while a current is passing through the anode does not explain all observed facts, but they can be well explained by the theory developed for the positive and negative difference effects.