The Structure of the Collodion Membrane and Its Electrical Behavior Ii, the Activated Collodion Membrane by Karl Sollner, Irving Abrams, and Charles W. Carr

In preceding communications t, 2 we were led to the conclusion that the electrochemical activity of collodion membranes, as manifested by concentration potentials, etc., is due principally to acidic impurities. Accordingly, different brands of collodion differ widely as to their activity, the purer brands being less active. The impure (but active) foreign brands of collodion, heretofore generally used by workers in the field of electrochemical membrane investigation, are no longer obtainable. In order to continue our investigation, it became necessary to find methods to produce active collodion membranes at will. The idea of inducing changes in the electrochemical characteristics of membranes is not entirely new. Many investigators have activated membranes by the adsorption of proteins, e.g. the proteinized membranes of Loeb. 8 Other investigators use other organic compounds, usually dyestuffs. These may be adsorbed like proteins or they may be dissolved in the collodion solution* previous to casting the membranes. Such membranes are interesting and useful in their own right, but are not altogether satisfactory substitutes for active collodion membranes. They very often show considerable asymmetry; moreover, the dyestuffs so far employed (according to the literature) are slowly released into the solution in contact with the membrane, whereby the character of the membrane is considerably changed. Meyer and Sievers 5 used an oxidation method to activate a cellophane membrane. Oxidation obviously increases the number of dissociable groups (carboxyl groups) in the membrane. As far as we know, this particular point was not studied further by these inves-