THE STRUCTURE OF THE COLLODION MEMBRANE AND ITS ELECTRICAL BEHAVIOR III. THE BASE EXCHANGE PROPERTmS OZ COLLODION Bx KARL SOLLNER, CHARLES W. CARP., AND IRVING ABRAMS

In preceding papers *-3 it was shown that electrochemical behavior of collodion membranes (at least in solutions of strong, weakly adsorbable electrolytes) is due to the presence of acidic impurities in the collodion. Highly purified preparations exhibit only low electrochemical activity (as measured by concentration potentials, anomalous osmosis, etc.), and in our opinion, even this low activity is due to traces of acidic impurities; the ideal pure nitrocellulose should, in solutions of strong, weakly adsorbable electrolytes, be void of any distinct electrochemical activity. I t was further pointed out that the charge density at the collodion-solution interface is the ultimate determining factor. This general concept was actually used some time ago in some very interesting attempts to put the theory of electrochemical membrane behavior on a quantitative basis (Teorell, 4 Meyer and SieversS). We came to the conclusion that a study of the base exchange capacity of the collodion-solution interfaces would be the best method of obtaining pertinent quantitative data to test these theories. The base exchange capacity of a given substance is defined as the maximum cation exchange which can take place between a base exchange body and an electrolyte solution. The base exchange capacity of a given interface should be the limiting value of the possible charge density. The actual effective charge density would be the product of the base exchange capacity and the degree of dissociation (or a similar function). In the present paper we shall attempt to determine whether or not a quanti-