1. The electrochemical behavior of membranes prepared from commercial collodion preparations varies widely, some preparations showing very high, other ones very low electrochemical efficiency ("activity").

2. The electrochemical activity of a collodion membrane depends entirely upon impurities of an acidic nature contained in the collodion used for casting the membrane.

3. The active acidic impurities are substantially due to partial oxidation which occurs in the manufacturing process. Sulfuric acid compounds; e.g., acid sulfuric acid esters play only a minor rôle, if any.

4. The electrochemical behavior of collodion membranes in solutions of strong electrolytes is decisively dependent upon the acidic groups built permanently into the collodion surfaces. Preferential ion adsorption plays only a minor, if any, rôle.

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