The Reversal of the Sign of the Charge of Membranes by Hydrogen Ions

The similarity between the influence of ions on free and on electrical endosmose through collodion membranes leads to the conclusion that this influence is due to an alteration of the density of the electrical charge of the membrane by the ions3 This conclusion rests on the assumption that the Helmholtzian theory of the double layer and the formula connecting the volume of transport of liquid with the density of charge is correct. We have seen that on this assumption the observations lead to the conclusion that the ions with the same sign of charge as the membrane increase and the ions with the opposite sign of charge diminish the density of charge of the membrane. Whether, therefore, a given ion increases or d~rMnishes the density of charge of the membrane depends upon the sign of the charge of the membrane, and, hence, the sign of the charge precedes the influence of ions on the density of charge. One of the problems in the theory of the double layer at the boundary of membrane and watery solution is therefore the origin of the sign of the charge of membranes in contact with water. Chemists consider the double layer at the boundary of membrane and water as ionic in character and as due to the preferential adsorption of one kind of ions by the membrane, while the watery phase of the double layer is formed by the ions with the opposite charge from those adsorbed. This view has been developed with remarkable lucidity and consistency by Perrin ~ who assumes that the H and OH