The effect of surface active substances on the diffusion of water through membranes

Abstract

According to the investigations of Jacques Loeb, the diffusion of water through membranes is a linear function of the solute, as would be expected according to the law of van't Hoff, only if the concentration of the salt solution is greater than M/16. In lesser concentrations than this the so-called “initial rate” of diffusion is represented by a curve having a maximum corresponding to a concentration varying from M/512 to M/256. If the concentration becomes greater the rate of diffusion decreases until a concentration of M/16 is reached. The experiments of Loeb, and of Bethe and Toropoff seem to indicate the identity of electro-osmosis and free osmosis in low concentrations, and in this way furnish the explanation of the influence of electrolytes on the rate of diffusion by the difference of effect of the ions on the quantity of charge on the Helmholtz double layer on the capillary walls. Grumbach has shown that surface active substances exert an influence on capillary electric forces and consequently on the diffusion potential. Our own investigations are concerned with the influence of surface active substances on the capillary kinetic phenomena. Collodion sacs of 50 cc. capacity were attached to upright manometer tubes of 2 mm. diameter. The sacs were made on the inside of a 50 cc. Erlenmeyer flask, coated twice with 4 per cent collodion, and dried for one-half hour after the first coating, and 4 to 5 hours after the second. The sacs were filled with electrolytes of M/32 concentration immersed in distilled water. In the case of a given electrolyte the manometer readings obtained with different sacs were relatively constant. Having established the normal rate of diffusion, the sacs were treated by filling them with solutions of surface active substances.