ELECTROKINETIC POTENTIALS. XI. THE EFFECT OF SODIUM SOAPS ON THE ELECTRIC MOMENT OF THE DOUBLE LAYER AT AN AQUEOUS-CELLULOSE INTERFACE

Abstract

1. Electrokinetic studies of aqueous solutions of sodium formate, sodium acetate, sodium propionate, sodium butyrate, sodium caprylate, sodium oleate and sodium oxalate have been conducted at a cellulose interface with the streaming potential technique. 2. It is suggested that in interest of clearness and accuracy the attempt to express electrokinetic data in terms of ``potentials'' be abandoned and that the electric moment of the double layer, which does not require a knowledge of the magnitude of the dielectric constant, be substituted for ζ. 3. It is indicated that after the fourth carbon atom has been added the electric moment of the double layer is essentially a constant. 4. It is noted that there is no correspondence between the ionization constant of the fatty acid from which the soap is derived and its effect on the electrokinetic conditions at the interface. This indicates that hydrolysis and the resulting OH ion plays a minor role. 5. It is pointed out that the electric moment of the double layer in the case of the longer chained soaps is almost independent of the concentration whereas that of the short chained soaps are much more sensitive to increased concentration. 6. The maximum electric moment is found at about 2×10−4 normal. This is true also for a number of salts.