The variation with pH of the electrophoretic mobility of suspended particles has been determined for Fe2O3, TiO2, SnO2, SiO2, Al2O3, and for a number of synthetic aluminosilicates. The properties of the natural substances have been compared with those of synthetic materials before and after ignition at high temperatures. In general, the dehydration and recrystallization caused by ignition of the precipitated materials tend to produce surfaces resembling those of the natural crystals.

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The streaming potential method has been used to observe changes in the electrical double layer at the surfaces of the minerals Al2O3, SnO2, Fe2O3, and TiO2 in the presence of electrolytes. In addition to the normal effects of preferential physical adsorption of ions, ion exchange involving surface hydroxyl groups offers a useful hypothesis for explaining the results. Anion-exchange mechanisms appeared to be of particular importance in the reactions of phosphate, molybdate, and citrate with the oxide surfaces. In general for the particular samples used, Al2O3 and SnO2 (having basic surfaces) exhibited more pronounced anion exchange than Fe2O3 and TiO2 which had acidic surface.