XVI.—The Stability of Suspensions. II. The Rate of Sedimentation of Kaolin Suspensions Containing Colloidal Silicic Acid

Abstract

Summary1. The experiments previously reported on the effect of salts at various hydrogen ion concentrations on the rate of sedimentation of kaolin suspensions have been extended so as to include the chlorides of the alkali metals, including ammonium but excluding rubidium.In acid suspensions the action in inhibiting sedimentation is least in the case of cæsium and greatest in the case of sodium. The results are discussed in the light of the Gedroiz-Wiegner theory of base exchange in soils and stability of clay suspensions.2. When kaolin suspensions contain a small quantity of colloidal silicic acid the normal effect appears to be one of slight protection.3. Under certain conditions the effect of silicic acid is to produce precipitation of a film of insoluble material over the surface of the particles. In this case an abnormally rapid sedimentation of the particles results, and there ensues an extremely rapid and complete precipitation.4. Under other conditions the presence of the silicic acid prevents the formation of a precipitate, and in this case the abnormal sedimentation occurring in the absence of silicic acid tends to disappear.5. The meaning of the terms “abnormal flocculation” and “anomalous flocculation” is discussed, and it is pointed out that the use of these terms is sometimes attended with ambiguity.