The Anomalous Flocculation of Clay

Abstract

IN NATURE of May 1, p. 624, there appears a letter from Dr. A. F. Joseph and Mr. H. B. Oakley regarding the so-called anomalous flocculation of clay. We should like to point out, however, that it is doubtful whether the experiments referred to in the first part of the letter could be expected to show anomalous flocculation as ordinarily understood. In the first place, it has been suggested by Comber (Journ. Agric. Sci., 1920, 10, 432; loc. cit., 1921, 11, 460 et seq.; and Trans. Faraday Soc., 1922, 17, 349) that the phenomenon referred to is dependent on the presence of colloidal silica in the outer surface of the particles, and the “highly purified clay” used by Dr. Joseph and Mr. Oakley might well have lost this coating. Further, the phenomenon is shown, not so much by differences in the minimum amount of ion required for flocculation, as by an increased rate of sedimentation when a sufficiency of the ion is present. It would be interesting to know whether the particular clay used would show the phenomenon of anomalous precipitation at higher concentrations of salts either alone or after the addition of colloidal silica.