These authors are studying the influence of pH and particle size on sedimentation volume, and on the velocity with which it is reached. They are using fractions from > 1.2 μ to < 0.3 μ, obtained by sedimentation, and buffer solutions of pH 1, 3, 5, 7, 8, 9, 10, as well as distilled water. For all pH's the volume of sedimentation and the time taken to attain it rise with decreasing particle size. For a given fraction the volume of sedimentation rises in the pH's near neutrality (7 and 8) and in distilled water, depending partly on the ions present, their nature and concentration, in the buffering solutions employed. The thixotropy and the base exchange capacity rise parallel with the sedimentation volume.