These authors are studying the influence of pH and particle size onsedimentation volume, and on the velocity with which it is reached. They areusing fractions from > 1.2 μ to < 0.3 μ, obtained by sedimentation, and buffer solutions of pH1, 3, 5, 7, 8, 9, 10, as well as distilled water. For all pH's the volume ofsedimentation and the time taken to attain it rise with decreasing particlesize. For a given fraction the volume of sedimentation rises in the pH'snear neutrality (7 and 8) and in distilled water, depending partly on theions present, their nature and concentration, in the buffering solutionsemployed. The thixotropy and the base exchange capacity rise parallel withthe sedimentation volume.