Abstract
Part 1 comprises an experimental investigation into the factors determining the magnitude of the sedimentation potentials developed by soft glass falling under gravity through dilute aqueous solutions of potassium chloride. The results of these determinations established the validity of using a modified form of the streaming potential equation to calculate the zeta potentials of solid surfaces from sedimentation potential measurements. Five further solid surfaces are also dealt with, sedimentation potentials set up in solutions of potassium chloride and barium chloride are determined, and the values of the calculated zeta potential compared, where possible, with published data obtained by other methods. Part 2 deals with some investigations of the sedimentation potentials developed in non-aqueous solutions. The majority of the work described is for the sedimentation of silica powder through toluene and ether. In view of the inconsistency of the results, and the absence of a suitable equation to interpret them, the investigations were not continued beyond a few preliminary determinations. A means of using sedimentation potential methods to determine the particle size distribution of heterogeneous samples of fine powders is described in Part 3. A theoretical treatment for the calculation of both a cumulative undersize distribution, and a particle size (or weight) distribution of a sample of a fine powder is developed. No knowledge of the system concerned is required, other than the rate of change of the sedimentation potential with time when an initially uniform dispersion of the powder is allowed to sediment under gravity. Particle size distributions calculated using experimental values obtained from suspensions of carborundum powder and Pyrex spheres are in fair agreement with the results obtained by microscopic counting and sizing.