Abstract: The use of glycerol retention measurements to calculate surface areas of clay minerals is described. Assuming that the glycerol retained on external surfaces is monomolecular in thickness, and that both this layer and the monomolecular glycerol layers adsorbed on internal surfaces of montmorillonite, vermiculite, and halloysite are of the density of liquid glycerol, it is calculated that each percentage of glycerol retained corresponds to an area of 17.6 square meters per gram on external surfaces and 35.3 on internal surfaces. The corresponding figures for ethylene glycol retention under these conditions are 22.3 and 44.6, respectively. For nonexpanding clays, surface areas calculated from glycerol retention values agree well with published figures derived from Brunauer, Emmett, and Teller (B.E.T.) gas adsorption measurements. For montmorillonites, surface areas agree reasonably well with published determinations based on B.E.T. treatment using polar adsorbates. Values of surface area are also presented for samples of vermiculite and endellite and for the nonexpanding clay minerals—illite, kaolinite, halloysite, and allophane.
Calculations of the surface area as a function of particle size for montmorillonites of hypothetically uniform particle sizes show that montmorillonites dispersed into very thin flakes must have an appreciable external surface. The ratio of internal to total surface is shown to furnish an estimate of the thickness of the individual montmorillonite flakes. Glycerol retention data for a Wyoming bentonite saturated with a number of different cations are interpreted as indicating particle thicknesses varying from 3 unit cells (about 30A) for Na+ saturation to about 20 unit cells for saturation with a number of polyvalent cations.