SummaryThe chloride‐exclusion volume of calcium‐saturated specimens of two bentonites and seven soils were determined over a range of electrolyte concentrations. These systems are believed to approximate the flocculated condition of most Manitoba soils. The montmorillonite was found to be arranged in tactoids or crystallites having an approximate 19Å basal spacing. The assumption of complete chloride exclusion from the interlayer volume over most of the concentration range combined with exclusion according to Gouy theory by the external surfaces provided a reasonable explanation of the experimental data. The number of montmorillonite layers comprising a tactoid, as calculated from the negative absorption determinations, was found to be strongly dependent upon the particle size of the montmorillo