PRETREATMENT OF SOILS AND CLAYS FOR MEASUREMENT OF EXTERNAL SURFACE AREA BY GLYCEROL RETENTION

Heat treatment at 600 ~ has been the usual procedure for irreversible collapse of expanding clay minerals prior to determination of the external surface area of clays and soils by glycerol retention. Evidence is presented showing that this treatment is unsuitable since it greatly reduces the external surface area of certain minerals and in-cre~ses that of others. Saturation with the triethylammonium cation avoids these difficulties and produces an effect analogous to the collapse of expanding minerals by stabilizing their basal spacing at 13.3/~. This prevents the entrance of glycerol between the unit layers and confines the sorption to the external surfaces of the particles