Abstract
Summary: A procedure for calculating both the external and total areas of soil particles from the relation between vapour pressure and moisture content is tested experimentally for four British clay soils. The calculated surface areas are compared with those obtained by the standard procedure from measurements using both water vapour and nitrogen, and their relation with the mineralogy of the clay fraction of the soil (as determined by X‐ray analysis) is examined. It is concluded that this new method is sufficiently accurate to be used as an indication of the clay mineralogy.