Specifies two methods for industrial calcined products. The first, using carbon tetrachloride vapour, is applicable if the density of the material exceeds 3.75 g/ml; the second, using water vapour, is applicable if the density of the material is lower than 3.75 g/ml. The adsorptive power is evaluated by exposure of a previously dried sample to an atmosphere saturated with carbon tetrachloride or water vapour at a conventional temperature. Measurement of the quantity of the corresponding vapour adsorbed after a conventional time. Has also been approved by the IUPAC.