Surface area of clays

In view of the assumptions employed in obtaining them, the surface areas of clays derived from adsorption and from desorption isotherms of nitrogen are in remarkable agreement. There is, in general, striking accord between the value from the adsorption isotherm, derived by using the BET equation, and the value from analysis of the desorption isotherm, obtained by using the Kelvin equation, micropore analysis, or a simple extrapolation of the pore size data into the micropore region. The latter empirical method, originally proposed by Innes, seems not only successful in this regard but may also be justified in terms of micropore geometry.