2700.     PIERCE, C., WILEY, J. W., AND SMITH, R. N.  Capillarity and Surface Area of Charcoal.  Jour. Phys. and Colloid Chem., vol. 53, 1949, pp. 669-683.

        Evidence in support of the view that adsorption by charcoal is due to capillary condensation chiefly rather than to formation of a surface layer, as in nonporous adsorbents.  The forces causing capillary condensation at low pressures are of the same type as those that cause multilayer adsorption on a plant surface, but because of the effects of opposite walls they are stronger at a distance of several molecular diameters from the substrate than is found for a plane surface.  If capillary condensation occurs, it is not possible to determine the surface area of a porous solid from an adsorption isotherm, and the commonly accepted values are much too large.  In capillaries a few molecular diameters in width, the Kelvin equation is not applicable.  Retentivity is greater for slightly activated samples than for more highly activated ones.