The structural system of chromatographic silica gel, as investigated by adsorption techniques and electron microscopy is highly porous having 63% porosity and composed of large irregular grains, arrange in disorderly manner, constituting the voids. Treatment at high temperature shrinks the materials on the expense of bound water. Most of the surface area and pore volume lie in the micropores. Organic vapours such as acetone, methyl alcohol, methyl ethyl ketones and methyl acetate were adsorbed on the gel between 0-37-degrees-C under vacuum. The data were taken on Cahn electrobalance- 1000. Isosteric heats of adsorption at number of temperatures and coverages were determined by applying Clausius Clapeyron equation. It is interpreted in terms of activation energies which suggests two types of adsorption processes.