Studies have been made of silica gels modified by chemical reaction of an alcohol or a chlorosilane with the surface hydroxyls of the gel. The over-all objective was correlation of the physical properties of such preparations with their behavior as adsorbents in gassolid and other types of chromatography. The present paper presents the results of the studies of physical characteristics which can be deduced from nitrogen adsorption isotherms. These include surface area, average heats of adsorption, and site energy distribution. In substantially ail cases, surface properties were changed by the chemical modification. The concentration of high-energy adsorption sites was generally reduced, and this resulted in a more uniform surface, superior for chromatography. The average adsorption energy was also reduced.IT IS GENERALLY accepted that exposed hydroxyl groups are present on the surface of a silica gel, distributed somewhat irregularly ; the surface is thus physically and chemically nonuniform. The small radius and acidity of the hydrogen atoms on the surface hydroxyls results in pronounced specific interaction with certain molecules (1-6).There exists a possibility of making a more uniform silica gel surface by substitution of more inert groups for the surface hydroxyls. This substitution should reduce the adsorption of molecules containing either x electrons, OW, or =NH groups. Two substitution reactions of this type have been investigated in the literature. These reactions may be written as:

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