Master of Science thesis from the Univesiti Sains Malaysia, December 1975. ❧ Abstract: The adsorption of benzene on silica gel samples with different stages of purification has been investigated by both sorption and dielectric measurements. ❧ The shape of the sorption isotherms obtained from all the samples is found to belong to Type IV of the BET classification. From the sorption data, various analyses, such as the BET method, pore size distribution, t-method and the like, have been carried out. The results indicate that prolonged purification of a commercial silica gel by treatment with acids, followed by washing with distilled water, not only removes impurities but also results in a drastic change in the pore structure of the gel. These changes involve a sharp decrease in the pore volume and surface area of the impure gel, due to removal of the majority of the narrow pores, a wider and more uniform distribution of pore sizes and an alteration of the pore shape. ❧ The adsorption of benzene on silica gel with its surface chemically modified by trimethylsilyl groups has also been investigated. Preliminary studies show that the reaction results in both the closure of narrow pores and an increase in the pore sizes, a process which is essentially similar to prolonged purification but gives gel of entirely different surface structure. ❧ The dielectric measurements have been carried out over the frequency range of 200 Hz to 100 kHz. The dielectric isotherms of the systems exhibit discontinuities . An attempt has been made to correlate this behaviour with the more generally acceptable interpretations in the literature, particularly those of Thorp and coworkers. No dielectric hysteresis has been observed in the systems investigated. An attempt has also been made to calculate the dielectric constant of the adsorbed phase using the extension of Bottcher's powder method as developed by McIntosh and his associates; however, no correlation is found to exist between the calculated dielectric constants and those of the bulk benzene. The systems investigated do not exhibit dielectric dispersion in the frequency range studied below the saturation values. In the 'interparticle condensation' region of the sorption isotherm, however, dielectric dispersion was observed at low frequencies . This phenomenon has been attributed to interfacial polarization arising from the heterogeneity of the composite dielectric.