ADSORPTION OF BENZENE AND ETHANOL UP TO HIGH RELATIVE PRESSURES ON FINELY DIVIDED SODIUM CHLORIDE: PART I. PARTICLE SIZE EFFECTS AND THE ADSORPTION OF BENZENE: PART II. THE LOWERING OF SURFACE FREE ENERGY BY ETHANOL

Abstract

Adsorption of benzene has been studied using four samples of fine sodium chloride. The range of relative pressures employed extended to 0.99. The data were employed to show that a correction to the relative pressure should be applied because of the curvature of the surface. The correction was made in the form of a reduction of the apparent relative pressure by application of the Kelvin equation, since the relative pressure over a convex surface would be less than over a plane surface. The adsorption data at high relative pressures for several samples of salt could then be represented by a common curve. It was further concluded that the thick-layer theory of adsorption due to Frenkel, Halsey, and Hill was applicable to adsorption on salt. Adsorption data for ethanol were then obtained and the reduction of surface free energy of the salt by the saturated vapor was evaluated. This figure was then combined with van Zeggeren's and Benson's value of the solid–liquid interfacial free energy for salt and ethanol to provide a provisional value of the surface free energy of sodium chloride of 227 ergs cm−2.