Adsorption of Methyl Alcohol Films on Rock-salt

The optical method of Rayleigh and Drude as recently modified by Frazer and Herzfeld has been applied to the study of methyl alcohol films on rock-salt. The isothermal adsorption has been studied at pressures ranging from ${10}^{-5\mathrm{}}$ mm to 11 cm mercury. The results indicate that a unimolecular layer is formed at a pressure between ${10}^{-5\mathrm{}}$ and ${10}^{-4\mathrm{}}$ mm of mercury, with no further adsorption until the region of 2-3 cm, when a second layer begins to form, with completion at 9-10 cm. The thickness of these layers is calculated to be in the neighborhood of 4.5-5.0A. The effect of thorough outgassing has been observed and the results have been interpreted to indicate that with decrease in temperature either an underlying unimolecular layer of water vapor is formed, or that there is a true increase in the natural ellipticity of the surface. In addition, it is possible to calculate the isothermal heat of adsorption from the experimental data.