An Optical Study of Adsorbed Films

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Abstract
The optical method of Rayleigh and Drude for the study of surface "transition layers" (Uebergangsschichten) has been experimentally modified so as to give greater accuracy, and has been applied to the study of adsorption on glass. Various substances were investigated, and of these only two, water and methyl alcohol, showed definite adsorption. Curves for these, plotting thickness of adsorbed layer against partial pressure, are given. Up to 5 or 6 mm pressure there is no detectable adsorption of water vapor (apart from the probable presence of the first mono-molecular layer). From then on there is a cluster formation which results in a gradual covering of the surface until at 12.5 mm pressure there is another mono-molecular layer present. Above 13 mm there is strong condensation. The results for methyl alcohol were similar. Adsorption began at 30 percent saturation and continued linearly up to 90 percent saturation pressure, when strong condensation set in. It is pointed out that the method is applicable to the study of surface conditions at the interface between any two phases.
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