The exchange of energy between a platinum surface and gas molecules

Abstract

Recent experiments by Roberts have shown, not only that the accommodation coefficients of helium and neon atoms impinging on a clean heated tungsten surface are extraordinarily low, but also that these values increase with time after cleaning the surface. To explain this increase he suggests the gradual formation of adsorbed films on the surface of the tungsten due to residual impurities in the gas. The primary object in starting the investigations to be described in this paper was to gain some information as to the nature of these films, the existence of which has also been postulated by Blodgett and Langmuir. For this purpose experiments have been carried out in which the emission of energy from electrically heated wires of platinum, a metal relatively resistant to contamination, has been investigated under varied conditions. Apparatus A pure platinum wire about 20 cm long and 0·025 mm diameter was silver-soldered to platinum leads of 0·4 mm diameter and mounted loosely in a vertical glass tube of approximately 5 cm diameter. The wire was connected, by double leads, to a Thomson bridge, by means of which the resistance could be determined and also controlled by suitable adjustment of the current. The potential drop along the wire was measured by means of a Siemens and Halske potentiometer. The mean temperature of, and the heat developed in, the wire could thus be determined.