Conduction of heat through rarefied gases

Abstract

In a previous paper we used a thermal method of indicating the degree of vacuum by measuring the rate of evaporation of liquid air in a Dewar flask exhausted in various ways. In the present work we have attempted to obtain information of the conduction of heat through twelve gases at pressures so low that the actual path of the molecule is comparable with its mean free path. It is to be expected that this condition will hold good over a range of pressure the greater the smaller the diameter of the containing vessel, and for this reason we worked in a long narrow tube. Previous investigations of this character have been carried out by Sir William Crookes and C. F. Brush, by measuring the rate of cooling of heated mercury thermometers placed inside globes exhausted by the Sprengel pump. The observations of the latter bear most closely upon the present work, and partly anticipate them. He points out that in the five gases he examined, at pressures up to a few millionths of an atmosphere, the heat-transmitting power of the gas varies directly as the pressure. This is to be expected from the kinetic theory, as pointed out by Smoluchowski de Smolan.