The Pressure Dependence of the Thermal Conductivity of Polyatomic Gases at 0°C

Abstract

A form of " hot wire " apparatus is described in which the hot wire is replaced by a thin-walled nickel tube ¼ in. in diameter mounted in a similar nickel tube in, in diameter. The gas under investigation occupies the narrow annular space between the two tubes. It is shown that the apparatus is completely free from convection up to pressures somewhat greater than 1 atm, and that the temperature discontinuity effect is inappreciable down to pressures of a few cm. of mercury. The apparatus is used to test the pressure dependence of the thermal conductivity of several polyatomic gases. The thermal conductivity (at 0 °C.) of the gases carbon dioxide and methane is found to increase slowly with the pressure over the range 10-80 cm. of mercury. It is suggested that this effect may be taken as evidence of the incomplete participation of the energy of vibration of the molecules in the conduction process.