Ultrasonic Velocities and Absorption in Gases at Low Pressures

Abstract

Improvements to an ultrasonic interferometer are discussed. As a result a greater sensitivity to acoustic reactions is obtained and the reproducibility of the data is greatly improved. Velocity measurements in dried CO2-free air, dried N2, and dried H2 are given. Amplitude absorption coefficients for H2, N2, and CO2 are also included. Measurements are made over the temperature range from 9°C to 36.6°C and over the pressure range from 82.17 cm Hg to 0.45 cm Hg. The frequencies extend from approximately 500 kc to 2.16 mc. A maximum value for the absorption in H2, attributed to molecular absorption, is located at an f/p ratio of approximately 10 mc/atmos.