Measurements with Ordinary Sound and Ultrasonics Carried Out in the Physical Laboratory of the University of Louvain

Abstract

During the last two years new measurements were started on the following subjects: 1. Measurements on the velocity of sound in gaseous mixtures in connection with thermal diffusion at ordinary pressures and high pressures. The velocity of sound is measured to determine the concentration of the gas mixtures. These measurements are carried out in connection with the theory of Clark, Jones, and Furry. From this theory it is possible to separate the ordinary diffusion coefficient from the thermal diffusion coefficient. 2. Development of an acoustical thermometer. As the velocity of sound, is proportional to the square root of the absolute temperature, a very accurate acoustical interferometer has been developed to measure the temperature of liquified gases (liquid helium, hydrogen, or oxygen). The same apparatus has also been used in another application: the determination of the conversion of normal hydrogen into para. 3. Measurements on the relaxation for the rotational energy in hydrogen gas. New measurements are carried out in normal-and parahydrogen at liquid oxygen temperatures. The velocity is measured as a function of pressure down to low pressures. 4. Debye-Sears-Lucas method is used for liquid helium. The diffraction pictures are analyzed by means of a microphotometer. The theory of Brillouin is discussed.