Abstract
The attenuation of sound waves in gas contained in a tube has been measured for air, oxygen and water vapour-oxygen mixtures at frequencies between 90 and 1,200 cycle, sec.[-1]. The magnitude of the Helmholtz-Kirchhoff coefficient has been determined for air contained in a smooth walled duralumin tube. The variation of the absorption with frequency and moisture content has been investigated for oxygen. The tube was terminated at one end by a fixed reflector and at the other by a plane diaphragm producing the sound waves. The impedance of the diaphragm-gas column system was investigated near the natural modes of the tube and analysed by means of a circle diagram to yield the attenuation coefficient. The magnitude of the Helmholtz-Kirchhoff coefficient with an air filled tube was found to be 15.3% higher than the theoretical value. The relaxation absorption in oxygen-water vapour mixtures was found to be in general agreement with the theory of Kneser. The value of the vibrational specific heat for oxygen was found to be (0.0332 +/- 0.0015)R. The frequency of maximum absorption was found to be a quadratic function of the water vapour concentration.