An Experimental Determination of the Velocity of Sound in Dry CO2-Free Air and Methane at Temperatures below the Ice Point

The fixed path acoustic interferometer has been used for the measurement of the velocity of sound in dry C${\mathrm{O}}_2$-free air and in methane between 90°K and the ice point. Acoustic resonance in a limited column of gas, coupled to a driven X-cut quartz crystal of fundamental frequency of about 600 kc per sec., is produced by temperature variation. The procedure is such that differences in temperature readings, when the temperature is rising and when it is falling, are reduced to an amount in keeping with the other errors of measurement. No molecular acoustic dispersion has been observed so that the results are made available with especial reference to their value for computations of specific heats. The results are given, within experimental error, by the formulae: for air, $v^2=3.8762\mathrm{}\times {10}^{2}T+806+1.8043\mathrm{}\times {10}^5{T}^{-1\mathrm{}}-2.0364\mathrm{}\times {10}^7{T}^{-2\mathrm{}}+3.007\mathrm{}\times {10}^{-2\mathrm{}}{T}^2$ and for methane, $v^2=6.6176\mathrm{}\times {10}^{2}T+1.0016\mathrm{}\times {10}^6{T}^{-1\mathrm{}}-1.3846\mathrm{}\times \times {10}^8{T}^{-2\mathrm{}}$.