The velocity of sound with derived state properties in helium at −175 to 150 °C with pressure to 150 atm

Abstract

The velocity of sound was determined in helium on 14 equally spaced isotherms from −175 to 150 °C and at pressures from 10 to 150 atm. The results were correlated with an abbreviated perturbation equation of state which employs both the Lennard‐Jones (n,6) and the exponential repulsion potentials. Six parameters in the equation of state were adjusted to fit the velocity data within the experimental precision of about 0.001%. The derived results reliably predict literature (P,V,T) values and other velocity‐of‐sound data for pressures as high as 7000 atm and for temperatures from −223 to 577 °C. A value of the gas constant was derived, R=8314.79±0.35 J K⁻¹⋅kmol⁻¹, which is statistically consistent with the accepted value. The results also support a recent gas thermometry result that indicates the 1968 temperature scale may be in error by 0.012 K at −183 °C.