Speed of sound in (0.4C(2)H(6)+0.6CO(2)) at temperatures between T=220 K and T=450 K and pressures up to p=1.2 MPa

The speed of sound u has been measured in {(1 - x(2))C2H6 +x(2)CO(2)} with x(2) approximate to 0.6, along seven isotherms at temperatures between T = 220 K and T = 450 K by means of a spherical resonator. The greatest pressur e on each isotherm was approximately p = 1.2 MPa except at T = 220 K where, to avoid condensation, it was restricted to p = 0.6 MPa. Corrections to th e speed of sound for the effects of vibrational relaxation have been calcul ated from a two-mode model containing relaxation times that were fitted to the excess sound absorption in the mixture and in both pure components. The corrected speeds of sound have a precision better than fl 10(-5). u and an estimated overall uncertainty of +/-1.10(-4) u. The precise composition of the sample used on each isotherm was determined from the experimental spee ds of sound extrapolated to the limit of zero pressure. Second and third ac oustic virial coefficients of the mixture and ordinary interaction second v irial coefficients are reported. (C) 1999 Academic Press.