Scaling equation of the C6H6
Elena T Shimanskaya, Yuriĭ I Shimansky
Experimental determination of the parameters of the extended scaling coexistence curve (CC) equation for benzene from triple point to critical point is discussed. The data array of coexisting liquid and vapour densities in the vicinity of the critical point was obtained by Toepler, prism, and microfloat methods. In the vicinity of the triple point the data obtained by other investigators were used. The temperature dependences of the order parameter and the CC diameter were analysed. A method for obtaining the critical exponents, b0 and b1, in the scaling CC equation is proposed, by means of the analysis of the temperature dependences of the effective indices, b0ef and b1ef, in various temperature (T) intervals of approximation. It is shown that experimental data approximations with fixed theoretical indices are not correct and that indices should be determined as free parameters and afterwards should be compared with theoretically predicted values. The unified scaling equation for the CC liquid and gas branches in the whole range of benzene CC points [4 x 10-5 < (Tc – T)/Tc < 0.5, where Tc is the critical point temperature] was obtained. This equation includes the asymptotic leading term, asymmetric and nonasymptotic correction terms. In this equation the values of the CC critical exponent, b0, and the exponent b1 of CC diameter singularity are:b0 = 0.352 ± 0.002 and b1 = 2b0 = 0.70 ± 0.05. The exponent b2 of the first nonasymptotic correction term is larger than the exponent of the first asymmetric correction term b1 (b2 > b1). Approximation of the experimental data by the classical CC equation appears to be invalid in any temperature region.