Vapor-pressure for the pure fluids from calorimetric measurements near the critical point

We report the values of second temperature derivatives of the vapor-pressure curve (d2PS/dT2) and chemical potential (d2μ/dT2) for pure fluids derived from precise two-phase isochoric heat capacity measurements over a wide temperature range including the critical region. The values of (d2PS/dT2) derived from CV2 measurements were compared with the values calculated from direct differentiation of the vapor-pressure equation from the literature. The derived (d2PS/dT2) data has been used to develop a scaling-type vapor-pressure equation in the critical region. A description of the vapor-pressure calculation procedure from CV2 measurements is given. The values of the critical pressure PC and slope of the vapor-pressure curve (dPS/dT)C at the critical point were calculated by using calorimetric measurements. The asymptotic behavior of the second temperature derivatives of the vapor-pressure curve (d2PS/dT2) and chemical potential (d2μ/dT2) near the critical point are discussed. The strength of the Yang–Yang anomaly, Rμ, defined by Fisher as Rμ=Aμ/(Aμ+AP), where Aμ and AP are the amplitudes of the singularity of −T(d2μ/dT2)≈Aμt−α and TVC(d2PS/dT2)≈APt−α was estimated from derived results.