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 (d(2)P(S) /dT(2)) and chemical potential (d(2)mu/dT(2)) for pure fluids derived from precise two-phase isochoric heat capacity measurements over a wide temperature range including the critical region. The values of (d(2)P(S)/dT(2)) derived from C-V2 measurements were compared with the values calculated from direct differentiation of the vapor-pressure equation from the literature. The derived (d(2)P(S)/dT(2)) 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 C-V2 measurements is given. The values of the critical pressure PC and slope of the vapor-pressure curve (dP(S)/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 (d(2)P(S)/dT(2)) and chemical potential (d(2)mu/dT(2)) near the critical point are discussed. The strength of the Yang-Yang anomaly, R-mu, defined by Fisher as R-mu = A(mu)/(A(mu) + A(P)), where A(mu) and A(P) are the amplitudes of the singularity of -T(d(2)mu/dT(2)) approximate to A(mu)t(-alpha) and TVC (d(2)P(S)/dT(2)) approximate to A(P)t(-alpha) was estimated from derived results. (C) 2003 Elsevier Science B.V. All rights reserved.