Isochoric heat capacity for toluene near phase transitions and the critical point

New measurements of isochoric heat capacity C-V for toluene near phase transitions and the critical point are presented. Measurements were made with a high-temperature, high-pressure, adiabatic calorimeter of nearly constant volume. The inner volume of the calorimeter is (104.441 +/-0.002) cm(3) at 297.15 K and 0.1 MPa. The heat capacity of the empty calorimeter C-0 was measured by use of a reference fluid (helium-4) with a well-known heat capacity (uncertainty of 0.1%). The temperature of the sample was measured with a 10 Omega PRT with an uncertainty of 10 mK. Uncertainties of the heat capacity measurements are estimated to be 2% to 3%. Measurements were made in the single- and two-phase regions. The experimental values of phase transition temperatures T-S(rho) and single- and two-phase isochoric heat capacities (C-V1, C-V2) on each measured isochore were determined by use of a quasi-static thermogram method. Measurements were made along 12 isochores between (199.3 and 525.0) kg.m(-3) in the temperature range from (411 to 620) K. The temperature dependence of single- (C-V1) and two-phase (C-V2) isochoric heat capacities along the coexistence curve and along near-critical isochores, the isochoric heat capacity jumps DeltaC(V), and the density and temperature on the coexistence curve near the critical point are discussed. The values of the critical parameters (critical temperature, density, and pressure) of toluene were derived from the experimental measurements of density, temperature, and heat capacity at saturation in the immediate vicinity of the critical point. The scaling equations were used to express measured values of C-V and density along the coexistence curve. The results of the measurements are compared with values calculated from various equations of state. The data can be used to improve the equation of state and to develop a crossover equation in the critical region.