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The vapor pressures of acetonitrile have been measured over the temperature and pressure range of 278 K and 4.3 kPa to 540 K and 4455 kPa. The upper limit exceeds the temperature at which decomposition of acetonitrile begins (about 536 K) so we were able to assess the effect of pyrolysis on the vapor pressures. Acetonitrile is strongly hygroscopic, and a comparison of results obtained with “wet” and “dry” samples allowed us to investigate in a similar way the effect of water as an impurity. The results have been correlated using generalized Wagner equations, a key feature of which is the use of the reversed reduced temperature τ = 1 − T/T c where T c is the critical temperature. The standard form with terms in τ, τ 1.5, τ 2.5, and τ 5 produced unacceptable systematic deviations; but the equation ln(p/p c) = (T c/T)(c 1τ + c 1.5τ1.5 + c 2τ2 + c 2.5τ2.5 + c 5.5τ5.5), where p c is the critical pressure, fits our results from 291 K to 535 K with a standard deviation of 63 × 10-6 in ln p and significantly extends the range of correlation, toward both the triple and critical points, compared with work already in the literature. By extrapolation to T c = 545.46 K, we obtain 4835 kPa for the critical pressure p c and 167 Pa for the triple-point pressure at T s+l+g = 229.35 K. An Antoine equation that describes the results below a pressure of 125 kPa with a standard deviation of 1.5 mK in the condensation temperature has also been obtained.

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Molar heat capacities at constant volume (C V) were measured with an adiabatic calorimeter for pure propane. The high purity of the samples was verified by chemical analysis. Temperatures ranged from the triple point of propane near 85 K to the upper temperature limit of the calorimeter at 345 K, while pressures ranged up to 35 MPa. Measurements were conducted on liquid propane in equilibrium with its vapor and on compressed liquid samples along isochores. Heat capacity results are reported for two-phase (C V (2)), saturated liquid (C σ), and single-phase (C V) isochores. Vapor pressure data are based on measurements of C V (2) along a two-phase isochore. Measurements were also made to determine the triple-point temperature of (85.525 ± 0.005) K and heat of fusion of (3508 ± 20) J·mol−1 for propane near its triple point. The principal sources of uncertainty in C V are the temperature-rise measurement and the change-of-volume work adjustment. The expanded uncertainty (i.e., a coverage factor k = 2 and thus a two-standard deviation estimate) for values of C V (2) is estimated to be 0.5 %; for both C σ and C V, it is 0.7 %.

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