The real part of the complex relative electric permittivity, ε r (T, p), of liquid methylbenzene has been determined with an estimated expanded relative uncertainty of ± 0.018 % from measurements of the complex capacitance of a concentric cylinder capacitor at temperatures between (293 and 393) K and pressures below 60.6 MPa. The measurements were corrected for the isothermal compressibility of the solid that formed the capacitor. The isothermal compressibility was determined by comparison of measurements of ε r (He, 303 K and 393 K, p) with ab initio results from quantum mechanics. The ε r (T, p) values obtained for methylbenzene were combined with the amount-of-substance density, ρ, which was obtained from the equation of state reported by Lemmon and Span (J. Chem. Eng. Data 2006, 51, 785−850), to calculate the molar polarizability, P, that was fit with an expanded (k = 2) relative uncertainty of ± 0.03 % by three parameters. The ε r (T, p) reported by Kandil et al. (J. Chem. Eng. Data 2008, 53, 1056−1065) from measurements with a radio frequency re-entrant cavity, a technique with entirely different sources of systematic error, were converted to P•ρ and they differed from 1•10 −3 at T = 290 K to −2.5•10 −3 at T = 406 K (with ⟨P•ρ⟩ ≈ 0.31 giving a relative difference of between 0.3 % and −0.8 %, respectively) at temperatures that overlap ours. At T = 298 K the measurements reported by Mospik (J. Chem. Phys. 1969Phys. , 50, 2559Phys. −2569 at a pressure between (0.1 and 20) MPa when converted to the product P•ρ are within −0.8•10 −3 (a relative difference of about −0.26 %) of our smoothing equation while at T = 273 K, about 20 K below our lowest temperature, the differences for P•ρ are −0.4•10 −3 (a relative difference of about −0.13 %).
The relative electric permittivity, ε r (T, p), of liquid heptane has been determined with an estimated relative expanded uncertainty of ± 0.018 % from measurements of the complex capacitance of a concentric cylinder capacitor at temperatures between (293 and 363) K and pressures below 60.6 MPa. The measurements were corrected for the capacitor's isothermal compressibility that was determined by comparison of measurements of ε r (He, 303 K and 393 K, p) with ab initio results from quantum mechanics. The measured ε r (C 7 H 16 , T, p) were combined with the amount-of-substance density, ρ, which was obtained from the equation of state reported by Span and Wagner (Int. J. Thermophys. 2003, 24, 41−109), to calculate the total molar polarizability, P, that was fit with an expanded (k = 2) relative uncertainty of ± 0.06 % to a correlation with three parameters. The ε r (T, p) obtained from the literature were converted to P•ρ, compared with our correlation, and found to have a relative difference of < ± 0.5 % at temperatures that overlap ours.
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