M.B Ewing

Thermophysical properties of alkanes from speeds of sound determined using a spherical resonator I. Apparatus, acoustic model, and results for dimethylpropane

Abstract The speed of sound in dimethylpropane between 250 and 323.15 K has been obtained from measurements of the frequencies of the radial modes of a spherical acoustic resonator; the acoustic model and the apparatus are described briefly. The radius of the resonator was obtained from the speed of sound in argon. Perfect-gas heat capacities and second and third acoustic virial coefficients for dimethylpropane have been calculated from the results, and estimates are given for the second and third ( p , V m , T ) virial coefficients.

The Temperature-Jump Effect and the Theory of the Thermal Boundary Layer for a Spherical Resonator. Speeds of Sound in Argon at 273.16K

The theory of the thermal boundary layer at the walls of a spherical acoustic resonator is discussed in detail. For gases at low pressures, the temperature-jump effect is found to make a significant contribution to the resonance frequencies of the radial modes but not to their acoustic losses. Experimental results are reported for argon at 273.16 K and pressures between 15 and 248 kPa, and compared with the theory. These were obtained using the four radial modes with lowest frequency of a spherical resonator with a radius of 60 mm. The thermal accommodation coefficient between argon and the aluminium wall of the resonator was found to be (0.84 ± 0.05). The results suggest that a determination of the gas constant with a fractional imprecision of 1 × 10-5 or better should be possible using a spherical acoustic resonator.

Thermophysical properties of alkanes from speeds of sound determined using a spherical resonator 2. n-Butane

Abstract The speed of sound in gaseous butane between 250 and 320 K has been obtained from measurements of the frequencies of the radial modes of a spherical acoustic resonator. Perfect-gas heat capacities and second and third acoustic virial coefficients have been calculated from the results. Methods of calculating (p, Vm, T) virial coefficients from acoustic results are discussed in detail and values for butane are given.

Chiral discrimination in liquids II. Excess molar enthalpies of {(1 − x)A+ + xA−}, where A denotes fenchone or α-methylbenzylamine

Abstract Small but definite chiral discrimination is revealed by measurements of the excess molar enthalpy H m E of the liquid (+) and (−) enantiomers of fenchone and of α-methylbenzylamine. For fenchone H m E is negative at 303.11 K; for α-methylbenzylamine H m E is positive at 303.11 K and though still positive at 313.11 K appears to be about to change sign and become negative at temperatures above approximately 340 K.

The (liquid + liquid) critical state of (cyxlohexane + methanol) IV. (T, x)p coexistence curve and the slope of the critical line

Abstract The (T, x)p coexistence curve of {xc-C6H12+(1−x)CH3OH} has been measured within 1.3 K of the critical temperature (Tc ≈ 318.4 K) at constant atmospheric pressure. In addition an estimate of ( ∂T c ∂p ) x = x c near atmospheric pressure has been obtained. The results have been analysed to determine the critical amplitude of the coexistence curve when the critical exponent β is fixed at the value calculated from theory. In addition, it has been shown that mole fraction is a better order parameter for this mixture than mass fraction and that the first symmetric Wegner-correction term is just significant.

The liquid-liquid critical state of (cyclohexane + methanol) I. Excess molar enthalpies for “(1 − x)c-C6H12 + xCH3OH’ within 1.3 K of the critical temperature

Abstract The excess molar enthalpies for “(1 − x)c- C 6 H 12 + x CH 3 OH ’ have been determined using dilution techniques at six temperatures above and five temperatures below the critical temperature Tc at constant atmospheric pressure. The critical temperature Tc was determined for each isotherm and all measurements were made within 1.3 K of Tc ≈ 318.3 K. The excess molar enthalpies are internally consistent to better than 0.04 per cent.

The liquid-liquid critical state of (cyclohexane + methanol) II. Use of the parametric equation of state to represent excess enthalpy in the critical region

Abstract A scaling law has been derived from the potential based on the parametric equation of state, to describe excess enthalpies near the liquid-liquid critical point of a binary mixture at constant pressure. The validity of the law has been tested by using it to represent excess enthalpies of (cyclohexane + methanol). Individual isotherms could be fitted to within the estimated experimental precision of the measurements over the range| x − x c | x c is the critical composition, but an additional asymmetric term was required to extend this range. When the temperature dependence was included the measurements could be represented to within 0.2 per cent over the same composition range. Values of the system-dependent variable a and the excess molar enthalpy at the critical point have been obtained.

A differential Burnett apparatus: virial coefficients for argon and neopentane at various temperatures☆

Abstract A differential Burnett apparatus, which is particularly suitable for measurements at low pressures in the range 2 to 170 kPa, is described. Experimental results for argon and neopentane at temperatures between 303.15 and 343.15 K are presented together with virial coefficients calculated by a new analysis which has advantages compared with conventional methods. The apparatus has also been used to determine the interaction virial coefficient of benzene + cyclohexane at 343.15 K.

The speed of sound in gases I. A cylindrical interferometer and the speed of sound in argon and in krypton

Abstract A fixed-pathlength variable-frequency ultrasonic interferometer based on a cylindrical resonator has been constructed. Measurements of the speed of sound in argon and krypton in the range 250 to 330 K and 20 to 100 kPa have been used to determine the acoustic pathlength. The acoustic virial coefficients are in good agreement with values obtained from the integration of pair potential-energy functions.

The speed of sound in gases. II: Acoustic virial coefficients and perfect-gas heat capacities for 2,2-dimethylpropane obtained using a cylindrical interferometer

Abstract The speed of sound in 2,2-dimethylpropane has been measured between 250 and 340 K and 7 and 100 kPa, or 0.8 of the vapour pressure, using a fixed-pathlength variable-frequency ultrasonic interferometer with a cylindrical cavity. Second and third acoustic virial coefficients and perfect-gas heat capacities are reported.