Abstract. We analyse the inverse reduced fluctuations (inverse ratio of relative volume fluctuation to its value in the hypothetical case where the substance acts an ideal gas for the same temperature-volume parameters) for simple liquids from experimental acoustic and thermophysical data along a coexistence line for both liquid and vapour phases. It has been determined that this quantity has a universal exponential character within the region close to the melting point. This behaviour satisfies the predictions of the meanfield (grand canonical ensemble) lattice fluid model and relates to the constant average structure of a fluid, i.e. redistribution of the free volume complementary to a number of vapour particles. The interconnection between experiment-based fluctuational parameters and self-diffusion characteristics is discussed. These results may suggest experimental methods for determination of self-diffusion and structural properties of real substances.

We consider the possibilities for prediction of liquids' density under pressure basing on the inverse reduced fluctuations parameter, which is directly connected with the isothermal compressibility. This quantity can be determined basing on the thermodynamical properties of saturated liquid and it consists of only two constant parameters within a relatively wide region close to the melting points. It is confirmed by the comparison with the experimental data on n-alkanes that the derived expression is a quite reasonable estimator without a necessity to fit data along some parts of isotherms for different temperatures. At the same time the obtained formula: i) can be reduced to the form of the Tait equation and ii) the resulting Tait's parameters in this representation have a clear physical meaning as functions of the excess entropy, which determines the mentioned reduced fluctuations.

This study reports the experimental density and speed of sound data of 1-chlorononane along seven isotherms from 293.15 to 413.15 K at pressures from saturation up to 196.1 MPa. The pertinent isothermal compressibility and isobaric coefficient of expansion data have been obtained by numerical differentiating of densities. In addition, the saturated liquid densities have been measured from 253.15 to 443.15 K, isobaric heat capacities from 248.15 to 448.15 K, and speeds of sound from 246.88 to 457.25 K. These results have been interpolated by polynomials to obtain the saturated liquid isobaric coefficient of expansion, adiabatic and isothermal compressibility, isochoric heat capacity, and internal pressure data. Performances of three predictive approaches having different degrees of complexity, namely the Critical Point-based Perturbed Chain Statistical Association Fluid Theory, the Statistical Association Fluid Theory of Variable Range Mie Potential parametrized by a Corresponding States approach of Mejía et al. (Ind. Eng. Chem. Res. 2014, 53, 4131), and the fluctuation theory-based Tait-like equation of state have been examined. The latter model has a superiority in estimating of the high-pressure data; however, unlike both statistical association fluid theory approaches, it utilizes the saturated liquid data. It has also been demonstrated that all the models successfully predict various phenomena related with replacement of hydrogen by chlorine in n-nonane molecule.

Experimental speeds of sound and densities are presented for the liquid phase of 1-iodohexane. The measurements were carried out along nine isotherms from (293.15 to 413.15) K at pressures from the saturation condition up to 200 MPa. The speed of sound was measured by a pulse-phase echo ultrasonic device at a frequency of (1 to 5) MHz with an uncertainty of ±0.2%. The density was measured by an acoustic piezometer with an uncertainty of ±0.3%. The experimental results have been used to calculate the isentropic compressibility, κ S .

Experimental speeds of sound and densities are presented for the liquid phase of 1-chlorohexane. The measurements were carried out along seven isotherms from (293.15 to 413.15) K at pressures from saturation up to 200 MPa. The speed of sound was measured by a pulse-phase echo ultrasonic device at a frequency of (1 and 5) MHz with an uncertainty of ± 0.2 %. The density was measured by an acoustic piezometer with an uncertainty of ± 0.3 %. The experimental results have been used to calculate isentropic compressibility (k S)with an uncertainty of ± 1 %. The temperature and pressure variation of sound speed, density, and isentropic compressibility are discussed. The experimental results were used to calculate various thermophysical properties such as isobaric thermal expansion coefficient (α P), isothermal compressibility (k T), temperature coefficient of pressure at constant volume ((∂P/∂T) V ), and internal pressure (P i).