C.A. Ten Seldam

Virial coefficients of hydrogen and deuterium at temperatures between −175°C and +150°C. Conclusions from the second virial coefficient with regards to the intermolecular potential

Abstract Values of the second and third virial coefficients of hydrogen and deuterium calculated from experimental PVT-data with the method of least squares and of the propagation of errors are presented in the temperature range from 150° to −175°C. Theoretical values of the second virial coefficient were calculated in the same temperature range, based on the Lennard-Jones potential field and on parameter values taken from literature, with corrections for the non-spherical part of the potential and for a number of quantum effects. Comparison shows that a satisfactory representation of the experimental data with a Lennard-Jones potential is impossible, even after adjustment of the parameter values to the experimental results. Additional information was obtained about the validity of the temperature scale.

On the energy levels of a model of the compressed hydrogen atom

Summary In the problem of the “compressed hydrogen atom” the boundary condition that the wave function φ must be zoer of infinite r , is replaced by the condition that φ must have a zero point at a finite r = r 0 . This leads to an investigation of properties of the zeros of the confluent hypergeometric function. The shifts of the 1 s , 2 s and 2 p levels by compression are calculated and tables and graphs are given for corresponding values of the energy and of r o .

Compressible laminar flow in a capillary

An equation based on the hydrodynamical equations of change is solved, analytically and numerically, for the calculation of the viscosity from the mass-flow rate of a steady, isothermal, compressible and laminar flow in a capillaiy. It is shown that by far the most dominant correction is that due to the compressibility of the fluid, computable from the equation of state. The combined correction for the acceleration of the fluid and the change of the velocity profile appears to be 1.5 times larger than the correction accepted to date.

Acoustic and Thermodynamic Properties of Ethanol from 273.15 to 333.1 5 K and up to 280 MPa

Abstract The velocity of sound in ethanol has been measured in the temperature range between 273.15 and 333.15 K and at pressures up to 280 MPa using the phase comparison pulse-echo method with two reflectors, which has been described previously. The density, isothermal compressibility, isobaric thermal expansion and the specific heat at constant pressure of ethanol have been evaluated from the measured sound velocity, using an improved method of computation.

The molecular polarisation of compressed non-polar gases

Synopsis The theory for the change of the Clausius-Mosotti function of non-polar gases under pressure, for a non-polar gas of interacting molecules is further developed on the basis of the statistical theory initiated by Kirkwood. The Clausius-Mosotti function is developed as a power series in powers of the density, the coefficients of which are expressed in terms of the polarisabilities and the intermolecular forces. The linear and the quadratic terms have been evaluated analytically or numerically for a Lennard-Jones (12-6) potential field and for a Herzfeld potential field. The results of the calculations are compared with recent measurements of Michels, Ten Seldam and Overdijk on the Clausius-Mosotti function of compressed argon.

The two-component lattice-gas model

Abstract In this article a description is presented of the two-component lattice-gas model. This model combines the essential features of the lattice theory of Guggenheim for a two-component system and the lattice-gas model for a one-component system. Computer calculations of the critical lines and the spinodal curves have been performed for various combinations of the energy parameters. The coordinates of the double plait points have been determined analytically.

The dielectric constant of argon at 25 °C and 125 °C for pressures up to 2700 atmospheres☆

Abstract Using the heterodyne beat method the dielectric constant of argon has been measured at 25°C and 125°C for pressures up to 2700 atmospheres. The influence of parasitic capacities and inductivities has been reduced to a minimum and for the remaining effects corrections have been applied. From the data obtained, the Clausius-Mosotti function has been calculated. Some aspects of the results are discussed.

Polynomial representation of experimental data; application to virial coefficients of gases

The reliability of the polynomial representation of experimentally determined functions has been investigated, with emphasis on the application to compressibility isotherms of gases. Methods are described to obtain the series coefficients together with their uncertainties as a consequence of the inaccuracy of the experimental data. Results are given for the 49.712°C compressibility isotherm of CO2.

Gas—gas equilibrium and the two-component lattice-gas model

Abstract A two-component lattice-gas model is developed to explain the phase equilibria in binary systems.

A Critical Evaluation of the Thermophysical Properties of Mercury

For the use of a mercury column for precise pressuremeasurements—such as the pressurized 30 meter mercury‐in‐steel column used at the Van der Waals–Zeeman Laboratory for the calibration of piston gauges up to nearly 300 MPa—it is highly important to have accurate knowledge of such properties of mercury as density, isobaric secant and tangent volume thermal expansion coefficients, and isothermal secant and tangent compressibilities as functions of temperature and pressure. In this paper we present a critical assessment of the available information on these properties. Recommended values are given for the properties mentioned and, in addition, for properties derived from theses such as entropy,enthalpy, internal energy, and the specific heat capacities.