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This article considers a unit of a unique design created at the Joint Institute for High Temperatures of the Russian Academy of Sciences, which implements the method of a pycnometer of constant volume and variable mass. The data are obtained on the density of liquid potassium on the saturation line and on the 100 atm isobar in the temperature range 336–2030 K. The relationship between the results of the methodology implemented at the Joint Institute for High Temperatures, Russian Academy of Sciences (JIHT RAS) and measurements of the compressibility of water and steam carried out at the Moscow Power Engineering Institute (MPEI), starting with the work of V.A. Kirillina 1953, is noted. The reliability of the experimental data on the density of liquid potassium in 1976–1977 is analyzed in comparison with the results of the new, independent measurements in 1990. The position of the ideal, as in a rarefied gas, coefficient of thermal expansion of the liquid on the saturation line and on the potassium isobar is found. The experimental data on density, compressibility, and ideal thermal expansion coefficients are used to estimate the position of the unit compressibility factor line and the inversion line of the Joule–Thomson effect for dense potassium in the temperature range K and pressures up to kbar. The considered data on the thermodynamic surface of liquid potassium require new experimental and theoretical work and expansion of the list of analyzed properties. [ABSTRACT FROM AUTHOR]

Many specific features and anomalies of the properties of water at low temperatures and negative pressures or hydrogen and nitrogen at megabar pressures and high temperatures are related to zero and negative coefficients of thermal expansion. A review of numerous examples of manifestation of these features for various materials in different states is presented. A set of data and methods for the analysis of negative thermal expansion coefficients is singled out for an independent line of research. [ABSTRACT FROM AUTHOR]