Available values of the surface tension of 81 common fluids were fitted by using the same model presently used in the REFPROP program V9.0 by NIST. A set of data was built for every fluid by including mainly those values given in the DIPPR and DETHERM databases. For some fluids, other available sources of data were added in order to obtain adequate sets. For every fluid, we checked the accuracy of the REFPROP program and we made a new fit in order to improve the performance of the correlation. We found good general agreement between the REFPROP predictions and the data for 44 fluids, and therefore only very slight improvements are made for them. For the other 37 fluids, the REFPROP correlation can be more clearly improved. In particular, our new correlation is significantly more accurate for ammonia, deuterium, ethanol, and neon, because the version of REFPROP used gives values in clear disagreement with other data sources.

Twenty two different analytical expressions for the compressibility factor of the hard sphere system have been collected and reviewed in order to perform two applications: Firstly, the accuracy of these expressions in reproducing six available computer simulation data sets for the hard sphere system, some of which are very recent, is tested. It is shown that there is not a direct relation between the simplicity or complexity of their analytical form and their accuracy. Secondly, the expressions, together with the Verlet–Weis formula for the temperature dependence of the molecular diameter, have been used to reproduce our molecular dynamics results for the pressure of the Lennard-Jones reference system proposed in the Weeks–Chandler–Andersen theory. We conclude that the approximation of using hard sphere equations of state together with the Verlet–Weis formula is very accurate at temperatures and densities near the Lennard-Jones critical point. At densities close to the triple point or to the liquid curve in the liquid–vapour equilibrium, the coincidence is adequate (deviations around 3%) only if the appropriate hard sphere equation of state is used.

Some points about the search for analytical expressions for the equation of state of the hard-disc fluid are discussed in the light of the most recent advances in the field. New and accurate equations of state for this fluid are proposed.