The saturation pressure for different objects in reduced variables and the justification of some empirical relations set from the van der Waals equation

We analyse the saturation pressure (SP) behaviour along the coexistence curve liquid–gas in reduced variables, containing only the Zeno line parameters. Using experimental and simulation data for substances (Ar, N2, Hg, Cs) and two models (van der Waals and Lennard–Jones) we create a global 3D picture of SP dependence on temperature and density. We also show that the well-known empirical Timmermans relation and partly Riedel equation are the consequences of the van der Waals equation and the rectilinear diameter law.