A. Introduction

In this section are presented practical methods for the calculation of the density of pure gases and liquids as a function of temperature and pressure. The selected methods are quite accurate and relatively easy to use. They can easily be implemented using calculators or spreadsheet programs. The more elaborate thermodynamic models such as equations of state, which in principle allow the calculation of all the thermodynamic properties of single substances or mixtures, are beyond the scope of this article for their implementation would require the development of computer programs with lengthy testing periods.

B. Pure gases

(a) Corresponding states principle

Pitzer et al. (1955) have shown that the compression factor of a given substance at reduced temperature and reduced pressure can be expanded as a power series in the acentric factor ω. In practice, they restricted the expansion of the compression factor Z to the following linear form: