Reduction into a rational fraction of a thermodynamic property of the liquid state: Experimental determinations in the case of CO2 and <i>n</i>-butane. Extension to the other properties

Abstract

The expansivity of liquid CO2 and of n-butane is determined as a function of pressure up to 4 kbar, from the melting temperatures up to the critical temperatures. The experimental method is piezothermal. The set of data is processed through a fit with a multipoint Padé approximant using an algorithm due to Werner. This particular technique determines, in its reduced form, the unique rational function relevant to the problem. The expansivity of the whole liquid phase is described in terms of a simple equation with four coefficients which enables calculation of the other thermodynamic properties. The general aspect of the phenomenological equations is discussed in this instance, underlining the particular behavior of the heat capacity as a function of pressure.