New vapour pressure measurements for argon and nitrogen and a new method for establishing rational vapour pressure equations
When collecting the thermodynamic properties of the pure fluids, nitrogen and argon, only a few reliable experimental values were found in some ranges of the areas of interest in spite of a relatively high quantity of measured data. Unfortunately the available experimental values are based on different temperature scales. New vapour pressure measurements for argon and nitrogen have been performed with specially developed low temperature equipment, to obtain some idea of the quality of the data available in this area. In parallel with the growing number of experimental vapour pressures, different formulae for representing the vapour pressure curves have been used by many authors. These equations are tested critically. Most of the relationships tested can only moderately fulfil the demands expected from such equations, especially in the critical range. Therefore, a new method of establishing a rational vapour pressure equation is presented here. The method has been used for nitrogen and argon without any restriction as to general validity. For these two substances the coefficients of a new vapour pressure equation are also given.