An ebulliometer for measurements of vapour pressure at low temperatures: the vapour pressures and the critical state of perfluoromethylcyclopentane

Comparative ebulliometry has been used to determine the vapour pressures of perfluoromethylcyclopentane between (T = 260K, p = 10.6 kPa) and (T = 434 K, p = 1590 kPa). The measurements at low temperatures were made using a new stainless steel ebulliometer with a condenser that automatically adjusted its temperature to the required value. Another set of stainless steel ebulliometers, with conventional water condensers, were used at high pressures. In addition, the critical temperature T-c = 451.44 K and pressure p(c) = 2171.8 kPa were determined using the static method. The three sets of results were correlated by an equation of the Wagner type with a standard deviation of 72 Pa in the vapour pressure. (C) 1998 Academic Press Limited.