PHASE BORDER AND DENSITY DETERMINATIONS IN THE CRITICAL REGION OF (CARBON-DIOXIDE PLUS ETHANE) DETERMINED FROM DIELECTRIC PERMITTIVITY MEASUREMENTS

We have determined the (p, T, rho, x) phase boundaries in three mixtur es of {(1 - x)CO2 + xC(2)H(6)) with x = (0.2516(6), 0.4924(5), and 0.7 397(8)), in the vicinity of the critical locus from measurements of th e relative dielectric permittivity epsilon(r). We combined accurate me asurements of epsilon(r) with the Clausius-Mossotti relationship to de termine the density. Measurements of epsilon(r) were made with two app aratuses: a reentrant cavity resonating at 375 MHz, and a coaxial cyli ndrical capacitor and bridge operating at a frequency of 1 kHz. The ph ase border was determined with uncertainties of approximately 0.5 per cent in density and 0.06 K in temperature, the latter corresponding to a fractional uncertainty of 1.2 . 10(-3) in pressure. The uncertainti es in temperature and pressure resulted from the size of the temperatu re steps that were used; smaller values could be attained. The uncerta inty in density resulted from uncertainty in the parameters relating t he density to epsilon(r). (C) 1997 Academic Press Limited.