The Static Dielectric Constant of the Water‐Benzene Mixture System to 400°C and 2800 bar

The water‐benzene mixture system at high temperature and high density is considered as a model system to study the dielectric properties of polar‐nonpolar binary mixtures. The static dielectric constant or permittivity ε and the density have been measured at 300, 350 and 400°C between 100 and 2800 bar for 7 different water‐benzene mixtures covering the whole range between pure water and pure benzene. Apparatus and procedure are described. An autoclave contains a cell closed with a flexible bellows. Inside the cell is a cylindrical condenser, filled with a sample mixture, separated from the pressurizing fluid. Thus dielectric and density measurements can be performed simultaneously with one sample.—Extensive tables with data are given. The uncertainty is believed to be below ±1% for most data. At 400°C and 2000 bar ε(χw = 1.0) is 19.40 and decreases to 9.67 (χw = 0.9) and to 3.68 (χw = 0.5). For pure benzene the value is 2.1. Several continuum theories are examined and discussed to represent the data. The best result was obtained with the Landau‐Lifshitz‐Looyenga relation. It needs dielectric constants of the pure partners and the mixture densities but requires no adjustable parameters. On the basis of the present investigation this relation is recommended also to estimate dielectric constants for dense, supercritical binary systems of water with nonpolar gases.