THE DIELECTRIC-CONSTANT AND DENSITY OF BENZENE TO 400-DEGREES-C AND 3000-BAR

A high pressure apparatus is described to measure simultaneously within one cell the dielectric constant and the density of non-polar supercritical fluids to 400-degrees-C and 3000 bar. Thus relations between the dielectric constant and the fluid density at any given temperature can be discussed with particular reliability. The apparatus consists of a cylindrical autoclave, which encloses a stainless steel belows containing the sample. A cylindrical capacitor (ca. 60 pF) is mounted inside the bellows. A back-up fluid of heptane is used to produce the pressure on the bellows. Measurements are made between 10 kHz and 1 MHz. Values of the dielectric constant epsilon are reported for 10 temperatures between 27.5 and 400-degrees-C and for pressures between 1 bar and 3000 bar. At 27.5-degrees-C and 1 bar epsilon is 2.273. At 100-degrees-C it varies from 2.124 to 2.425 between 1 and 2800 bar. At 400-degrees-C and 3000 bar epsilon = 2.198. The probable error is below 0.2%. Density measurements cover the same range. The temperature dependence of epsilon at constant density is very small. The Clausius-Mossotti-function is presented for the whole region. In accordance with existing theories it can be described as a three-term series in powers of density and a T-1-term.