Measurement and correlation of the (p, ρ, T) relation of liquid n-heptane, n-nonane, 2,4-dichlorotoluene, and bromobenzene in the temperature range from (233.15 to 473.15) K at pressures up to 30 MPa for use as density reference liquids

Comprehensive (p, ρ, T) measurements on n-heptane, n-nonane, 2,4-dichlorotoluene, and bromobenzene were carried out in the homogeneous liquid phase for temperatures from (233.15 to 473.15) K at pressures up to 30 MPa. The measurements were performed by using an accurate single-sinker densimeter based on the Archimedes’ buoyancy principle. The total uncertainty of the measurements in density was estimated to be 0.02% (level of confidence 95%), except for densities at T ⩾ 413.15 K, where the uncertainty was estimated to be 0.03%. Based on the experimental results, accurate correlation equations for the density of the four liquids have been established. Comparisons with previous results of other experimentalists and with values calculated from current equations of state are presented. The purpose of this work was to provide accurate correlation equations for the densities of the four selected liquids so that these liquids can be used as density reference liquids for the calibration of densimeters and, in particular, for the calibration of vibrating-tube densimeters.