A Liquid Density Standard Over Wide Ranges of Temperature and Pressure Based on Toluene
Mark O. McLinden, Jolene D. Splett
The density of liquid toluene has been measured over the temperature range -60 °C to 200 °C with pressures up to 36 MPa. A two-sinker hydrostatic-balance densimeter utilizing a magnetic suspension coupling provides an absolute determination of the density with low uncertainties. These data are the basis of NIST Standard Reference Material(R) 211e for liquid density over the temperature range -50 °C to 150 °C and pressure range 0.1 MPa to 30 MPa. A thorough analysis of the uncertainties is presented; this includes effects resulting from the experimental density determination, possible degradation of the sample due to time and exposure to high temperatures, dissolved air, uncertainties in the empirical density model, and the sample-to-sample variations in the SRM vials. Also considered is the effect of uncertainties in the user's temperature and pressure measurements. This SRM is intended for the calibration of industrial densimeters.