A NEW DIFFERENTIAL DENSIMETER FOR LIQUIDS AT LOW-TEMPERATURES

A novel differential hydrostatic densimeter for measurements in liquid s at low temperatures has been developed. The technique is based on th e Archimedes principle and combines a vibrating-wire sensor with a mag netic suspension. Two identical weights are immersed in two liquid sam ples whose difference in density is measured. Each weight is suspended from one end of a lever arm and the difference in the apparent weight s is transmitted to a vibrating-wire sensor. The resonant frequency of the wire is directly related to the difference in the densities of th e two liquids. A glass wall separates the vapour phases above the liqu ids and a magnetic coupling device is used to transmit the tension to the vibrating wire. The differences in density between liquid ethane a nd liquid propane have been determined in order to evaluate the perfor mance of the densimeter. Measurements were made along the saturation l ine between T = 114 K and T = 151 K showing absolute deviations from t he literature not greater than ca. +/-0.2 per cent. The value of the l iquid ethane density was measured relative to the literature density d ata for propane with a precision of +/-0.02 per cent. (C) 1998 Academi c Press Limited.