New apparatus for measuring the density of mercury

A new apparatus is being set up for measuring the density of mercury at 20 degrees C with a relative uncertainty of 0.5 x 10(-6) by hydrostatic weighi ng of a sinker of known volume and mass. Two small sinkers of about 50 cm(3 ) were calibrated by hydrostatic comparison with silicon density standards. Thus, in the first stage, a relative uncertainty of 2 x 10(-6) of the merc ury density can be reached. The quantity of mercury needed for the measurem ents is 1 1. Also, density comparisons of different mercury samples can be carried out with a relative uncertainty of 0.5 x 10(-6). To reach a relativ e uncertainty of 0.5 x 10(-6) in the density of mercury, a 500 cm(3) hollow cube is to be manufactured from tantalum. Its volume will be determined by means of an interferometer, with a relative uncertainty of 0.15 X 10(-6). Measurements will be performed for the gravitation experiment of Zurich Uni versity using 1 m(3) of mercury, and for mercury samples used in primary pr essure standards. Design and results of first tests of the hydrostatic weig hing apparatus are reported.