Solid density determination by the pressure-of-flotation method

After a short overview of flotation methods and experiments, basic equations for the pressure-of-flotation method are given including a temperature and composition dependence of the liquid's thermal expansion and compressibility. Then, the pressure-of-flotation experiment of PTB is described. A new calibration procedure using doped silicon samples is presented. Now, density comparisons of silicon samples can be performed with an uncertainty less than 0.1 ppm for density differences up to 10 ppm, i.e. for practically all undoped silicon samples. Current applications of the method and an outlook to future developments are discussed. Relative uncertainties of the order of 10(-9) seem to be possible and would allow new applications.