Precision density measurements of solid materials by hydrostatic weighing

A review on the precision hydrostatic weighing of solid materials is given. Using single-crystal silicon spheres as a solid density standard, densities of silicon crystals, metals, glasses and polymers were measured. Details on the structure of the measurement system, the procedure for the solid density measurement and the uncertainty evaluation are given. The density of a 1 kg silicon sample has been measured with a relative combined standard uncertainty of 1.2 × 10−7. When the covariances in input quantities are taken into account, the relative combined standard uncertainty in measuring the density difference between the silicon sphere and the silicon sample may be reduced to 3.6 × 10−8. Uncertainty sources in the hydrostatic weighing and the effect of covariance on the uncertainty are discussed.