Primary calibration of the volume of silicon spheres

For direct density determination by so-called absolute procedures, the mass and the volume of a body must be determined. The paper gives an overview of dimensional measurements of silicon spheres used as density standards. Relative uncertainties for diameter measurements of less than 10 −8 can only be achieved with interferometric procedures. After introducing optical interferometry the two main types of interferometers used are described in detail: plane-face interferometers and interferometers with spherical beam path. At present, uncertainties of 1 nm can be achieved for a diameter determination of silicon spheres, which corresponds to a relative volume uncertainty of Δ V / V = 3 × 10 −8 .