DENSITY OF SILICON-CRYSTALS

Measurements of silicon crystal density for the determination of the A vogadro constant are reviewed. Volume, mass and hydrostatic-weighing m easurements are considered from the technical standpoints of error sou rces and uncertainty of measurement. The outlook on the possibility of achieving experimental uncertainties of less than 10(-7) is described . Attention is paid to the necessity of reducing the sources of uncert ainty in the density arising from the surface, such as silica layers a nd damaged crystalline layers.