Determination of the Avogadro constant from precision density measurements on a silicon sphere

Density measurements with relative uncertainty of 1/spl times/10/sup -7/ have been made on a highly polished 1 kg single crystal silicon sphere. The molar mass, crystal quality and lattice parameter have been measured elsewhere, enabling a determination of the Avogadro constant to be made. The purpose is to obtain a definition of the kilogram in terms of a specific number of /sup 12/C atoms.