The Avogadro constant — Recent results on the molar volume of silicon

The density p of two silicon crystals has been determined by precision hydrostatic weighing, based on very accurate solid density standards (SDS´s). Densities of additional crystals were gained from density differences measured by the temperature-of-floatation method. The molar mass M of the crystals was determined by comparing the isotopie abundances against the known abundances of the National Bureau of Standards (NBS) reference material SRM 990 using activation analysis and mass spectroscopy. Combining the measured values for M and p leads to M/p = (12.058 822 ± 0.000 013) cm³/mol. With the known volume of the unit cell the following value for the Avogadro constant was calculated: NA = (6.022 137 ± 0.000 007) × 10²³ mol⁻¹.