Experimental Determination of Air Density Using a 1 kg Mass Comparator in Vacuum

The density of ambient air has been determined by a straightforward experimental method. The apparent masses of two artefacts having about the same mass and surface, but different well-known volumes, have been compared by using a 1 kg balance in vacuum and in air. The differences of apparent masses and volumes yield the air density with a relative uncertainty (1σ) of 5 × 10 -5 . From measurements made using a third artefact, surface sorption effects caused by the change between vacuum and air conditions gave a coefficient of about 0,2 μg cm -2 .