This work is a follow-up to a previous study that was aimed at reducing the uncertainty of the air density correction used to correct mass comparisons for the effects of air buoyancy. To clarify the difference observed previously in moist air between two absolute methods (CIPM-81/91 formula and air buoyancy artefacts determination), additional measurements were carried out in moist air, dry nitrogen and vacuum. The results obtained by the two methods for nitrogen density were in good agreement while the discrepancy was confirmed for the moist air density. A comparison of a 1 kg stainless steel mass against a 1 kg Pt/Ir mass standard was carried out to compare the accuracy of these two methods. The results of this comparison made in moist air, dry nitrogen and vacuum by using buoyancy artefacts gave an agreement within 1 µg. Our particular results confirmed the good accuracy of the air buoyancy artefacts method and reinforced the hypotheses that the accuracy of the air density using the CIPM formula is limited by the estimation of its composition.

06.30.Dr Mass and density

51.30.+i Thermodynamic properties, equations of state

Instrumentation and measurement

Plasma physics

Issue 4 (August 2004)

Received 18 February 2004

Published 30 June 2004