Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Determination of the molar mass of argon from a high precision acoustic comparison



XiaoJuan Feng, Jintao Zhang, Michael R. Moldover, Inseok Yang, Mark Plimmer, H. Lin


This article describes the accurate determination of the molar mass of a sample of argon gas used for a determination of the Boltzmann constant. The method due to one of the authors [Moldover et al., J. Res. Natl. Bur. Stand. 93, 85-144 (1988)] uses the ratio of the square speed of sound in the gas under analysis and in a reference sample of known molar mass. The results are in good agreement with determinations by gravimetric mass spectrometry, that the fractional difference arising from the two independent procedures is bounded within 0.37×10-6 for the argon sampling from the same container. The uncertainties with both procedures are consistent.


acoustic thermometry, speed of sound, Boltzmann Constant, Argon, Argon Isotopes


Feng, X. , Zhang, J. , Moldover, M. , Yang, I. , Plimmer, M. and Lin, H. (2017), Determination of the molar mass of argon from a high precision acoustic comparison, Metrologia, [online], (Accessed April 23, 2024)
Created May 17, 2017, Updated October 12, 2021