amagat
Number densityexact by definition
One amagat is the number density of an ideal gas at 0 °C and 101.325 kPa, 2.686780111 × 10²⁵ m⁻³, known as the Loschmidt constant. It is exact, because pressure, the Boltzmann constant and the reference temperature are all exact by definition.
Watch out: Some sources define the amagat at 20 °C or at 1 bar instead of 0 °C and 1 atm, which changes it by up to 7%. Spectroscopic databases mean the 0 °C, 101.325 kPa version, and so does this entry.
| 1 amagat | 2.6867801e+25 m⁻³ |
Named for Émile Amagat and used as a density unit in high-pressure gas physics and in atmospheric spectroscopy, where absorption path lengths are quoted in centimetre-amagats so that a measurement is independent of the temperature and pressure the sample happened to be at.