Loschmidt constant
The Loschmidt constant or Loschmidt's number (symbol: n0) is the number of particles (atoms or molecules) of an ideal gas in a given volume (the number density). It is usually quoted at standard temperature and pressure, the 2010 CODATA recommended value is 2.686 7805(24)×1025 per cubic metre at 0 °C and 1 atm and the 2006 CODATA recommended value was 2.686 7774(47)×1025 per cubic metre at 0 °C and 1 atm. It is named after the Austrian physicist Johann Josef Loschmidt, who was the first to estimate the physical size of molecules in 1865. The term "Loschmidt constant" is also sometimes used to refer to the Avogadro constant, particularly in German texts.
The Loschmidt constant is given by the relationship:
where p0 is the pressure, kB is the Boltzmann constant and T0 is the thermodynamic temperature. It is related to the Avogadro constant, NA, by:
where R is the gas constant.
Being a measure of number density, the Loschmidt constant is used to define the amagat, a practical unit of number density for gases and other substances:
such that the Loschmidt constant is exactly 1 amagat.
In the CODATA set of recommended values for physical constants, the Loschmidt constant is calculated from the gas constant and the Avogadro constant:
...
Wikipedia