Amagat

An amagat is a practical unit of number density. Although it can be applied to any substance at any conditions, it is defined as the number of ideal gas molecules per unit volume at 1 atm (= 101.325 kPa) and 0 °C (= 273.15 K). It is named after Emile Amagat, who also has Amagat's law named after him. The abbreviated form of amagat is "amg."

Definition

Number density in amg, denoted here by $\eta$, is defined as

$\eta ={\frac {n}{n_{0}}}$,

where n₀ = 1 amg = 2.686 7774×10²⁵ m⁻³ = 44.614 981 mol/m³ is the Loschmidt constant.

In practice, number density of an ideal gas at pressure P and temperature T can be calculated as

$\eta =\left({\frac {p}{p_{0}}}\right)\left({\frac {T_{0}}{T}}\right)\,{\rm {amg}}$,

where T₀ = 273.15 K and p₀ = 101.325 kPa.

Example

Number density of an ideal gas (such as air) at room temperature (20 °C) and 1 atm (101.325 kPa) is

$\eta =\left({\frac {1\,{\rm {atm}}}{p_{0}}}\right)\left({\frac {273.15\,{\rm {K}}}{(273.15+20)\,{\rm {K}}}}\right){\rm {amg}}=0.932\,{\rm {amg}}$.