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 Émile 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 7805×10²⁵ m⁻³ = 44.615 036 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

$\eta= \left(\frac{1\, {\rm atm}}{p_0}\right)\left(\frac{273.15\, {\rm K}}{(273.15+20)\, {\rm K}}\right) {\rm amg}=0.932\, {\rm amg}$.