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×10th May 2019 @ 3 min read

An amagat is a unit of number density. It is similar to Loschmidt constant which is the molecular density quoted at STP (*T* = 273.15 K, *P* = 1 atm). 1 amagat is defined as the number of molecules of an ideal gas per unit volume at STP. 1 amagat is equivalent to Loschmidt constant. The symbol used for amagat is amg or Am (rarely). It is a non-SI unit.

The number is named after Émile Hilaire Amagat. He was a French physicist and also known for Amagat’s law of additive volume.

1 amagat equals the number of ideal gas molecules per cubic metre at STP (*T* = 273.15 K, *P* = 1 atm).

As mentioned earlier, Loschmidt constant *n*_{0} equals 1 amagat at STP.

1 amagat can easily be calculated from the ideal gas equation,

where:*P*_{0} is the standard pressure, 101 325 Pa;*N*_{A} is the Avogadro’s constant, 6.022 140 6 × 10^{23}mol^{−1};*R* is the ideal gas constant, 8.314 459 8 J mol^{−1}K^{−1};*T*_{0} is the standard temperature, 275.15 K.

Let number density *η* be defined as:

where *n* is the molecular density at non-standard temperature *T* and non-standard pressure *P*, *n*_{0} is the molecular density at standard temperature *T*_{0} and standard pressure *P*_{0}.

The molecular density using the ideal gas equation is defined as:

Inserting the molecular density equation into the number density equation, we get,

Using *P*_{0} = 101 325 Pa and *T*_{0} = 273.15 K, we get the below equation.

Here, *P* is pressure in pascal, *T* is temperature in kelvin.

From the above equation, we can calculate the number density at any pressure and temperature.

If we put *P* = *P*_{0} = 101 325 Pa, and *T* = *T*_{0}= 273.15 K, we get number density equals 1 amg.

Calculate the number density in amg at pressure 2.0 × 10^{4} Pa and temperature 300 K.

Using *P* = 2.0×10^{4} Pa and *T* = 300 K,

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