Amagat's law or the Law of Partial Volumes is used to describe the behaviour and properties of (non-ideal) gas mixtures. In chemistry, Amagat's law (1880) states the volume of a gas mixture is equal to the sum of volumes of two gases, if the temperature and the pressure stays the same. . This is the experimental expression of volume as an extensive quantity. It is named after Emile Amagat.
The law allows the behaviour of gas mixtures to be approximated as a perfect gas, using an experimentally derived correction factor (z), which is applied to the perfect gas equation pV = znRT. The law determines the gas mixture critical pressure and critical volume. These critical parameters can be read off a compressibility chart to determine the compressibility factor (z). See also: Ideal gas