Amagat’s experiment along with graph:

Regnault, Andrew, Amagat and other scientists proved that real gases do not exhibit ideal behavior or nature. Ideal gas follow gas laws i.e. Boyle’s law and Charles law. According to the Boyle’s law product of pressure (P) and volume is constant, at constant temperature. Therefore, for ideal gas due to change of P, PV should be constant at constant temperature as  v

Amagat determined the volume of different real gases at different pressure (P) but at  a fixed temperature. Then, he plotted PV against P in a graph, where he got several  lines. There lines are called Amagat’s curve. For a fixed quantity of an ideal gas at constant temperature, PV should remain constant in spite of the variation of P and consequently the line got by plotting PV against P will be a straight line parallel to X-axis denoting pressure. It has been observed that in case of real gases the plots of PV against P are linear but not parallel to the X-axis.

In case of gases containing small molecules, like H2 and He, the value PV increases steadily with the increase of pressure from the very beginning. But for O2, N2, CO2  and other gases containing big molecules, PV at first decrease and then reaching the minimum rise with the increase of pressure.

different volume of gases

Therefore, it is undoubtedly proved that, real gases do not obey gas laws i.e. they Deviate from ideal behavior. But at high temperature real gases behave like ideal gases which can be understood by the following figure.

increasing of temperature