Methods of Liquefaction of Gases
The modern methods of cooling the gas to or below their T and hence of liquefaction of gases are done by Linde's method and Claude's method.
(i) Linde's method : This process is based upon Joule-Thomson effect which states that “When a gas is allowed to expand adiabatically from a region of high pressure to a region of extremely low pressure, it is accompained by cooling.”
(ii) Claude's method : This process is based upon the principle that when a gas expands adiabatically against an external pressure (as a piston in an engine), it does some external work. Since work is done by the molecules at the cost of their kinetic energy, the temperature of the gas falls causing cooling.
(iii) By adiabatic demagnetisation.