liquid air

Air that has been cooled so much that it has liquefied. This happens at temperatures below about −196°C/−321°F. The various constituent gases, including nitrogen, oxygen, argon, and neon, can be separated from liquid air by the technique of fractional distillation.

Air is liquefied by the Linde process, in which air is alternately compressed, cooled, and expanded, the expansion resulting each time in a considerable reduction in temperature. With the lower temperature the molecules move more slowly and occupy less space, so the air changes phase to become liquid.