..
air 05 Air can be liquefied, nitrogen evaporates first

 * Left photo: Air (1) can be liquefied by compression (2), water cooling (3),
                           Expansion (4) more cooling (6) to obtain liquefied air (5).
* Middle photo: Liquid nitrogen is poured out of a thermos.
* Right photo:    It boils at a temperature of minus 196° C being a suitable coulant.
  (Oxygen boils at - 183°C, so nitrogen separates first during distillation of liquid air).