2. Place a clean dry test-tube in liquid nitrogen so that the lower half is immersed. Leave for about 15 minutes until about 2cm of liquid air has condensed in the tube. Take care that the mouth of the test-tube protrudes from the container. If the test-tube does not protrude from the container, liquid nitrogen will be obtained rather than liquid air because the space above the liquid nitrogen will be filled with nitrgoen gas and not air.

Remove the test-tube from the liquid nitrogen and stand it in a test-tube rack. As it warms up, nitrogen will boil off first (at 77K) and will extinguish a lighted or glowing splint. After a few seconds, oxygen will start to boil off (at 90K) and will relight a glowing splint.

This illustrates the industrial fractional distillation of liquid air.