3. Make a U-tube from copper pipe to fit the vaccuum flask. Place this in the liquid nitrigen and pass a stream of oxygen through it from a cylinder. After a couple of minutes, liquid oxygen will have condensed inside the U-tube and can be poured into a test-tube which has been previously cooled in liquid nitrogen.

Note the pale blue colour. Hang the test-tube containing the liquid oxygen by cotton thread from the ceiling of the laboratory and bring a powerful magnet up to it. The tube will be pulled away from the vertical slightly, showing that oxygen is paramagnetic. This does not occur with liquid nitrogen.

Any remaining liquid oxygen can be poured onto a tissue on a heat-proof mat or sand tray. The tissue will burn vigorously when ignited with a burning splint.

(See also 11. The Properties of Liquid Oxygen)