Oxygen makes up about one fifth of the air. It is colourless and has no smell, so we need a test to identify it. The test for oxygen uses a glowing splint.
Light a wooden splint, let the flame go out, and leave the end glowing red. Insert the glowing splint into a test tube of the gas. If the gas is oxygen, the splint relights.
The splint relights because oxygen is needed for burning. A tube of pure oxygen contains much more oxygen than ordinary air, so the glowing splint burns again with a flame.
In other gases such as nitrogen or carbon dioxide, the glowing splint does not relight. Be careful not to mix this up with the test for hydrogen, which uses a burning splint and gives a pop.
