Four gases can be identified with simple tests. Oxygen relights a glowing splint. A splint that is glowing but not flaming is pushed into the gas, and if the gas is oxygen the splint bursts back into flame.
Hydrogen is tested with a lit splint. If hydrogen is present it burns with a squeaky pop. The pop happens because the hydrogen reacts quickly with oxygen in the air to make water.
Carbon dioxide is tested by bubbling the gas through limewater. Limewater is a colourless solution that turns cloudy when carbon dioxide is added.
Chlorine is a pale green, poisonous gas, so it must only be tested in a fume cupboard. Chlorine turns damp blue litmus paper red and then bleached white.
