Which gas is it? Testing common gases

Most gases are colourless, so chemists identify them by tests. Oxygen relights a glowing splint, because it helps things burn. Hydrogen burns with a squeaky pop when a lighted splint is held at the mouth of the tube. Carbon dioxide turns limewater milky and puts out a flame. Ammonia has a sharp smell and turns damp red litmus paper blue, because it is alkaline. Nitrogen gives none of these results: it simply puts out a flame. Air is mostly nitrogen with about one fifth oxygen.