Nitrogen is a gas with no colour and no smell. It is most of what you breathe — about four fifths of the air — but your body does not use that gas the way it uses oxygen. You breathe nitrogen in and out and almost nothing happens. Plants need nitrogen to grow, though actually they cannot take it from the air as it is; it has to be changed into other forms first, often nitrates in the soil. In a lab, liquid nitrogen is so cold it can freeze a flower in seconds. The name came into English from French nitrogène, a word the French chemist Jean-Antoine Chaptal made in 1790. If you split the surface, it is nitro- + -gen, “that produces.” It was tied to niter, an old name for a salt used in gunpowder. This is a science word you will meet in school, on weather and farm news, and on a tank in a lab.