1813-1885

Irish chemist who discovered the critical point—that temperature above which it is impossible to liquefy a gas no matter how much pressure is applied. Before Andrews discovered this it was believed that many gases could never be liquefied. This insight allowed scientists to liquefy oxygen, hydrogen, nitrogen, and other gases, which were then known as "permanent gases," for the first time by lowering their temperatures. Andrews also proved that ozone, which creates the sour smell near a spark source, is a form of oxygen.