argon

Colourless, odourless, non-metallic, gaseous element, atomic number 18, relative atomic mass 39.948. It is grouped with the noble gases (rare gases) in Group 0 of the periodic table of the elements. It was long believed not to react with other substances, but observations now indicate that it can be made to combine with boron fluoride to form compounds. It constitutes almost 1% of the Earth's atmosphere, and was discovered in 1894 by British chemists John Rayleigh and William Ramsay after all oxygen and nitrogen had been removed chemically from a sample of air. It is used in electric discharge tubes and argon lasers.

Argon may be separated from atmospheric nitrogen in three ways: (1) by passing it over red-hot turnings of magnesium; (2) by sparking the gas with excess of oxygen in the presence of caustic alkali; (3) by dissolving the more soluble argon in water. Commercially it is obtained by the fractional distillation of liquid air. It can be condensed to a colourless liquid which boils at −187°C/−304.6°F and freezes at −189.6°C/−309.28°F.