Argon, a chemical element that is a colorless, odorless, tasteless gas at ordinary temperatures and pressures. Argon, which is somewhat heavier than air, is found in the atmosphere and in some volcanic gases. About 0.94 per cent of the atmosphere is argon. Argon is one of the noble, or inert, gases and does not form any stable chemical compounds.

Argon is used in inert-gas shields for arc welding. It is also used as an unreactive atmosphere in which highly reactive materials, such as titanium, can be handled and processed. Silicon and germanium crystals for transistors are sometimes grown in argon atmospheres. Argon is mixed with neon to produce blue and green "neon" lights. Mixtures of argon and other noble gases are also used to fill fluorescent and incandescent lamps. Argon is prepared commercially by distilling liquid air.

Argon was discovered in 1894 by Lord Rayleigh and William Ramsay.

Symbol: Ar (formerly A). Atomic number: 18. Atomic weight: 39.948. Specific gravity: gas, 1.38 (air = 1); liquid, 1.40 (water = 1). Melting point: -308.6 F. (-189.2 C.). Boiling point: -302.5 F. (-185.7 C.). Argon has three stable isotopes: Ar-36, Ar-38, and Ar-40. It belongs to Group 0 (Inert Gases) of the Periodic Table and has a valence of 0.