Argon

·noun A substance regarded as an element, contained in the atmosphere and remarkable for its chemical inertness.

II. Argon ·add. ·noun A colorless, odorless gas occurring in the air (of which it constitutes 0.93 per cent by volume), in volcanic gases, ·etc.;

— so named on account of its inertness by Rayleigh and Ramsay, who prepared and examined it in 1894-95. Symbol, A; at. wt., 39.9. Argon is condensible to a colorless liquid boiling at -186.1° C. and to a solid melting at -189.6° C. It has a characteristic spectrum. No compounds of it are known, but there is physical evidence that its molecule is monatomic. Weight of one liter at 0° C. and 760 mm., 1.7828 g.