argon

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A colorless, odorless, inert gaseous element constituting approximately one percent of Earth's atmosphere, from which it is commercially obtained by fractionation for use in electric light bulbs, fluorescent tubes, and radio vacuum tubes and as an inert gas shield in arc welding. Atomic number 18; atomic weight 39.948; melting point -189.3°C; boiling point -185.9°C. See Table at element.

Century Dictionary and Cyclopedia

1. n. A name given by Lord Rayleigh and Professor William Ramsay to a new constituent of the atmosphere discovered by them in 1894. It is an inodorous gas, singularly inert chemically.
2. n. A gaseous element having, in the pure state as a gas, a density of 19.96 (H=1) and an atomic weight of 39.6. It exists in the atmosphere, and is also obtained from the gases yielded by the water of some springs, and, with helium (which see), from certain minerals and from meteoric iron. It was first recognized in 1895 by Lord Rayleigh and Professor W. Ramsay, who separated it from the nitrogen with which it had till then been confounded largely because of its chemical inertness, it being more indifferent to reagents than even that element. It yields two characteristic spectra, marked respectively by certain prominent red and blue lines. This element, the first of five previously unknown gases existing in the atmosphere, exhibits the same chemical inertness or incapacity for combination as the others, with which when first examined it was more or less mixed. It can now be separated from them by reduction to the liquid state and fractional distillation of the mixture. When liquefied it boils under normal pressure at —186.1° C., and in the solid state it melts at —189.5° C. Argon is nearly 2½ times as soluble in water as nitrogen. As a gas it is more opaque to the Röntgen rays than either nitrogen or oxygen. It forms about 94 per cent. by volume or 1.33 per cent by weight of the atmosphere. The fact that this substance was actually obtained by Cavendish in 1785 is interesting, although he did not pursue its examination or ascertain its elementary character.

Wiktionary

1. n. A chemical element (symbol Ar) with an atomic number of 18.

GNU Webster's 1913

1. n. (Chem.) 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.

WordNet 3.0

1. n. a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere