Gās, n.

(pron. gāz to some extent), n. [Fr. gaz; a word invented by the chemist Van Helmont, who died in 1644. Cf. D. geest, A-S. gāst, O. Sax. gest, Ger. geist, spirit, ghost; M. H. Ger. gist, gest, N. H. Ger. gischt, güscht, yeast, froth, gischen, güschen, to foam, froth, ferment.]

1. An aëriform fluid;—a term used at first by chemists as synonymous with air, but since restricted to fluids supposed to be permanently elastic, as oxygen, hydrogen, &c., in distinction from vapors, as steam, which become liquid on a reduction of temperature. In present usage, since Faraday succeeded in liquefying many of the supposed permanent gases, the term has resumed nearly its original signification, and is applied to any substance when in the elastic or aëriform state.
2. (Popular Usage.) A mixture of carbureted hydrogen and olefiant gas or bi-carbureted hydrogen, which gives a brilliant light when burned, and is the common gas used for illuminating purposes.