Cyanogen \Cy*an"o*gen\ (s?-?n"?-j?n), n. [Gr. ky`anos a dark blue substance + -gen: cf. F. cyanog[`e]ne. So called because it produced blue dyes.]

(Chem.) A colorless, inflammable, poisonous gas, C2N2, with a peach-blossom odor, so called from its tendency to form blue compounds; obtained by heating ammonium oxalate, mercuric cyanide, etc. It is obtained in combination, forming an alkaline cyanide when nitrogen or a nitrogenous compound is strongly ignited with carbon and soda or potash. It conducts itself like a member of the halogen group of elements, and shows a tendency to form complex compounds. The name is also applied to the univalent radical, CN (the half molecule of cyanogen proper), which was one of the first compound radicals recognized.

Note: Cyanogen is found in the commercial substances, potassium cyanide, or prussiate of potash, yellow prussiate of potash, Prussian blue, Turnbull's blue, prussic acid, etc.

Source: Webster's Revised Unabridged Dictionary (1913)