Cyanogen, CN or Cy, although intrinsically of little importance, is one of the most interesting compounds of carbon. It was the first known compound body which was proved to be able to unite with elements in the same way as these substances unite with each other. Thus hydrogen, H, unites with chlorine, Cl, to form hydrochloric acid, and sodium, Na, unites with chlorine to form chloride of sodium, NaCl. Like these elements, H, Cl, or Na, each a single substance, the group CN, consisting of 12 parts of carbon and 14 of nitrogen, enters into combination, acting as if it also were for the time being an element; thus it forms cyanide of sodium, NaCN, or NaCy, and hydrocyanic acid, HCN, or HCy. There are now many thousands of such radicles known, of which the groups methyl, CH3, ethyl, C2H5, &c. may be taken as other examples.
Cyanogen is a colourless, poisonous gas, which burns with a purplish flame. It is soluble in water, and can be condensed to a liquid, under a pressure of about four atmospheres (60 lb. per sq. inch). It may be obtained by heating the cyanide of mercury, HgCy2, when the cyanogen passes off in the gaseous state.
Cyanogen forms poisonous compounds with metals called cyanides, of which the best known is the cyanide of potassium, a salt of much importance in photography and metallurgy. With hydrogen it forms the deadly prussic or hydrocyanic acid, while it is united with oxygen in cyanic acid. See HYDROCYANIC ACID, POTASSIUM.
Cyanic Acid is a compound of cyanogen which can hardly be prepared in the free state, owing to its great tendency to decompose. It forms a class of salts called cyanates, of which the chief is the cyanate of potash. This salt is produced when cyanogen gas is passed into solution of potash. The formula of cyanic acid is HCyO, that of the potash salt being KCyO.