A series of isomeric liquid hydrocarbons of the formula CMH1S, having boilingpoints ranging from 160 degrees to 190 degrees C, but as they exist in essential or ethereal oils they are mixtures of terpenes and not chemical individuals, and are often associated with oxidized bodies allied to and, in many cases, derived from them. Pinene is the chief terpene contained in the American and German turpentine oils, lsevopinene is the chief constituent of French turpentine, whilst sylvestrene and hemiterpene, or dipentene, together with pinene, are contained in varying proportions in the Russian and Swedish oils. Indian turpentine contains pinene and two new terpenes named carene and longifolene. Oil of oiange contains limonene. Fennel oil and some eucalyptus oils contain phellanurene. Dextropinene rotates the polarized iay to the right and laevopinene to the left. Citrene is contained in the oil of citron, hesperidene in the oil of orange, thymene in the oil of thyme, carvene in the oil of cumin, and these terpenes have the formula C10H12, etc., most of which are well defined crystalline compounds with definite meltingpoints.All the terpenes also yield peroxide of hydrogen when a.roxidized in the presence of water. Isoprene is the bestknown hemiterpene, whilst dipentene is associated with cineol in Oleum cina, and can be easily prepared from pinene and some other terpenes. These compounds are further referred to in the descriptions of the various essential oils in which they occur or under their distinct names. Another associated class of hydrocarbons o* the formula CjSH24 are termed “sesquiterpenes.”

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Definition of  TERPENES