TERPENES AND THEIR DERIVATIVES. 599 



monobromata, C, H 15 BrO, a white crystalline substance having a mild 

 camphoraceous odor and taste. Heating with nitric acids converts 

 camphor into camphoric add, acidum camphoricum, CgH^CO.,!!)^ 

 a colorless, crystalline, fusible substance having an acid taste ; it is 

 slightly soluble in water, readily in alcohol and ether. 



Cineol. Eucalyptol, C 10 Hi 8 0, is found in the volatile oils of different species 

 of eucalyptus, as also in the oils of some other plants. It is liquid at the ordi- 

 nary temperature, but solidifies when cooled to a little below the freezing-point 

 of water. It has an aromatic, distinctly camphoraceous odor. 



Menthol, C 10 H 19 OH (Mint-camphor). Found together with a ter- 

 pene in oil of peppermint, and separates in crystals on cooling the oil. 

 Menthol is nearly insoluble in water, fuses at 43 C. (109 F.), and 

 boils at 212 C. (414 F.). It has the characteristic odor of pepper- 

 mint. 



Terpin hydrate, Terpini hydras, C 10 H 20 O 2 .H 2 O, is the hydrate of 

 the diatomic alcohol terpin, and is formed from pinene under the 

 influence of alcohol and nitric acid. It forms colorless crystals, melt- 

 ing at 117 C. (243 F.), is readily soluble in alcohol, but sparingly 

 soluble in water, ether, or chloroform. 



Resins are obtained, together with the essential oils, from plants. 

 Mixtures of a resin and a volatile oil are known as oleo-resins, while 

 mixtures of a resin or oleo-resins and gum are known as gum-resins. 

 The name balsam is also used for a certain group of oleo-resins. 



The resins are mostly amorphous, brittle bodies, insoluble in water, 

 but soluble in alcohol, ether, fatty and essential oils ; they are fusible, 

 but decompose before being volatilized ; they all contain oxygen and 

 exhibit somewhat acid properties. 



Turpentine, the oleo-resin of the conifers, contains besides the oil of 

 turpentine a resin called colophony, rosin, or ordinary resin, consisting 

 chiefly of the anhydride of abietic acid, C 44 H 64 O 5 . 



Copaiva balsam consists of a volatile oil and a resin, the latter 

 being principally copaivic acid, C 20 H 30 O 2 . 



Of fossil resins may be mentioned amber and asphalt, the latter 

 having most likely been formed from petroleum. 



QUESTIONS. What substances are known as terpenes : where are they found 

 in nature? Give the composition of the principal groups of terpenes. Men- 

 tion the general properties of essential oils, and name some of the important 

 ones. What is the source of rubber ; how is it converted into vulcanized and 

 hard rubber ? State the composition and properties of camphor. 



