BENZENE SERIES. AROMATIC COMPOUNDS. 373 



Terpenes are the chief constituents of a large number of essential 

 oils, such as oil of turpentine, juniper, lemon, rosemary, bergamot, 

 lavender, etc. Terpenes are readily acted upon by many agents, and 

 hence undergo numerous changes. One of these changes is polymeri- 

 zation i. e., conversion into compounds of the composition C 15 H 24 

 and C 20 H 32 , which may be eifected by heating a terpene in a sealed 

 tube, or by shaking it with concentrated sulphuric acid or with 

 certain other substances. Oxygen and hydrochloric acid combine 

 directly with terpeues ; dilute nitric acid oxidizes them readily with 

 the formation of a number of organic acids ; bromine and iodine 

 convert them into cymene. 



Oil of turpentine , C 10 H 16 , is the terpene most largely used. It is a 

 thin, colorless liquid of a characteristic aromatic odor, and an acrid, 

 caustic taste; it is insoluble in water, soluble in alcohol, and an excel- 

 lent solvent for resins and many other substances. When treated 

 with hydrochloric acid gas direct combination takes place and a 

 white solid substance of the composition C 10 H 16 HC1 is formed, which 

 is known as terpene hydrochloride, or artificial camphor, on account 

 of its similarity to camphor both in appearance and odor. 



Experiment 58. Through 10 or 20 c.c. of oil of turpentine pass a current of 

 hydrochloric acid gas for some time, or until a quantity of a solid substance has 

 separated. Collect this substance, which is artificial camphor, upon a filter ; 

 notice its characteristic odor. Heat some of it ; hydrochloric acid is set free. 



Terebene, C 10 H 16 , is the optically inactive modification of terpene, obtained 

 from oil of turpentine by mixing it with sulphuric acid, distilling, washing 

 the distilled oil with soda solution, redistilling and collecting the portions 

 which pass over at a temperature of 156 to 160 C. (313 to 320 F.). Terebene 

 resembles oil of turpentine in most respects, but has not the unpleasant odor of 

 this oil. 



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 . 



