TERPENES AND THEIR DERIVATIVES. 597 



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. 



Camphene is the only solid hydrocarbon of the terpene group, and occurs in 

 the oil from Pinus Sibirica. It is obtained by heating the above pinene hydro- 

 chloride with alcoholic potash. 



Limonene is the principal constituent of orange oil, and is found in a large 

 number of other oils, as the dextro modification. Laevolimonene occurs in 

 pine-needle oil. 



Dipentene is the inactive modification of limonene, and can be prepared by 

 heating pineiie, camphene, sylvestrene, or limonene to 250-270 C. for several 

 hours. 



Terebene, Terebenum, consists chiefly of dipentene with other hydrocar- 

 bons, and is obtained from oil of turpentine by mixing it with sulphuric acid, 

 distilling, washing the distilled oil with soda solution, redistilling, and collect- 

 ing the portions which pass over at a temperature of 155-165 C. (311- 

 329 F.). Terebene resembles oil of turpentine in most respects, but has not 

 the unpleasant odor of this oil. 



Sylvestrene is found in Swedish and Russian oil of turpentine. 



Phellandrene is widely distributed in volatile oils; notably in the water- 

 fennel oil and eucalyptus oil. 



Sesquiterpenes, C 15 H 24 . These are likewise widely distributed in 

 the vegetable kingdom, and are very similar in their general proper- 

 ties to the terpenes proper, but have a higher boiling-point. Of 

 those, well characterized, may be mentioned : cadinene, from oil of 

 cade and a large number of other volatile oils ; caryophyttene, from oil 

 of cloves ; humulene, from oil of hops ; santolene y from oil of sandal- 

 wood; cedrene, from oil of cedarwood ; and zingiberene, from oil of 

 ginger. 



Rubber, Elastica (Caoutchouc) is the dried milky juice found in 

 quite a number of trees growing in the tropics. It consists chiefly 

 of hydrocarbons of the terpene series, having a very large molecular 

 weight and a complex molecular structure. 



The commercial article is yellowish-brown, has a specific gravity 

 of 0.92 to 0.94, is soft, flexible, insoluble in water and alcohol, 

 but soluble in carbon disulphide, ether, chloroform, and benzene. It 

 is not acted upon by dilute mineral acids ; concentrated nitric and 

 sulphuric acid, as well as chlorine, attack it after a time. It is hard 

 and tough in the cold ; when heated it becomes viscous at 125 C. 

 (257 F.), and fuses at 170-180 C. (347-356 F.) to a thick liquid, 

 which, on cooling, remains sticky, and only regains its original char- 

 acter after a long time. 



Vulcanized rubbw is India-rubber which has been caused to enter 



