374 CONSIDERATION OF CARBON COMPOUNDS. 



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. 



India-rubber, Blastica (Caoutchouc), is the dried milky juice found 

 in quite a number of trees growing in the tropics. The principal 

 constituents are hydrocarbons of the composition C 20 H 32 , C IO H 16 , and 

 C 5 H 8 . 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 rubber is india-rubber which has been caused to enter 

 into combination with from 7 to 10 per cent, of sulphur by heating 

 together the two substances to a temperature of 130-150 C. (266- 

 302 F.). Vulcanized rubber differs from the natural article by 

 possessing greater elasticity and flexibility, by resisting the action of 

 solvents, reagents and atmosphere to a higher degree, and by not 

 hardening when exposed to cold. 



Hard rubber, vulcanite, or ebonite, is vulcanized rubber, containing 

 from 20 to 35 per cent, of sulphur, and often also tar, white-lead, 

 chalk, or other substances. It is hard, tough, and susceptible of a 

 good polish. 



Gutta-percha is the concrete juice of a tree Isonandra gutta. It 

 resembles india-rubber both in composition and properties. At ordi- 

 nary temperature it is a yellowish or brownish, hard, somewhat 

 flexible, but scarcely elastic substance ; when warmed it softens, and 

 is plastic above 60 C. (140 F.) ; at the temperature of boil ing- water 

 it is very soft. It is insoluble in water, alcohol, dilute acids and 

 alkaline solutions ; soluble in oil of turpentine, carbon disulphide 

 and chloroform. 



Stearoptens or Camphors are substances closely related to the 

 terpenes and to cymene both in physical and chemical properties ; 

 while terpenes are liquids, camphors are crystalline solids. Borneo 



