RESINS. 383 



bacco in ordinary pipes. This oil is extremely poison- 

 ous. It is to be understood that these oils do not exist 

 ready formed in the substances from which they are 

 obtained, but are produced in the re-arrangement of 

 atoms, which takes place when organic bodies are sub- 

 jected to a high temperature. 



960. CAMPHORS. Several of the oxy- 



What is the . J 



origin of the genated essential oils deposit white crystal- 

 wnphonf line solids by cold These are frequently 



isomeric with the oils themselves, and are called cam- 

 phors. Ordinary gum camphor is obtained like the es- 

 sential oils, by the distillation of the leaves of the Lau- 

 rus Camphor i with water. Its volatile character is the 

 occasion of a singular appearance, when small bits of 

 the substance are thrown upon warm water. The par- 

 ticles are seen to sail about as if they were possessed 

 of life, owing to the propelling effect of the vapor 

 which escapes beneath them. ,/A 



How are re- 961. RESINS. The resins, of which 



sins formed? ordinary pine rosin may serve as an exam- 

 ple, are formed by the action of oxygen upon the essen- 

 tial oils. Oil of turpentine may be thus partially con- 

 verted into resin, by long exposure to the air. On sub- 

 sequently heating it, only a portion is found to be vola- 

 tile, while a resinous mass remains behind. Turpen- 

 tine, or pitch of pine trees, is thus formed in nature, 

 from the oil of turpentine, as it exudes from the 

 trees. But the conversion is only partial, so that the 

 turpentine yields, on distillation, a portion of oil, while 

 rosin remains behind. Resins are easily distinguished 

 from gums by their insolubility in water ; they are, on 



