84 CHEMISTRY. 



Camphor is a solid volatile oil, having all the characters of the 

 essential oils. 



Resi?is. — These are generally found in vegetables associated with 

 some volatile oil. Common rosin affords a good example; it is pro- 

 cured from turpentine, which is a compound of rosin and the volatile 

 oil of turpentine When turpentine is distilled, the oil passes off, 

 leaving the rosin behind. 



Resins are insoluble in water, but soluble in alcohol, and in vola- 

 tile and fixed oils ; they are inflammable, and yield on distillation car- 

 buretted hydrogen, and several other products ; a moderate degree 

 of heat imparts an adhesive quality to them. Some resins resemble 

 fixed oils, in containing two principles, one being more soluble in 

 alcohol than the other. Resins are also susceptible of saponification. 

 Concentrated nitric acid acts upon resins with an explosive violence. 



The most important resins, beside rosin, are lac, copal, 7nastic, and 

 dragoyi's blood. 



Amber is a fossil resin. 



Caoutchouc, or India rubber, is an exudation from a tree, resem- 

 bling both the volatile oils and the resins. It is peculiar in being 

 elastic. 



Balsams. — This term is properly used to express a native 

 compound of resin, volatile oil, and benzoic acid, as in the balsams 

 of Tolu and Peru. The name is also given to compounds of resins 

 and volatile oils, as copaiva. 



The term Gum-resins is applied to a class of vegetable sub- 

 stances, consisting of a mixture of gum and resin, with some other 

 principles : they comprise some of the most valuable medicines, as 

 opium, gamboge, ammoniac, assafxtida, myrrh, scammony, &c. 



SECTION V. 



OF ETHER, ALCOHOL, AND SOME OTHER COMPOUNDS OF THE 

 RADICAL ETHYL. 



The radical ethyl has not been isolated ; its composition is ex- 

 pressed by C^H^. Common ether is an oxide of ethyl, C-^H^O ; and 

 alcohol is a hydrated oxide of ethyl, C*FPO-j-HO. Consequently, 

 the conversion of alcohol into ether only requires the removal of an 

 atom of water. The rationale then of the action of sulphuric acid 

 on alcohol, is merely to remove the water upon which the alcohol 

 depended for its existence. There is hardly any acid with which a 

 peculiar ether bearing its name has not been formed, such as nitric 

 ether, acetic etlter, tartaric ether, &c. 



The oxide of ethyl, in consequence of being procured by the 

 action of sulphuric acid on alcohol, was formerly called sulphuric 



