ALCOHOLS. 267 



oil of turpentine a resin called colophony, rosin, or ordinary resin, 

 consisting chiefly of sylvic acid, C 44 H 64 5 . 



Copaiva balsam consists of a volatile oil and a resin, the latter 

 being principally copaivic acid, C 20 H 30 2 . 



Caoutchouc, C 8 H 14 , and gutta-percha, C 10 H 16 , are intimately re- 

 lated to the essential oils and resins. Caoutchouc heated with 

 sulphur combines with it (becomes " vulcanized "), and is then 

 more elastic and does not become brittle when cold. 



Of fossil resins may be mentioned amber and asphalt, the latter 

 having most likely been formed from petroleum. 



QUESTIONS. 



381. How do hydrocarbons occur in nature, and by what processes 

 are they formed in nature or artificially ? 



382. State the general physical and chemical properties of hydro- 

 carbons. 



383. What is the general composition of the pafaffines. 



384. State the composition and properties of methane, and also the 

 conditions under which it is formed in nature. 



385. What is coal, what are its constituents, from what is it derived, 

 and by what process has it been formed ? 



386. What is crude coal-oil, what is petroleum ether, and what 

 is petrolatum? 



387. How is illuminating gas manufactured, and what are its chief 

 constituents ? 



388. Mention some of the important substances found in coal-tar. 



389. What is understood by aromatic substances ; from which series 

 of hydrocarbons are they derived, and what is the name and composi- 

 tion of the first member of that series ? 



390. Mention of essential oils : occurrence in nature, physical prop- 

 erties and composition of some of the more important oils. 



40. ALCOHOLS. 



Constitution of alcohols. The old term " alcohol " originally 

 indicated but one substance (ethyl alcohol), but is now applied 

 to a large group of substances which may be looked upon as 

 being derived from hydrocarbons by replacement of one, two, 

 or more hydrogen atoms by hydroxyl, HO. 



Any hydrocarbon may be converted into an alcohol radical 



