VOLATILE OILS AND RESINS 87 



turpentine its peculiar, pungent odor. It dissolves sulphur, 

 rubber, phosphorus, and resins. It hums with a very 

 smoky flame, and on exposure to the air it absorbs oxygen, 



and hardens, much like the drying oils. For this reason it 

 is used very largely in making paints and varnishes. It is 

 also employed to some extent in medicine. 

 (/) Oil of Wintergreen is practically all methyl salicylate, 



OH 



/ \COO.CH 3 



\ ./ 



It is distilled from the wintergreen plant, or teaberry, and 

 from the bark of the sweet birch, both native to America. 

 The oil is yellow, heavier than water, and has a Aery pleasant 

 taste and odor. It is used in pharmacy to conceal the taste 

 of nauseous drugs, as a medicine, and for flavoring. Since 

 methyl salicylate can be prepared synthetically, the artificial 

 product is largely sold in place of the true oil. 



77. Resins.- -These compounds are yellow or brown 

 solid substances, more or less transparent, brittle, and 

 found as natural or induced exudations from plants. Some 

 of them are supposed to be derived by oxidation of terpenes. 

 Their function in plants may be to serve as a protective 

 coating for wounds and cuts. This prevents evaporation 

 and decay until new cells can be formed to permanently 

 cover the wound. As resins ooze out of the plant, usually 

 from special tubular " resin ducts," they are sticky, thick 

 liquids, but on exposure to the air they change either by 

 oxidation or evaporation of some natural volatile solvent, 

 like an essential oil. Resins are insoluble in water, soluble 

 as a rule in alcohol and in other organic solvents. They 

 decompose on heating away from the air, and burn with a 

 smoky flame. Their chemical composition is very complex, 

 some of them consisting mostly of esters, others of acids, 

 and still others of uncertain compounds classed under the 

 name of resenes. In addition to being of a complex nature 



