384 ORGANIC CHEMISTRY. 



the other hand, readily soluble in alcohol or ether. 

 They are not liable to decay, like most other substan- 

 ces of vegetable origin. Copal, shellac, mastic, and 

 amber, are all resins. The latter is found in certain 

 coal mines, and at the bottom of the sea, and has 

 probably had its origin in the forests of some primeval 

 age. 



962. EXPLANATION. The action of 



Explain the ~ , ... , 



above trans- the oxygen of the air, m the above case, 

 formation? ^ similar to that which occurs in the con- 

 version of alcohol into vinegar. A portion of the hy- 

 drogen is burned out, as it were, and removed in the 

 form of water, while another portion of oxygen takes 

 its place. 



963. USE OF THE RESIN VARNISHES. 



what use is 



made of the The resins are principally employed for the 

 T arT varnishes production of varnishes. These are simply 

 made? solutions of resins in alcohol, ether, or 



spirits of turpentine ; or an intimate mixture of the 

 latter with fused resin and oil. In preparing copal var- 

 nish, which is the most brilliant and durable, the resin 

 is first fused, then incorporated with heated oil, and 

 afterward diluted with spirits of turpentine. A com- 

 mon varnish for maps, engravings, and similar objects, 

 is made by dissolving mastic with a little Venice tur- 

 pentine and camphor, in spirits of turpentine. Pounded 

 glass is added to the pulverized material during the 

 process of solution. The object is covered with a so- 

 lution of isinglass before using this varnish, to prevent 

 its absorption. Shellac, in alcohol, is employed to 

 impart to wood or other material a resinous coating^ 



