90* RESINS. 



superfluous edges cut close to the glass by sharp scissors ; the 

 fresh surfaces being then brought into contact and pressed 

 together adhere perfectly. 



Caoutchouc when heated to about 450 enters into fusion and 

 forms a viscid adhesive mass. Distilled at a higher temperature, 

 it yields a fluid product, which is a mixture of several hydro* 

 carbons, differing greatly in volatility, the most volatile boiling 

 at 90 ; and the least volatile at 680. According to Himly, all 

 these volatile oils are of the type C 5 H 4 , but from their exami- 

 nation by Gregory and by Bouchardat, some of them resemble 

 olefiant gas or C 4 H 4 . Caout chine of Himly is of one of these 

 liquids, of which the boiling point was constant at 339. 

 Messrs. Enderby observed that the liquid distilled from 

 caoutchouc is a solvent of that substance. 



RESINS. 



From their endless variety, these bodies form one of the most 

 extensive and indefinite classes of vegetable principles. Like 

 the resin of turpentine, which may be taken to represent them, 

 they flow from the tree dissolved in essential oils, which are 

 removed by distillation with water. In the liquid or soft state, 

 they are named balsams, which are all compounds or mixtures, 

 like turpentine, of resin and essential oil. There is every reason 

 to suppose a close relation in composition between the oil and its 

 associated resin, the last being often obviously the product of the 

 oxidation of the former. The oxidation of the oil may occur 

 by the combination of the entire oil as a radical with oxygen, 

 or by the oxidation of hydrogen, and its removal from the oil 

 in the form of water, and the replacement of the hydrogen lost 

 by oxygen, in equivalent proportions. The point is not decided 

 by the analytical information we at present possess, but M. 

 Liebig adopting the following composition for : 



Oil of turpentine C 40 H 32 or C 20 H 16 

 And for : 



Resin of turpentine C 40 H 30 O 4 or C 20 H 15 O 2 , 



prefers to represent the oil as the hydruret of a radical, or as. 



