RESINS. 905 



C 20 H 15 4- H, which, like the hydruret of acetyl in olefiant gas is ca- 

 pable of combining directly with hydrochloric acid, and forming 

 a double hydruret, C 20 H 15 + HC1, or artificial camphor. The 

 same hydruret is converted into the resin of turpentine by the 

 oxidation and replacement of its atom of hydrogen by an 

 atom of oxygen, making C 20 H 15 + O, and the absorption of an ad- 

 ditional atom of oxygen by this compound, making C^H^Og. 



Every natural resin is a mixture of several resins, quite as 

 the essential oils are mixtures. They are separated from each 

 other by their unequal solubility in hot or cold alcohol, in 

 ether, in potash and carbonate of potash, or the different solu- 

 bilities of their compounds with metallic oxides in these and 

 other menstrua. M. Unverdorben, who first threw light on the 

 composition of the natural resins, separated from some, five and 

 more resins, all quite distinct substances. They are heavier 

 than water, and become negatively electrical when rubbed. 

 Some of them which are slightly soluble in water, have a bitter 

 taste, but most of them are quite insoluble in water, and taste- 

 less. They are fusible by a temperature above 212, and are 

 decomposed by a strong heat. Many resins, when dissolved, 

 redden litmus, combine with bases and possess all the cha- 

 racters of acids ; some even decompose alkaline carbonates. 

 Others are neutral, and do not combine with bases. A large 

 number of the resins have been examined and analysed by Pro- 

 fessor Johnston, to whose memoirs on the resins contained in 

 the late volumes of the Philosophical Transactions, I must refer 

 for information respecting individual resins. 



N 



Amber is found in beds of wood-coal, and appears to be 

 altered resin of the trees. It is a brittle, hard substance, usu- 

 ally nearly transparent, sometimes almost colourless, but com- 

 monly yellow or even deep brown, and often includes insects. 

 Its density is 1.065. Amber is insoluble in water, alcohol dis- 

 solves about one-eighth of it, refusing to dissolve the rest. Al- 

 kalies also act only partially on amber. About 1 per cent of 

 amber is insoluble in ether; what remains dissolves in oil of 

 turpentine and naphtha. Amber thus appears to be a mixture 

 of resins and a bitumen. It contains also succinic acid, which 

 is obtained from it by dry distillation. 



