444 COMPOUND PRODUCTS. CHAP. I. 



lation was first pointed out by Bucquet, in 1774, who 

 found them to be resins united to the benzoic acid,* 

 which they yield by means of the action of heat. 

 This latter circumstance is sufficient to entitle them 

 to a separate consideration. They are obtained by 

 means of incisions made in the bark, from which 

 a viscous juice exudes, which is afterwards inspis- 

 sated by the action of the fire or air ; or they are 

 obtained by means of boiling the part that contains 

 them. 



Howob- They are thick and viscid juices,, but become 

 readily concrete. Their colour is brown or red ; 

 their smell aromatic when rubbed ; their taste 

 acrid ; their specific gravity 1 'OQO, 



Properties. They are unalterable in the air after becoming 

 concrete. They are insoluble in water, but boiling 

 water abstracts part of their acid ; they are soluble 

 in the alkalies and nitric acid.-f- When heated, they 

 melt and swell, evolving a white and odorous 

 smoke. 



Species. The principal of the balsams are the following : 

 Benzoin, Storax, Styrax, Balsam of Tolu, Balsam 

 of Peru. 



Benzoin. It was long supposed that this sub- 

 stance was the produce of a species of Laurus ; 

 but it appears, from the observations of Mr. Dry- 

 ander, to be the produce of a species of Styrax, 

 a tree which grows in Sumatra, and is denominated 

 the Styrax benzoin. It flows from incisions made 



* Fourcroy, vol. viii. p. 4-3. 



f Thomson's Chemistry, vol. iv. p. 327- 



