OAK BARK. 181 



lished in England in 1756, and at once opened a 

 wide field to the researches of chemistry. He care- 

 fully analyzed the bark and the skin, both in the raw 

 and the prepared state. The part of the bark which 

 was found efficacious in tanning, he extracted from 

 other extraneous matter, and gave to it the name of 

 tannin, from the use to which it was applied. Previ- 

 ously to this accurate and scientific investigation, this 

 vegetable principle had been confounded with gallic 

 acid, under the name of the astringent principle. 

 Tannin is a brittle substance of a brown colour ; it 

 breaks with a vitreous fracture ; does not attract mois- 

 ture from the air ; and is extremely astringent to the 

 taste. 



The hides of animals, when divested of the hair, 

 epidermis, and any fleshy or fatty parts adhering to 

 them, consist wholly of gelatin, a substance capable 

 of being dissolved in water, and forming with it a 

 jelly which is well known under the name of glue. 

 Tannin is likewise very soluble in water ; but a union 

 of the two forms an insoluble imputreseerit compound, 

 and hence the efficacy of tannin in the preparation of 

 leather. 



Since the discovery of M. Seguin, the first chemists, 

 both on the Continent and in England, have made the 

 art of tanning a matter of scientific inquiry. They 

 speedily discovered that tannin abounds in the vege- 

 table kingdom. 



Sir Humphrey Davy, to whom the science of che- 

 mistry owes so many of its most splendid discoveries, 

 after a careful investigation of the subject, was led to 

 the conclusion, that in " all substances possessed of 

 the astringent taste, there is great reason to suspect the 

 presence of tannin ; it even exists in substances which 

 contain sugar and vegetable acids. I have,'' he adds, 

 " found it in abundance in the juice of sloes; and my 

 friend Mr. Poole, of Stowey, has detected it in port 



