SECT. IX. TANNIN. 411 



even by a solution of common salt. A seventh is 

 obtained from the common Kino of the shops, 

 which is an extract from the Cocoloba urifcra. Its 

 solution throws down gelatine of a rose colour, and 

 forms with salt of iron a deep green precipitate. 



Tannin may be obtained from a great variety of Plants 

 other vegetables also, as well as those already enu- ? nt 

 merated, but chiefly from their bark ; and of barks, 

 chiefly from those that are astringent to the taste. 

 The following table exhibits a general view of the 

 relative value of different species of barks, as ascer- 

 tained by Sir Humphry Davy.* It gives the 

 average obtained from 480lb. of the entire bark 

 of a middle-sized tree of the several different spe- 

 cies, taken in the spring, when the quantity of 

 tannin is the largest. 



Ib. lb. 



Oak 29 Sycamore 11 



Spanish Chesnut 21 Lombardy Poplar 15 



Leicester Willow (large) 33 Birch 8 



Elm 13 Hazel U 



Common Willow (large) 11 Black Thorn I (f 



Ash 16 Coppice Oak 32 



Beech 10 Inner rind of Oak bark 72 



Horse Chesnut 9 Oak cut in autumn 21 



Tannin, which is /regarded by chemists as being Uses, 

 the general principle of astringency, has been 

 found to be of the very first utility in its applica- 

 tion to medicine. The medical virtues of Peruvian 



* Elern. of Agri. Chem. p. 79. 



