VEGETABLE COMPOUNDS. 167 
3. TANNIN. 
620. This is the substance which gives astringent vege- 
table substances their peculiar character. It is obtained 
in great quantities from the Gall-nut, in which it is mixed 
with water, gallic acid, and mucilage. It is obtained also 
from barks ; the barks of the Oak and Horse Chestnut yield 
it abundantly. It may be obtained also from bruised grape- 
seeds. It is soluble in water and in alcohol, but insoluble in 
ether. Catechu, prepared from the wood of the Acacia ca- 
techu, and Kino, from the Eucalyptus resinifera, contain 
large quantities of tannin. It exists in the various kinds of 
tea, and in tormentil root, in considerable quantities. Tan- 
nin is characterised by precipitating solutions of animal 
jellies, and giving a bluish black or green precipitate with 
salts of the peroxide of iron. It has been analyzed by Ber- 
zelius, and found to consist of 
Carbon, 5: 2 =x 
Oxygen, . ° : 45 
Hydrogen, . ; 7 4.45. 
100 parts. 
CHAP. VL_GENERAL VIEW OF THE CHEML 
CAL COMPOSITION OF VEGETABLES. 
621. There are altogether fifteen simple bodies entering 
into the composition of vegetables :— 
Oxygen, These three elements, with a small ade 
Hydrogen, ture of the following nega: make 
Carbon, up the vegetable frame. 
Nitrogen. a. 
Sulphur (usually in combination with oxygen forming. oe 
Sulphurie Acid). > 
horus (in combination with oxygen in the form of 
Phosphoric Acid). 5 Z 
_ Chlorine (forming, wih orien Soe 
