102 PLANT COMPOUNDS 



bark, stem, leaves, flowers, and fruit. They derive their 

 name from the fact that they will tan hides to make leather. 

 They are obtained by extracting the various materials with 

 water and contain in addition to the tannins soluble carbo- 

 hydrates, coloring matter, gums, and other water soluble 

 materials. In fact their value frequently lies partly in the 

 extractive material other than the tannins. 



Chemically they are very complex and not well known. 

 Some of them contain digallic acid (Section 88, e); some 

 contain compounds of gallic acid with dextrose, as glucosides ; 

 while others contain various acids derived from gallic acid 

 or from protocatechuic acid, 



COOH 

 OH 



OH 



Their properties are about the same as those of tannic 

 acid. The property of precipitating gelatine makes them 

 valuable for tanning hides, and that of precipitating metallic 

 salts, for dyeing. Their principal use is in tanning hides, 

 in calico printing, dyeing, and making inks. 



The following are a few of the principal kinds of tannin- 

 containing materials : 



(a) Root of Canaigre, a beet-like plant, growing in south- 

 western United States, and Mexico. It contains 30 per 

 cent, of tannin. 



(b) Wood of Quebracho, a tree from South America, con- 

 taining 24 per cent, of tannin; and of Catechu or Cutch, 

 an Indian tree. 



(c) Wood and bark of Chestnut, containing 8 to 12 per 

 cent, of tannin, and of Hemlock, 10 to 14 per cent, of tannin. 

 Fig. 24 shows hemlock bark and logs being collected for 

 tanning purposes. 



(d) Bark of Oak, containing 5 to 15 per cent, of tannin; 

 and of Mangrove, a West African tree, 9 to 30 per cent, of 

 tannin. 



(e) Leaves of Sumach, containing 15 to 30 per cent, of 

 tannin; and of Gambier, an Indian shrub. 



