428 TANNIC ACIDS. 



JRatanhia-tannic acid, in ratanhia-root, filix-tannic 

 acid, in fern-root, and tormentill-tannic acid, in tormen- 

 till-root, conduct themselves very similarly to quino- 

 tannic acid and oak-bark-tannic acid. When boiled 

 with dilute acids they are all resolved into sugar and 

 reddish-brown bodies, which possess the greatest simi- 

 larity with oak-red and quino-red; and when fused 

 with potassa they yield phloroglucin and protocate- 

 chuic acid. 



Caffetannic acid, C 15 H 18 8 (?). In coffee. Coffee 

 is boiled with alcohol ; the acid precipitated by means 

 of lead acetate; and the precipitate decomposed by 

 sulphuretted hydrogen. Gummy mass; easily soluble 

 in water; colors ferric salts green. With ammonia 

 it becomes rapidly green in the air. Subjected to 

 dry distillation, it yields pyrocatechin (p. 305) ; when 

 fused with potassa, protocatechuic acid. Heated with 

 potassa-ley, it is decomposed, forming an uncrystalline 

 sugar and caffeic acid (p. 378). 



