CELL-CONTENTS AND FORMS OF CELLS. 203 



hydrolysis with acids. Both of these groups may be subdivided 

 into two classes, namely, (A) those which probably are deriva- 

 tives of protocatechuic acid and {B) those which are derivatives 

 of gallic acid. A class name has been given to include these 

 subgroups, namely, " tannides " or " tannoids." The first sub- 

 group (A) would then include the protocatechuic-tannides or 

 -tannoids, and the second (B) would comprise the gallic-tannides 

 or -tannoids. In working out a system of classification of this 

 kind Kunz-Krause {Sivhciz. WocJi. /. Chem. ti. Pharm., 1898, p. 

 424) has arranged all of the possible tannides or tannoids and 

 has given the formulae for a number which have not yet been 

 found in nature. 



Chemical Properties of Tannins. — The tannins are amor- 

 phous substances and do not form crystalline salts. They are 

 soluble in water, alcohol, ethyl acetate, or a mixture of alcohol 

 and ether. They are almost insoluble in anhydrous ether, chloro- 

 form, and the other immiscible solvents. The solutions give dis- 

 tinct color reactions or precipitates with ferric chloride, stannous 

 chloride, and acetates of copper and lead. They form soluble 

 compounds with iodine and prevent the latter from giving the 

 characteristic blue reaction with starch. Solutions of tannin 

 give insoluble precipitates with cinchonine and other organic 

 bases. Tannins are, furthermore, especially in alkaline solutions, 

 powerful reducing agents, their resulting products being of a 

 dark red or yellowish-red color. 



Upon treatment of tannins with dilute acids, or fusing with 

 the alkali hydroxides, or heating alone, several classes of products 

 are formed. 



I. When heated in a sealed tube at 100° C. solutions of tannin 

 in a I per cent, solution of hydrochloric acid yield either crystal- 

 lizable acids, or phlobaphenes, or insoluble red substances. (A ) 

 The following glucosidal tannins yield crystallizable acids : The 

 tannin from nut-galls, divi-divi (fruit of Cccsalpinia coriaria), 

 myrobalans (fruit of Terminalia Chebiila), rind of pomegranate 

 fruit, and coffee. (B) Phlobaphene is a reddish, or brownish-red, 

 amorphous substance formed from the tannin of willow bark. It 

 is insoluble in water but soluble in alcohol, dilute solutions of 

 the alkalies and alkali carbonates, and solutions of borax. (C) 



