212 TANNINS 



infusion of gall nuts to undergo fermentation, obtained gallic 

 acid. Within recent years this change has been studied anew 

 by Feriibach,* who isolated a tannin splitting enzyme, tannase, 

 from Penicillium, and also by Pottevin,f who isolated a similar 

 enzyme from the mould Aspergillus . 



This change, which may be represented by the equation — 

 C,,H, A + H2O = 2C,H„05 

 may be effected more rapidly by boiling gallotannic acid with 

 dilute sulphuric acid. 



When, therefore, it was found by Schiff:|: that gallic acid 

 could be converted back into the anhydride by means of phos- 

 phorus oxychloride it was assumed that this substance, which 

 was called digallic acid, was identical with " tannin ". This 

 view came to be generally accepted, although objections were 

 raised from time to time on the ground that the physical con- 

 stants, such as electrical conductivity and absorption of light, 

 of natural tannin and synthetic digallic acid were different. § 



The formula which Schiff in 1871 assigned to his synthetic 

 product was as follows : — 



— co.o- 



HOk .OH HOOCL JoH 

 OH 

 but it was not until Dekker |1 pointed out that natural tannic 

 acid was optically active, that real doubt was cast on this 

 formula. Dekker accordingly proposed an alternative formula 

 containing an asymmetric carbon atom as follows : — 



OH OH 

 — C f'^OH 



HO V /'OH CO 



OH 

 Other suggestions were offered by Iljin H and by Nierenstein ** 



*Fernbach: " Compt. rend.," igoo, 131, 1214. 

 t Pottevin : " Compt. rend.," 1900, 131, 1215. 

 + Schiff: " Ber. deut. chem. Gesells.," 1871, 4, 232. 

 §Walden: "Ber. deut. chem. Gesells.," 1897, 30, 3151; 1898, 31, 3167. 

 II Dekker: "Ber. deut. chem. Gesells.," 1906, 39, 2497. 

 IT Iljin: "Journ. Prakt. Chem.," 1900, (2), 82, 422. 



** Nierenstein : "Ber. deut. chem. Gesells.," 1908, 41, 77; 1909, 42, 1122; 

 1910, 43, 628. 



