ELLAGIC ACID 205 



this reason it was regarded by Schiff* as being identical 

 with natural gallotannic acid. This view was first shown by 

 Walden f to be untenable, since the physical properties of the 

 two substances are quite different, and the position was sub- 

 sequently cleared up by the synthetic work of Fischer (see 

 p. 213). 



Reactions. 



1. Gallic acid is precipitated from solution by lead acetate ; 

 on adding, caustic potash a carmine-coloured precipitate is 

 formed, which dissolves in excess to a raspberry-red solution. 



2. Ferric chloride produces a blue-black colour or pre- 

 cipitate according to the strength of the solution ; excess of 

 ferric salt changes the colour to green, while excess of gallic 

 acid reduces the ferric salt to ferrous and destroys the colour. 



3. Iodine solution produces a transient red colour. 



4. Gallic acid does not precipitate gelatine from solution. 

 (Distinction from tannic acid.) 



5. When heated with concentrated sulphuric acid it turns 

 green and then purple, being converted into rufigallic acid, 

 C 14 H 8 O 8 , a substance used in dyeing. 



6. Potassium cyanide gives a pink colour which disappears 

 on standing, but returns again on shaking with air. 



7. Lime water gives a blue coloration or precipitate ; in 

 very dilute solutions a reddish colour is produced. 



ELLAGIC ACID. C 14 H 6 O 8 . 



Closely related to gallic acid is the substance known as 

 Ellagic acid, its name being obtained by the inversion of the 

 word gallic. 



Its constitution is, according to Graebe, best represented 

 by the formula 



/ C \ OH 



H0 



. CO/ 



* Schiff: " Ber. deut. chem. Gesells.," 1871, 4, 232, 967; 1879, 12, 33; 

 "Annalen," 1873, 170, 143. 



+ Walden: " Ber. deut. chem. Gesells.," 1897, 30, 3153; 1898, 31, 3167. 



