142 



CUPULIPER^E 



CONSTITUENTS. Tannin 65 to 77 per cent. (Acidum Tannicum, gallotan- 

 nic acid 105 a), chemically known as digallic acid, CuHioOg. It is a 

 yellowish-white amorphous substance, insoluble in absolute 'ether, 

 chloroform, benzol, benzin, and carbon disulphide, soluble in glycerine, 

 alcohol, and water ; precipitated blue-black by ferric salts, and white by 



*FiG. 59. Quercus lusitanica Branch and nutgall. 



gelatin. It appears to exist, in part at least, as a glucoside and digallic 

 acid. Digallic acid may be considered as an anhydride of gallic acid, 

 CyHeOe, formed from two molecules of the latter by elimination of one 

 molecule of water. Gallic acid also exists in galls. It is precipitated 

 blue-black by ferric salts, ; the color disappearing on boiling, and is 

 not affected by gelatin when gum is absent. 



