ELLAGITANNIC ACID 293 



of pyrogallol tannins. The quantity of this substance present 

 in different plants varies considerably ; it is greatest in divi- 

 divi. Amongst the other tannins giving ellagic acid bloom 

 may be mentioned algarobilla, myrobalans, chestnut tannin, 

 pomegranate tannin, valonia, etc. 



Ellagitannic acid, unlike ellagic acid (p. 285), is soluble 

 in water or alcohol ; prolonged boihng with water converts it 

 into ellagic acid. It has been variously described by different 

 authors as a glucoside, as a hydrated soluble form of ellagic 

 acid, or as a condensation product of ellagic acid with gallic 

 acid.* 



TANNINS AS GLUCOSIDES. 



Although many of the tannins are substances of a gluco- 

 sidic nature and occur in the plant in combination with a 

 carbohydrate complex such as glucose (e.g. gallotannic acid, 

 p. 288) this has not as yet been established in all cases. 



To determine whether a tannin is a glucoside or not the 

 following procedure is recommended by Procter, f 



The tannin must first be carefully purified from glucose, 

 gums, or other bodies likely to interfere. This may be done 

 by extracting according to Pelouze's method (p. 289), or, if 

 the tannin is to be extracted from an aqueous solution, by 

 agitating with ether to remove gallic acid and then saturating 

 the aqueous solution with common salt and shaking with ethyl 

 acetate, which extracts the tannin. The ethyl acetate is then 

 evaporated o&, the last traces being expelled by the repeated 

 addition of small quantities of ether. 



Another method is to extract with alcohol and to evapo- 

 rate off the alcohol at as low a temperature as possible, and 

 then to take up the residue with a large volume of water 

 whereby the phlobaphenes (see p. 297) are precipitated and 

 may be filtered off. The infusion is then precipitated with 

 successive small quantities of lead acetate ; the first and last 

 portions are rejected and the middle fraction after washing is 



* Cf. Nierenstein : " Ber. deut. chem. Gesells.," 1907, 40, 4575 ; 1909. 

 42» 353 ; 1910, 43, 1257. 



t Procter : " Leather Industries Laboratory Book," London, 2nd ed., 

 1908. 



