272 TANNINS AND [CH. XII 



till one is found which gives a filtrate quite free from 

 tannin, as shown by ferric chloride, gelatin solution, lead 

 acetate, etc. 



(a) Shaking with acetic ether (ethyl acetate). 

 Add about half the volume of acetic ether and shake 

 thoroughly, allow the layers to separate and draw off the 

 lower layer. To the separated lower layer add again 

 about the same volume of fresh acetic ether and repeat 

 the process. 



Warm the separated lower layer (aqueous solution) 

 on the water-bath till all smell of acetic ether has dis- 

 appeared and test portions of the cold solution for tannin 

 as above. 



If the solution gives no tannin reactions the tannin is 

 completely removed by ethyl acetate, and this method can 

 be applied to the whole of the solution. 



If on the other hand the solution still gives the tannin 

 reactions, probably acetic ether will not remove the whole 

 of the tannin, and it will be better to try some other 

 method, such as (y3) or (7). 



(/3) Shaking with magnesia or lead carbonate. 



Add freshly ignited magnesia or pure lead carbonate 

 (about 4 grs. per 100 c.c. of liquid), shake thoroughly and 

 allow to stand for three or four hours with frequent 

 shaking. Filter and test the filtrate for tannins. This 

 process seldom fails to completely remove tannins from an 

 aqueous solution, but in some cases a considerable quantity 

 of Pb or Mg salts soluble in water may be produced. 



If all the tannins are not removed by this process it is 



