68 
THE TANNINS. 
afterwards with more exactness investigated by Seguin. 
Proust endeavored to discover a method of separation.” 
In 1832, Geiger, by a series of investigations on tan¬ 
nin and the action of that substance on iron salts, came 
to the following conclusions : (1) All tannins are iden¬ 
tical, (2) the iron-green tannins become iron-black if 
the free acid present be neutralized by an alkali or by 
iron, and (3) the iron-black tannins by the addition of 
some acid, especially tartaric, become iron-green. Ber¬ 
zelius, however, did not accept this, and he stated in 
his Jahresbericht that he too had noticed this peculiarity 
of the tannins with iron salts under different circum¬ 
stances, but attributed it to a play of colors, since by 
standing a black precipitate separated. 
In Buchner’s Repertorium fur die Pharmacie, 46 , 
316, 1833, we find a review of a prize essay by A. W. 
Buchner on the subject of “ The most Eecent Discov¬ 
eries on lannic Acid or the so-called Tannin (Gerb- 
stoff).” This was written in answer to the following 
questions, offered in 1824 by the Harlem Royal 
Academy of Natural Sciences : 
u Is the so-called tannin, which we extract from dif¬ 
ferent plants, a true principle, or have we given this 
name to different plant principles which possess the 
general properties of astringency and of forming 
leather ? 
• A 
‘‘By what means can we best extract these substances 
from the various plants in a state of purity, and how 
determine that they are unmixed and distinct? 
“ Which is the best and most ready method for pre¬ 
paring tanning materials from the charcoal of indigo 
and other vegetable substances with acid, and how 
