98 
THE TANNINS. 
by boiling an alcoholic solution of gallic acid and ar¬ 
senic acid, the arsenic to be removed from the filtrate by 
hydrogen sulphide, the solution evaporated to dryness, 
dissolved in a small quantity of alcohol, ether added in 
excess, filtered, and the filtrate evaporated to dryness. 
In a former paper Sell iff supposed he had prepared a 
triacetyl and a tetraacetyl derivative of tannic acid, but 
later investigation convinced him that only the pentace- 
tyl tannin existed, the other compounds being mixtures 
which resulted from the digallic acid containing some 
intermediate products with phosphorus. 
Schiff at first concluded that “ the compound present 
in the plants which yield tannic acid is probably a very 
unstable glucoside of polygallic acid, perhaps of the 
formula indicated by Strecker.” “The least purified 
tannic acid is then the purest, since it contains the 
largest proportion of sugar.” 
Later he made the following statement: “ That the 
glucose present in imperfectly purified natural tannin 
does not exist in the free state is proved by the fact that 
ether-alcohol and anhydrous alcohol dissolve such tan¬ 
nin freely. Unaltered tannin is probably a glucoside 
of digallic acid 
QnH 28 0 22 = C 6 H 12 0 6 + 2C 14 H 10 O 9 - 2H 2 0. 
This formula corresponds with 23 per cent, glucose, 
and the amount of this substance obtained from natural 
tannin varies from nothing to 22 per cent., according to 
the extent to which the tannin has been subjected to 
purification. 
C. Etti in 1884 coincided with SchitFs view of the 
constitution of tannic acid. 
