50 
THE TANNINS. 
squeezed out) for eighteen or twenty hours with frequent 
agitation, filtered, and 10 cc., with 20 cc. of indigo solu¬ 
tion in 750 cc. of water, titrated with the permanganate 
as before. The difference between the amount of per¬ 
manganate in the first and second titrations represents 
the tannin or oxidizable matter removed by hide. The 
“ not tannin,” or oxidizable matter not removed by 
hide, should not much exceed 5 per cent. 
The titration is best carried out in a porcelain dish, 
although a beaker-glass on a white surface may be 
used. 
Having the value of the permanganate in tannin, we 
next take the infusion prepared as previously described 
and carry out the titration Avith permanganate and 
treatment with hide on it, by using 10 cc. of the infu¬ 
sion, 20 cc. of the indigo solution, and 750 cc. of 
water. After obtaining the permanganate value of 
this infusion, 50 cc. more of the latter are agitated for 
from sixteen to eighteen hours Avith 3 grammes of hide 
poAvder as before, and 10 cc. of the filtrate titrated in 
the presence of 20 cc. of the indigo solution and 750 
cc. ot water. From these data it is easy to calculate 
the percentage of tannin in the material from which the 
infusion was made. 
Yon Schroder found by the use of Hammer’s 
method that the pure tannin does not represent the 
full value of the tanning material, and suggested that 
the tannin found be multiplied by 1.05. 
Neubauer used animal charcoal instead of hide 
powder for absorbing the tannin ; it has been found, 
hoAvever, to absorb other substances than tannin in con¬ 
siderable quantity. 
