DETECTION AND ESTIMATION OF TANNINS. 41 
gave only 0.036 gramme dry residue, containing 0.008 
gramme ash. 
In order to estimate a sample of tannin extract, from 
12 to 16 grammes of a solid or 22 to 28 grammes of a 
liquid sample were taken, dissolved in distilled water, 
made up to one litre, and filtered ; 100 cc. were evap¬ 
orated to dryness, dried, and weighed, thus giving the 
total amount of soluble matter; 250 cc. of the solution 
were placed in a dry flask with one gramme of hide 
powder and shaken for two hours, then filtered into 
another flask and this treatment with one gramme of 
hide powder twice more repeated, and then a fourth 
time with 2 grammes of hide powder. This quan¬ 
tity (5 grammes) was considered quite sufficient to ex¬ 
tract all tanning material. The solution was then fil¬ 
tered for the fourth time and 100 cc. evaporated and 
dried. The difference between this weight and that 
obtained by the first evaporation indicated the amount 
of tannin. 
Bone tissue as well as hide powder is available for 
this process, which has many points of value, and, if 
the correction for the solubility of the hide powder or 
bone tissue could be accurately made, it would be the 
most satisfactory and exact of the numerous methods 
that have been proposed. In actual practice, however, 
it has been found almost impossible to get a gelatinous 
tissue that is not somewhat soluble in water, which 
solubility should be added to the amount of tannin 
found, but, as most of the soluble portion is capable of 
being precipitated by tannin, it is not proper to add 
the whole amount of tissue which is dissolved by water, 
therefore the correction is an unknown quantity, and, 
4* 
