METHODS OF DETERMINING ADULTERANTS. 891 
approximately 750 ce distilled water. The permanganate solution is now added, a 
eubic centimeter at a time, the liquid being vigorously stirred after each addition, 
until the color changes to a light green; the addition of permanganate is continued 
more slowly, drop by drop, until the whole liquid takes on a bright golden-yellow 
color (Councler and Schroeder), or, if preferred, until the pure yellow liquid shows a 
faint pinkish rim (Procter). The burette reading is now taken, and furnishes the 
value (a) of the formula. It is absolutely necessary to vigorously stir the liquid 
during the whole operation. It is best to repeat this titration, as well as that 
which follows inthe next step of the analysis, and take a mean of several readings. 
(b) 100 ce of the tea-infusion (filtered if not sufficiently clear after decantation) are 
mixed with 50 ce of the gelatine solution in an Erlenmeyer flask, then 100 ce of 
the salt-acid solution and 10 grams of kaolin are added, and the whole vigorously 
shaken in the well-corked flask. Several minutes’ shaking is necessary. If these 
directions are carefully followed the precipitate will settle very rapidly, leaving a 
clear, supernatent liquid which filters with great ease. The use of kaolin, as recom- 
mended by Procter, is an important modification of the original method, without 
which it is often impossible to separate the precipitate. The whole liquid is filtered 
and 25 ce of the filtrate (—10 ce of the original infusion) are mixed with 25 ce 
of indigo-carmine solution and about 750 ce water, and a titration made as under (a). 
The burette reading gives the value b of the formula. 
The value a is the amount of permanganate solution necessary to oxidize all oxidi- 
zable substances present; b, the amount required to oxidize the substances other 
than tannin; hence a— b—c — permanganate solution required by the tannin. Ac- 
cording to Neubauer, .04157 grams of gallo-tannic acid is equivalent to .063 grams 
oxalic acid; therefore, knowing the amount of oxalic acid equivalent to the perman- 
ganate required to oxidize the tannin, we can easily caleulate the amount of this 
latter substance present. 
The above method for tannin was selected after experiments with several other 
methods. The general advocacy of its use by a number of very able analysts and 
the satisfactory results obtained in this Department led to its adoption for this work. 
Unfortunately, owing to the great variations in the results obtained by different 
methods and the acknowledged inaccuracy of many of these methods, the value of 
a large number of tannin determinations, by various authorities, is doubtful. For 
work of this kind the method of analysis should be clearly stated, and as far as pos- 
sible, for the sake of uniformity, analysts should all adopt the same method in order 
that their work may be comparable with that of others. 
Water.—The moisture may be determined in the usual manner by drying 1 or 2 
grams of the powdered tea three hours at 100° C. in a flat dish, and calculating the 
water from the loss in weight. This method probably entails a slight loss of theine, 
which is credited to the moisture, but the error is very small and is negligeable. 
_ Ash, total—Two grams of the powdered tea are incinerated, at as low a temperature 
as practicable, and the percentage calculated as usual. 
Ash, soluble and insoluble.—The total ash is treated on a filter with hot water until 
all the soluble matter is dissolved; the solution is evaporated to dryness, and the 
residue ignited at a moderate temperature. The per cent soluble ash is caleulated 
from the weight of this residue; the insoluble ash is determined by ditference. 
Ash insoluble in acid.—The water insoluble residue from the soluble ash determina- 
tion is treated with hydrochloric acid. The undissolved portion is washed with 
water, dried and weighed, and its percentage calculated. 
Ash, alkalinity.—The soluble matter obtained in determining the soluble ash is dis- 
solved in a little water and titrated with = acid. The alkalinity is caleulated as 
potassic oxide (K20.). 
Extract, total, and insoluble leaf.—Two grams of finely powdered tea are successively 
extracted with seven portions of 50 ce each of boiling water. The extract is 
