890 FOODS AND FOOD ADULTERANTS. 
Nitrogen.—Tea contains a very high proportion of nitrogen. The analyses of Mr. 
Kozai, tabulated on page 879, will show how this nitrogen is distributed in the pre- 
pared leaf. 
The nitrogen of teas should be determined by the absolute method, or Kjeldaht 
method, modified for alkaloids. These methods are fully described in the text-books 
on quantitative analysis, and in Bulletin 24, page 217, of the Chemical Division of 
this Department. 
Albuminoid nitrogen.—Stutzer’s' method.—Prepare cupric hydrate as follows: Dis- 
solve 100 grams of pure cupric sulphate in 5 liters of water, and add 2.5 cubie centi- 
meters of glycerin; add dilute solution of sodium hydrate until the liquid is alka- 
line; filter; rub the precipitate up with water containing 5 cubic centimeters of 
glycerin per liter, and then wash by decantation or filtration until the washings 
are no longer alkaline. Rub the precipitate up again in a mortar with water con- 
taining 10 per cent of glycerin, thus preparing a uniform gelatinous mass that can 
be measured out with a pipette. Determine the quantity of cupric hydrate per 
cubic centimeter of this mixture. To 1 gram of this substance add 100 cubic centi- 
meters of water in a beaker; heat to boiling, or, in the case of substances rich in 
starch, heat on the wer bath ten minutes; add a quantity of cupric hydrate mixture 
containing 0.7 to 0.8 grams of the iydrate; stir thoroughly; filter when cold; wash 
with cold water, and put the filter and its contents into the concentrated sulphuric 
acid for the determination of nitrogen after Kjeldahl. For the above filtration use 
Schleicher and Schiill’s No. 589 paper, or Swedish paper, either of which contains 
so little nitrogen that it can be left out of account. 
Tannin.—Lowenthal’s® method as improved by Councler and Shroeder, and Procter.—In 
the estimation of tannin by this method the following standard solutions and re- 
agents are required: 
(1) Potassium permanganate solution containing, approximately, 1.33 grams of the 
salt per liter. 
“N- 
(2) Tenth-normal aay oxalic acid solution, for use in standardizing the perman- 
ganate solution. 
(3) Indigo-carmine solution, containing 6 grams of this indicator and 50 ce concen- 
trated sulphuric acid per liter. 
(4) Gelatin solution, prepared by swelling 25 grams of gelatin for one hour in a 
saturated solution of common salt, then heating until the solution is complete, and 
finally, after cooling, making up to one liter (W. H. Krug’s method of preparing this 
solution). 
(5) Salt-acid solution, prepared by mixing 975 ce saturated common salt solution 
and 25 ec concentrated sulphurie acid. 
(6) Powdered kaolin. 
The potassium permanganate solution is standardized in the usual manner by ox- 
alic acid. It is obvious, in the analytical manipulations which follow, that the end 
reaction (golden yellow or pink tinge) which is adopted in the first process must also 
be employed in the second. The indigo-carmine should be very pure and especially 
free from indigo-blue. 
(a) Five grams of finely powdered tea are placed in a flask of approximately 500 ce 
capacity and boiled thirty minutes with 400 ce distilled water. The watershould be 
cold when added to the sample. After the completion of the boiling, the flask is 
cooled and the solution and residue are transferred to a half-liter flask and the vol- 
ume made up to 500 ce. The solution required for analysis is filtered off if neces- 
sary. To10 cc of the tea infusion, 25 ce indigo-carmine solution are added, and 
’ Bulletin 31, Div. Chem., U. S. Dept. Agric., p. 189. 
* Councler and Schroeder, Ztsch. anal. Chem. 25,121. Procter, Journ. Soc. Chem. 
JS PRE JAtoe 
