890 FOODS AND FOOD ADULTERANTS. 



Nitrogen. Tea contains a very liigli proportion of nitrogen. The analyses of Mr. 

 Ko/ai, 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. Stuizer'* 1 method. Prepare cupric hydrate as follows: Dis- 

 solve 100 grams of pure cupric sulphate in 5 liters of water, and add 2.5 cubic 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 Avash by decantatiou 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 water bath ten minutes ; add a quantity of cupric hydrate mixture 

 containing 0.7 to 0.8 grams of the 'lydrate; 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. 



Tuinrin. Liitrenthfil'*- method an improved 1>y 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. 



(2) Tenth-normal ( ~ ) oxalic, acid solution, for use in standardizing the perman- 

 ganate solution. 



(3) Indigo-carmine solution, containing fi grams of this indicator and 50 cc 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 cc saturated common salt solution 

 and 25 cc concentrated sulphuric 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 cc 

 capacity and boiled thirty minutes with 4<K) cc distilled water. The water should 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 cc. The solution required for analysis is tillered on" if neces- 

 sary. To 10 cc of the tea infusion, 25 cc indigo-carmine solution are added, and 



1 Bulletin 31, Div. Chem., U. S. Dept. Agric., p. 189. 



" Counclrr and Sell roe, I cr, /tscli. anal. ('hem. 25, 121. Procter, .lourn. Sue. ('hem. 

 !'!., 3, 82. 



