150 METHODS OF ANALYSIS. 



10. Phosphates. 



Determine P 2 O 6 in the soluble and insoluble ash as directed under " I. Ferti- 

 lizers," page 1. 



11. Petroleum Ether Extract. 

 Proceed as directed under " XXII. Coffee," on page 154, paragraph 22. 



12. Protein. 

 Proceed as directed under " XXII. Coffee," on page 153, paragraph 15. 



13. Crude Fiber. 



Proceed as directed under " VI. General Methods," page 56. 



14. Volatile Oil. 



Distil 100 grams of tea with 800 cc of water, extract the filtrate several 

 times with petroleum ether, evaporate the combined petroleum ether extracts 

 at the room temperature, dry in a desiccator, and weigh. 



15. Caff em (or Thein) Dvorkovitsch Method." 



Digest 10 grams of the powdered tea with 200 cc of boiling water for five 

 minutes and decant the solution; repeat the treatment twice and boil the 

 residue twice with 200 cc of water. Make up the combined solutions to 1,000 cc 

 and extract a portion with petroleum ether to remove the fat, etc. To 600 cc 

 of the fat-free solution (equivalent to 6 grams of tea) add 100 cc of 4 per cent 

 barium hydroxid, mix, and filter. To 583 cc of the filtrate (equivalent to 5 

 grams of tea) add 100 cc of a 20 per cent solution of sodium chlorid, and 

 extract three times with chloroform. Distil the greater part of the chloro- 

 form from the combined extracts, place the residue in a tared dish, evaporate 

 the remainder of the chloroform, dry at 100 C., and weigh. The caffein 

 is usually of sufficient purity to render a nitrogen determination unnecessary. 



16. Tannin Proctor's Modification of LowenthaPs Method. 6 

 (a) PREPARATION OF REAGENTS. 



(1) Potassium permanganate. Make up a solution containing 1.33 grams 

 per liter. 



(2) Tenth-normal oxalic acid. Make up a solution containing 6.3 grams 

 per liter. 



(5) Indigo carmine. Make up a solution containing 6 grams of indigo carmen 

 (free from indigo blue) and 50 cc of concentrated sulphuric acid per liter. 



(4) Gelatin solution. Prepare by soaking 25 grams of gelatin for one hour 

 in a saturated sodium chlorid solution, heat until the gelatin is dissolved, and 

 make up to 1 liter after cooling. 



(5) Mixture. Combine 975 cc of saturated sodium chlorid solution and 25 cc 

 of concentrated sulphuric acid. 



(6) Powdered kaolin. 



Ber. d. chem. Ges., 1891, 24: 1945. 



6 U. S. Dept. Agr., Division of Chemistry, Bui. 13, Part 7, p. 890. 



