336 METHODS OF ANALYSIS [Chap. 



11 PROTEIN. -TENTATIVE. 



Determine nitrogen as directed under I, 18, 21 or 23. Subtract the percentage 

 of nitrogen present as caffein from the percentage of total nitrogen to obtain the 

 percentage of nitrogen present as protein. Multiply this result by 6.25 to obtain 

 the percentage of protein. 



12 CRUDE FIBER.— TENTATIVE. 

 Proceed as directed under VIII, 68. 



13 VOLATILE OIL.— TENTATIVE. 



Add 100 grams of tea to 800 cc. of water, distil, extract the distillate several times 

 with petroleum ether, transfer the combined petroleum ether extracts to a tared 

 dish, evaporate at room temperature, dry in a desiccator and weigh. 



CAFFEIN. 



14 Modified Stahlschmidt Method. — Tentative. 

 Proceed as directed under XXVI, 15. 



Proctor Modification of the Lowenthal Method^. — Tentative. 



1 5 REAGENTS . 



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

 per liter and obtain its equivalent in terms of N/10 oxalic acid. 



(b) N/IO oxalic acid. 



(C) Indigo carmine solution. — Make up a solution containing 6 grams of indigo 

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



(d) Gelatin solution. — Soak 25 grams of gelatin for an hour in saturated sodium 

 chlorid solution, heat until the gelatin is dissolved and make up to 1 liter after 

 cooling. 



(e) Acid sodium chlorid solution. — ^Acidify 975 cc. of saturated sodium chlorid solu- 

 tion with 25 cc. of concentrated sulphuric acid. 



(f ) Powdered kaolin. 



DETERMINATION. 



16 



Boil 5 grams of the tea for 30 minutes with 400 cc. of water; cool, transfer to a 

 500 cc. graduated flask and make up to the mark. To 10 cc. of the infusion, filtered 

 if not clear, add 25 cc. of the indigo carmine solution and about 750 cc. of water. 

 Add from a burette the potassium permanganate solution, a little at a time while 

 stirring, until the color becomes light green, then drop by drop, until the color 

 changes to bright yellow or to a faint pink at the rim. Designate the number of 

 cc. of permanganate used as "a". 



Mix 100 cc. of the clear infusion of tea with 50 cc. of the gelatin solution, 100 cc. 

 of the acid sodium chlorid solution and 10 grams of the powdered kaolin, and shake 

 several minutes in a stoppered flask. After settling decant through a filter. Mix 

 25 cc. of the filtrate with 25 cc. of the indigo carmine solution and about 750 cc. of 

 water and titrate with permanganate as before. The number of cc. of permanganate 

 used subtracted from that obtained above, "a", gives the amount of permanganate 

 required to oxidize the tannin. One cc. of N/10 oxalic acid is equivalent approxi- 

 mately to 0.004157 gram of tannin (gallotannic acid). 



