TEA. 151 



(b) DETERMINATION. 



Obtain the value of the potassium permanganate in terms of the oxalic acid. 

 Boil 5 grams of the tea for half an hour with 400 cc of water; cool, transfer 

 to a graduated 500 cc 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 cau- 

 tiously, drop by drop, until the color changes to bright yellow or, further, to a 

 faint pink at the rim. The number of cubic centimeters of permanganate used 

 furnishes the value a of the formula given below. 



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

 of salt acid solution, and 10 grams of kaolin, and shake several minutes in a 

 corked flask. After settling decant through a filter. Mix 25 cc of the filtrate 

 (corresponding to 10 cc of the original infusion) with 25 cc of the indigo solu- 

 tion and about 750 cc of water, and titrate with permanganate as before. The 

 number of cubic centimeters of permanganate used gives the value Z>; a b=c; 

 c equals the amount of permanganate required to oxidize the tannin. Assume 

 that 0.04157 gram of tannin (gallotannic acid) is equivalent to 0.063 gram 

 of oxalic acid. 



