METHODS OF DETERMINING ADULTERANTS 889 



Analyses of first-crop China lean of the ncason of 1800 Continued. 



* Total amount of theine, tannin, and products <>f fermentation is represented by A for brevity. 

 ANALYTICAL METHODS. 



In the following' paragraphs are presented the methods adopted for 

 the estimation of the various constituents of teas. 



Caffeine or theine, C 8 H| N 4 O2. After experiments with a number of methods for 

 the estimation of caffeine, the following was adopted on account of its simplicity and 

 the accuracy of the results : 



'Transfer 3 gs of powered tea into a 300 cc flask, add about 250 cc of water; heat 

 gradually to the boiling point, using a small fragment of tallow to prevent frothing; 

 boil gently 30 minutes, washing down any particles of tea which may collect on the 

 flask above the liquid. After the liquid begins to boil the flask should be filled al- 

 most to the neck and water should bo occasionally added to keep its level at this 

 point. Several samples may easily be extracted in this way at the same time, since 

 they require but little attention after regulating the flame of the lamp. After boil- 

 ing 30 minutes, cool, add a strong solution of basic acetate of lead in sufficient quan- 

 tity for the removal of precipitable substances; usually about 3 cc are required; com- 

 plete the volume to 300 cc, mix thoroughly, and filter, rejecting the precipitate un- 

 washed. Treat 50 cc of the filtrate with H 2 S for the removal of the lead ; boil off the 

 excess of HjS ; filter into a separately funnel, washing the precipitate with hot water, 

 or an aliquot part of the filtrate may be taken and washing of the precipitate may 

 thus be avoided. The error from the volume of the precipitate is very slight. 



Extract the water solution in the separatory funnel seven times with chloroform; 

 collect the chloroform solution of caffeine in a small tared flask, and remove the 

 solvent by distillation; dry the caffeine at 75 C. two hours, weigh, and calculate 

 the percentage. 



Jour. nnal. Chem. 4, 4, p. 390. 



