METHODS OF DETERMINING ADULTERANTS. 891 



approximately 750 << distilled water. The permanganate solution is now added, a 

 onbic centimeter at a time, the liqaid being vigorously stirred after each addition, 

 until the color changes to a light green; the addition of permanganate is continued 

 more slowly, drop by drop, until the whole liquid takes on a bright golden-yellow 

 color (Councler and Schi'oeder), or, if preferred, until the pure yellow liquid shows a 

 faint pinkish rim (Procter). The burette reading is now taken, and furnishes the 

 value (a) of the formula. It is absolutely necessary to vigorously stir the liquid 

 during the whole operation. It is best to repeat this titration, as well as that 

 which follows in the next step of the analysis, and take a mean of several readings. 

 (/>) 100 cc of the tea-infusion (filtered if not sufficiently clear after decantation) are 

 mixed with 50 cc of the gelatine solution in an Erlenmeyer flask, then 100 cc of 

 the salt-acid solution and 10 grams of kaolin are added, and the whole vigorously 

 shaken in the Avell-corked flask. Several minutes' shaking is necessary. If these 

 directions are carefully followed the precipitate will settle very rapidly, leaving a 

 clear, supernateut liquid which filters with great case. The use of kaolin, as recom- 

 mended by Procter, is an important modification of the original method, without 

 which it is often impossible to separate the precipitate. The whole liquid is filtered 

 and 25 cc of the filtrate (=10 cc of the original infusion) are mixed with 25 cc 

 of indigo-carmine solution and about 750 cc water, and a titration made as under (a). 

 The burette reading gives the value b of the formula. 



The value a is the amount of permanganate solution necessary to oxidize all oxidi- 

 zable substances present; b, the amount required to oxidize the substances other 

 than tannin; hence a 1) = c = permanganate solution required by the tannin. Ac- 

 cording to Xeubauer, .04157 grams of gallo-taunic acid is equivalent to .063 grams 

 oxalic acid; therefore, knowing the amount of oxalic acid equivalent to the perman- 

 ganate required to oxidize the tannin, we can easily calculate the amount of this 

 latter substance present. 



The above method for tannin was selected after experiments with several other 

 methods. The general advocacy of its use by a number of very able analysts and 

 the satisfactory results obtained in this Department led to its adoption for this work. 

 Unfortunately, owing to the great variations in the results obtained by different 

 methods and the acknowledged inaccuracy of many of these methods, the A-alue of 

 a large number of tannin determinations, by various authorities, is doubtful. For 

 work of this kind the method of analysis should be clearly stated, and as far as pos- 

 sible, for the sake of uniformity, analysts should all adopt the same method in order 

 that their work may be comparable with that of others. 



Waler. The moisture may be determined in the usual manner by drying 1 or 2 

 grams of the powdered tea three hours at 100 C. in a flat dish, and calculating the 

 water from the loss in weight. This method probably entails a slight loss of theine, 

 which is credited to the moisture, but the error is very small and is negligeable. 



Ash, total. Two grams of the powdered tea are incinerated, at as low a temperature 

 as practicable, and the percentage calculated as usual. 



Ash, soluble and insoluble. The total ash is treated on a filter with hot water until 

 all the soluble matter is dissolved; the solution is evaporated to dryness, and the 

 residue ignited at a moderate temperature. The per cent soluble ash is calculated 

 from the weight of this residue; the insoluble ash is determined by difference. 



Ash insoluble in acid. The water insoluble residue from the soluble ash determina- 

 tion is treated with hydrochloric; acid. The undissolved portion is washed with 

 water, dried and weighed, and its percentage calculated. 



Ash, alkalinity. The soluble matter obtained in determining the soluble ash is dis- 

 solved in a little water and titrated with A acid. The alkalinity is calculated as 



potassic oxide (K 2 O.). 



Extract, total, and insoluble leaf. Two grams of finely powdered tea are successively 

 extracted with seven portions of 50 cc each of boiling water. The extract is 



