152 ADULTERATION AND DETECTION. 



These results being arrived at by the employment of a 

 valid but rather inconvenient method of weighing out ten 

 grams of tea-leaves and boiling them with water as long 

 as anything is dissolved out of them, and afterwards dry- 

 ing up the exhausted leaves, first at a low temperature 

 and then at a higher one, finally weighing the exhausted 

 leaves. The loss in weight is the weight of the tea- 

 extract, care being taken to weigh the original tea and 

 the exhausted tea-leaves in the same state of dry ness. 

 The results, as will be observed, are stated both in the 

 dried tea and in the tea in its ordinary commercial con- 

 dition. But, instead of weighing the tea-leaves before 

 and after extraction and taking the difference in weight 

 as the weight of the extract there is a more convenient 

 process that of evaporating down the extract itself to 

 dryness and weighing it. The drying up of the exhausted 

 leaves and the getting them into the same hygroscopic 

 condition as the original tea presenting considerable prac- 

 tical difficulties. 



The evaporation of the infusion to dryness and the 

 weighing of the dry extract is also a tedious process in 

 its unmodified state. But if a given quantity of tea be 

 boiled with successive portions of water no more tea- 

 extract is yielded than if the same tea be boiled once 

 with a large quantity of water, but whether the infusion 

 is kept for a length of time just at the boiling-point or 

 whether it be made to boil vigorously makes some differ- 

 ence in the result, brisk-boiling extracting about one- 

 tenth more than slow boiling, so that if the boiling be 

 very vigorous half an hour's boiling is just as effective as 

 an hour's slow boiling. 



Founded on these observations an assay of the tea-ex- 

 tract may be made by the following simple process : Put 

 ten grams of tea into a pint flask and pour on about 



