148 ADULTERATION AND DETECTION. 



deposit at the bottom of the vessel or will be found 

 adhering to its sides if used in large quantities. While 

 Silica is readily recognized by the increased amount of 

 ash insoluble in the water obtained by calcimining a 

 sample of the tea so adulterated, as above described. 



SAND AND MINEEAJL MATTER IN TEAS 



Is frequently introduced into tea with the object of add- 

 ing weight, and is best detected by the " ash-test." As for- 

 merly stated, the leaves of genuine tea, or tea of fair com- 

 mercial value, yield from 5 to 6 per cent, of ash or mineral 

 matter on incineration, 2 per cent, of which is again solu- 

 ble in water. This rate is fairly constant, and ranges from 

 5 in Black teas to 6 per cent, in pure Green, rarely yield- 

 ing as low as 5 in the former and never exceeding 6 in the 

 latter, while many of the teas of commerce are found to 

 yield from 13 to 20 per cent, of ash on incineration. 

 Such teas are unmistakably sophisticated, and will be 

 found, on analysis, to contain sand or other mineral 

 matter in their composition. 



To determine the amount of mineral matter contained 

 in teas so adulterated, proceed as in the case of spurious 

 and spent leaves/which analysis may be again confirmed by 

 a determination of the ratio of soluble to insoluble matter 

 contained in the ash. The result is obtained by boiling 

 the ash in a little water and filtering the precipitate, 

 drying, burning, weighing and subtracting the residue or 

 insoluble matter from the original weight of the ash. By 

 this process both the soluble and insoluble parts are 

 ascertained, and if the sample be pure, but 3 to 3 y 2 per 

 cent, of insoluble will remain, any increase of these 

 figures clearly denoting adulteration to that extent. 



Where the burning of the leaves is inconvenient, the 

 following operation may be substituted : Weigh a sample 



