ADULTERATION AND DETECTION. 145 



Peligot has also pointed out that tea leaves differ from 

 other leaves by their extraordinary richness in nitrogen, 

 the prepared leaf being by the process of curing ren- 

 dered still more nitrogenous than the raw or spent leaves, 

 the former averaging, according to his experiments, 6 

 per cent, of nitrogenous matter, and the latter 4.37, so 

 that if the tea-leaf be unique in containing such a high 

 percentage of nitrogen, it is obvious that a determination 

 of nitrogen in tea may also be useful as a method of 

 identification. 



The tea-extract also yields a comparatively large quan- 

 tity of ammonia when it is boiled with potash or perman- 

 ganate of potash, and it is probable that this character- 

 istic may also prove very valuable in the testing of tea. 

 A solution containing about 10 per cent, of solid potash, 

 free from ammonia and nitrogenous matter is required 

 for the purpose, and easily obtained. So that a deficiency 

 of theine, a deficiency of nitrogen, and a deficiency of 

 ammonia are all indicative of the presence of foreign 

 leaves in tea. 



SPENT OR EXHAUSTED LEAVES IN TEA 



Are principally used in the adulteration of Black teas, 

 and is effected by adding or substituting leaves that have 

 been at least once used, and from which all the vital 

 properties have been extracted. The Chinese being 

 inveterate tea-drinkers, large quantities of these leaves 

 are always to be had for the purpose, they are re-dried 

 and subjected to a treatment of gypsum or terra-japonica, 

 in order to make them retain their curl, and then glazed 

 or " faced " with a preparation composed of either 

 graphite or silica to enhance their appearance ir the 

 hand; a decoction obtained from catechu or logwood 

 being next added to impart a tea-like color to the liquor 

 when infused This vile compound is known to the 



