42 Transactions of the 



The excess of lead is precipitated from the filtrate by hydrogen 

 sulphide (HjS), and the liquid is evaporated to crystallisation, 

 the crude product being purified by sublimation. Theine crystal- 

 lises in long silky needles, which contain one molecule of water. 

 The crystals are soluble in water, alcohol, and ether. When 

 gradually heated, they sublime without decomposition. When 

 acted upon by a nitrate and subsequently by ammonia, theine 

 yields a purple-coloured product, similar to that obtained from 

 an urate. When boiled with potash theine is decomposed with 

 evolution of methylia (CNHs). An ounce of good tea contains 

 about ten grains of theine. 



THE TANNIN, OR TANNIC ACID. 



This has the composition C^yHjoOi,. It can be obtained 

 from a solution of tea by precipitating with sulphate of iron 

 (FeSO,), or a solution of glue or gelatine. Tannin is an uncrys- 

 tallisable mass, soluble in water and alcohol, but insoluble in pure 

 ether. When heated to 215° it yields pyrogallic acid. It forms 

 from 13 to 18 per cent, of the whole weight of the dried tea leaf, 

 and is more completely extracted the longer the tea is infused. 

 Tannic acid, though naturally colourless, has a tendency to become 

 dark-coloured when exposed to the air. This is the reason why 

 the same leaves, when dried quickly, will give a green or natural 

 colour, and when more slowly, a black one. 



THE GLUTEN. 



This is the principal ' flesh-former.' According to the chemical 

 classification of food, the \flesh-formers' in tea average about 

 18 per cent., and the ^heat-producers' 72 per cent. Tea also 

 contains a very small quantity of water and mineral matter. 



Tea is not only adulterated in China for export, but also when 

 it arrives in England. Among black teas adulterated by the 

 Chinese * scented pekoe,' ' scented caper,' and ' black gunpowder ' 

 hold a prominent place, being mixed with an imitation of tea 

 formed of tea dust and fragments of rice, or with glazing sub- 

 stances, such as blacklead, indigo, turmeric, and a powder re- 

 sembling mica. In green teas were detected, by Dr Hassel, 

 Prussian blue, China clay, turmeric, and a white powder variously 

 composed, but usually consisting of kaolin, soap-stone, or calcium 

 sulphate. The colouring of green teas is an operation performed 

 solely for the advantage of Europeans, the Chinese making little 

 difficulty in exhibiting the process. * Tea,' they sometimes say, 

 ' is in our opinion better without Prussian blue and gypsum ; 

 but as foreigners seem to prefer an admixture of those ingredients 

 with their tea, to make it look uniform and pretty, and as the 



