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 in 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 Chinese as “Bastard tea,” and is rarely sold alone, being used principally for mixing or blending with pure teas. The presence of spent or exhausted leaves in either Green or Black tea is best determined by estimating the amount of tannin contained in the liquor after infusion, and for which experiment various tests are in use. A large proportion of the tea-extract is found to consist of tannin (tannic acid), there being much more in Green than in Black tea, the larger portion of that originally existing in the latter being dissipated by the extra fermentation to which this variety is subjected in curing and firing. Green teas contain on an average about 15 per cent. of tannin, Black teas never exceeding 10 per cent. This rate, however, varies considerably from different causes, such as age, quality, soil and climatic condition of the districts of growth, the main average being 12 and 9 per cent. respectively in pure teas. Spent or exhausted leaves, on the other hand, contain only 2 per cent. on an average at the highest estimate, a difference of 7 to 10 per cent. of tannin, as will be observed, in favor of pure teas.