In the microscopic examination of tea, the sample should be moistened with hot water and spread out on a glass plate, and then submitted to a careful inspection, especial attention being directed to the general outline of the leaf and its serrations and venations. The presence of exhausted tea-leaves may often be detected by their soft texture and generally disintegrated appearance. If a considerable quantity of the tea be placed in a long glass cylinder and agitated with cold water, the colouring and other abnormal substances frequently become detached, and either rise to the surface of the liquid as a sort of scum, or fall to the bottom as a sediment. In this way Prussian blue, indigo, soapstone, gypsum, sand, and turmeric can often be separated, and subsequently recognised by their characteristic appearance under the microscope. The separated substances should also be subjected to a chemical examination. Prussian blue is detected by heating with a solution of sodium hydroxide, filtering, acidulating the filtrate with acetic acid, and then adding ferric chloride, when, in its presence, a blue colour will be produced. Indigo is best recognised by the microscopic examination. It is not decolorised by caustic alkali, but it dissolves in sulphuric acid to a blue liquid. Soapstone, gypsum, sand, and metallic iron, are identified by means of the usual chemical reactions. A compound very aptly termed “Lie-tea,” is sometimes met with. It forms little pellets, consisting of tea-dust mixed with foreign leaves, sand, etc., and held together by means of gum or starch. This falls to powder if treated with boiling water. In the presence of catechu, the tea infusion usually assumes a muddy appearance upon standing. In case iron salts have been employed to deepen the colour of the infusion, they can be detected by treating the ground tea-leaves with acetic acid, and testing the filtered solution with potassium ferrocyanide. Tea should not turn black upon immersion in hydrosulphuric acid water, nor should it impart a blue colour to ammonia water. The infusion should be amber-coloured, and not become reddened by the addition of an acid.