DOUGLAS GREEN.--This pigment, which is fairly permanent, and possessed of considerable covering power, owes its name to the chemist who proposes its use, and its colour to the oxide of chromium. The method by which it is prepared is as follows:--Solutions of barium chloride and potassium chromate are mixed together. To the barium chromate thus produced is added one-fifth of its weight of concentrated sulphuric acid, whereby partial decomposition is brought about, resulting in a mixture of barium chromate, barium sulphate, and chromic acid. This mixture is dried, and calcined in a crucible at bright red heat, the effect of which is that the chromic acid is converted into green oxide of chromium, and, being scattered throughout the mass, imbues it with a green colour. EMERALD GREEN.--This is quite an old-fashioned pigment, having been in use some 80 years. It is a combination of acetate and arsenite of copper, and varies in tint from a dark to a pale green, always with a bluish cast. It possesses good covering power, and can be used either as an oil-or as a water-colour, but particularly as the latter, and is much used in paper staining. In composition it varies considerably, as there are some half-dozen industrial methods of making it; but in general terms it usually contains over 50 per cent. of arsenious acid, and about 30 per cent. of oxide of copper, together with various impurities. Following are some of the processes by which it is manufactured. (1) According to the method introduced by Liebig, 1 part of verdigris is heated in a copper kettle with sufficient distilled vinegar to effect its solution, and to this is added a solution of 1 part of arsenious acid in water. The result is a precipitate of a dirty green colour, which is dissolved in a new quantity of vinegar and boiled for some time. In this way is obtained a new precipitate, granular and crystalline, and exhibiting a splendid green colour. When this has been filtered off, washed, and drained, it is boiled with one-tenth of its weight of commercial potash, in order to deepen and brighten the colour and destroy the bluish tint. Should the waste liquor obtained after the filtration of the pigment from the second boiling in vinegar contain any remaining copper, arsenious acid is added; and if arsenious acid be present, copper acetate is added; while if acetic acid survives it may be used again for dissolving another lot of verdigris. (2) Form a paste with 1 part verdigris in sufficient boiling water, pass it through, a sieve to remove lumps, and gradually add it to a boiling solution of 1 part arsenious acid in 10 parts water, the mixture being constantly stirred until the precipitate becomes a heavy granular powder, when it is filtered through calico, and dried very carefully.