The Brunswick greens are in the front rank of green pigments so far as covering power is concerned, and, when made from reliable materials, are reasonably durable under the influence of air and light, in which respect, however, they vary considerably. They can be used as water colours, but are superior in oil paints. Precautions are necessary in mixing them with other pigments. By the action of sulphuretted hydrogen, or sulphur in any form, the colour is darkened to a notable degree; by the action of acids, the chrome is destroyed and the green becomes blue; by the action of alkalies, both the blue and the yellow constituents are affected, and the green gives place to a reddish hue. The pale and medium shades are yellow greens; the deep and extra deep are blue greens. These colours can be distinguished by heating them with caustic soda, which turns them brownish in tone, owing to the destruction of the Prussian blue. If the residue be filtered, and to the filtrate some acid and ferric chloride be added, a blue precipitate will be obtained, indicative of the presence of Prussian blue. On washing the residue with water and treating with hydrochloric acid, the brown colour disappears, and, in most cases, only a white residue of barytes is left; sometimes the residue may have a faint yellowish colour. The solution in hydrochloric acid will give the characteristic tests for iron. The yellow element can be recognised by boiling in hydrochloric acid, filtering, and allowing the filtrate to cool, when crystals of lead chloride will deposit; these, separated out and dissolved in boiling water, will give the characteristic tests for lead, such as a white precipitate with sulphuric acid, and yellow precipitate with bichromate of potash. The filtrate will have a green colour, indicative of chromium. CHINESE GREEN.--Another name for the vegetable pigment known in China as Lokao (q.v.) CHROME GREEN.--This name is often applied to any green in which chrome enters as an element, but more particularly to the modern Brunswick greens described on pp. 114-118; and to the green which bears the name of its first maker, Guignet, and described under the title of Guignet’s Green, see p. 125. COBALT GREEN.--This remarkably stable, but somewhat costly, pigment is also known by the names of Rinmann green and zinc green, the former after the name of the chemist who first prepared it, and the latter because it contains a large proportion of zinc. It is in fact a combination of the oxides of cobalt and zinc, and was originally produced in the following manner:-½ lb. pure cobalt ore was dissolved in 4 lb. concentrated nitric acid, and added to a solution of 1 lb. zinc in 5 lb. nitric acid; the mixture was diluted with water, and a solution of potash carbonate was added, throwing down a pinkish precipitate, which was washed on a filter, dried, and calcined at a high temperature.