=Manufacture of Emerald Green from Verdigris.=—By boiling for several hours, 70 parts of ordinary verdigris are dissolved in water; in a second vessel 100 parts of arsenious acid are dissolved in 1,500 parts of hot water; the verdigris solution is filtered through a cloth into a larger wooden vessel and mixed with two-thirds of the arsenic solution. The mixture is well stirred and allowed to stand for some hours. A precipitate of dull green colour is formed. This consists of copper arsenite. After three to four hours the remaining one-third of the arsenic solution is added; the precipitate then changes into the double salt of which emerald green consists. The use of such dilute solutions as are given in these directions is essential when a product of particularly good colour is required. Emerald green is a crystalline substance which is deeper in colour in proportion to the size of its crystals. Large crystals can only be formed from very dilute solutions; when strong solutions are used, the emerald green has never the deep colour possessed by the product of dilute solutions. In the place of ordinary (basic verdigris) the so-called distilled verdigris (neutral copper acetate) can be used, of which seventy-six parts are required for the quantity of arsenious acid given. The emerald green made from ”distilled” verdigris is of a yet deeper colour than that made from ordinary verdigris, but is considerably dearer. Such emerald green is commercially described, very incorrectly, as distilled emerald green. The method given by Liebig is as follows: 4 parts of basic verdigris and 3 parts of arsenious acid are separately dissolved in boiling vinegar; the liquids are mixed and evaporated until a precipitate of emerald green separates. According to Ehrmann and Kastner, 70 parts of verdigris and 56 to 63 parts of arsenious acid are separately dissolved, the boiling solutions mixed and boiled until the dirty green precipitate changes into a bright green. In consequence of the rapid formation of the precipitate due to the boiling, the colour is pale green; if a dark-coloured product is required, the solutions are allowed to cool before mixing. After several days a very dark-coloured precipitate separates from the liquid; it consists of comparatively very large crystals of emerald green. =Manufacture of Emerald Green from Copper Sulphate.=—There are two processes. Either the solution of copper sulphate is mixed with an acetate, by which it is converted into copper acetate, and then with arsenious acid, or copper arsenite is precipitated from the solution of copper sulphate and then converted into emerald green by treatment with acetic acid. If acetic acid can be cheaply obtained, the latter process is to be recommended.