=Casselmann’s Green= approaches emerald green in brightness. It consists of a compound of copper sulphate with copper hydroxide and water, CuSO₄.3Cu(OH)₂.½H₂O. This pigment is obtained by mixing solutions of 4 equivalents of copper sulphate and 3 equivalents of sodium acetate at a certain temperature. The author’s experiments have shown that the best results are obtained when the solutions are mixed at a temperature of about 100° C. With this object the solutions are placed in vessels standing in a pan of boiling water; when their temperatures have risen to about 100° C. they are quickly mixed, the mixture stirred, and the precipitate allowed to settle. When the precipitate is cautiously treated with very weak caustic soda solution a rather deeper colour is obtained. This treatment should not be continued too long, or the precipitate may acquire an ugly bluish shade. =Lime Green= is a mixture of copper arsenite and calcium sulphate. It is thus a pigment which ought no longer to be used, on account of its poisonous properties. It is made by boiling milk of lime with excess of arsenious acid so long as the latter is dissolved. To this solution of calcium arsenite, copper sulphate solution is added so long as a precipitate is formed. A mixture of copper arsenite and calcium sulphate is precipitated. =Patent Green= is similar in composition to lime green. A solution of calcium acetate is made by adding quicklime or pure powdered limestone to acetic acid; copper sulphate solution is then added, when gypsum is precipitated and copper acetate remains in solution. A hot solution of arsenious acid is next added, and the precipitated copper salt mixed with the gypsum at the bottom of the vessel. =Copper Borate.=—A pale green precipitate of copper borate is obtained by adding a solution of 3 parts of borax to a solution of 2 parts of copper sulphate. It must be dried at a very moderate temperature, or it will decompose. When perfectly dry the precipitate can be heated to a red heat without decomposition; according to the temperature employed different shades are obtained. It is most convenient to take tests out of the crucible from time to time during the ignition, and to quickly cool the crucible when the desired shade is obtained. When levigated this pigment may be used in oil, or as a porcelain colour. =Copper Silicate (Egyptian Blue).=—When a solution of water-glass is added to a solution of copper sulphate a pale green precipitate of copper silicate is obtained, which can be heated to redness without alteration. When 70 parts of white quartz sand, 15 parts of copper oxide, 25 parts of chalk and 6 parts of soda are fused together a glass is produced which, after pouring into water, grinding and levigating, exhibits a pretty blue and very permanent colour. It appears from the examination of the colours of the Egyptian mural paintings that this pigment was already known to the ancient Egyptians. CHAPTER XXX. VERDIGRIS.