(3) Acetate of copper is mixed with a sufficient quantity of water heated to 122° F., to make a homogeneous and liquid paste. To 10 parts of acetate of copper in this condition is added a solution of 8 parts of arsenious acid in 100 parts of boiling water, the whole being then kept in a state of ebullition. The addition of a little acetic acid helps to develop the beauty of the colour. When precipitation is complete, the clear liquor is drawn off, and forms a convenient solvent for the next charge of arsenic, the operation being facilitated by adding a little carbonate of potash, forming an arsenite of potash. The precipitate constituting the desired green pigment is filtered off and dried at the lowest effective temperature. (4) Dissolve 5 lb. of sulphate of copper in water, and add to it a solution of 1 lb. of lime in 2 gallons of vinegar. Mix 5 lb. of white arsenic with sufficient water to form a paste. Add the arsenic paste to the copper and lime mixture, and leave the whole at rest in a moderate degree of heat. Mutual decomposition slowly ensues, with consequent formation of the green pigment, which is filtered off, washed, and dried with the same precaution as before. When sulphate of copper is used in the production of emerald green, it is very desirable that it shall be free from sulphate of iron, which is a common impurity in the commercial article, and greatly detracts from the purity and brilliance of the pigment. A good method of eliminating this iron is to add to the sulphate of copper solution a small quantity of a gelatinous precipitate of carbonate of copper, produced by decomposing a copper sulphate solution by a soda carbonate solution, and washing. On adding the gelatinous carbonate of copper, with agitation, the iron is soon thrown down in flakes of oxide, and pure sulphate of copper may be filtered off. (5) Braconnot proceeds as follows:--A solution of 3 lb. of sulphate of copper is made in a small quantity of hot water; and a second solution of 3 lb. of arsenious acid and 4 lb. of commercial carbonate of potash in boiling water. When the evolution of carbonic acid gas has ceased, the two liquors are mixed together while being kept continuously stirred; the result is an abundant precipitate of a dirty yellowish-green colour. On adding a slight excess of acetic acid, a fine crystalline green is developed; this is washed with boiling water on a filter, and dried very slowly and carefully. (6) A rough and ready process is to mix white arsenic with water, and then stir in an equal weight of verdigris, allowing the mixture to be at rest for a time in a moderately warm temperature till the pigment is completely precipitated, when it is washed on a filter, and dried very gradually.