When neutral nitrate of copper is decomposed by an insufficiency of a potash carbonate solution, the flocculent precipitate of copper carbonate formed at first is gradually changed into a subnitrate of copper which is precipitated as a heavy green powder. In practice the operation is conducted as follows:--Copper scales are calcined in a reverberatory or muffle furnace, till all the suboxide is converted into protoxide, or until a sample dissolves in nitric acid without evolution of red nitrous vapours. The copper nitrate solution is heated and decomposed by a clear solution of potash carbonate, and when the effervescence subsides, small doses of potash carbonate solution are added, till but little undecomposed copper remains in the solution. To recover this last portion, the clear liquor is decanted, and the green precipitate is washed several times with small quantities of water. All the liquors are collected, and the remaining copper is precipitated by potash solution. The green carbonate of copper is introduced into a new solution of copper nitrate, in which it is transformed into a basic salt. The previous liquors are evaporated till they afford crystals of nitrate of potash, which is a valuable secondary product. BRIGHTON GREEN.--The following recipe has been published for making this pigment. Dissolve separately 7 lb. sulphate of copper and 3 lb. sugar of lead, each in 5 pints of water; mix the solutions, stir in 24 lb. of whiting, and when the mass is dry grind to powder. BRUNSWICK GREEN.--(_a_) Old process. The Brunswick green of former days was closely allied to Bremen green, essentially consisting of a basic chloride or oxychloride of copper, and possessing all the faults incidental to that class of copper salt. While having fairly good covering power, and capable of being used either as a water colour or an oil colour, it was tedious and therefore expensive to prepare, and not thoroughly durable under exposure to air and sunlight. Nevertheless it was a useful bluish-green pigment. Following are some of the many methods by which it has been prepared:-- (1) Poor oxidised copper ores are moistened with hydrochloric acid, and spread out exposed to the air. The metal is thus rendered very susceptible to the action of chlorine, and is even attacked by solutions of ammonium chloride and of common salt. The sub-chloride produced is rapidly transformed into oxy-chloride, and forms a fine light-green pigment.