Copper-plating solutions, made by dissolving the green precipitate from a copper sulphate solution with potassium cyanide, should he worked hot. A temperature of from 150° P. to 180 P. gives the hest results, the copper deposit being brighter and more coherent than at lower temperatures. When large bulks of alkaline copper solutions are necessary, and it is found inconvenient to beat them, it is advisable to precipitate the copper from a solution of its sulphate with liquor ammonia, then add more of this to dissolve the precipitate, and finally add the potassium cyanide. Work this cold and revive by adding a little liquor ammonia from time to time.