The bronze known in the trade as " arsenic bronze," diluted with an equal quantity of water, is used for blackening aluminium. First the exposed parts of the surface should be curl' d, not straight-grained, with emery-paper; then the metal should be quickly dipped into the fluid and as sharply withdrawn, and drained. If on the first immersion the bronze has not taken well all over, the process should be repeated. If the preparation is too strong, there is a danger that the acid will eat away the metal. A recipe for arsenic bronze is hydrochloric acid, 12lb.; sulphate of iron, l1 b.; pure white arsenic, lib. To this, for aluminium, must be added an equal quantity of water; and, when the metal has blackened, it should be dried in a mixture of blacklead and sawdust. Only sufficient sawdust is required to soak up the moisture. The exposed parts then may be lacquered.