The best plan of melting brass is to melt the copper in a black-lead crucible first, dry the zinc as much as possible, and immerse the whole of the zinc into the copper when the latter is not hotter than barely to continue fluid. Drop a piece of borax the size of a walnut into the pot. When the surface of the hot metal is kept covered by fine charcoal, or by borax, it is prevented from burning, and the smallest loss of zinc is sustained.

The melting together of tin and copper is less difficult than that of zinc and copper, because tin is not so liable to evaporate as zinc, and little metal is lost. The appearance of the alloy may be improved by covering the melted metal with about one per cent, of dried potash; or, better still, a mixture of potash and soda. This flux has a remarkable influence on the colour, and particularly on the tenacity of the alloy. The former becomes more red, and the latter stronger. The scum forming on the surface by this addition ought to be removed before the metal is cast. Tin and copper are liable to separation in cooling: this can be prevented, at least partly, by turning the mould containing the fluid metal, and keeping it in motion until it is chilled.

Copper and lead unite only to a certain extent: 3 lead and 8 copper is ordinary pot metal. All the lead may be retained in this alloy, provided the object to be cast is not too thick. When the cast is heavy, or much lead is used, it is pressed out by the copper in cooling. 1 lead, 2 copper, separates lead in cooling - it oozes out from the pores of the metal: 8 copper and 1 lead is ductile; more lead renders copper brittle. Between 8 to 1 and 2 to 1 is the limit of copper and lead alloys. All these alloys are brittle when hot or merely warm.

Equal parts of copper and silver and 2 per cent. of arsenic form an alloy similar to silver, a little harder, however, but of almost equal tenacity and malleability. Antimony imparts a peculiar beautiful red colour to copper, varying from rose-red in a little copper and much antimony, to crimson or violet when equal parts of these metals are melted together.

Common brass for castings: 20 copper, 2 1/2 tin, 1 1/4 zinc.

Hard brass for castings: 25 copper, 4 1/2 tin, 2 zinc.

Red brass for fine castings: 24 copper, 5 zinc, 1 bismuth; add the bismuth last before pouring off.

Red brass for turning: (a) 24 copper, 5 zinc, 1/2 lead; add the lead last before pouring off. (6) 32 copper, 10 zinc, 1 lead, (c) 160 lb. copper, 50 lb. zinc, 10 lb. lead, 44 oz. antimony.

Rolled brass: 32 copper, 10 zinc, 1 1/2 tin.

Yellow brass: (a) 70 copper, 30 z;nc. (6) 20 lb. copper, 10 lb. zinc, 1 to 5 oz. lead added just before pouring.

Brightening And Colouring Brass

The work to be brightened and coloured is first annealed in a red-hot muffle, or over an open fire, allowing the cooling to extend over one hour; the object of the heating being to remove the grease or dirt that may have accumulated during the process of fitting. Soft soldered work, however, must be annealed before fitted together, and afterwards boiled in a lye of potash; this is also done with work having ornamental surfaces. Next, it is immersed in a bath of diluted oil of vitriol or aquafortis, which may be made with two or three parts of water, and one of acid; but the old acid that contains a small quantity of copper, in solution, is frequently preferred. The work is allowed to remain in this liquid for one or two hours, according to the strength of the acid; it is then well rinsed in water, and scoured with sand applied with an ordinary scrubbing brush, and washed. The pickling bath is made by dissolving one part of zinc in three parts of nitric acid of 36° B. in a porcelain vessel, and adding a mixture of eight parts of nitric acid, and eight parts of oil of vitriol.

Heat is then applied, and I when the liquid is boiling the work is plunged into it for half a minute, or until the violent development of nitrous vapour ceases, and the surface is getting uniform. Then it is plunged into clean water, and well rinsed, to remove the acid. The ordinary dark greyish-yellow tint, which is thus very often produced, is removed on immersing the work again in aquafortis for a very short time. Then it is plunged into clean or slightly alkaline water, well rinsed to remove the acid, and plunged into warm dry beech or boxwood saw-dust, and rubbed until quite dry. To prevent the action of the atmosphere it is lacquered; if a green tint is to be produced, the lacquer is coloured with turmeric. A dark greyish but agreeable tint is obtained by immersing the work previously in a solution of white arsenic in hydrochloric acid, or in a solution of bichloride of platinum, under addition of some vinegar, or rubbing with plumbago. (See also iii. 13.)