Another formula recommended by the same authority as a good depositing solution for coating iron and steel by the battery process (id. p. 208) is the following, viz.: Dissolve ammoniuret of copper in a solution of cyanide of potassium. Nine hundred or 1000 parts of water, containing 80 parts of cyanide of potassium, dissolves 40 parts of the blue ammoniuret, and forms a colorless liquid.

Spencer's solution for the galvanic deposition of copper on iron is made by decomposing a solution of sulphate of copper in water, by the addition of a solution of the acetate, sulphate, or nitrate of ammonia. This bath is said to furnish upon iron a copper deposit of any desired

thickness.

Under the head of GALVANOPLASTY proper we shall refer to some of the recent improvements introduced for obtaining copper on the commercial scale by galvanic precipitation, the continuous production of heavily coated steel wires for telegraphic and other purposes, and the like.

CHAPTER XI.

ELECTRO-BRASSING.

BRASS deposits are much more frequently used in the arts than those of pure copper. Brass is preferred for those small articles of iron or zinc which are made in imitation of similar ones of brass, which are more expensive. Wood-screws, hooks, rings for furniture and curtains, hooks and eyes for dresses, wires of all sizes for chaplets, etc. etc., are made of iron or zinc plated with brass, so as to resemble those of real brass.

Moreover, all the manufacturers of bronze composition, lamps, clocks, chandeliers, statues, and other articles made of zinc or cheap alloys, begin by a brass deposit, before the bronze composition is applied. (For bronzing consult special chapter.)

Besides the fact that the bronzing operation is more easy and satisfactory upon a brass surface, there is also the advantage that, if, whether purposely or by constant use, the surface of the object becomes abraded, there appears the handsome yellow color of the underground, and the whole piece looks as if made of the more costly alloys of copper and zinc, or copper and tin.

The preliminary and finishing operations are the same for brass as for copper deposits. The disposition of the baths and apparatus is also similar; the formulæ alone are different.

Heat is seldom employed in electro-brassing, although it is preferred by those who electro-plate, with this alloy, iron or zinc wire in coils. The best temperature for this class of work is found to be from 120° to 140° Fahr.; and the coils are allowed to dip into the bath one-half or two-thirds of their diameter only.

The bath is contained in a sheet-iron boiler (Fig. 79), heated either by direct fire, steam, or hot water. The inside is lined with brass sheets connected with the positive pole. A stout copper or brass rod, in the direction. of the length of the boiler, rests upon the edges, and the contact of the two metals is prevented by interposed pieces of India-rubber tubing. The rod is connected with the negative pole by a binding screw.

The binding wire is removed from the coils, and the wires loosened and spread out as seen in Fig. 80. The two extremities are bent together, and, with a stronger wire, a triangular handle is formed which contains the

whole of a coil, and leaves a certain play necessary for the operation.

The iron wire, thus disposed, is cleaned by dipping into a pickle of diluted sulphuric acid, and suspended to

a stout, round peg fixed in the wall (Fig. 81), so that the coil may be made to rotate easily. After a scrubbing

with wet, sharp sand and a hard brush, the coil receives a primary deposit of pure copper in an apparatus similar to that just described. It is then carried to the brassing bath, and suspended therein from the horizontal rod. In this position, only a part of the coil at a time dips into the solution and receives the deposit, which, to be continuous, requires that the coil be turned, now and then, one-half or one-fourth of its circumference. Experience has demonstrated that, by dipping the coil entirely into the liquid, which is easily done by giving the proper bends (Fig. 82) to the supporting rod, the operation is not so successful. With this latter disposition, moreover, it is not so easy to spread the wires upon the rod.

The wires are washed, dried in sawdust, and then in a stove, and lastly passed through a draw-plate in order to impart to them the fine polish of true brass wire.

Copper and brass wires are also covered with brass electro-deposits, in order to give them various shades. The brass wires of Lyons and Germany, used for trimmings and epaulets, are thus prepared, either preparatory to gilding or silvering, or simply to arrive at special shades more pleasing than those of pure copper or pure brass. These wires, passed through the drawplate, are sold under the name of false gold. It is evident that the

composition of the brassing bath must be such as to give, with the battery, a deposit resembling gold.

Formula for Brassing Baths.

Dissolve together, in 1000 parts of water, 25 parts of sulphate of copper, and 25 to 30 parts of sulphate of zinc; Or, 12 parts of acetate of copper, with 12 to 15 parts of fused chloride of zinc;

To which add a solution of 100 parts of carbonate of soda, which immediately produces an abundant precipitate of the carbonates of copper and zinc, which is allowed to settle. When the precipitate has completely subsided, decant the supernatant liquor, and replace it by fresh water two or three times, after as many settlings.

Lastly, pour upon the precipitate 1000 parts of water containing in solution 100 parts of carbonate of soda and 50 parts of bisulphite of soda; and then, while stirring with a glass or wooden rod, add thereto cyanide of potassium until the liquid is perfectly clear, or at least until nothing but the grayish-black iron, often found in the cyanide, or the brown-red oxide of iron from the sulphate of zinc, remains in suspension. An additional quantity of from 2 to 3 parts of ordinary cyanide improves the conducting power of the liquid.

Other formulæ, which have proved satisfactory in regu lar every-day work, are given herewith, viz.:

First Formula.

COLD BRASSING BATH FOR ALL METALS.

Carbonate of copper (recently prepared)
Carbonate of zinc (recently prepared)
Carbonate of soda (crystals)

part 1000 parts