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to be coppered. Fig. 78 represents a convenient form of anode for this purpose.

During the operation, the bath attacks and slowly dissolves the copper anode; but here theory is not quite in accord with practice, since this solution is not sufficiently rapid to compensate for the loss of metal, and to maintain the proper saturation of the bath. When the deposition

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is found to be going on too slowly, we must bring up bath by the addition of a certain quantity of acetate of copper and of cyanide of potassium (equal weights).

Some operators substitute the sulphate, or the cyanide, of copper, for the acetate of this metal. The first should be rejected on account of its too great acidity, which uselessly destroys part of the salts of the bath. The second is too expensive, and does not give more satisfactory results than the acetate, which is to be preferred on account of its comparative cheapness and its perfect neutrality. Moreover, the acetates of potassa, or soda, or ammonia, formed by double decomposition, are without any bad effects during the operation.

Carbonate of copper, recently precipitated and dissolved in just enough cyanide of potassium to discolor it, may also be employed. This mixture is added to worn-out baths to revivify them; but it is preferable not to wait until they are worn out, and to make up for the losses by adding, now and then, a small quantity of the double cyanide of potassium and copper already indicated.

When a bath has been too often recharged with salts, it becomes too dense, and its electric conductivity diminishes. The pieces plunged into it receive no deposit, or

only an imperfect one, although the relative quantities of copper salt and of dissolving agents are in suitable proportions. The working quality may, in such case, be restored by the addition of water.

When the anode has too large a surface, or remains immersed in non-working baths, the liquor becomes overloaded with copper, turns blue or green, and requires the addition of cyanide of potassium to the point of discoloration.

It happens sometimes that the anode becomes covered with a brownish or whitish coating preventing its solution; the bath then becomes gradually poorer in metal, and ceases to give a deposit. In this case, an addition must be made of a solution of acetate of copper in ammonia, until the blue coloration which it causes begins to disappear with difficulty. If too much is added, the excess must be corrected with cyanide of potassium. To sum up, an attentive and intelligent operator will always be able, with cyanide of potassium and salt of copper, to maintain the materials of his bath in a proper state of equilibrium.

Some operators copper silver articles before gilding them. This is done partly to give the deposit greater solidity, and partly to avoid the whitening at the angles, which otherwise soon shows itself as the result of wear and friction.

Large pieces of silverware may be coppered in any of the baths before mentioned. Very small articles, on the other hand, are simply threaded upon a zinc or iron wire, or placed in a perforated ladle with granules or cuttings of either of these metals. By plunging the whole for a few minutes in a very dilute, but very acid, solution of sulphate of copper, the zinc or the iron dissolves, tak ing the place of the copper in the solution, and the latter

is deposited as a uniform and adherent coating upon the silver, which acquires a magnificent pink color.

When the article thus coppered is intended to be gilded or silvered, it is quickly passed without drying or scratch-brushing, through the quicking bath, rinsed in cold water, and at once immersed in the depositing bath.

We append, in conclusion, a number of formulæ and methods from sundry reliable sources, which may be found useful.

The following method is that employed by Serin & Co., of Paris, for the electro-deposition of copper upon iron,

viz.:

a. Preparation of the articles. The articles are first immersed in dilute sulphuric acid, then washed in cold, followed by hot, water; they are then immersed in boiling alkali, from which they are removed and transferred to a bath of milk of lime, in which they are allowed to remain for several weeks.

b. Preparation of the first copper bath.

Water

Cyanide of potassium

100 parts.

4 to 4 66

Dissolve in this, cyanide of copper, until a saturated solution is obtained.

c. Treatment of the articles in the bath. The articles are allowed to remain in this bath for about an hour, with the employment of a moderately strong current (sufficiently strong to manifest a lively evolution of gas). In this bath, the articles take on a thin copper coating, when they are ready for the subsequent operation.

d. Preparation of the second copper bath. Dissolve in water, with the aid of heat, so much sulphate of copper that the solution, when cold, shall register 24° Baumé. Dilute with water to 20° Baumé, and add enough sul

phuric acid to bring the specific gravity of the solution to 22° Baumé. This solution forms the second copper bath.

e. Treatment of the articles in the second copper bath. The articles, thinly coppered in the first bath, are transferred to the second copper bath just described, through which the current has been directed before the articles are introduced. In this bath, the articles can be coated with a copper coating of great adhesion and of any desired thickness. When properly coated they are removed from the bath, washed in clean water, dried, and polished.

Instead of the first thin coating of copper here described, the articles may be first given a coating of lead by galvanic deposition, upon which they may be coppered in the second bath.

f. Preparation of the lead bath. Dissolve litharge in water containing 10 per cent. of caustic potassa. Anodes of lead plates are used to maintain the saturation of the bath. The galvanic current does not require to be strong.

L. Elsner's procedure for the electro-deposition of copper is as follows (Winckler, Handbuch der Metallüberzügen, 1881, p. 218): Dissolve 1 part of powered bitartrate of potassium in 10 parts of rain water, and add to this solution, freshly precipitated hydrated carbonate of copper (prepared by precipitating, in the cold, a dilute solution of sulphate of copper with a dilute solution of carbonate of sodium or potassium, and washing with water) until no more is taken up, that is, until the last portions added remain undissolved. The solution is then made decidedly alkaline by the addition of carbonate of potassium, filtered, and the clear liquid constitutes the copper bath. A current, of moderate strength only, is required, the copper anodes dissolving readily, and maintaining the metallic strength of the solution.

For electro-coppering cast iron, the same authority re

commends a saturated aqueous solution of sulphate of sodium, to which as much hydrated carbonate of copper (or hydrated oxide of copper) is added as it will take up. The clear, dark blue solution which is filtered off from the undissolved residuum, rendered decidedly alkaline by the addition of carbonate of sodium, serves as the copper bath. Cast-iron objects are soon covered with a matt rose-colored deposit of copper.

Watt (Electro-metallurgy, 7th ed., p. 35) recommends the following formulæ for the galvanic deposition of copper on iron or zinc, viz. :

1. Add to a solution of sulphate of copper, a solution of cyanide of potassium. Wash the greenish precipitate several times with cold water, and dissolve in cyanide of potassium.

2. Pour into a solution of sulphate of copper, a solution of ferrocyanide of potassium until no further precipitation takes place. Wash as above, and dissolve in cyanide of potassium. Work the solution hot.

3. Dissolve 8 ounces of sulphate of copper in 1 quart of hot water; when cold, gradually add liquid ammonia (sp. gr. .880), stirring after each addition, until the precipitate that at first forms is dissolved. Add cyanide of potassium until the blue color of the ammonio-sulphate of copper disappears; then add cyanide of potassium; and work the solution at a temperature of about 130° Fahr. Watt pronounces this "a very good solution for coppering."

Gore (Electro-metallurgy, 1877, p. 207) dissolves cyanide of copper to saturation in water containing about 2 pounds of cyanide of potassium to the gallon; then adds about four ounces more of the potassic salt per gallon, to form free cyanide. This solution is adapted for electrocoppering upon zinc, iron, etc., and should be used at a temperature of about 150° Fahr.

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