Cleansing Copper and its Alloys.

The mode of cleansing copper, brass, bronze, maillechort, oreide, similor, French gold, Mannheim gold, British metal, German silver, and, generally speaking, all alloys in which the proportion of copper predominates, is the same. It comprises six operations:1. Cleansing by fire or by alkalies.

2. Dipping.

3. Dipping in old aqua fortis.

4. Dipping in fresh aqua fortis.

5. Dipping in mixed acids for a bright or dead lustre. 6. Dipping in nitrate of mercury.

Cleansing by Fire or by Alkalies.

The articles for electroplating are generally soiled by adhering greasy matters, derived during the operations of manufacture, such as rolling, spinning, soldering, polishing with oil, etc., or simply from contact with the hands. The foreign substances, and especially those of organic nature, are destroyed by heating the pieces on all sides over a gentle fire of charcoal. A muffle furnace, heated up to a dull red heat, is to be preferred; but small articles may be cleansed in a heated revolving cylinder.

This operation is not adapted to very delicate articles, such as filigree and spangled work, neither to table-forks and spoons, which must retain their sonorousness and toughness, nor to those pieces the different parts of which are united by solders which are fusible below the temperature to which they would be subjected in reheating. In such cases, the articles are submitted to a more or less

* Of these six operations, four only are indispensable; the third and sixth may be dispensed with in many cases, which we shall examine further on.

prolonged boiling in alkaline solutions, either of potassa or soda, which saponify the fatty substances and thus render them soluble in water.

The operation is performed in a cast-iron kettle, in which a more or less concentrated solution of carbonate of potassium or sodium, or of American potash, is maintained at the boiling-point, usually with the use of a coil of pipe through which steam is passed. Roseleur gives the preference to caustic potassa dissolved in ten times its weight of ordinary water. This solution lasts quite a long time, and, when it has lost part of its power, it may be revived by the addition of a few fragments of caustic potassa. At the boiling-point this solution will cleanse copper completely in a few seconds. If the articles to be cleansed are joined with tin solder, they must not be allowed to remain too long in the caustic liquor, which may dissolve the solder and strongly blacken the copper. The lye kettle should be provided with a lid, or cover, to retard the otherwise rapid absorption, by the caustic liquor, of carbonic acid from the air, or of the acid vapors of the workshop, which would diminish its alkalinity, and consequently its cleansing qualities.

Dipping.

The articles are then dipped in a mixture of from five to twenty parts (by weight) of sulphuric acid of 66° Baumé to one hundred parts of water.

Copper articles may remain any length of time in the dipping bath without suffering any injury; but it is absolutely necessary that they should not be removed until the black coating of oxide of copper (cupric oxide), caused by the heating operation above described, is entirely dissolved. The remaining coat of red oxide of copper (cuprous oxide) is unacted upon by the sul

phuric acid. It should be remarked that articles having parts made of iron or zinc, should not be submitted to the action of sulphuric acid, as such parts will be entirely dissolved; therefore, the use of all implements, wires, or hooks of iron, zinc, or steel must be avoided. A dipping bath which, from previous operations, contains copper in solution, will not suit for such articles as contain iron, tin, tin solder, antimony, bismuth, or lead. In these cases, a newly made dipping bath with a small proportion of acid must be used.

The articles cleansed by alkalies must be washed before being plunged into the dipping bath, or pickle, as it is sometimes called; and we cannot insist too much on the necessity of thoroughly and rapidly rinsing in fresh' water all the articles, both before and after each of the operations that are to follow.

The various manipulations which we shall presently indicate, and which complete the cleansing, should succeed each other without interruption; and the articles should be actively moved about in the acid bath (pickle) and also in the rinsing water.

In order to prove the importance of these operations, we do not hesitate to state, that, even with very inferior electroplating solutions, good results may be arrived at if the cleansing is perfect, while the converse is not true.

After dipping and rinsing, the various pieces are attached to a brass wire, or simply hooked upon copper hooks represented by Figs. 1 and 2. Small articles of jewelry are simply suspended to a stout copper wire, as seen in Figs. 3 and 4.

For the construction of these hooks copper is to be preferred to brass, and for careful workers, we recommend the use of hooks of glass, which are not expensive

and not liable to be acted on by the acids. Any one can make such hooks or supports, by bending glass rods, by

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Fig. 1.

Fig. 2.

the heat of a charcoal fire, or of a gas-burner, into the shape shown in Fig. 5, which is handy for the manipulations required in the cleansing vessels.

Fig. 3.

Fig. 5.

Fig. 4.

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Those objects which cannot be suspended or attached to hooks, are placed in baskets or perforated ladles of

stoneware or porcelain (Figs. 6, 7, and 8), or what is less economical, but sometimes absolutely necessary, into

baskets of brass wire cloth (Fig. 9), having the mesh fine or coarse, according to circumstances.

Those who have frequently to cleanse very small articles, will find it advantageous to employ a basket of platinum wire cloth, which, although expensive in first cost, will be found cheaper in the end, on account of its indifference to the action of the chemical substances used in the cleansing operations.

Dipping in Old Aqua Fortis.

The material employed for this purpose is the spent aqua fortis (nitric acid), already weakened by previous dippings, and of which there is always a supply on hand. After thorough rinsing in water, the articles that have