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To Coat Copper with Zinc

be thinly coated with the above preparation To granulate the zinc, a clean surface of copper may be coated with zinc by placing the two metals in contact in a solution of caustic soda or potash. (See Fig. I., No. 3665.) In the cold the deposit of zinc takes place slowly, but at 100° it is effected rapidly. and afterwards heated for a few minutes in a muffle or over a Bunsen burner.

3658. Platinizing Copper, Yellow Metal, and Brass. In order to obtain a platinizing fluid capable of platinizing copper, yellow metal, and brass, add to a moderately concentrated solution of chloride of platinum, finely powdered carbonate of soda, until effervescence ceases; next some glucose, and afterwards just so much common salt as will cause a whitish-colored precipitate. When it is desired to apply this mixture for platinizing, the objects to be treated are placed in a vessel made of zinc and perforated with holes; the vessel is then placed, with its contents, for a few seconds in the mixture thus described, which, just previous to using, should be heated to 140° Fahr. On being removed from the zinc vessel, the objects are to be washed with water and dried in sawdust. 3654. Purcher's Method of Coating Zinc with Iron. Dissolve 5 ounces pure sulphate of iron, and 3 ounces sal-ammoniac, in 5 pounds of boiling water, and immediately immerse the objects to be treated. After from 1 or 2 minutes the loose black deposit is removed by brushing it off with water. The principal effect of this operation is a perfect cleaning of the surface. The immersion in the hot iron solution is then repeated, with the difference that the objects, when taken out, are heated, without rinsing, over a pan of live coals as long as the ammoniacal vapors are evolved. When, after several immersions, the coating is considered thick enough, it is polished by brushing, and will ever afterward Plating. be a perfect protection against oxidation. It imparts a fine black lustre to the coated sur- -is placed a concentrated solution of chloride faces.

3659. Stolba's Method of Nickel may be of porcelain, but preferably of copper Into the plating vessel-which of zinc, which is then diluted with from 1 to 2 3655. Process for Covering Articles volumes of water, and heated to boiling. If of Zinc with Copper or Brass by One Immersion. To give zinc a coat of copper or brass for the purpose of a subsequent silvering or gilding, the following solutions are used: For copper alone, a solution of sulphate any precipitate separates, it is to be redissolved by adding a few drops of hydrochloric acid. As much powdered zinc as can be taken on the point of a knife is thrown in, by which the vessel becomes covered internally with a The of copper, saturated at the common tempera- coating of zinc. The nickel salt-for which ture, is mixed with a solution of cyanide of purpose either the chloride or sulphate may potassium, adding as much of the latter as is be used is then added until the liquid is disnecessary to redissolve the precipitate thrown tinctly green; and the articles to be plated, down at first. The prussic acid disengaged during this operation must be carried off by a draught or flue. When the mixture is clear, To or of its volume of water of ammonia is added, and then diluted with water to a density of 8º Baumé. For brass, sulphate of copper and sulphate of zinc are used in equal propreviously thoroughly cleaned, are introduced, together with some zinc fragments. boiling is continued for 15 minutes, when the coating of nickel is completed, and the process is finished. The articles are well washed with water and cleaned with chalk. If a thicker coating be desired, the operation may be reportion, and prepared as before. 2 parts sul- peated. Professor Stolba found that copper phate of zinc and 1 of sulphate of copper give vessels thus plated were scarcely tarnished a bright brass coating.

Previous to their dip-after several months' use in the laboratory. face of the copper; this action will go on as in another vessel, the same action will take Electrotyping. This is a pro cess for depositing a coating of metal long as the two metals are kept in contact. on objects, metallic or otherwise, by the Or if, instead of causing the two metals to agency of a current of galvanic electricity, touch, a wire be attached to each, and their Before entering into any description of the opposite ends are placed in a little dilute acid methods employed, it will be necessary to give some indispensable preliminary direc- place between the zinc and copper as when tions, in order that the whole matter may be they were in contact; but in this instance, more clearly understood. The matter is main- the ends of the two wires which dip into the ly derived from the 4th edition of Napier's vessel containing acid will undergo a change: the one attached to the zinc will give off Manual of Electro-Metallurgy. 3661. Solution of Copper for Electro- a quantity of hydrogen gas, while the one typing. Crush fine sulphate of copper in attached to the copper, supposing it to be crystals, and expose to the air for some time. also copper, will rapidly dissolve.

Figure 1. Represents the zinc and copper, This oxidizes any iron that may be present.

Stir the sulphate of copper into pure cold placed in dilute sulphuric acid, brought into water, until the water will dissolve no more; contact; in this experiment, gas will be seen then let it settle, and decant the clear solu. escaping from the copper. tion; add to it about one-fourth its quantity of water, and it is ready for use.