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To Silver the Metals

Commence by cleansing them with nitric acid; rub them afterwards with a mixture of cyanide of potassium and powdered silver; then, after washing with water, they are plunged alternately into the liquors Nos. 1 and 2 (see No. 3626), until they appear sufficiently silcovered with zinc wire in spiral turns of about 6 inches from each other, which also serves as a means of suspension. The bath consists of a solution of 8 parts caustic soda in 100 parts water, of which 11 quarts aro mixed with 50 ounces Rochelle salts and 125 ounces sulphate of copper, making a liquid of a density equal to 190 Baumé. It retains its activity as long as the copper is kept replaced, and deposition from it proceeds with great regularity. The material of the vessel is vered. If working with iron, it should be best when made of wood, lined with guttafirst immersed in a solution of sulphate of percha, and covered with a wooden lid. When copper. The process which has been de- the coating is of sufficient thickness, the obscribed presents above all others the advan- ject is removed from the bath, first washed tage of very solid results, and of employing chemical agents of low price. 3633. To Coat Copper Plates with Brass. Expose the plates, heated sufficiently, to the fumes of zinc. Zinc boils and is vaporized by heating it to a white heat. 3634. To Coat the Inside of Copper Vessels with Brass. Dissolve 1 part zinc amalgam (see No. 3539) in 2 parts muriatic acid; add 1 part argol (crude tartar), and add sufficient water to fill the vessel; then boil it in the vessel. 3635. To Deposit Copper upon Cast Iron. The pieces of cast iron are first placed in a bath made of 50 parts hydrowith water slightly acidified with sulphuric acid, and then with pure water until the disappearance of all traces of acid; after this it passes into a drying room heated to 1320 Fahr. The bronzing, when required, is obtained by a bath of sulphide of sodium, or by means of the same bath as above, somewhat modified, that is, by increasing the proportion of copper to a threefold, in which case the bath no longer deposits copper, but, to all appearances, bronze. By reducing the points of contact between the iron and wire, though retaining the spiral turns at uniform distances, the deposit gradually assumes a number of colors in the following series, viz.: orange, chloric acid, specific gravity 1.105, and 1 silver-white, pale yellow, golden yellow, carpart nitric acid; next, in a second bath, com- mine, green, brown, and dark bronze. As soon posed of 10 parts nitric acid, 10 parts of chloride of copper, dissolved in 80 parts of the same hydrochloric acid as just alluded to.

The objects are rubbed with a woolen rag and a soft brush, next washed with water, and again immersed until the desired thickness of copper is deposited. When it is desired to give the appearance of bronze, the copper surface is rubbed with a mixture of 4 parts salammoniac and 1 part each oxalic and acetic acids dissolved in 30 parts water. as the desired color is attained, the object is washed in warm water, and again dried at 1320.

Between each subsequent change of color is an interval of about 5 minutes. The reaction is more decided when the alkaline reaction of the bath is stronger. For indoor work or ornaments the time of immersion may vary from 3 to 72 hours; for outdoor objects a much longer time would be necessary. 3638. To Tin Iron Pots and other Domestic Articles. The articles are cleaned with sand, and, if necessary, with acid, and 3636. Graeger's Process for Covering Iron and Steel with Copper without a put then in a bath, prepared with 1 ourco Battery. The objects are first well cleaned, cream of tartar, 1 ounce tin salt (protochlorico and then painted over with a solution of of tin), 10 quarts water. This bath must bo protochloride of tin, and immediately after- kept at a temperature of 190° Fahr., in a ward with an ammoniacal solution of sulphate stoneware or wooden tank. Bits of metallic of copper. The layer of copper thus produced zinc are put into and between the different. adheres so firmly to the iron or steel, that the pieces. When the coat of tin is considered different objects can be rubbed and polished thick enough, the articles are taken out of with fine chalk without injuring the deposit. the fluid, washed with water, and dried.