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Cold Tinning

Rub pure tinfoil and quicksilver together until the amal- as possible; then introduce the brass or copgam becomes soft and fusible, clean the sur- per and it will be tinned in a few seconds. face to be tinned with spirits of salt (hydro- 3649. Το Galvanize Iron. The differchloric acid), and, while moist, rub the amal-ence between galvanized plates, so-called, and gam on, and then evaporate the quicksilver "sheet-tin," is, that the latter is sheet-iron by heat.

3644. Stolba's Method of Tinning Copper, Brass, and Iron in the Cold, and without Apparatus. The object to be coated with tin must be entirely free from oxide or rust. It must be carefully cleaned, covered with a thin coating of block-tin, while the former is sheet-iron covered with a thin coating of zinc. To effect the latter result, the iron plates are first immersed in a cleansing bath of equal parts of sulphuric or muriatic acid and water, used warm. (See No. and care be taken that no grease spots are 3266.) They are then scrubbed with emery left; it makes no difference whether the ob- or sand, to clean them thoroughly and detach ject be cleaned mechanically or chemically. all scales, if any are left; after which they are Two preparations are requisite for the purpose immersed in a preparing bath of equal parts of tinning. Zinc powder-the best is that pre- of saturated solutions of chloride of zinc and pared artificially by melting zinc and pouring chloride of ammonium, from which bath they it into an iron mortar. (Sce No. 3312.) It are directly transferred to the fluid metallic can be easily pulverized immediately after bath, consisting of 20 chemical equivalents of solidification; it should be about as fine as zinc to 1. of mercury; or, by weight, 640 writing sand. A solution of protochloride of pounds of zinc to 106 of mercury, to which tin, containing 5 to 10 per cent., to which as are added from 5 to 6 ounces of sodium. As much pulverized cream of tartar must be soon as the iron has attained the temperature added as will go on the point of a knife. of this hot fluid bath, which is only 680°

The object to be tinned is moistened with Fahr., it may be removed, and will then be the tin solution, after which it is rubbed hard with the zinc powder. The tinning appears at once. The tin salt is decomposed by the zinc, metallic tin being deposited. When the object tinned is polished brass or copper, it appears as beautiful as if silvered, and retains its lustre for a long time. This method may be used in a laboratory to preserve iron, steel, and copper apparatus from rust; and would become of great importance if the tinning could be made as thick as in the dry way, but this has not as yet been accomplished.