3751. Galvanic Tinning

3751.      Galvanic Tinning. M. Mais-trasse-Dupré, it appears, had been commissioned by the French government to apply, by galvanic means, tin upon divers objects which had been made of so-called galvanized iron - that is, iron covered with zinc. To this purpose he applied galvanic elements made of copper and zinc plates, the length of which is 48 inches, the width 28 inches, placed in a leaden trough and separated and isolated by means of wooden partitions. The copper sheet was immersed in a mixture of equal parts of acetate of lead and common salt, and the zinc element was placed in weak sulphuric acid, specific gravity 1.060. This battery remains in constant action and working order for 8 days, at an outlay of only 2 francs. When the objects which are galvanically tinned are afterwards heated to the melting point of tin, the goodness and durability of hot-tinned materials is thus obtained. Copper thus tinned (galvanically), and afterwards heated, is superficially converted into bell metal, while the method of tinning galvanically has the great advantage over the old method, that it can be applied to objects to which the method of tinning in ordinary use is not applicable.

3752. To Electroplate with Brass

3752.     To Electroplate with Brass. Brass can be deposited when the solution is composed of 1 part sulphate of copper in 4 parts hot water, 8 parts sulphate of zinc in 16 parts of hot water, 18 parts cyanide of potassium in 36 parts of hot water. These are mixed, and 250 parts of water added. Instead of a copper positive electrode plate, one of brass is necessary; the solution is required to be kept nearly boiling, and a powerful battery to be used.

3753. To Prepare Cyanides of Copper and Zinc

3753.    To Prepare Cyanides of Copper and Zinc. For copper, dissolve 1 ounce of sulphate of copper in 1 pint of hot water. For zinc, dissolve 1 ounce of the sulphate of zinc in 1 pint of hot water, and proceed the same as for cyanide of silver. (See No. 3697 (To Prepare Cyanide of Silver).)

3754. Cyanide Solution of Copper or Zinc

3754.    Cyanide Solution of Copper or Zinc. Dissolve 8 ounces (troy) cyanide of potassium, and 3 ounces cyanide of copper or zinc in 1 gallon of rain or distilled water. They should be used at about 160° Fahr.; with a compound battery of 3 to 12 cells.

3755. Cyanide Solution of Copper

3755.    Cyanide Solution of Copper. To prepare copper solutions by means of cyanide of potassium, for covering iron and other positive metals, there are several methods, but the method adopted in manufacturing purposes is as follows: To a solution of sulphate of copper, add a solution of ferrocyanide of potassium (yellow prussiate of potassa), so long as a precipitate continues to be formed ; this is allowed to settle, and, the clear liquor being decanted, the vessel is filled with water, and when the precipitate settles, the liquor is again decanted, and these washings are repeated until the sulphate of potash is washed quite out. This is known by adding a little chloride of barium to a small quantity of the washings; if no white precipitate is formed by this test, the precipitate is sufficiently washed. A solution of cyanide of potassium is now added to this precipitate until it is dissolved, during which process the solution becomes warm by the chemical reaction that takes place. The solution is filtered, and allowed to repose all night. If the solution of cyanide of potassium that is used is strong, the greater portion of the ferrocyanide of potassium crystallizes in the solution, and may be collected and preserved for use again. If the solution of cyanide of potassium used to dissolve the precipitate is dilute, it will be necessary to condense the liquor by evaporation, to obtain the yellow prussiate in crystals ; the remaining solution is the coppering solution. Should it not be convenient to separate the yellow prussiate by crystallization, the presence of that salt in the solution docs not interfere with its power of depositing copper.