The Electro-Plating and Electro-Refining of Metals; Being a New Ed. of Alexander Watt's Electro-Deposition

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1902 edition. Excerpt: ...to each gallon of bath will be sufficient. He has usually noticed that brassing solutions evolve hydrogen most freely when poor in metal, and when containing a large excess of cyanide. A solution richer in metal, and containing but a moderate excess of cyanide, generally yields better results, both as to colour and general character of the deposit. A great deal depends, however, upon the amount of current and its tension, and also upon the temperature of the bath. A solution rich in copper and zinc is best worked at about 130 Fahr., or even higher. When the solution becomes partly exhausted of its metals, owing to the brass anodes not becoming freely dissolved in the solution, it. is always advisable to add fresh concentrated cyanide solutions of the zinc and copper salts from time to time, taking care, however, only to add them in sufficient quantity to obtain the desired effect--a coating of good colour with but trifling evolution of hydrogen at the negative electrode. Bacco's Solution.--The following solution is said to yield a brass deposit upon zinc work that will stand burniHhiug, and the deposit may be obtained either by simple immersion or by the battery. A solution is first prepared by dissolving equal parts of sulphate of zinc and sulphate of copper in water. A strong-solution of cyanide of potassium is then added in sufficient quantity to redissolve the precipitate formed; to the resulting solution one-tenth to one-fifth of liquid ammonia is added, and the solution is then diluted with water until it stands at about 8" Baume. For a light-coloured deposit of brass 2 parts sulphate of zinc to I part sulphate of copper are used. In adding cyanide to the solution of the sulphates, great care must be taken to a%'oid inhaling the...