M. TECHNOLOGY. 580 



deposition. Many organic acids are adapted to this purpose. 

 Oxalates of copper, combined with a very large excess of bi- 

 noxalate of quadroxalate of potash, equivalent to free acid, 

 the whole dissolved in ten to fifteen times as much water, 

 aflTords a most excellent solution. To produce a very heavy 

 deposit, an electrical current must be employed with it. 14 

 C, 1873, CCVIIL, 50. 



TINNING, COPPERING, AND SILVERING BRASS, IRON, ZINC, ETC., 



BY THE WET METHOD. 



In a memoir by 0. Paul, on the best method of depositing 

 one metal on another, we are informed that the operation of 

 tinning brass, copper, and German-silver articles, by boiling 

 in a tin solution, succeeds best with a solution of cream of 

 tartar in an enameled iron vessel, to which pure granulated 

 tin lias been added. If sufficient tin be employed, and the 

 liquid frequently stirred, the coating will be heavy enough 

 after boiling two hours. It is best to place the articles in 

 the vessel first, and to scatter the tin over them. Iron arti- 

 cles, as buckles, nails, etc, may also be tinned in the wet way, 

 by a method less generally known. It is, however, essential 

 that they be first thoroughly cleansed, by dipping in a mixt- 

 ure of one part of nitric acid and ten parts of water; then 

 lightly coated with copper, by adding, gradually (in more 

 than an hour), to this liquid only so much of a solution of 

 sulphate or acetate of copper as may be necessary slowly to 

 produce a very slight covering of copper. They must then 

 be rinsed, and more heavily coppered by wetting them uni- 

 formly with a solution of one part of proto-salt of tin, two 

 parts of water, and the addition of two parts of muriatic acid, 

 allowing the excess to drain off, and then shaking, rubbing, 

 or scouring them with a solution of ammonio-sulphate of 

 copper. This is a deep-blue liquid, obtained by dissolving 

 one part of sulphate of copper in sixteen parts of water, and 

 adding first ammonia, until the precipitate formed at first is 

 redissolved, and then powdered chalk. The copper deposits 

 rapidly on the iron, and is very adherent. The same process 

 answers for zinc, with the omission of the treatment with the 

 tin -salt solution. The iron and zinc articles thus copper- 

 coated can then be tinned by the usual process, or, still bet- 

 ter, in a solution of three parts of cream of tartar and one 



