216 



ELECTRO-METALLURGY 



plating and gilding, which is most extensively carried on both at homo and abroad. 

 Kesults that were unattainable, and others attainable only at groat cost, are readily 

 produced by this mode of manipulating. The liquids most in use are the cyanide 

 solutions, first introduced by Messrs. Elkington. They are prepared in various ways. 

 Cyanide of potassium is added carefully to dilute solution of nitrate of silver ; and the 

 white deposit of cyanide of silver is washed, and then dissolved in other cyanide of 

 potassium ; or lime-water is added to the nitrate solution, and the brown deposit of 

 oxide of silver is washed, and, while moist, is dissolved in cyanide of potassium ; or 

 common salt is added to the nitrate solution, and the white deposit of chloride of silver 

 is washed and dissolved in cyanide of potassium. Or a solution of cyanide of 

 sium is placed in the trough B, fig. 794, and the current from three or four cells is 

 passed into it from a silver plate at c, which combines with and is dissolved in the 

 liquid, converting it into a cyanide of silver solution. To prevent silver being ab- 

 stracted by deposition at m, as the current leaves the trough, the metal at m is placed 

 within a porous cell of cyanide solution, so as to limit the action. 



Gold solution is obtained by dissolving the anhydrous peroxide of gold in cyanide 

 of potassium, or by treating chloride of gold with cyanide of potassium, or by using 

 a gold plate and a voltaic current with a solution of cyanide of potassium in the samo 

 way as described for silver, and allowing the action to continue until the solution is 

 sufficiently strong of gold. With those solutions electro-plating and gilding are readily 

 accomplished. There are other solutions more or less valuable, which will be found 

 in the books that treat upon the subject. 



Fig. 799 shows a single-cell arrangement for plating. The zinc is outside, and is 



799 



bent to embrace both sides of the porous cell. The article to be plated is within this 

 cell, because, being the vessel of smaller capacity, less of the more valuable silver 

 solution is required, and there is less of loss or waste. The same holds good in a 

 greater degree of gold. In a few minutes the article is covered with silver. If a few 

 drops of sulphuret of carbon are added to the silver solution, the silver is deposited 

 bright. Gold does not come down quite so rapidly as silver. 



Except for mere experiment, these operations are better accomplished, and with 

 less waste, by using distinct batteries, as a, fig. 800, the solution of gold or silver being 

 in a distinct trough b, plates of silver or gold, as the case may be, being suspended 

 in front of the article to be coated. One or two cells, according to the result re- 

 quired, are used for plating ; and three or four for gilding. But gilding is never so 

 well accomplished as it is with hot solutions. The modes of keeping solutions hot 

 vary with circumstances, and with the extent of the operations. Fig. 801 is an 

 arrangement for operations on a small scale. The vessel a b, containing the gold 

 solution, rests over a small stove or spirit-lamp. The objects to bo gilt are suspended 

 by wires to the conducting rod d, in connection with the zinc end of the battery ; and 

 the gold wire or plate c is connected with the other end. A temperature of from 100 

 to 200 is desirable ; the higher temperatures require fewer battery colls ; with the 

 highest, one will suffice. The solution, of course, evaporates under the influence of 

 heat ; and distilled water must bo added to supply the loss, before each fresh ope- 

 ration. 



Plating and gilding are successfully, and, in point of economy, advantageously, 

 carried on at Birmingham, in <more than one manufactory, by means of m;ij, r ii<:t<>- 

 electricity. In the article on ELECTHO-TELEGUAPHY will bo found a description of this 

 form of electric force, and the means by which it is produced. An electro-magnet is 



