124 ELECTRO-PLATING. 



is this : an iron solution is first made by dissolving a quantity of 

 copperas in water, placing it on a fire till it begins to boil : a little 

 nitric acid is then added nitrates of potash and soda will do just as 

 well the iron, which is thus per-oxidized, may be precipitated 

 either by ammonia, or carbonate of soda; the precipitate being 

 washed, muriatic acid is added till the oxide of iron is dissolved. 

 This forms the solution for dissolving the copper. When the solu- 

 tion becomes almost colourless, and has ceased to act on the copper, 

 the addition of a little ammonia will precipitate the iron again; after 

 a little exposure, the copper remains in solution, which is decanted 

 off and preserved for recovering the copper ; this is done by neutra- 

 lizing the ammonia by an acid, and putting in pieces of iron, which 

 deposit the copper in the metallic state. The precipitate of iron 

 is again dissolved in muriatic acid, and employed in dissolving the 

 copper. Thus the iron may be used over and over again with little 

 trouble, and the persalt of iron will be found to dissolve the copper 

 more rapidly than an acid : persulphate of iron must not be used, as 

 it dissolves the silver along with the copper. The silver article is 

 then cleaned in the usual way (page 108), and heated to redness 

 over a clear charcoal fire, which gives it the appearance of dead 

 silver, in which state it may be kept, or, if desired, it may be 

 scratched and burnished. 



When ammonia is added to the solution of copper and iron, both 

 these metals are precipitated together as a brown precipitate. The 

 iron is mostly all converted into peroxide, and the copper into sub- 

 oxide the copper only dissolving out by exposure, by the reduction 

 of the peroxide of iron to the protoxide, in which state it exists when 

 the ammonia is added. When the persulphate of iron is used for 

 dissolving copper, and ammonia is then added to the solution, the 

 same results take place : the precipitation of both copper and iron. 

 But the compound seems not so stable, the copper passing more 

 quickly into an oxide, which dissolves in the ammonia. However, 

 with free ammonia, either with the chloride or sulphate, the oxidation 

 of the metals is slower than with water alone. 



Copper moulds intended for receiving a deposit must be pro- 

 tected on the back, but if the solution is very strong, there is every 

 danger that it will decompose the protecting substance, thus render- 

 ing the solution very dirty, and causing a sediment. For the pur- 

 pose of protecting the mould, various suggestions and experiments 

 have been made ; amongst other substances, pitch has been tried : it 

 is easily affected alone, but on boiling a little of it in potash, a heavy 

 and dirty sediment is left, destitute of any adhesive property ; on 

 putting a quantity of this sediment into a pot nearly filled with melted 

 pitch, a violent effervescence will take place, setting free-a volume 

 of white fumes having a creosotic smell. After all effervescence has 



