Various baths are used to remove silver from old electroplated articles.
Their composition depends upon the base on which the metal is deposited.
Silvered iron articles are placed as anodes in a solution of 1 part
potassium cyanide in 20 parts of water. As kathode a silver anode or a
copper one lightly oiled may be used. From the latter the silver easily
rubs off. For copper articles a mixture of fuming sulphuric acid and
nitric acid (40º Beaumé) may be used. The presence of any water in this
mixture will bring about the solution of the copper. Or fuming sulphuric
acid may be heated to between 300º and 400º F., some pinches of dry
pulverized potassium nitrate may be thrown in and the articles at once
dipped. These methods effect the solution of the silver, leaving the
copper unattacked.