76 HYDROMETALLURGY. [III. 



silver-foil is tlius platinized : J oz. platinum is dissolved in 

 nitromuriatic acid, evaporated to dryness, dissolved in 1 qt. 

 rain water, 3—4 oz. oil of vitriol added. The silver-foil, having 

 been dipped for a few moments in strong nitric acid, is hung 

 on the cathode (zinc-pole), and platinum-foil on the anode 

 (copper-pole) of a battery ; the silver is covered with a gray 

 coating of platinum. 



The best silvering liquid is a solution of 1 pt. of the crys- 

 tallized double salt, cyanide of silver and potassium, in 10 pts. 

 water, to which ^ cyanide of potassium is added, and the whole 

 boiled until it ceases to smell of ammonia. When the double 

 salt alone is used, a platinum anode must be used, for a silver 

 anode becomes coated with cyanide of silver, and impairs the 

 conducting power. But the latter may be employed in the 

 above liquid, because the cyanide of potassium dissolves the 

 cyanide of silver and keeps the surface of the silver anode 

 bright. The exhausted solutions are evaporated to dryness, 

 and to the fusing residue a little saltpeter is gradually added 

 to destroy cyanide of potassium. 



The gilding liquid is thus prepared. 10 pts. gold are dis- 

 solved in nitromuriatic acid, diluted and filtered to remove the 

 chloride of silver, 3 pts. common salt added, and the whole 

 evaporated to dryness. The residue is dissolved in water, 

 precipitated by an excess of ammonia, the yellowish-brown 

 precipitate filtered, washed, and dissolved in a sufficient quan- 

 tity of cyanide of potassium. An excess of this cyanide is 

 then added, and the liquid is diluted with 64 pts. water. To 

 destroy the cyanate of potassa, it is boiled until ammonia 

 ceases to come off, and then 64 pts. more water are added. 

 If the solution be warmed, the gilding is a beautiful matt. 

 Exhausted gold solutions are evaporated to dryness and may 

 be fused alone, or fused together with silver residues, and the 

 silver extracted from the gold by nitric acid. 



Cfalvanic Crilding. — Extracted from an essay by the Duke 

 of Leuchtenberg, in the Bulletin de I'Acad., St. Petersburg, 

 1847. He draws attention to the special care required to 

 precipitate gold above all other metals, and notices particularly 



