THE DEPOSITION OF COPPER 435 



the metallic chlorides to a saturated solution of acid j)otassium 

 carbonate and allows the mixture to stand for twenty-four hours 

 there is deposited on the walls of the vessel a slight film of 

 metallic copper mixed with basic ferric carbonate. 



The solubility of the acid carbonates of iron and copper is 

 largely increased under pressure.' The greater concentration 

 of the metallic ions thus obtained produces a ready reduction 

 of copper even in the presence of concentrated solutions of the 

 acid alkaline carbonates. 



In a thick-walled flask holding a saturated solution of potas- 

 sium bicarbonate is placed a tube containing a solution of fer- 

 rous and cupric chlorides. The flask is then filled with carbon 

 dioxide, tightly sealed, and the contents of the tube mixed with 

 the alkaline bicarbonate. The precipitate formed gradually 

 loses carbonic acid, finally assuming the brick-red color already 

 noted. The supernatant ruddy liquid owes its color to the pres- 

 ence of some basic ferric carbonate which, when the solution is 

 warmed, deposits as ferric hydroxide. The precipitate contains 

 finely divided copper which cannot readily be freed from the inti- 

 mately associated ferric iron by treatment with hydrochloric acid 

 because of the solvent action of ferric chloride, but on digesting 

 the original mixture a short time a coagulum may usually be 

 formed from which, by repeated agitation with water, the heavier 

 metal is separated. The copper thus obtained is of characteristic 

 appearance ; is insoluble in hydrochloric acid, soluble in nitric, 

 the solution showing the presence of copper and absence of 

 iron. 



The reduction of copper from the cuprous condition may 

 be effected in the same manner as from the cupric. This is 

 readily shown by substituting for the cupric salt in the above 

 reaction cuprous chloride dissolved in a solution of chloride of 

 sodium. From one gram of cuprous chloride more than half 

 the metal may be easily isolated as pure copper free from ferric 

 iron. 



From these results it is quite evident that the conditions 



' R. Wagner : Zeit. f. analyt. Chem. Vol. VI, p. 167. 



