313 ON THE PRECIFITATION OF SILTER BY COPPER. 



XV. 



Note on the Precipitation of Silver hy Copper : hy Mr, GaV- 



LUSSAC*. 



Silver nrecipi- -i-vJLOST chemists are of opinion, that the precipitate, 

 tatei from its obtained by leaving a slip of copper in a solution of nitrate 

 solution by _ ., . w f ^ . i i t 



copper im- <^' Silver, IS an alloy ot the two metals, and that consequently 



pure : Jt is impossible to procure pure silver by this process. This 



is the truth of the fact, when no attention is paid to parti- 

 cular circumstances: but if we examine the different stages 



of the precipitation, and attend to the causes that produce 

 but may be ^. i i, • ^ ■ ^ . ■ ^^ 



obtained other- ttiem, we shall soon perceive, that \t is easy to obtain silver 



wise. free from the copper by which It is precipitated. 



_. - ^ In fact, the first portions of silver separated are commonly 



tions separated pure, and do not give a blue tinge to ammonia, when they 

 pure: ^j.^^ dissolved in nitric acid. It is only in proportion as the 



copper enters into solution, that we find any in the precipi- 

 tate; so that toward the end of the process the quantity be- 

 comes very evident. If therefore we separate the first por- 

 and the whole tions of silver, we shall find them exempt, from copper: 

 d'^^d^^ "^b"" ^"^» ^° obtain considerable quantities, we may take the 

 adding nitrate whole of the precipitated silver, as 1 have done, wash it, 

 of silver. 2^^ digest it with a smaU quantity of nitrate of silver: by 

 these means, the copper will be redissolved, and a corre- 

 sponding quantity ef silver precipitated. 

 An affinity be- I am fur from thinking, that the mutual action of metals 

 tween the itie- jg incapable of occasioning the formation of alloys in me- 

 tals may occa- „. . . , > i j .i i^ • ^i. 

 sion aft alloy to Gallic precipitations: I oniy conclude, that, in the experi- 



falldowp, bnt ment I have just related, the precipitation of the copper 

 ngt in this case. .^ ^^^ occasioned by the affinity between this metal and sil- 

 ver; since in this case we ought to have the same alloy in 

 every stage of the precipitation, and besides this could not 

 be destroyed by being placed in contact with a fresh quan- 

 Galvanism acts ^^^^ of nitrate of silver. Precipitation in general being the 

 in the precJpi effect of a galvanic pfoccss : it appears to me, that the' 

 **"^' copper, which is reduced by hidrogen as well as silver, is 



precipitated with this metal by the same cause. Many other 

 metallic precipitations would exhibit similar results, 



• Annales de Chim. vol. LXXVIII, p. 91. 



. XVI. 



