164 ELECTROLYSIS. 



time to time a small quantity of an ammonical dissolution of 

 copper. The bath is gradually charged with oxalate of iron 

 through the scouring of the pieces, and the presence of this salt, 

 instead of interfering with the copper deposition, seems, on the 

 contrary, to favour it and render it more regular. The same 

 bath can therefore be indefinitely used. 



When the piece has received, on all its surface, a sufficiently 

 thick deposition of copper so as not to be influenced by the 

 sulphuric acid, the operation is completed in a bath of sul- 

 phate of copper, simply composed of a saturated solution of 

 about 10 per 100 of free sulphuric acid. This bath has the 

 advantage of being more economical than the previous one, and 

 of giving a more rapid deposition, at the same time requiring a 

 smaller current power. 



It will be understood from the foregoing that the problem of 

 coppering cast iron is perfectly solved by the cupric ammonical 

 oxalate. There only remains to be found the means of pre- 

 venting the destructive action which inevitably arises wherever 

 copper and iron are in juxtaposition. 



For the last ten years, the Societe du Yal d'Osne has 

 supplied to the trade the most gigantic pieces which have ever 

 been electro-coppered. We saw at the 1878 Exhibition two 

 bulls ten feet long, weighing each 1600 kilogrammes (over 1J 

 ton), which had been so coppered (in one piece), and were real 

 masterpieces of manufacture. 



WALENN'S PROCESS. M. Walenn, a short time ago, made 

 known in London the following process for coppering iron and 

 cast iron : 



The preparation of pieces of metal, iron or cast iron, before 

 being put in the bath, does not differ from what is done in other 

 factories. An iron casting, for example, is at first scoured in 

 dilute sulphuric acid, then rinsed in running water and dipped 

 into a boiling solution of caustic potash. The piece so heated 

 is put into the bath, which by its composition finishes the 

 scouring should there be occasion for it. 



As soon as the equilibrium of temperature is established 

 the electric current is set on. The liquid used for the copper 

 deposition is a mixture of potassic cyanide and neutral ammonic 



