158 ELECTROLYSIS. 



artistic fineness of the cast-iron piece. Coppering has the dis- 

 advantage of being expensive and of necessitating a somewhat 

 elaborate installation ; at the same time it is injurious to the 

 workmen's health. 



Notwithstanding these inconveniences, the coppering of cast 

 iron is beyond contest one of the most beautiful problems which 

 has excited the inventor's imagination, and one of those of 

 which the solutions have been the most ingenious and the most 

 clever. The works of Messrs. Oudry, Weil, and Gauduin, 

 amongst many others, are a proof of the labours of mankind in 

 this particular branch of industry. 



The oldest process for coppering iron is due to Baron Euolz, 

 and consists in decomposing the double cyanide of copper and 

 potassium by means of a strong electric current. It gives pretty 

 good results on very homogeneous iron and on steel on the 

 condition that the pieces are perfectly scoured. As to ordinary 

 iron, and especially cast iron, which always contains flaws, holes, 

 and impurities of all kinds, the copper coating is never con- 

 tinuous on them, and rust soon makes its appearance at the 

 points where the coating has not been effected. If it is sought 

 to increase the thickness of the coating by putting the object 

 in an acid bath of cupric sulphate, the acid, getting through 

 the coating, attacks the subjacent metal and destroys all ad- 

 herence. 



This process is also an expensive one, as cyanides are of a 

 high price, they become destroyed with time, and require a 

 strong current to become decomposed. 



OUDKY PROCESS. After a long series of tedious and ex- 

 pensive experiments, M. Oudry, despairing of succeeding in 

 depositing on cast iron a coating of copper uniting the requisite 

 conditions of adherence, solidity, and duration, devised a mixed 

 process consisting in coating the cast iron with a plumbagoed 

 varnish and depositing the copper over that coating. 



The varnish is composed of red lead, of resinous materials 

 capable of thoroughly resisting the action of the air, and of 

 plumbago which acts as a conductor to the surface. The bath 

 may contain an acid solution of sulphate of copper without any 

 fear of the cast iroft being attacked and without the necessity of 



