718 THE APPLICATIONS OF PHYSICAL FORCES, [BOOK v. 



overcome, we will only mention here what concerns the fundamental 

 operation; that is to say, the adhesion of the copper deposits on object 

 whose dimensions prevent their being prepared and cleaned with the 

 minute care of the silversmith. It was found absolutely insufficient 

 to simply cover the surface with a layer of plumbago. The acidity of 

 the baths attacked the metallic surfaces long before the deposit had 

 attained the suitable thickness ; M. Oudry therefore covers them first 

 with an insulating coating unattackable by acids, applying it with a 

 pencil after cleaning, and touching up with a file and scraper those 

 parts of the ornaments that require it. This coating, chiefly formed 

 of benzine, is left to dry, and then the object is plumbagoed on the 

 outside and covered with an earthy non-conducting paste wherever 

 the copper is not to be applied. It is then plunged into one of the 

 vessels, or great tubs that form the baths (Fig. 463.) At the end 

 of five or six days, the thickness of the deposit reaches a millimetre, 

 and the operation is terminated. All that is left is to give the copper 

 the appearance of bronze, which is done by rubbing the surface with 

 a brush soaked in a solution of ammonio-acetate of copper. 



The lamps of Paris, the monumental fountains of the Place Louvois 

 and the Place de la Concorde, the outer gates of the New Opera, and 

 several metallic architectural ornaments, have been coppered by this 

 process, by which means beautiful and durable objects are substituted 

 for the old iron castings which could not be preserved, even by painting, 

 from rust and destruction. The electro-metallurgic industry, by the 

 services of all sorts it can render to other industries, has undoubtedly 

 a great future before it. 



