C:IAP. ix.l ELECTRO-PLATING. 703 



being pulverulent, had all the consistence, compactness, and ductility 

 of the purest metals, as furnished by metallurgical operations. More- 

 over by replacing the copper plate of the pile by moulds of medals, or 

 plates engraved in relief or intaglio, he obtained faithful reproductions 

 in intaglio, or relief, of the originals. Such is the origin of electro- 

 typing, which a clever Englishman discovered also for himself the 

 following year. The invention soon obtained a great development, 

 and was the starting-point of numerous artistic and industrial appli- 

 cations, and the subject of important improvements. 



The processes which constitute electro-typing give deposits which 

 are exact models of the objects to be reproduced without adhering to 

 them. But it is possible also to obtain very thin deposits, which 

 adhere to the surface of the objects and act as a protective covering 

 without sensibly altering its contour, or its form : the processes 

 employed in this case constitute gold-plating, silver-plating, copper- 

 plating, &c., according as the deposited metal is gold, silver, copper, &c. 

 Such is the difference, as far as results are concerned, between electro- 

 typing and what is sometimes called galvanizing or electro-plating. 

 The principle is the same, but the processes are different; indeed, 

 as we shall see, they were discovered independently. The invention of 

 electro- gilding goes back in fact much further than electro-typing. 



In 1805, a professor of chemistry at the University of Pavia, Louis 

 Brugnatelli, discovered a means of gilding medals, and little articles 

 of silver, by means of a batter} r . He used a solution of chloride of 

 gold in ammonia (ammonio-chloride of gold), in which he plunged the 

 article to be gilded, and made it communicate with the negative pole 

 by a steel or silver wire. But this invention remained unknown and 

 unapplied. In 1840 M. de la Eive, the illustrious physicist of the 

 Academy of Geneva, after long researches made for the purpose of 

 relieving the working gilders from the dangers arising from the em- 

 p.ioyment of mercury, succeeded in gilding brass, copper, and silver by 

 means of the battery. The liquid he employed was a solution of 

 chloride of gold as neutral as possible and very weak (five to ten 

 milligrammes of gold to a centimetre cube) in a cylindrical bag made 

 of a bladder. This diaphragm was plunged in a glass vessel con- 

 taining water suitably acidulated. The article was immersed in the 

 solution of gold. A zinc cylinder joined by a silver thread to the 

 object to be gilded caused the production of the electric current, 



