390 ELEMENTARY LESSONS ON [CHAP. xi. 



through the cell, the mould being the kathode ; a plate 

 of copper being employed as an anode, dissolving gradu- 

 ally into the liquid at a rate exactly equal to the rate of 

 deposition at the kathode. This use of a separate 

 battery is more convenient than producing the electro- 

 types in the actual cell of a Daniell's battery. The 

 process is largely employed at the present day to repro- 

 duce repousse* and chased ornament and other works of 

 art in facsimile, and to multiply copies of wood blocks 

 for printing. Almost all the illustrations in this book, 

 for example, are printed from electrotype copies, and not 

 from the original wood blocks, which would not wear so 

 well. 



421. Electroplating. In 1801 Wollaston observed 

 that a piece of silver, connected with a more positive 

 metal, became coated with copper when put into a 

 solution of copper. In 1805 Brugnatelli gilded two 

 silver medals by making them the kathodes of a cell 

 containing a solution of gold. Messrs. Elkington, about 

 the year 1840, introduced the commercial processes of 

 electroplating. In these processes a baser metal, such 

 as German silver (an alloy of zinc, copper, and nickel) 

 is covered with a thin film of silver or gold, the solutions 

 employed being, for electro -gilding, the double cyanide 

 of gold and potassium, and for electro -silvering the 

 double cyanide of silver and potassium. 



Fig. 157 shows a battery and a plating- vat containing 

 the silver solution. From the anode is hung a plate of 

 metallic silver which dissolves into the liquid. To the 

 kathode are suspended the spoons, forks, or other 

 articles which are to receive a coating of silver. The 

 addition of a minute trace of bisulphide of carbon to the 

 solution causes the deposited metal to have a bright 

 surface. If the current is top strong, and the deposition 

 too rapid, the deposited metal is grayish and crystalline. 



In silvering or gilding objects of iron it is usual first 

 to plate them with a thin coating of copper. In gilding 



