228 



SCIENTIFIC RECREATIONS. 



and consists in the fact that if a plate of metal be suspended and attached 

 to the positive pole of a galvanic battery and immersed in a solution of the 

 same metal, the conducting substance hung opposite at the negative pole 

 becomes coated with the metal immersed in the solution. 



Suppose we take a plate of silver, and immerse it in cyanide of silver 

 dissolved in cyanide of potassium ; a coating of silver will be deposited 



Fig. 232. Trough for electro-deposition. 



upon the nickle spoon or other article suspended at the other pole. But to 

 make the coating adhere the spoons, forks, etc., are prepared for the bath 

 by cleansing in caustic potash to remove grease, and washed in nitric acid to 

 remove all traces of oxide, then are scoured with sand. Next, a thin coat- 

 ing of mercury is put on by immersion in solution of nitrate of mercury. 

 Finally, they are hung in the bath. A metal rod is hung across the bath 



Fig. 233. Plates immersed. 



(fig. 232), and the plate is immersed. If the rod to which the articles are 

 suspended be attached to the zinc or negative pole, and the plate of silver 

 to the positive pole of the battery, decomposition begins, and the silver 

 begins to attach itself to the suspended objects. If it be desirable to give 

 the plated articles a thick coating, they are retained for a long time in the 

 bath, which is of some non-conducting material. The dull appearance is 

 easily removed by brushing and burnishing, and then the " Electro-plate " is 



