218 



ELEMENTS OF GENERAL SCIENCE 



namely, that the copper is taken off the plate attached to 

 the positive terminal of the battery, which plate we shall 

 hereafter call the anode, and is deposited upon the carbon 

 rod where the current leaves the solution, which rod we shall 

 hereafter call the cathode. This is an example of a chemical 

 effect produced by passing electricity through a solution, 

 and it is evident that water may conduct the current if 

 the proper chemical is dissolved in it. 



FIG. 108. Materials for studying copperplating 



If we change the connections on the plating tank by 

 exchanging the wires on the binding posts, and then close 

 the switch for several minutes, the copperplated cathode 

 will lose a part or all of the copper, and the anode will 

 regain this amount. 



In plating it is essential that the solution be of the proper 

 composition and density and that the anode be composed of 

 the metal it is desired to deposit on the objects. The solution 

 must contain a compound of this same metal. The objects 

 to be plated are always attached to the cathode. In this 

 way nickel-plating, brass-plating, zinc-plating, silver-plating, 



