SOME USES OF ELECTRICITY 



electric current is able to separate a liquid into its various 

 constituents and to deposit one of the metal constituents on 



the negative electrode. 



Since copper is constantly 

 taken out of the solution of cop- 

 per sulphate for deposit upon the 

 negative electrode, the amount of 

 copper remaining in the solution 

 steadily decreases, and finally there 

 is none of it left for deposit. In 

 order to overcome this, the posi- 

 FIG. 208, -Carbon rods in a solution j electrode should be made of 



of copper sulphate. 



the same metal as that which is 



to be deposited. The positive metal electrode gradually dis- 

 solves and replaces the metal lost from the solution by deposit 

 and electroplating can continue as long as any positive 

 electrode remains. 



Practically all silver, gold, and 

 nickel plating is done in this way ; 

 machine, bicycle, and motor attach- 

 ments are not solid, but are of 

 cheaper material electrically plated 

 with nickel. When spoons are to 

 be plated, they are hung in a bath 

 of silver nitrate side by side with 

 a thick slab of pure silver, as in 

 Figure 209. The spoons are con- 

 nected with the negative terminal 

 of the battery, while the slab of 

 pure silver is connected with the 

 positive terminal of the same bat- 

 tery. The length of time that the current flows determines 

 the thickness of the plating. 



FlG. 209. Plating spoons by elec- 

 tricity. 



