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GENERAL SCIENCE 



Electroplating. When an electric current is sent through a dilute 

 copper sulphate solution in which there is a piece of iron, the iron 

 will become covered with copper if the current enters the solution 

 over a piece of copper and leaves the solution over the iron. Silver, 

 gold, and nickel plating are done this way. 

 When the article is to be plated with silver, 

 the material is placed in a silver solution. 

 Then the current enters the liquid over a 

 silver bar, leaving the solution over the 

 spoon or other article to be plated. 



The solution is called an electrolyte. 

 The wires over which the current passes in 

 and out of the solution are called electrodes. 

 The wire by which the current enters is 

 called the anode and the one by which the 

 current leaves is called the cathode. 



Electrolytic Method of Cleaning Silver. 

 The tarnishing of metals is generally due 

 to the formation of oxides on the metals 

 through the chemical action of oxygen and 

 the water vapor in the air. Unlike other 

 metals silver and gold are not tarnished by 

 oxygen or moisture of the air. Silver, how- 

 ever, readily forms black silver sulphides on 

 coming in contact with the sulphur compounds which are produced 

 from the burning of coal and illuminating gas. Some foods contain 

 sulphur compounds; eggs, especially, being an example. 



The usual method of cleaning silver with silver polishes is to rub 

 the silver sulphide from the silver with some form of very fine 

 polishing powder or paste. This method, however, constantly 

 removes the silver, requiring a new plate after a period of time. 

 The best way of cleaning silver is through the electrolytic method. 



Fill an enamel or agateware dish partly full of a clean solution of one teaspoon- 

 ful either of washing or baking soda and one teaspoonful of common table salt 

 to each quart of water, and place directly on the burner to boil. Drop a sheet 

 of aluminum or clean zinc into the dish and place the tarnished silver in with 

 the metal. See that the silver is entirely covered with the cleaning solution, 



FIG. 304. Why do the 

 wires become very hot? 

 Why do they glow? 



