142 



MAGNETS AND ELECTRICITY 



The resistance furnace (Fig. 133) has two poles able to deliver a 

 powerful current. We "close the circuit" by packing between the 

 poles the materials that are to be heated. The resistance due to 



the materials changes the energy 

 of the current into heat. In the 

 intense heat of electric furnaces 

 man has been able to turn metals 

 like gold and platinum into 

 vapors, and to prepare many 

 substances of great commercial 

 importance. Among these are 



graphite (cf. 119), carborundum, a very hard abrasive (scouring 

 and polishing material), and calcium carbide, a gray solid that reacts 

 with water to give acetylene, the gas used in acetylene lamps (cf. 

 257). 



FIG. 132. 

 Electric Arc Furnace. 



159. Electroplating. We have learned that when the 

 electric current is passed through dilute sulphuric acid, 

 hydrogen collects at one pole, and oxygen at the other 

 (cf. 100). If the current 

 is passed through a solu- 

 tion of copper sulphate, 

 copper is formed at one 

 pole, and oxygen and sul- 

 phuric acid at the other. 

 In this case the copper 

 sulphate is used up. But 



FIG. 133. 



Resistance Furnace. The materials to be 

 heated are poured through the hoppers 

 A, A, and the current is passed between 



if the pole at which the 



current enters the solution is of copper, the copper sul- 

 phate is not used up. What happens is that copper wastes 

 away at one pole, and is deposited at the other. An 

 object placed at the receiving pole will be electroplated 

 with copper. 



