EXERCISES 149 



4. What is meant by the terms " triple plate, quadruple plate," 

 etc., as applied to silver utensils? 



5. How could a slab of impure copper be purified by the electric 

 current? 



6. How could coal be converted into energy at the mine, and this 

 energy distributed without the shipping of the coal? 



7. When the lighting system of a trolley car is on the same circuit 

 as the power, the lights often burn low while the car is being started, 

 but burn brightly when the car is in motion. What does this show as 

 to the power required to start the car as compared with that needed to 

 keep it moving? 



8. What advantages has electric power over steam power for factory 

 use? For the home? 



