2o6 Common Science 



FIG. 112. A battery of three dry cells. 



through a solution from one lead plate to another until 

 a chemical substance is stored on one of them ; then, 

 when the two lead plates are connected by a wire, the 

 electrons run from one to the other. This kind of 

 battery is called a storage battery, and it is much used 

 in submarines and automobiles. 



But all the different batteries work on the same gen- 

 eral principle : A chemical solution divides into two parts, 

 one with many electrons and the other with a less num- 

 ber. One part of the solution gathers on one pole (piece 

 of metal in the solution) and charges it positively; 

 the other part gathers on the other pole and charges 

 it negatively. Then the electricity flows from one pole 

 to the other. 



Positive and negative poles. Before people knew 

 anything about electrons, they knew that electricity 

 flowed from one pole of a battery to the other. But 

 they always said that it flowed from the carbon to the 

 zinc ; and they called the carbon the positive pole and 



