MAGNETISM AND ELECTRICITY 



177 



When the battery is fully charged and in good condition, 

 the positive plate is a dark reddish brown or chocolate color, 

 while the negative plate is slate-colored. On discharging 

 the battery, the SO 3 

 is obtained from sul- 

 phuric acid, which 

 combines with 

 water and forms 

 lead sulphate with 

 lead. When the 

 battery is recharged 

 the current releases 

 the SO 3 , restoring 

 the plates to their 

 previous condition. 

 Storage batteries 

 are measured in 

 ampere-hours . 

 Thus a 100 ampere- 

 hour battery will 

 give a continuous 



as 



FIG. 76. One Form of Storage Battery. 



discharge of 



amperes for 8 hrs. 



Theoretically, it should give a discharge of 25 amperes for 



4 hrs., or of 50 amperes for 2 hrs. 



The capacity of a cell is proportional to the exposed area 

 of the plates, the number of plates, and the active material 

 present. 



211. Arrangement of Electrical Apparatus. A group of 

 cells or electrical apparatus may be arranged in different 

 ways. The wire from the zinc of the first cell may be 



