HOW WE SECURE ELECTRICAL ENERGY 



243 



the blotting paper is placed a damp paste of sal ammo- 

 niac, powdered carbon, and other substances. The cell 

 is tightly sealed with a layer of pitch shown at E. The 

 chemical action takes place as in the wet cell between 

 the zinc can and the sal-ammoniac paste. The zinc 

 is gradually eaten away until it breaks through. When 

 this happens the moisture in 

 the cell evaporates, drying out 

 the paste, and the cell is no 

 longer usable. Old dry cells 

 can sometimes be restored by 

 punching holes through the 

 zinc, soaking in water, and re- 

 sealing the holes with wax. 



Dry cells are used in flash- 

 lights, radios, and many places 

 where electric current is 

 needed. 



Exercise. A flashlight using 

 three small dry cells was found 

 not to light. The cells, which had 

 slipped into the case freely when 

 new, were now stuck and diffi- 

 cult to remove. When removed they were found to have 

 expanded and to be covered with a white substance. Infer 

 a probable cause for the failure of the light to work. 



FIG. 383. CROSS SECTION OF 

 DRY CELL 



Negative Plate 



Positive Plate 



Wood Separator 



Negative 

 Group 



Positive 

 Group 



The storage battery is a common source of elec- 

 trical energy. The development of the automobile and 

 radio has made the storage battery a commonplace 

 device in the experience of many boys and girls. Be- 

 cause it is an important part of the automobile and 

 demands careful use and attention, everyone should 

 know about it. 



The storage battery stores chemical energy. Many 

 persons believe that the storage battery is a sort of 

 tank or reservoir in which electricity is stored for- fu- 

 ture use. This, however, is not true, for the storage 

 battery gets its electrical energy from chemical ener- 

 gy in exactly the same way that the wet cell or the 

 dry cell does. It is different from these only in that 

 its chemical energy can be restored when it has been 

 used up while this is impossible in the wet cell and 

 the dry cell. 



FIG. 384. PARTS OF A STORAGE BATTERY 



FIG. 385. CROSS SECTION OF A STORAGE BATTERY 



Your experiment has taught you that if two lead 

 plates are placed in a solution of sulphuric acid and 

 a current of electricity is run into the cell from dry 

 cells or other source, a chemical action goes on in the 

 cell as shown by the gas which is given off and also 

 by the change to a deep brown color of one of the 

 plates. This is called charging the cell, and the im- 

 portant thing that is happening is that the plates are 

 being made unlike by the chemical action. The brown 

 substance is a compound of lead and oxygen, lead 

 peroxide. 



When the source of current is taken away, the 

 storage battery will give electrical energy because it 

 has two unlike plates, one of lead and one of lead 

 peroxide, dipping into a solution of sulphuric acid. 

 When the cell is delivering electricity the lead per- 

 oxide plate is the positive and the pure lead plate 

 the negative. In the commercial storage battery (see 



