USES OF MAGNETS AND CELLS 409 



one made from sal-ammoniac (ammonium chloride) dissolved in 

 water. Zinc and carbon are used for electrodes. The current flows 

 from the carbon to the zinc on the wire outside the battery. 



Dry Cells. The " dry cell " is made up of a zinc jar in which is 

 packed damp sal-ammoniac surrounded by manganese dioxide. 

 Pitch is placed over the top of the materials to prevent the water 

 from evaporating. A piece of carbon is placed in the center of the 

 cell from which the current flows. 



Open an old dry cell and examine the structure. 



Parallel and Series. Batteries, lights and many electrical in- 

 struments are wired in parallel or series according to the re- 

 quirements. 



Batteries are wired in parallel by running wire from the zinc 

 to the zinc, and from the carbon to the carbon, thence to the instru- 

 ment. 



The result of parallel connection in batteries is to produce a 

 large number of amperes and the voltage equal to one cell. Electro- 

 plating work requires such conditions. 



Whenever we wire batteries to door bells we need as much 

 voltage as possible to drive the current over the wires, for they may 

 be 100 feet or more in length. 



The batteries are wired in series from carbon to zinc. 



Electric lights for our homes are wired in parallels since the 

 lights must be turned on independently of each other. 



Where two or more electric bells are operated from the same 

 push button they should be wired in parallel. 



Storage Cell. The storage cell is used in automobiles, in homes 

 and in schools for many purposes requiring the use of electricity. 

 These cells must be charged. The electricity does not really go into 

 the cell and stay there but stores up its energy in the cell. This 

 energy once stored up is a source of current in the opposite direc- 

 tion from which the current passed into it. 



Project: 'Find out how storage cells are made; the different places where 

 they are used; how they are charged; when we know they are fully charged, and 

 what the cell contains. 



