2l6 



Common Science 



FIG. 121. Electrical apparatus : A, plug fuse; B, cartridge fuse ; C, knife 



switch ; H, lamp socket ; 



inch between the free end of the long wire and the free end 

 of the short wire. Try making the electricity flow from the 

 short wire into the long one through a number of different 

 things, such as string, a key, a knife, a piece of glass tubing, 

 wet cloth, dry cloth, rubber, paper, a nail, a dish of mercury 

 (dip the ends of the wire into the dish so that they both 

 touch the mercury at the same time), a dish of water, a 

 stone, a pail, a pin, and anything else that you may like to 

 try. 



Each thing that makes the bell ring is a good conductor. 

 Each one that will not make it ring is a poor conductor 

 or an insulator. Make a list of the things you have 

 tried ; in one column note the good conductors, and in 

 another column note the insulators and poor conductors. 



The water and wet cloth did not ring the bell, but 

 this is because the pressure or voltage of the electricity 

 in the batteries is not very high. In dealing with high- 

 power wires it is much safer to consider water, or any- 

 thing wet, as a pretty good conductor of electricity. 

 Absolutely pure, distilled water is an extremely poor 

 conductor; but most water has enough minerals dis- 

 solved in it to make it conduct electricity fairly well. 

 In your list you had better put water and wet things 

 in the column with the good conductors. 



