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CELLS AND BATTERIES ' 59

“ open ” most of the time and current is only drawn occa-
sionally and then only for short periods.

If the current is drawn for any appreciable length of
time hydrogen gas will collect on the carbon cylinder and
the cell will become polarized. When polarized it will not
deliver much current.

Many methods have been devised for overcoming this difli-
culty, but even the best of them are only partially successful.

The usual method is to employ a chemical depolarizing
agent. Figure 56 shows a Leclanche cell provided with a
depolarizer.

The carbon is in the form of a plate placed in a porous
cup made of earthenware and filled with manganese dioxide.

Chemists class manganese dioxide as an oxidizing agent,
which means that it will furnish
oxygen with comparative ease. ‘
Oxygen and. hydrogen have a 1 in l:
strong chemical afiinity or attrac- :1" I '

 
 
 
  
   

  
     
  

Wit. '3". a
tion for each other.

     
 

 

        

If the carbon plate is packed .

in manganese dioxide any hy- 7 ." llhll...,'.' ,
' . ' “M W? .-

drogen Wthh tends to collect on CELL
the carbon and polarize the cell Fm. 56. — A Leclanche Cell,
is immediately seized by the Sh°wing the P°r°us Cup-
oxygen of the manganese dioxide and united with it to form
water.

This form of Leclanche cell is called the disk type. It is
capable of delivering a stronger current for a longer period

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