CHAP, in.] ELECTRICITY AND MAGNETISM. 



143 



ments of carbon and powdered binoxide of manga- 

 nese, a substance which slowly yields up oxygen and 

 destroys the hydrogen bubbles. If used to give a 

 continuous current for many minutes together, the 

 power of the cell falls off owing to the accumulation of 

 the hydrogen bubbles ; but if left to itself for a time the 

 cell recovers itself, the binoxide gradually destroying the 

 polarisation. As the cell is in other respects perfectly 

 constant, and does not require renewing for months or 

 years, it is well adapted for domestic purposes. Three 

 Leclanche' cells are shown joined in series, in Fig. 76. 



Fig. 76. 



In more recent forms the binoxide of manganese is 

 applied in a conglomerate attached to the face of the 

 carbon, thus avoiding the necessity of using a porous 

 inner cell. 



Mons. Niaudet has also constructed a zinc-carbon cell 

 in which the zinc is placed in a solution of common salt 

 (chloride of sodium), and the carbon is surrounded by 

 the so-called chloride-of-lime (or bleaching-powder), which 

 readily gives up chlorine and oxygen, both of which 

 substances will destroy the hydrogen bubbles and 

 prevent polarisation. This cell has a higher E.M.F. 

 and a less resistance than the Leclanche'. 



174. De la Rue's Battery. Mr. De la Rue has 

 constructed a perfectly constant cell in which zinc and 



