Alternating  Current  on  a  Polari.zable  Electrode,       339 
The  direct  current  I  in  the  direction  from  large  to  small 
electrode  in  the  electrolyte  is 
1     C ir    _        x    J      i/B\    12       1    /B'\4   1     4 
4.3 
UJ-  22"1       4  '  UJ'  &' 
-\B'2 
/B'\4 
if  we  neglect  I  —  )    and  higher  powers. 
4W. 
-Xz02 
>02q2eh 
;d/cm 
8ttW. 
^362. 
V%KVJ 
NI 
=  const 
(7)' 
where  N=  -—  =  the  frequency. 
We  are,  of  course,  led  to  the  same  relation  as  before.  The 
magnitude  of  the  effect  depends  upon  the  smallness  of  the 
concentration  of  the  complex  substance. 
With  the  third  case,  however,  there  is  a  marked  difference. 
If  the  concentration  of  the  mercury  salt  is  very  great,  the 
changes  of  concentration  that  take  place  are  negligible.  If 
the  velocity  of  reaction  were  infinite,  there  would  be  no  effect 
— indeed,  no  polarization  would  be  possible.  This  is,  however, 
not  the  case;  and  changes  take  place  in  the  concentration  of 
the  mercury  ions,  though  not  of  the  un dissociated  part. 
Following  Kriiger,  we  take  the  case  of  a  mercury  salt  Hg A, 
which  is  dissociated  in  very  small  quantity,  according  to  the 
equation 
HgA— Hg-+A' (8) 
If,  now,  c  is  the  concentration  of  the  Hg  ions  and  cr  that 
of  the  undissociated  part,  then  we  have  the  equation  of 
chemical  kinetics  : 
--£-*•'- v, « 
where  k±,  h2  are  the  velocities  in  the  two  respective  directions 
of  the  reaction.  A  certain  very  thin  layer  of  thickness  hx  is 
supposed,  in  which  the  polarization  phenomena  take  place. 
The  quantity  of  Hg  ion  which  is  brought  into  the  solution 
by  the  alternating  current  in  every  moment  must  be  equal  to 
that  which  disappears  according  to  the  equation  (9). 
