332         Dr.  Gundry  on  the  Asymmetrical  Action  of  an 
to  this  theory  we  arrive  at  the  Nernst  formula  for  the  E.M.F. 
of  polarization : 
n       *ec  ' 
where  R  is  the  gas-constant,  6  the  absolute  temperature,  and 
n  the  valency  of  the  ion  concerned. 
c0  is  the  ionic  concentration  in  the  neighbourhood  of  the* 
large  electrode  (which  remains  practically  unaltered),  and 
c  the  concentration  of  Hg  ions  in  the  layer  of  electrolyte- 
immediately  overlying  the  small  electrode. 
If  now  c  oscillates  symmetrically  about  a  moan  value,.. 
the  logarithm,  being  an  asymmetrical  function,  changes- 
asymmetrically. 
We  have 
R0, 
E  = 
c  +j  sin  mt 
in   the  direction   corresponding  to  a    cathodic   polarization.. 
Without  the  alternating  current 
ill  = loo-  -° . 
n       °  c 
The  E.M.F.  in  this  direction  will  be  increased  or  diminished 
according  as  j  sin  mt  is  negative  or  positive.  It  follows, 
however,  from  the  asymmetry  of  the  function,  that  the- 
increase  when  j  sin  mt  is  negative  has  a  far  greater  effect 
on  the  polarization  (E.M.F.)  than  the  diminution  when 
;  sin  mt  is  positive.  This  asymmetry  falls  away  naturally 
when  j  is  so  small  as  compared  with  c  that,  in  the  expansion 
of  the  logarithm  in  series,  only  the  first  term  need  be  re- 
tained, i.  e.  in  the  condition  of  initial  capacity.  So  soon, 
however,  as  this  condition  is  passed,  the  asymmetry  comes 
into  play,  and  this  all  the  sooner  and  the  more  markedly  the 
smaller  c  is.  It  follows,  therefore,  that  the  mean  value 
of  the  E.M.F.  is  not  zero,  but  that  a  direct  current  is  pro- 
duced, which  flows  from  the  small  electrode  to  the  large 
electrode  in  the  solution.  The  asymmetry  brings  with  it  an 
effect  equivalent  to  an  apparent  dilution  of  the  salt  in  the 
neighbourhood  of  the  small  electrode,  even  when  the  mean 
concentration  really  remains  unaltered  (or  even  when  the 
mean  concentration  is  really  increased  by  the  alternating 
current,  as  will  be  shown  sometimes  to  be  the  case). 
Physically  worded,  this  effect  arises  because  a  diminution 
from  a  small  initial  value  of  the  concentration  causes  a  much 
