Passage  of  Electricity  through  Liquids.  532 
thus,  in  spite  of  this  difference  in  the  mode  of  conduction,  the 
electrolytes  must  be  subject  to  the  same  laws  of  the  distribution 
of  the  current  as  the  metals.  Hence  both  Ohm's  law  and 
KirchhofF's  propositions  on  derived  currents  must  hold,  and  the 
potential  of  free  electricity  in  the  case  of  a  linear  conductor  must 
be  coustant  within  the  same  section. 
Ohm's  law  has  been  so  much  tested  for  electrolyzable  liquids 
with  an  undivided  circuit  that  it  can  be  taken  as  sufficiently 
proved. 
Yet  in  one  particular  case  the  laws  of  divided  circuits  seem 
to  experience  an  exception.  Poggendorff*  found  that  the  resist- 
ance of  a  very  thin  platinum  wire  stretched  in  the  axis  of  a  ver- 
tical glass  cylinder  of  3J  inches  diameter  was  unaltered  when 
this  cylinder  was  filled  to  a  height  of  6f  inches  with  dilute  sul- 
phuric acid.  There  was  no  trace  of  a  lateral  extension,  or  of  a 
division  of  the  current  between  the  metal  and  the  liquid. 
Jacobi  subsequently  f  made  similar  experiments  with  German- 
silver  or  platinum  wires  which  were  stretched  on  a  wooden 
trough  20  inches  long  by  3£  broad  and  4  high,  lined  with  ma- 
rine glue.  In  one  case,  when  the  trough  was  filled  with  sulphate 
of  copper,  a  very  slight  diminution  of  the  resistance  of  the  Ger- 
man-silver wire  was  observed  by  the  aid  of  Wheatstone's  bridge; 
in  another  experiment  with  German-silver  wire  and  platinum 
wire  a  diminution  of  the  resistance  could  not  be  detected  by  the 
same  method ;  on  the  other  hand,  at  the  end  of  the  German-silver 
wire  towards  the  negative  pole  of  the  circuit  there  was  a  depo- 
sition of  copper,  while  at  the  other  end  the  wire  was  attacked 
and  even  eaten  through.  The  deposition  of  copper  and  the  cor- 
rosion were  strongest  at  the  ends.  The  platinum  wire  showed 
only  a  trace  of  a  copper  precipitate  at  the  end  turned  towards 
the  negative  pole. 
It  has  therefore  been  supposed,  and  Wiedemann  has  also  ex- 
pressed the  idea  J,  that  this  apparent  irregularity  in  the  division 
of  the  current  between  wire  and  liquid  has  its  origin  in  a  pola- 
rization at  the  limit  of  metal  and  liquid,  produced  by  the  electro- 
chemical decomposition  of  the  liquid,  and  that,  when  this  pola- 
rization is  wanting,  part  of  the  electric  current  actually  does 
flow  through  the  liquid. 
The  following  experiments  have  confirmed  this  supposition. 
A  glass  trough,  442  millims.in  length,  60*6  millims.  in  breadth, 
and62#5  millims.  in  height,  was  constructed  of  plate  glass  cemented 
with  sealing-wax.  In  the  middle  of  the  bottom-plate  a  platinum 
wire  of  the   same  length   and  0076  millim.  in  diameter  was 
*  Pogg.  Ann.  vol.  lxiv.  p.  54  (1845). 
t  Ibid.  vol.  lxix.  p.  181(1846). 
%  Wiedemann,  Galvanismus,  vol.  i.  p.  138. 
