Action  of  Metals  and  Liquids 
73 
Influence  of  Friction. 
To  ascertain  if  the  friction  of  one  of  the  electrodes  against  the 
liquid  had  similar  effects  to  those  produced  by  the  direct  application 
of  heat,  I  employed  the  apparatus  shown  in  fig.  10.  The  sketch 
does  not  require  explanation. 
Experiment  1. — By  immersing  two  stout  copper  wires  vertically 
in  an  acidulated  solution  of  cupric  sulphate  and  rotating  one  of  them 
at  a  speed  of  about  5000  revolutions  per  minute,  the  rotating  wire 
became  electropositive. 
Experiment  2. — With  a  saturated  solution  of  bornx,  the  rotating 
wire  was  positive. 
Experiment  3. — With  a  solution  of  cyanide  of  potassium,  the 
rotating  wire  was  negative. 
Experiment  4. — With  stout  platinum  wires  in  an  acidulated  solu- 
tion of  cupric  sulphate,  the  rotating  wire  became  negative. 
Experiment  5. — With  platinum  wires  in  a  solution  composed  of 
200  grains  of  carbonate  of  potassium  in  40  ounces  of  distilled  water, 
the  rotating  wire  was  faintly  positive,  and  similarly  in  a  very  dilute 
solution. 
Experiment  6. — With  two  platinum  disks  one  above  the  other 
in  a  strong  solution  of  carbonate  of  potassium,  revolving  the  upper 
disk  at  a  speed  of  about  5000  revolutions  per  minute  made  it  electro- 
positive. 
Experiment  7. — With  an  acidulated  solution  of  cupric  sulphate, 
the  revolving  disk  became  feebly  negative. 
On  comparing  these  results  with  those  obtained  by  unequal  tempe- 
rature, we  find  that  the  directions  of  the  currents  in  the  two  classes 
of  cases  were  reverse  with  copper  in  solutions  of  acidulated  cupric 
sulphate  and  cyanide  of  potassium,  and  similar  in  a  solution  of  borax  ; 
and  with  platinum  in  solutions  of  acidulated  cupric  sulphate  or  car- 
bonate of  putassium  the  influence  of  friction  and  of  increased  tern- 
