68       Royal  Society : — Mr.  G.  Gore  on  the  Thermo-electric 
The  currents  obtained  with  copper  plates  were  no  doubt  influ- 
enced in  their  amounts  (if  not  also  in  their  direction)  by  the  oxidizing 
action  of  the  air  upon  the  liquid  and  metal  at  their  line  of  mutual 
contact ;  for  we  know  that  metals  in  contact  with  liquids  oxidize 
much  more  quickly  if  oxygen  has  access  to  their  wet  surfaces.  And 
the  currents  were  also  influenced  by  the  action  of  unequal  temperature 
upon  this  air-contact  line ;  for  we  know  that  wet  metals  oxidize  still 
more  rapidly  if  heat  is  applied. 
Influence  of  line  of  contact  of  liquid  and  metal  with  the  air. 
That  the  length  of  line  of  contact  of  the  liquid  and  copper  with 
the  air  is  capable  of  producing  electric  currents  was  shown  by  the 
following  experiments : — 
Two  strips  of  sheet  copper  of  the  annexed  form  (fig.  5),  f  inch  wide, 
Fig.  5. 
Fig. 
6. 
and  12  inches  long  in  the  longest  limb,  were  cut  from  contiguous 
parts  of  a  sheet  of  copper,  and,  after  being  perfectly  cleaned,  were 
coiled  into  the  shape  represented  by  the  annexed  sketch,  fig.  6. 
They  were  then  placed  in  a  flat-bottomed  porcelain  dish  and  con- 
nected with  the  galvanometer,  one  of  the  spirals  being  supported  at 
About  I  inch  higher  than  the  other  by  means  of  a  triangle  of  glass 
rod.  The  liquid  to  be  examined  was  then  poured  into  the  dish  until 
it  just  (and  completely)  covered  the  lower  spiral,  and  the  direction 
and  amount  of  the  permanent  deflection  noted.  The  positions  of  the 
spirals  were  then  reversed  and  the  electrical  effects  again  noted. 
Experiment  1. — With  a  liquid  composed  of  100  grains  of  cya- 
nide of  potassium  dissolved  in  12  ounces  of  water,  whichever  of  the 
spirals  was  only  partly  submerged  and  therefore  had  the  longest  air- 
line, was  strongly  electro-negative  to  the  wholly  submerged  one. 
Experiment  2. — With  a  mixture  of  one  measure  of  strong  nitric 
acid  and  ten  measures  of  water,  deflections  of  somewhat  less  amount, 
but  in  precisely  similar  directions  to  those  of  experiment  I,  took 
place. 
Experiment  3. — With  dilute  hydrobromic  acid  the  directions  of 
the  deflections  were  also  similar,  but  still  less  in  amount. 
Experiment  4. — With  a  half-saturated  solution  of  borax  very  feeble 
deflections,  agreeing  in  direction  with  those  of  the  other  experiments, 
were  obtained. 
These  results  show  the  necessity  (which  I  have  already  mentioned) 
of  excluding  air-bubbles  from  beneath  the  copper  dishes,  and  of  not 
