66       Royal  Society  : — Mr.  G.  Gore  on  the  Thermo-electric 
of  potassium ;  bromide  of  potassium  (strong  solution) ;  iodide  of 
potassium  (strong  solution)  ;  carbonate,  acid  carbonate,  and  bichro- 
mate of  potassium  ;  aqueous  ammonia;  chloride  of  ammonium  ;  cya- 
nide and  ferrocyanide  of  potassium  ;  acetate  of  zinc ;  and  acetate  of 
sodium.  And  negative  in  the  following  ones : — nitric,  chloric,  hy- 
drobromic,  hydrofluosilicic,  and  sulphuric  acids ;  ferrous  sulphate ; 
chloride  of  copper  (strong  solution)  ;  sulphate  of  copper ;  sulphate 
of  zinc  (strong  solution)  ;  nitrate  and  iodide  of  sodium  (weak  solu- 
tions) ;  bromide  and  iodide  of  potassium  (weak  solutions)  ;  iodate 
of  potassium  ;  chrome  alum ;  nitrate  of  ammonium ;  oxalic,  acetic, 
tartaric,  and  citric  acids.  The  number  of  liquids  in  which  hot  cop- 
per was  positive  was  thirty-six,  and  of  those  in  which  it  was  negative 
was  twenty. 
In  several  instances  where  the  hot  metal  was  negative  with  a  weak 
solution,  it  became  positive  with  a  strong  one — for  instance,  with 
sulphate  of  zinc,  nitrate,  iodide,  and  sulphate  of  sodium,  bromide 
and  iodide  of  potassium ;  but  with  chloride  of  copper  the  reverse 
occurred.  These  results  may  be  connected  with  the  fact  that  in  weak 
neutral  solutions  the  chemical  actios  is  generally  the  most  feeble,  and 
therefore  interferes  the  least  with  the  direct  influence  of  the  heat  in 
producing  electric  currents. 
The  influence  of  free  hydrochloric,  hydrocyanic,  boracic,  ortho- 
phosphoric,  and  chromic  acids  was  to  make  the  hot  copper  positive  ; 
whilst  that  of  nitric,  chloric,  hydrobromic,  hydrofluosilicic,  sulphuric, 
and  some  of  the  organic  acids  was  to  make  it  negative. 
In  consequence,  probably,  of  the  small  amount  of  interference  by 
chemical  action  in  solutions  of  oxalic,  acetic,  tartaric,  and  citric 
acids,  the  direct  influence  of  the  heat  made  the  copper  negative — 
similar  to  its  influence  on  platinum  in  all  acid  liquids  which  do  not 
attack  that  metal. 
The  nature  of  the  acid  in  a  salt  appears  to  exert  much  more  in- 
fluence than  that  of  the  base  on  the  direction  of  the  current ;  for 
instance,  in  nearly  all  chlorides,  including  those  of  a  considerable 
variety  of  bases,  hot  copper  was  positive,  probably  because  copper  is 
more  readily  attacked  by  acids  than  by  bases. 
In  all  decidedly  alkaline  liquids  the  hot  copper  was  positive ; 
this  is  similar  to  the  behaviour  of  platinum  in  such  solutions,  and  is 
probably  due  to  the  same  cause,  viz.  the  direct  influence  of  the  heat, 
as  well  as  to  chemical  action. 
The  results  also  show  that  the  quantity  of  the  current  obtained  with 
any  given  liquid  generally  increases  with  the  number  of  molecules  of 
the  substance  contained  in  the  solution ;  in  some  cases,  however,  as 
with  sulphuric  acid,  carbonate  of  potassium,  chloride  of  ammonium, 
and  acetate  of  zinc,  there  was  a  limit  to  this  increase ;  and  beyond 
that  limit  the  quantity  of  the  current  decreased  up  to  the  point  of 
saturation  of  the  liquid. 
In  the  great  majority  of  cases  the  value  of  the  deflection  increased 
much  more  rapidly  than  the  strength  of  the  solution,  particularly 
with  solutions  of  sulphate  of  magnesia,  and  also  of  hydrochloric  acid 
and  of  chloride  of  sodium,  probably  because  two  causes  operated, 
