Action  of  Metals  and  Liquids, 
55 
ing  that  changes  of  electrical  state  occur  in  metals  under  such  cir- 
cumstances ;  but  a  further  examination  of  the  relations  of  the  tem- 
perature and  chemical  change  to  the  electrical  state  has  not,  that  I  am 
aware,  yet  been  made. 
;  In  an  investigation  on  the  development  of  electric  currents  by  un- 
equally heated  metals  in  liquids  (Phil.  Mag.  1857,  vol.  xiii.  p.  1),  I 
found  that  hot  platinum  was  electro-negative  to  cold  platinum  in 
liquids  of  acid  reaction,  and  positive  to  it  in  alkaline  ones,  provided 
in  all  cases  chemical  action  was  completely  or  sufficiently  excluded. 
In  the  present  experiments  I  have  endeavoured  to  ascertain  what 
electrical  changes  are  produced  in  cases  where  chemical  action  more 
freely  occurs,  and  I  have  therefore  employed  not  platinum  plates, 
but  plates  composed  of  ametal(copper)  which  is  more  easily  corroded. 
To  effect  the  object  I  had  in  view,  I  used  the  apparatus  shown  in 
section  in  fig.  1,  aud  in  perspective,  with  its  wooden  support,  in  fig.  2. 
'.  A  and  B,  fig.  1,  are  two  open  thin  glass  dishes,  6  J  inches  dia- 
meter, and  1|  inch  deep,  with  open  necks.  .  The  dishes  are  joined 
together,  water-tight,  by  a  bent  glass  tube,  C,  about  I  inch  in  dia- 
meter ;  and  the  whole  arrangement  is  securely  fixed  upon  a  wooden 
frame  or  stand,  so  that  it  may  be  at  once  placed  in  an  exactly  hori- 
zontal position,  or  inverted  to  pour  out  its  contents.  D  and.E  are 
two  dishes  of  sheet  copper  of  moderate  thickness,  made  from  con- 
tiguous portions  of  a  sheet  of  metal  to  ensure  electrical  homoge- 
neity in  the  experiments.  Wires  of  similar  metals  are  attached  to 
the  dishes  for  the  purpose  of  connexion  with  a  galvanometer.  A 
galvanometer,  containing  about  180  turns  of  moderately  fine  copper 
wire,  is  sufficiently  sensitive  for  the  experiments.  The  outside  of  the 
metal  dishes  must  be  made  perfectly  clean  and  bright  immediately 
before  each  experiment. 
In  using  the  apparatus  it  is  first  set  exactly  horizontal,  and  a  known 
and  measured  volume  of  the  clear  liquid  to  be  examined,  at  the  tern- 
