4 
ME.  G-ASSIOT  ON  THE  STEATIEICATIONS  AND  DAEK  BAND  IN 
commutator,  the  stratifications  appear  from  the  upper  wire,  while  the  lower,  which  is 
now  negative,  has  the  blue  and  red  glow ; but  in  this  case  there  is  a phosphorescent  light 
from  the  surface  of  the  mercury  at  d to  the  lower  wire. 
13.  When  the  connexion  with  the  battery  is  broken,  the  negative  wire  (if  the  dis- 
charge has  been  continuous  for  a short  time)  is  found  to  be  black,  and  the  sides  of  the 
glass  tube  covered  for  a certain  distance  with  minute  greyish  dust,  which  comes  off  as 
the  mercury  ascends  in  the  tube ; this  is  probably  the  condensed  vapour  of  mercur}', 
from  the  vicinity  of  the  heated  negative  wire,  as  the  mercury  removes  the  particles  as  it 
ascends  the  tube,  without  leaving  any  trace  on  its  surface. 
14.  In  some  experiments  which  I made  as  far  back  as  October  1854,  I noticed  a 
deposit  when  the  discharge  was  made  from  platinum  Avires  sealed  in  a glass  globe, 
exhausted  by  means  of  the  air-pump.  I showed  the  globe  to  Dr.  Fakadat,  who  kindly 
tested  and  examined  the  deposit,  and  found  it  to  be  finely  dmded  platinum  in  the 
metallic  state.  At  the  time  I did  not  follow  up  the  experiment ; it  now  occuiTed  to  me 
to  test  this  action  in  the  apparatus,  similar  to  fig.  1,  Plate  I.  (of  which  I had  several 
constructed) : I made  the  discharge  constantly  in  the  same  direction,  the  upper  wire  being 
negative ; the  result  was  that  the  upper  portion  of  the  tube,  as  far  doum  as  a line  di’a’U'n 
even  with  the  end  of  the  wire,  was  covered  with  platinum  in  a minute  state  of  diwsion ; 
when  this  deposit  is  examined  by  transmitted  light  it  is  translucent,  presenting  to  the 
eye  an  extremely  thin  bluish-black  film ; but  by  refiected  light,  either  on  the  outside  or 
inside,  it  has  the  appearance  of  highly  polished  silver,  refiecting  the  light  as  ffoin  the 
finest  mirror^. 
15.  When  the  upper  wire  is  negative  and  the  lower  positive,  if  the  mercury  in  the 
globe  is  allowed  slowly  to  ascend  the  tube  the  stratifications  collapse,  but  the  dark  band 
between  them  and  the  negative  glow  remains ; as  the  mercury  rises,  the  stratification 
merges  into  a series  of  rings  on  the  surface  of  the  mercury,  which,  when  the  cii’cuit  of 
the  primary  is  broken,  is  not  found  to  be  tarnished,  but  as  bright  as  when  the  experi- 
ment commenced. 
16.  If  the  upper  wire  is  positive  and  the  lower  negative,  as  soon  as  the  mercury 
ascends  above  the  negative  wire,  a beautiful  lambent  bluish  white  vapour  appears  to 
arise,  while  a deep  red  stratum  becomes  visible  on  the  surface  of  the  mercury ; as  the  mer- 
cury ascends  in  the  tube,  the  stratified  discharge  from  the  positive  uire  coUapses,  gbing 
the  appearance  of  a compressed  spiral ; on  exhausting  the  globe  the  mercury  descends 
in  the  tube  and  the  stratification  expands,  as  if  the  pressure  on  a spiral  spring  had  been 
removed. 
If,  during  the  exhaustion,  the  descending  mercury  is  permitted  to  remain  stationary 
* Since  I wrote  the  above  my  attention  has  been  drawn  to  Mr.  Grove’s  paper  in  the  Philosophical 
Magazine,  March  1853,  of  which  the  following  is  an  abstract. 
On  the  interior  of  the  tube  was  a dark  pulverulent  deposit,  far  too  minute  in  quantity  for  analysis,  but 
which  had  evidently  proceeded  from  the  platinum ; the  only  possible  mode  in  which  I can  account  for  this 
experiment  is,  that  this  deposit  consisted  of  an  oxide  or  peroxide  of  platinum. 
