ELECTRO-CHEMICAL  COLORING   OF  METALS. 
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in  this  paper,  so  as  to  furnish  me  with  a  means  of  preparing 
this  oil  in  larger  quantity  than  I  have  heretofore  obtained  it. — 
Ohem.  News,  London,  July  6,  1861. 
ON   ELECTRO-CHEMICAL    COLORING  AND  THE  DEPOSITION 
OF  PEROXIDE  OF  IRON  ON  PLATES  OF  STEEL  AND  IRON. 
By  M.  Becquerel, 
Priestly  was  the  first  to  obtain  colored  rings  by  means  of 
electricity,  by  receiving  strong  charges  from  a  battery,  with  a 
surface  of  about  two  square  metres,  on  metal  plates,  by  means 
of  metallic  points  directed  perpendicularly  to  their  surface. 
Nobili,  in  1827,  afterwards  produced  colored  rings  on  plati- 
num, gold,  silver,  and  brass  plates,  by  putting  them  in  communi- 
cation with  one  of  the  two  poles  of  a  voltaic  pile,  plunging  them 
into  metallic  and  nonmetallic  solutions,  and  then  by  directing 
perpendicularly  to  their  surface  a  platinum  point  connected  with 
the  other  pole.  With  positive  silver,  for  instance,  and  solution 
of  sea  salt,  he  obtained  a  series  of  concentric  circles  surrounded 
with  irises,  the  tints  being  slightly  dimmed  by  contact  with  the 
air.     On  heating  the  plates  all  the  rings  took  a  red  tint. 
I  began  to  study  the  electro-chemical  coloration  of  metals 
in  1843,  my  chief  object  being,  not  to  produce  colored  rings, 
but  to  deposit  on  plates  of  gold,  platinum,  copper,  and  silver, 
thin  and  uniform  layers  of  peroxide  of  lead  presenting  successive- 
ly, according  to  the  duration  of  the  operation,  which  was  gener- 
ally very  short,  the  rich  colors  of  the  spectrum.  The  operation 
consists  in  plunging  into  an  alkaline  solution  of  protoxide  of 
lead  the  piece  to  be  colored,  put  in  connection  with  the  posi- 
tive pole  of  a  voltaic  pile  charged  with  nitric  acid  and  compo- 
sed of  many  layers  of  plates,  and  closing  the  circle  with  a 
platinum  wire  in  communication  with  the  negative  pole,  and  of 
which  but  the  point,  which  alone  touches  the  alkaline  solution, 
is  continually  in  motion.  In  contact  with  the  object  to  be 
colored,  the  protoxide  of  lead,  which  forms  the  positive  elec- 
trode super-oxidises,  becomes  insoluble  in  the  alkali,  and  de- 
posits itself  on  the  surface  in  slight  adherent  layers,  producing 
the  color  of  the  thin  plates.    Air  and  light  gradually  fade 
