174  NEW  PROCESSES  FOR  COVERING  METALS,  ETC. 
produce  a  series  of  results  which  it  has  hitherto  been  found  im- 
possible to  produce,  either  directly  or  in  a  durable  manner. 
Coppering. 
Composition  of  the  Coppering  Solution.- — In  ten  litres  of  water 
dissolve, 
Crystallized  sulphate  of  copper     .        .       350  grammes. 
Crystallized  sodio-potassic  tartrate        .  1*500 
Soda  lime  containing  from  50  to  60 
per  cent,  of  free  soda       .       .       .       800  " 
This  solution,  which  always  gives  very  satisfactory  results, 
contains  nearly  two  equivalents  of  tartaric  acid  to  one  of  oxide 
of  copper.  * 
Action  of  Various  Metals  on  this  Solution. — Iron,  cast  iron 
and  steel,  as  well  as  the  metals  whose  oxides  are  insoluble  in 
potash  and  soda,  undergo  no  change  when  introduced  into  these 
baths.  For  coppering,  the  zinc  or  lead  is  plunged  into  the  bath, 
•care  being  taken  that  the  iron,  cast  iron  or  steel  articles  should 
not  touch  each  other,  but  that  one  of  them  should  be  in  contact 
with  the  zinc.  The  copper  was  thus  deposited  upon,  and  strong- 
ly adhered  to  the  iron. 
The  coating  of  copper  increased  within  certain  limits  with  the 
duration  of  the  immersion.  The  author  feels  bound  to  admit 
that  galvanic  action  alone  will  not  effect  the  coppering  of  iron, 
cast  iron  and  steel,  under  the  foregoing  conditions. 
In  fact,  the  metals  whose  oxides  are  insoluble  in  potash  or 
soda,  and  form  only  one  basic  oxide,  become  covered  in  the  baths 
with  but  a  pellicle  of  copper,  the  thickness  of  which  does  not  in- 
crease with  the  length  of  time  of  immersion. 
!Pure  tin  introduced  into  the  cold  solution  does  not  become 
coppered ;  by  contact  with  zinc  it  oxidizes  ;  the  protoxide  of  tin 
there  formed  reduces  the  copper  solution,  and  protoxide  of  red 
copper  is  precipitated.  The  liquid  holds  no  copper  in  solution 
after  an  excess  of  tin  has  been  for  some  time  immersed  in  it. 
Process  of  coppering. — The  iron,  cast  iron,  or  steel  articles  are 
thoroughly  cleansed  by  acidulated  water  ;*  they  are  then  washed 
*  The  water  acidulated  with  sulphuric  acid  to  2°  B.  The  action  shoald 
be  continued  from  five  to  twenty  minutes. 
