124        NEW  PROCESS  OF  MANUFACTURING  SODA,  ETC. 
sity.    The  surface  has  a  coppery  reflection.    In  fracture,  it  has 
a  uniform  aspect,  a  crystalline  texture,  and  a  greenish  and  - 
brilliant  metallic  reflection. 
It  now  remains  to  treat  this  crude  ferruginous  soda,  so  as  to 
draw  off  on  one  side  the  soluble  carbonate  of  soda,  and  on  the 
other  the  insoluble  sulphuret  of  iron.  The  method  used  with  the 
crude  calcareous  soda  would  give  only  bad  results.  In  fact,  the 
mass  expands  on  the  action  of  water,  becomes  very  voluminous, 
difficult  to  wash,  and  affords  a  liquid  containing  much  caustic 
soda  and  also  sulphuret  of  sodium. 
The  washing  is,  however,  easy  after  a  preparatory  operation 
which  M.  Kopp  calls  "  delitation."  It  is  as  follows  :  The  crude 
ferruginous  soda  left  exposed  to  the  air  under  a  shed,  undergoes 
a  change,  which  is  the  more  rapid  if  the  air  be  charged  with 
moisture  and  carbonic  acid.  The  lustre  fades,  the  block  breaks 
to  pieces  and  becomes  covered  with  an  abundant  blackish  pul- 
verulent material ;  and  this  goes  on  so  rapidly  that  in  a  few  hours 
it  is  reduced  to  a  hillock  of  this  powdered  substance. 
This  change  is  due  to  the  absorption  of  oxygen,  water  and 
carbonic  acid,  while  heat  is  given  out,  which,  without  care,  may 
rise  even  to  ignition,  in  which  case  the  powder  has  a  reddish  as- 
pect, and  contains  sulphate  of  soda  with  10  to  15  per  cent,  of 
carbonate  of  iron  and  a  little  sulphuret.  But  this  high  heat  is 
prevented  by  removing  the  powder  from  the  surface  as  it  accumu- 
lates, so  as  to  leave  the  interior  open  to  the  air  and  carbonic  acid. 
Water  then  separates  from  it  carbonate  of  soda,  and  the  residue 
consists  principally  of  sulphuret  of  iron. 
M.  Kopp  aids  the  process  by  an  artificial  supply  of  cold  and 
moist  carbonic  acid,  as  the  action  of  the  air  is  very  slow.  This 
process,  which  he  calls  "  carbonation"  is  as  follows:  In  a  cham- 
ber, at  a  height  of  two  and  a  half  meters,  a  grating  of  cast-iron 
is  placed,  whose  spaces  are  one  and  a  half  centimetres.  The 
earth  is  removed  to  about  a  depth  of  one  meter.  The  roof  of 
the  chamber  is  about  two  and  a  half  meters  above  the  grating. 
The  walls  have  numerous  holes  for  the  passage  and  circulation 
of  the  air.  In  the  lower  part,  the  carbonic  acid  is  introduced. 
The  blocks  of  crude  ferruginous  soda  are  placed  on  the  grating, 
on  their  small  face  ;  and  as  they  crumble,  the  powder  falls  below 
where  it  encounters  and  rapidly  absorbs  the  carbonic  acid.  A 
