8  Pi 
NEW  PROCESS  OF  MANUFACTURING  SODA,  ETC.  125 
block  of  250  kil.  requires  as  a  maximum  a  space  of  a  meter,  and 
the  process  is  complete  in  eight  or  ten  days.  Consequently  a 
space  of  20  meters  by  10,  will  answer  for  200  blocks,  which  will 
furnish  more  than  50,000  kilograms  in  ten  days,  equivalent  to 
5000  kilograms  a  day.  Ten  metric  quintals  of  coke,  worth  in 
England  7  to  8  francs,  suffices  to  carbonate  90  to  100  quintals 
of  dry  and  pure  carbonate  of  soda. 
The  material  when  ready  for  lixiviation  should  be  pulverulent, 
fine,  gray  or  blackish-gray  in  color,  and  without  hard  fragments. 
It  is  well  to  use  a  coarse  seive  to  remove  the  stony  matters  pre- 
sent, retaining  them  to  be  lixiviated  apart,  taking  care  to  reject 
the  insoluble  residue.  The  sifted  powder  forms  with  water  a  lye 
which  is  clear  in  five  or  ten  minutes,  holding  a  heavy  deposit, 
with  often  a  coppery  reflection. 
The  lixiviation  should  be  carried  on  methodically  either  by 
filtration  or  decantation,  by  means  of  warm  water  at  30°  to  409 
O.  Weak  solutions  are  used  in  lixiviating  new  portions  of  the 
powder. 
When  the  exterior  temperature  is  not  too  high,  the  solutions 
furnish  after  24  to  48  hours,  without  concentration,  an  abun- 
dance of  finely  crystallized  limpid  carbonate  of  soda.  By  dropping 
in  a  bit  of  dry  carbonate  of  soda,  the  crystallization  is  often 
hastened. 
The  residue,  principally  sulphuret  of  iron,  is  received  on  a 
filter  or  porous  surface.  In  this  state,  it  alters  slowly.  It  is 
dried  by  heat  or  pressure  and  made  into  a  brick.  It  is  so  com- 
bustible that  it  will  take  fire  below  100°  C,  when  the  drying  is 
nearly  complete.  This  sulphuret  affords  the  sulphur  for  making 
sulphuric  acid,  in  which  change,  the  iron  becomes  peroxyd  and 
is  then  ready  to  be  used  again.  It  is  thus  seen  that  a  single 
proportion  of  sulphur  may  be  utilized  a  large  number  of  times, 
in  transforming  common  salt  into  sulphate  of  soda.  But  the 
oxyd  of  iron  gradually  becomes  impregnated  with  the  impurities 
of  the  common  salt,  the  sulphate  of  soda  and  coal,  and  it  must 
then  be  renewed ;  yet  it  may  be  used  when  it  contains  even  40 
per  cent,  of  impurities. 
When  the  oxyd  of  iron  contains  sulphate  of  soda,  it  is  neces- 
sary to  change  the  proportions  of  the  mixture  for  the  crude 
