CHLORIDE  OF  POTASSIUM  FROM  CARNALLITE.  315 
of  Camargue,  in  the  south  of  France,  by  the  process  of  BalartL 
It  is,  however,  obtained  from  carnallite  so  much  more  cheaply 
that  it  already  competes  in  Paris  with  the  French  article,  and 
threatens  entirely  to  supersede  it. 
Carnallite  is  found  at  Stassfurth  in  inexhaustible  quantities. 
The  superficial  extent  of  the  bed  of  "  refuse  "  salt  is  estimated 
to  be  450  square  kilometres,  in  which  the  strata,  consisting 
chiefly  of  carnallite  (containing  about  60  per  cent.)  has  a  thick- 
ness of  19  metres. 
The  small  portion  of  the  bed  which  has  been  opened  at  Stass- 
furth and  Anhalt  already  assures  to  the  business  of  manufactur- 
ing chloride  of  potassium  an  almost  unlimited  future.  Unfor- 
tunately, however,  the  business  has  been  driven  with  feverish 
speed — 18  manufactories  have  been  erected  there — so  that  the 
demand  for  saltpetre  and  alum  cannot  absorb  the  production.  It 
has  therefore  been  necessary  to  seek  other  uses  for  it.  What 
first  presented  was  the  conversion  of  the  chloride  of  potassium 
into  carbonate  of  potassa  (potashes),  which  can  be  accomplished 
in  the  same  manner  as  chloride  of  sodium  is  converted  into  car- 
bonate of  soda.  The  chloride  of  potassium  may  be  changed  to 
sulphate  of  potassa  by  heating  it  with  sulphuric  acid.  This  may 
then  be  roasted  with  carbonate  of  lime  and  charcoal,  by  which 
sulphuret  of  calcium  and  carbonate  of  potassa  are  produced,  the 
latter  of  which  may  be  removed  by  water.  In  the  south  of 
France  a  large  amount  of  carbonate  of  potassa  is  obtained  in  this 
way.  Sulphuric  acid,  however,  is  not  used  there  to  convert  the 
chloride  of  potassium  into  sulphate  of  potassa,  but  this  is  done 
by  means  of  sulphate  of  magnesia.  The  mother  liquors  of  the 
sea-salt  afford,  by  evaporation  in  the  air,  in  the  first  place,  an 
almost  pure  chloride  of  sodium,  then  a  mixture  of  sulphate  of 
magnesia  and  chloride  of  sodium,  and  finally  a  very  impure  chlo- 
ride of  potassium.  Considerable  quantities  of  the  two  last  de- 
posits are  dissolved  in  boiling  water,  so  that  one  atom  of  chlo- 
ride of  potassium  comes  into  contact  with  more  than  two  atoms 
of  sulphate  of  magnesia  ;  upon  cooling,  a  double  salt  of  sulphate 
of  magnesia  and  sulphate  of  potash  crystallizes  out,  in  beautiful 
large  crystals  (MgO,S03+KO,SOs+6HO),  while  chloride  of 
magnesium  is  formed  at  the  same  time.   This  salt  is  decomposed 
