PRECIPITATION  OF  VARIOUS  SALTS,  ETC. 
45 
muriatic  acid  is  allowed  to  dissolve  at  the  surface  of  a  liquid  in 
repose,  as  is  usually  done  in  the  condensation  of  this  acid. 
The  separation  of  chloride  of  potassium  from  the  mother- 
liquors  of  salt  marshes  is  more  rapid,  more  complete,  and  cheap- 
er than  the  process  now  employed,  whieh  consists  in  concentra- 
ting the  mother-liquors  by  heat,  and  leaving  them  to  crystallize 
under  conditions  of  temperature  which  are  not  always  to  be  ob- 
tained with  certainty.  Moreover,  the  product  obtained  is  a  triple 
chloride  of  sodium,  potassium,  and  magnesium,  a  compound  which 
must  be  purified  by  successive  crystallizations,  causing  a  loss  of 
time,  fuel,  and  material.  By  the  action  of  muriatic  acid  upon 
the  mother-liquors,  nearly  the  whole  of  the  chlorides  of  sodium 
and  potassium  contained  in  them  is  obtained ;  the  chloride  of 
magnesium  remains  in  the  solution,  which  may  be  employed  in 
the  manufacture  of  chloride  of  lime.  The  chlorides  of  sodium 
and  potassium  are  separated  without  difficulty,  either  by  dividing 
the  precipitation,  or  by  their  different  degrees  of  solubility  when 
hot  and  cold. 
The  advantages  of  this  process  in  the  production  of  crude  salt 
do  not  appear  to  be  doubtful.  About  salt-works  there  are  gene- 
rally manufactories  of  sulphate  of  soda,  which  are  a  constant 
source  of  muriatic  acid.  The  whole  of  this  acid  is  not  collected 
in  some  places,  its  sale  being  difficult  from  the  cost  of  transport. 
Supposing  that  all  the  muriatic  acid  produced  would  be  sold,  100 
kilogrms.  of  salt  converted  into  sulphate  of  soda  would  reproduce 
rather  more  than  33  per  cent,  of  their  weight  in  common  salt. 
If  it  were  found  more  advantageous  to  apply  all  the  muriatic  acid 
in  precipitation,  a  much  larger  quantity  of  salt  would  be  regen- 
erated in  this  manner.  100  kilogrms.  of  chloride  of  sodium, 
decomposed  by  sulphuric  acid,  give  62.39  kilogrms.  of  muriatic 
acid,  which  require  109-1  kilogrms.  of  water  to  furnish  a  solution 
of  the  density  of  the  muriatic  acid  of  commerce  (1*18).  This 
quantity  of  water  at  the  ordinary  temperature  would  dissolve, 
and  consequently  allow  of  the  precipitation  of  38»18  kilogrms.  of 
salt. 
The  solution  of  muriatic  acid,  if  it  be  not  sold,  will  give  when 
gently  heated  43*2  kilogrms.  of  gas,  which  precipitate  26-45 
kilogrms.  more  salt ;  and  the  solution,  when  deprived  of  all  the 
gas  which  it  is  capable  of  giving  off,  will  represent  acid  with  16 
