ON  THE  MANUFACTURE  OF  SALTPETRE. 
121 
ing.  I  found  that  no  hydrometers  were  used  for  ascertaining 
the  density  of  the  liquids,  but  that  everything  was  done  on  the 
"  guess  "  principle.  By  following  this  process  a  loss  will  always 
occur  ;  for  how  is  it  possible  to  tell  when  all  the  materials  have 
thoroughly  dissolved?  Moreover,  it  takes  a  longer  time  to  dis- 
solve the  materials  together  than -it  would  occupy  if  the  muriate 
and  nitrate  were  dissolved  separately. 
The  chemical  action  is  too  well  known  to  be  described  here  ;  I 
will,  therefore,  proceed  to  consider  the  best  way  of  preventing 
any  loss  of  materials.  I  would  recommend  that  the  muriate  of 
potash  should  be  dissolved  in  as  little  water  as  possible ;  then 
dissolve  the  nitrate  of  soda  also  in  as  little  water  as  may  be  con- 
venient, add  the  two  solutions  together  and  boil  for  one  hour  or 
so.  This  will  precipitate  a  portion  of  the  muriate  of  soda, 
which  may  be  "  fished  "  out  of  the  pan.  The  liquid  will  now  be 
found  to  have  a  specific  gravity  of  about  1-200, 1/250,  or  1*275, 
according  to  the  manner  in  which  the  "  dissolving  and  boiling  " 
down  is  conducted.  The  liquid,  after  remaining  at  rest  2  hours 
or  so,  may  be  run  into  the  coolers  in  the  usual  way  to  allow  the 
nitrate  of  potash  to  crystallize  out  of  the  liquor ;  of  course  all 
the  nitrate  of  potash  does  not  crystallize  out.  A  quantity  re- 
mains in  the  "mother  liquor,"  a  portion  of  which  may  be  used 
for  dissolving  the  raw  materials.  The  mother  liquor,  however, 
should  not  be  too  strong,  as  neither  the  muriate  nor  nitrate  dis- 
solve well  in  strong  mother  liquor ;  about  15  Twaddell  will  be 
found  about  the  strength.  When  the  "  mothers  "  begin  to  in- 
crease and  become  too  many  for  "dissolving"  purposes,  they 
must  be  salted  down  and  crystallized.  This  is  done  by  placing 
them  in  an  evaporating  pan,  and  boiling  them  down  to  about  35° 
or  so,  Twaddell ;  care  must  be  taken  to  remove  the  muriate  of 
soda  as  it  falls  to  the  bottom  of  the  pan.  This  may  be  done  by 
means  of  perforated  ladles.  There  is  sure  to  be  a  little  nitrate  of 
potash  clinging  to  the  muriate  of  soda,  and  the  manner  of  sepa- 
rating this  must  be  considered.  Even  when  there  is  so  much  as 
5  per  cent,  of  potash  mixed  with  the  muriate  of  soda,  it  will 
scarcely  pay  to  extract  it,  unless  coals  are  very  cheap  ;  for  the 
entire  mass  would  have  to  be  dissolved,  and  the  liquor  evapo- 
rated down  to  the  crystallizing  point.    I  would  recommend  the 
