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ON  THE  MANUFACTURE  OF  SALTPETRE. 
ON  THE  MANUFACTURE  OF  SALTPETRE. 
By  J.  H.  Swindells. 
I  have  lately  examined  several  lots  of  refuse  (muriate  of  soda, 
&c.)  from  various  saltpetre  makers,  and  find  a  serious  loss  of  pot- 
ash and  other  materials.     The   refuse  from  saltpetre  works 
is  mostly  sold  for  manure,  either  alone  or  mixed  with  other  sub- 
stances.  From  the  analysis  I  give  below  it  will  be  seen  that  this 
refuse  in  many  cases  contains  a  large  amount  of  potash,  &c,  thus 
showing  bad  and  careless  working. 
Analysis  of  muriate  of  soda. 
Muriate  of  soda,  ....  70-50 
Muriate  of  potash,  ....  8-81 
Nitrate  of  potash,       .  .  .  .  6.15 
The  rest  was  made  up  of  sulphate  of  lime,  insoluble  matter, 
and  water.  Another  sample  showed  very  near  working ;  it  gave 
me 
Muriate  of  soda,         .  .  .  .  9743 
Nitrate  of  soda,         .  ,  .  .1-10 
Insoluble  matter,  sulphate  of  lime,  &c,  formed  the  remainder. 
Twelve  samples  of  refuse  gave  me  an  average  of  5*6  per  cent, 
of  potash  lost  in  working.  Several  samples  gave  me  a  large 
amount  of  insoluble  matter,  owing,  1  should  imagine,  to  the 
"sweeping  up"  of  the  factory,  and  to  the  muriate  of  potash, 
which  in  many  cases  I  know  contains  a  larger  amount  of  foreign 
matter  than  it  ought  to  do,  although  it  is  sold,  generally  speak- 
ing, with  a  guarantee  that  it  contains  "  80  per  cent." 
I  will  now  give  a  short  account  of  the  method  generally  fol- 
lowed in  the  manufacture,  and  a  recommendation  of  my  own  to 
prevent  loss  of  materials.  In  all  the  manufactories  I  have  been 
able  to  visit  the  process  was  asibllows  :  A  certain  weight  of  mu- 
riate of  potash  and  nitrate  of  soda  was  put  into  an  iron  pan  along 
with  a  quantity  of  water.  The  steam  was  then  blown  into  the 
"mixture,"  which  is  stirred  about  till  such  time  as  it  is  thought 
the  muriate  and  nitrate  are  dissolved.  The  liquid  is  then  run  or 
syphoned  into  a  tank,  and  after  a  certain  time  the  resulting 
crystals  are  removed,  and  invariably  refined.  The  last  process 
is  simply  done  by  dissolving  down  the  crystals  and  re-crystalliz- 
