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260  ON  CHEMISTRY  APPLIED  TO  THE  ARTS. 
of  superphosphate  of  lime  is  so  simple  that  any  farmer  possess- 
ing a  knowledge  of  the  mere  rudiments  of  chemistry  can  make 
it  for  himself,  by  which  he  will  not  only  effect  great  economy,  but 
also  secure  genuineness  of  product.  All  he  requires  is  a  wooden 
vessel  lined  with  lead,  into  which  he  can  place  1000  lbs.  of  ground 
boiled  bones,  1000  lbs.  of  water,  and  500  lbs.  of  sulphuric  acid 
sp.  gr.  1-845  (or  concentrated  vitriol),  mixing  the  whole,  and 
stirring  well  for  about  twelve  hours.  After  two  or  three  days  a 
dry  mass  remains,  which  only  requires  to  be  taken  out  and  placed 
on  the  land  by  means  of  the  drill,  or  to  be  mixed  with  water  and 
sprinkled  on  the  land.  When  very  large  quantities  of  this  manure 
are  required,  the  plan  devised  by  Mr.  Lawes  appears  to  be  the 
best  suited.  It  consists  in  introducing  into  the  upper  end  of  a 
slightly-inclined  revolving  cylinder  a  quantity  of  finely-ground 
boiled  bones,  together  with  a  known  proportion  of  sulphuric  acid 
of  sp.  gr.  1*68.  As  the  materials  slowly  descend  by  the  revo- 
lution of  the  cylinder  they  become  thoroughly  mixed,  and  leave 
it  in  the  form  of  a  thick  pasty  mass,  which  is  conducted  into  a 
large  cistern  capable  of  containing  100  tons,  or  a  day's  work. 
This  is  allowable  to  remain  for  twelve  hours,  when  it  is  removed, 
and  is  ready  for  use.  Most  manufacturers  find  it  necessary  to 
add  to  the  phosphate  of  lime  of  bones  other  sources  of  phosphates, 
such  as  coprolites,  or  the  fossil  dung  of  antediluvian  animals, 
which  have  been  found  in  large  quantities  in  Suffolk,  Cambridge- 
shire, and  elsewhere,  and  contain  from  36  to  62  per  cent,  of 
phosphate  of  lime,  and  from  7  to  38  per  cent,  of  organic  matter. 
Others  employ  a  mineral  substance  called  apatite,  containing 
about  92  per  cent,  of  phosphate  of  lime,  and  found  also  in  large 
quantities  in  Spain  Norway,  France,  &c.  Others,  again,  em- 
ploy guanos  rich  in  phosphate  of  lime,  such  as  those  of  Kooria 
Mooria  Islands  and  Sombrero  phosphates.  The  following  is 
the  average  composition  of  the  superphosphate  of  lime  of  com- 
merce : — 
Soluble  phosphate       .       .       .    22  to  25  per  cent. 
Insoluble      "     .       .       i       .      8  "  10 
Water  10  "  12  « 
Sulphate  of  lime  .       .       .       .    35  "  45  " 
Organic  matter    .        .       .       .    12  "  15  " 
Nitrogen,  0-75  to  1*5  per  cent. 
