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ACID  PHOSPHATE. 
A PAPER  READ  BEFORE  THE  AGRICULTURAL  SEMINAR. 
By  C.  C.  James. 
For  the  manufacture  of  good  commercial  acid  phosphate  from 
phosphate  rock  two  things  are  absolutely  necessary: 
ist. — Fine  grading  of  the  rock. 
2nd. — Correct  proportioning  of  the  rock  and  acid. 
As  the  rock  coming  from  the  mine  contains  large  pieces  and 
hard  lumps  it  must  be  crushed  first  and  put  into  the  proper  con- 
dition so  that  it  may  be  easily  acted  upon  by  the  sulphuric  acid. 
The  rock  as  it  comes  from,  the  cars  is  passed  through  a jaw 
crusher  which  brings  it  down  to  the  right  size  for  feeding  to  the 
pulverizer  mill. 
PULVERIZERS. 
There  are  a number  of  mills,  such  as  the  Bradley,  Fuller- 
Lehigh,  Sturtevant,  etc.,  which  are  guaranteed  to  do  the  work 
in  the  shortest  time  and  with  the  least  power,  but  each  industry 
has  to  find  out  from  experience  which  is  the  best  mill  for  its  indi- 
vidual purpose.  In  some  operations  a very  fine  granular  ma- 
terial is  desired  with  as  little  powder  as  possible ; in  others  an 
impalpable  powder  is  of  particular  importance,  for  instance,  in 
the  cement  industry.  But  for  the  manufacture  of  superphos- 
phate, a material  is  required  which  will  be  sufficiently  fine  to 
pass  a 6o-mesh  sieve  and  yet  not  be  composed  entirely  of  pow- 
der. A cement-like  powder  would  be  difficult  to  mix  with  the 
acid  for  the  reason  that  the  particles  are  so  fine  and  set  so  closely 
together  that  it  is  not  at  all  porous.  As  soon  as  it  is  stirred  with 
the  acid  the  reaction  goes  on  rapidly  at  the  surface  and  forms  a 
coating  of  acid  phosphate  and  gypsum  around  the  pulverized 
rock  leaving  a core  in  the  center  perfectly  dry  and  unacted  upon. 
On  the  other  hand  if  the  rock  has  not  been  ground  sufficiently  a 
similar  condition  is  brought  about.  Moreover  the  resultant  acid 
phosphate  is  wet  and  unfit  for  use  due  to  the  fact  that  the  re- 
action goes  on  so  slowly  that  there  is  not  sufficient  heat  generated 
to  evaporate  the  excess  moisture. 
The  ideal  material  would  consist  of  a mixture  of  flour-like 
powder  and  small  rock  particles  which  under  the  microscope 
would  look-  like  a mass  of  very  sharp,  jagged,  and  uneven  rocks. 
The  more  torn  and  crushed  is  the  appearance  the  better  the  ma- 
terial is  for  acidulating  purposes. 
BUHR  STONES. 
The  Buhr  stone  mill,  possibly  the  oldest  type  of  fine  grinding 
mill,  is  still  used  extensively  and  the  material  produced  is  very 
