Air  separation. — This  is  a  method  of  cleansing  clays  which  has  been
rarely  tried,  yet,  in  some  of  the  cases  where  it  has  been  used,  is  said  to
have  met  with  success.  It  is  especially  applicable  to  those  clays  from
which  it  is  necessary  to  remove  simply  coarse  or  sandy  particles.  The
process  consists,  in  brief,  in  feeding  the  dry  clay  into  a  pulverizer,  which
reduces  it  to  the  condition  of  a  very  fine  powder.  As  the  material  is
discharged  from  the  pulverizer  into  a  long  box  or  tunnel,  it  is  seized  by
a  powerful  current  of  air,  which  at  once  picks  up  the  fine  particles  and
carries  them  along  to  the  end  of  the  airway,  where  they  are  dropped  into
a  bin.  The  coarser  particles,  which  are  too  heavy  to  be  picked  up  by
the  current,  drop  back  and  are  carried  through  the  pulverizer  once  more.
Such  a  method  would  be  especially  applicable  to  kaolins  that  are  free
from  iron,  but  probably  would  not  be  found  adaptable  to  many  of  those
containing  ferruginous  particles.
There  are  several  forms  of  separators, on  the  market.  In  the  Ray-
mond pulverizer  and  separator  the  material  is  pulverized  in  the  lower
part  of  the  machine  and  then  thrown  upward,  the  finer  particles  being


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FIG.  1.— View  showing  portion  of  sand-troughs,  settling-tanks,  and  drying-racks
at  a  kaolin-washing  plant.     (After  Ries,  Md.  Geol.  Surv.,  IV,  p.  270,  1902.)


.  2. Filter-press  for  removing   water   from   washed   or   blunged  clays.     The

portion  at  the  left  end  has  been  emptied  and  the  leaves  of  clay  taken  from  it
are  on  the  car.  The  workman  is  just  removing  a  leaf  of  clay  from  the  press.
