WHITE    CLAYS    OF    SOUTH    MOUNTAIN,  PENNSYLVANIA.  329 
until  the  entire  width  of  the  clay  belt  is  mined.  The  adjoining 
crosscuts  are  then  mined  in  the  same  way.  By  this  method  a  dis- 
tance of  250  feet  to  the  north  ot  the  main  tunnel  and  700  feet  to 
the  south  have  been  mined  out. 
The  white  clay  belt  is  variable  in  width,  ranging  from  120  feet  to 
400  feet  in  places,  which  makes  the  lateral  tramway  drifts  very 
crooked  and  long,  and  it  is  the  intention  of  the  company  to  con- 
struct a  new  diagonal  tunnel  to  intercept  the  farthest  workings  at 
the  south  and  thus  furnish  a  direct  outlet  for  the  tram  cars. 
The  Philadelphia  Company's  mill  and  mine  are  the  largest  and  best 
equipped  in  the  region.  The  mill  is  a  long,  low  building  located  just 
below  the  month  of  the  tunnel.  The  mine  cars  bring  the  crude  clay 
to  the  upper  floor,  where  it  is  shoveled  into  blunger  mills  and  churned 
with  pure  filtered  mountain  water  by  a  set  of  oppositely  revolving 
paddles.  After  thorough  mixing  it  passes  as  a  milky  liquid  or  slip 
over  inclined  tables  of  fine  wire  screen,  which  oscillate  rapidly  side- 
wise  and  remove  the  coarser  particles  of  sand.  The  slip  is  then  run 
over  steeply  inclined  screens  of  very  fine  silk  bolting  cloth,  200  meshes 
to  the  inch,  or  finer,  the  clay  and  water  playing  upon  them  from  jets 
above.  Only  the  impalpable  clay  passes  through,  the  coarser  mate- 
rial sliding  off  on  the  surface.  This  patented  process  produces  the 
clay  of  the  finest  grade,  but  the  waste  from  it  is  excessive.  It  is 
unfortunate  that  some  use  can  not  be  made  of  the  fine  clayey  sand 
that  is  now  poured  out  on  the  great  white  dump  that  disfigures  the 
landscape. 
The  purified  slip  is  collected  in  large  vats  and  distributed  to  the 
settling  tanks,  where  bluing  is  added  to  whiten  the  clay.  After 
standing  twenty-four  hours  the  water  is  drawn  off  from  the  top  and 
is  used  again.  The  thick  slip  in  the  bottom  of  the  tanks  is  pumped 
into  filter  presses  and  forced  in  until  160  pounds  pressure  is  obtained 
and  kept  at  this  pressure  until  the  water  ceases  to  run  out.  These 
presses  are  made  of  a  series  of  double  concave  iron  plates,  2  feet 
square,  with  vertical  grooves  on  the  concave  surfaces.  A  double 
sheet  of  heavy  canvas  is  placed  over  the  surface  of  the  plates  to  let 
the  water  out  and  to  prevent  the  clay  from  adhering  to  the  iron. 
The  clay  slip  is  forced  into  the  presses  through  a  hole  in  the  center 
of  the  plates,  and  when  the  spaces  are  filled  and  pressure  is  exerted 
the  water  passes  through  the  canvas  and  down  the  grooves  in  the 
plates.  The  molded  corrugated  cakes  of  clay,  1^  inches  thick,  are 
conveyed  by  belt  to  a  tile  machine,  where  they  are  remolded  into 
6-inch  tiles  3  feet  in  length,  so  they  will  dry  rapidly  in  the  ovens,  to 
which  they  are  carried  by  small  cars. 
The  clay  is  sold  either  in  bulk,  in  small  pieces,  or  pulverized,  in 
bags.  About  one-half  the  output  is  pulverized.  The  mill  has  a 
capacity  of  1 00  tons  a  day  and  an  average  production  of  60  tons.     It 
