WHITE    CLAYS    OF    SOUTH    MOUNTAIN,  PENNSYLVANIA.         333 
although  handsome  and  ornamental  they  are  more  absorbent  than 
the  vitrified  brick  made  of  the  Henry  Clay  stock. 
Harrisburg  Clay  Company. — The  Harrisburg  Clay  Company  works 
the  only  active  mine  outside  of  Mountain  Creek  Valley.  It  is  in  the 
same  general  syncline,  however,  just  over  the  divide  from  that  of  the 
Cumberland  Clay  Company.  Although  it  is  a  small  plant  it  produces 
clay  of  very  high  grade,  said  to  be  as  pure  as  any  in  the  district. 
The  mine  is  on  low  ground  and  is  operated  by  a  short  incline  and 
tunnel  running  in  about  20  feet  to  the  clay  and  60  feet  west  with  the 
clay.  It  is  operated  by  tram  and  steam  hoist.  The  bed  of  clay 
appears  to  be  rather  thin  and  not  much  stoping  can  be  done.  If  it  is 
a  bedded  deposit,  the  formations  must  lie  nearly  flat  in  the  bottom  of 
the  syncline,  but  it  may  have  moved  to  this  position  from  the  steep 
slopes  above.  Another  tunnel  was  started  farther  south,  but  had  not 
yet  reached  the  deposit.  The  clay  is  hauled  by  wagon  several  hun- 
dred feet  to  the  refinery,  which  is  equipped  with  1  horizontal  washer 
similar  to  the  screw-and-blade  type  of  ore  washer,  flotation  troughs, 
2  settling  tanks,  2  presses,  and  2  ovens  of  20  cars  capacity.  The 
production  of  this  plant  is  about  7  tons  a  day,  which  has  to  be  hauled 
one-half  mile  to  the  railroad. 
USES    OF    WHITE    CLAY. 
Paper  manufacture. — Pure  white  clay,  such  as  is  obtained  from  the 
South  Mountain  factories,  is  used  chiefly  in  the  manufacture  of  paper. 
Wall  paper,  the  cheaper  writing  papers,  and  all  paper  requiring  a 
smooth,  absorbent  surface  for  fine  printing  are  made  in  part  of  clay, 
or  some  other  mineral,  such  as  pulverized  calcium  sulphate  or 
barium  sulphate.  The  advantages  of  the  South  Mountain  clay  over 
other  substances  for  this  purpose  is  its  white  color,  freedom  from 
iron,  fine  grain,  absorptiveness,  and  its  light  weight,  which  causes  it  to 
remain  in  suspension.  The  clay  is  made  into  a  thin  cream  with  water 
and  a  small  amount  of  resin  sizing  to  make  it  adhere  to  the  libers  of 
the  paper  bod}^,  and  is  fed  into  the  paper-machines  with  the  pulp. 
The  amount  of  clay  should  not  exceed  10  per  cent  in  paper  for  per- 
manent publication,  but  for  chromolithographs  and  publications  of 
temporary  value,  35  to  40  per  cent  of  clay  may  be  used,  as  the  ink  is 
absorbed  more  rapidly  and  the  impression  is  clearer. 
Brick  and  tile  manufacture. — Excellent  building  brick  of  light  color 
are  made  from  the  unrefined  clay,  but  it  requires  an  admixture  of  a 
more  plastic  clay  to  give  it  body.  The  potash  which  it  contains 
causes  it  to  fuse  readily,  and  the  brick  acquires  a  semivitreous  texture, 
which  makes  it  both  hard  and  impervious — qualities  which  adapt  it  to 
street  paving  and  to  exterior  finishing.  Its  pleasing  color  also  adds 
to  its  attractiveness  for  building  purposes.     The  Mount  Holly  Brick 
Bull.  315—07 22 
