454 
CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
its  present  success  largely  to  the  works  of  the  Lehigh  district. 
Previous  to  the  commencement  of  Portland-cement  manufacture  in 
Pennsylvania,  dry  processes  had  not  been  looked  upon  with  favor. 
The  European  plants  then  in  existence  used  wet  processes  exclusively, 
differing  only  in  the  amount  of  water  that  was  used. 
A  dry  process  can  not  well  be  used  in  stationary  kilns,  whether  of 
dome  or  chamber  type,  for  even  if  the  mixing  be  done  dry  it  will  be 
necessary  to  add  water  in  making  the  mixture  into  bricks.  The  nat- 
ural result  was  that  these  early  plants  used  water  very  liberally — 
almost  as  freely  as  the  Michigan  marl  plants  of  to-day,  and  with  far 
more  excuse  for  doing  so. 
With  the  introduction  of  the  rotary  kiln  a  dry  process  became  not 
only  possible  but  advisable,  and  the  Lehigh  practice  of  to-day  is  the 
result.     The  usual  Lehigh  practice  may  be  summed  up  as  follows: 
The  cement  rock  is  crushed  and  dried,  the  first  of  these  operations 
often  taking  place  in  the  quarry.  Large  gyratory  crushers  are  com- 
monly used  for  this  work,  while  the  drying  is  usually  done  in  rotary 
driers.  The  necessary  amount  of  limestone,  also  previously  crushed 
and  dried,  is  added,  and  the  two  materials  are  mixed  and  further 
reduced  together.  Occasionally  a  smaller  gyratory  crusher,  breaking 
to  say  one-half  inch,  is  the  next  step  in  the  process  of  reduction.  Com- 
monly, however,  the  mixture  goes  to  ball  mills,  comminuters  or 
Williams  mills,  and  then  to  tube  mills.  Some  of  the  plants  use  Griffin 
mills  in  place  of  those  noted,  while  the  Atlas  plant  uses  the  Hunting- 
don mill. 
The  raw  mixture  is  ground  to  a  fineness  usually  not  exceeding  85 
per  cent  through  a  100-mesh  sieve,  and  often  falling  much  lower. 
Compared  with  the  practice  at  plants  using  limestone-clay  mixtures, 
this  is  coarse  work.  It  is  less  harmful  than  might  be  expected,  how- 
ever, owing  to  the  fact  that  most  of  the  mixture  is  made  up  of  cement 
rock  which  is  already  naturally  well  mixed. 
The  mixture  is  usually  dampened  (to  prevent  too  much  of  it  being 
blown  out  of  the  kiln)  and  fed  to  rotary  kilns.  Except  at  the  new 
Edison  plant  at  Stewartsville,  these  kilns  are  commonly  6  feet  in  diam- 
eter and  60  feet  in  length. 
Analyses  of  Lehigh  district  cements. 
Silica  (Si02) 
Alumina  (A1203) 
Iron  oxide  (Fe203) 
Lime  (CaO) 
Magnesia  (MgO) 
Alkalios  (K20,  Na20)  . 
Sulphur  trioxide  (S03) 
Per  ct. 
21.30 
7.65 
2.85 
GO.  95 
2.95 
1. 15 
1.81 
Per  ct. 
21.96 
8.29 
2.67 
60.52 
3.43 
(«) 
1.49 
Per  ct. 
21.1 
8.0 
2.5 
65. 6 
2.4 
(a) 
(a) 
Per  ct. 
20.87 
7.60 
2.66 
63.04 
2.80 
(a) 
1.50 
Per  ct. 
19.06 
7.47 
2.29 
61.23 
2.83 
1.41 
1.34 
Per  ct 
21.65 
8.09 
2.93 
63.10 
2.00 
(a) 
1.02 
Per  ct. 
22.68 
6.71 
2.35 
62.30 
3.41 
(«) 
1.88 
Per  ct. 
21.08 
7.86 
2.48 
63.68 
2.62 
(«) 
1.25 
Per  ct. 
24. 23 
4.80 
1.86 
63.01 
3.20 
(«) 
1.20 
Per  ct. 
24.48 
4.51 
2.68 
64.33 
2.59 
(«) 
1.41 
aNot  determined. 
