ICKEL.l 
AMERICAN    CEMENT    INDUSTRY. 
505 
tides,  and  has  also  two  important  chemical  effects.  One  is  thai  the 
slag,  if  of  suitable  chemical  composition,  is  rendered  strongly  hy- 
draulic; the  other,  that  most  of  the  sulphur  is.  removed  in  the  form 
of  hydrogen  distilphide.  After  granulation  the  slag  is  dried,  usu- 
ally in  rotary  driers,  the  Ruggles-Coles  being  a  favorite  American 
type. 
The  lime  used  for  mixture  with  the  slag  should  be  low  m  mag- 
nesia, well  burned,  and  carefully  slaked.  After  slaking  and  drying, 
the  lime  is  ready  for  mixture  with  the  granulated  and  dried  slag, 
which  usually  lias  received  a  preliminary  reduction  in  a  crusher,  ball 
mill,  Kent  mill,  or  other  comparatively  coarse  reducer.  The  pro- 
portions used  will  vary  from  20  to  40  parts  of  lime  for  100  parts 
of  slag.  The  mixture  and  final  reduction  is  usually  accomplished 
in  the  American  plants  in  tube  mills.  The  composition  of  a  number 
of  American  and  European  slag  cements  is  shown  in  the  following 
table  of  analyses  collected  from  various  sources: 
Analyses  showing  composition  of  slag  cements. 
Constituent. 
Si02... 
A1203  - 
FeO___ 
CaO  __ 
MgO  _  _ 
S 
so3 
Loss  on  ignition 
Choindez, 
Switzer- 
land . 
19.5 
17.5 
54.0 
Donjeux,        Saulnes, 
France.  France. 
24.85 
12.10 
8.85 
49.20 
1 .  75 
1.80 
1 .  35 
5.  05 
22.45 
13.95 
8.80 
51.10 
1.85 
Chicago, 
111. 
28.  05 
11.40 
.54 
50.  29 
2.90 
1.37 
3.39 
Ensley, 
Ala. 
11.70 
51.71 
1 .  89 
1.81 
The  composition  of  good  slag  cements  may  vary  within  the  fol- 
lowing limits:  Silica,  22  to  30  per  cent;  alumina  and  iron,  11  to  L6 
per  cent;  lime,  49  to  52  per  cent;  magnesia,  less  than  1  per  cent; 
sulphur.  Less  than  1.1  per  cent.  It  will  be  noted  that  the  lime  con- 
tent is  lower  and  the  alumina-iron  content  higher  than  in  a  cement 
of  the  Portland  type.  Slag  cements  also  differ  from  Portland  cement 
in  being  lower  in  specific  gravity  and  lighter  in  color.  Normally 
they  set  slower  than  Portland  cement,  though  this  defect  can  be 
overcome  by  treatment  during  manufacture.  They  are  deficient  in 
resistance  to  mechanical  wear  and  do  not  set  satisfactorily  in  dry 
situations.  For  use1  under  water  or  in  permanently  damp  ground, 
however,  thev  would  seem  to  be  of  service. 
