504 
CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
of  manufacture,  ultimate  and  rational  composition,  and  properties. 
Seven  plants  are  at  present  engaged  in  the  manufacture  of  slag- 
cement  in  the  United  States,  the  total  product  for  some  years  past 
being  given  in  the  table  on  page  498. 
The  writer  has  discussed  the  manufacture  of  slag  cement  in  detail 
in  a  recent  publication."  A  brief  resume  of  the  technology  of  the 
material  in  question  is  here  given. 
As  to  composition,  the  material  used  in  the  manufacture  of  slag- 
cement  must  bo  basic  blast-furnace  slag.     Tetmajer  stated  that  the 
CaO 
ratio  ^r^p  should  never  be  less  than  unity,  and  that  the  best  results 
were   obtained  when  the  ratio    s-~(/'  gave   a  value  of  0.45  to  0.50. 
Prost  and  Mahon  later  obtained  good  results  from  slags  in  which  the 
alumina  was  much  higher  than  indicated  by  Tetmajer's  ratio,  and 
analyses  of  slags  used  in  practice  are  shown  in  the  following  table, 
with  the  ratios  n^r  and  ^/L  :]  calculated  for  each  slag: 
ulUo  Ol'    'o 
Analyses  of  slags  in  actual  use. 
SiQ2 . . 
ALA- 
FeO . . 
CaO-. 
MgO  . 
CaS_. 
CaS04 
S 
so3... 
CaO) 
SiOJ 
AU):; 
Si< ), 
Constituent. 
Middles- 
boro, 
England. 
31.50 
18.  56 
40  oo 
:;.  is 
2.21 
.45 
1.34 
.59 
Bilboa, 
Spain. 
32.  90 
13.25 
.40 
47.  30 
1 .  37 
3.42 
1.44 
.41 
Choindez, 
Switzer- 
land. 
20.  24 
24.74 
.49 
46.83 
.88 
.59 
.32 
1.78 
.93 
Saulnes, 
France. 
31 .  50 
16.62 
.  62 
40. 10 
1.40 
Chicago, 
111. 
32.  20 
15.50 
48. 14 
1 .  49 
48 
Slags  allowed  to  cool  slowly  are  only  feebly  hydraulic,  even  if  of 
proper  chemical  composition.  When  used  in  the  manufacture  of 
slag  cement,  therefore,  the  slag  must  be  cooled  as  suddenly  as  pos- 
sible. This  is  effected  by  bringing  the  slag,  as  it  issues  from  the 
furnace,  in  contact  with  a  jet  or  stream  of  cold  water.  This  sudden 
cooling  "granulates"  the  slag,  i.  e.,  breaks  it  up  into  porous  par] 
"Mineral  industry,  Vol.  X.  See  also  Mineral  Resources  I'.  S.  1900,  p.  747,  where  a 
description  of  two  Alabama  slag-cemenl  pi. mis  is  given. 
