222 
CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
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 5^2 and * :j calculated for each slag: 
kSi0 2 Si<J 2 
Analyses of slags in actual use. 
Constituent. 
Si0 2 . 
A1 2 3 
FeO . 
CaO _ 
MgO^ 
CaS__ 
CaS0 4 
S __.. 
so 3 _. 
CaO 
Si0 2 
A1A 
SiO, 
Middles- 
boro, Eng- 
land. 
31.50 
18. 56 
12. 22 
3. IS 
2.21 
.45 
:•} 
L.34 
59 
Bilboa, 
Spain. 
32. 90 
13.25 
.46 
47. 30 
1.37 
3.42 
Choindez, 
Switzer- 
land. 
26.24 
24.74 
.49 
46. 83 
.88 
.59 
.32 
1.44 
.41 
1.78 
. 93 
Sanlnes. 
France. 
31.50 
16.62 
. 02 
46. 10 
1.40 
Chicago, 
111." 
32. 20 
15. 50 
48. 14 
2. 27 
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 possible. 
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 particles, and 
has also two important chemical effects. One is that the slag, if of 
suitable chemical composition, is rendered strongly hydraulic; the 
other, that most of the sulphur is removed in the form of hydrogen 
disulphide. After granulation the slag is dried, usually in rotary 
driers, the Ruggles-Coles being a favorite American type. 
The lime used for mixture with the slag should be low in magnesia, 
well burned, and carefully slaked. At Chicago, where the Whiting 
process is used, a small percentage of caustic soda is added to the 
water used for slaking, the effect being to accelerate the set of the 
cement. After slaking and drying, the lime is ready for mixture with 
the granulated and dried slag, which usually has received a prelimi- 
nary reduction in a crusher, ball mill, Kent mill, or other compara- 
tively coarse reducer. The proportions used will vary from 20 to 40 
parts of lime to 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: 
