ECKEL. ] 
SLAG 
37 
age of magnesia, according- to the character of the limestone that has 
been used in the alkali plant. When a limestone low in magnesium 
carbonate has been used the resulting waste is a very satisfactory 
Portland-cement material. . 
The following analyses are fairly representative of the waste obtained 
at alkali plants using the ammonia process: 
Analyses of alkali waste. 
Silica (Si0 2 ) 
Alumina ( A1 2 3 ) 
Iron oxide (Fe 2 3 ) 
Lime (CaO) 
Magnesia (MgO) 
Alkalies (Na 2 0, K 2 0) 
Sulphur trioxide (S0 3 ) ... 
Sulphur (S) 
Carbon dioxide (C0 2 ) 
Water and organic matter 
0.60 
3.04 
53.33 
0.48 
0.20 
n. d. 
n. d. 
42. 43 
n. d. 
1.75 
0. 01 
50. 60 
5. 35 
0. 64 
n. d. 
0.10 
41.71) 
1.98 
1.41 
1.38 
48.29 
1.51 
0.64 
1.26 
n. d. 
39.60 
:;. so 
0.98 
1.62 
50. 40 
4.97 
0. 50 
n. d. 
0.06 
n. d. 
n. d. 
Of the analyses quoted in the preceding table, those in the first and 
third columns represent materials which are used in Portland-cement 
manufacture in England and the United States. The alkali wastes 
whose analyses are given in the second and fourth columns are too 
high in magnesia to be advisable for such use. 
BLAST-FURNACE SLAG. 
True Portland cements, which must be sharply distinguished from 
the slag (or puzzolan) cements described on pages 357-372, can be 
made from a mixture of blast-furnace slag and limestone which is 
finely powdered, and is then burned in kilns and the resulting clinker 
pulverized. 
The slags from iron furnaces consist essentially of lime (CaO), silica 
(Si0 2 ), and alumina (A1 2 3 ), though small percentages of iron oxide 
(FeO), magnesia (MgO), and sulphur (S) are commonly present. Slag 
may therefore be regarded as a very impure limestone or a very cal- 
careous clay, from which the carbon dioxide has been driven off. 
In the United States two plants manufacture true Portland cement 
from slag, as noted on pages 137 and 294. 
