224 
CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
Cecil von Schwarz, in a paper read before the Iron and Steel Insti- 
tute of Great Britain, has recently described in detail German and 
Belgian practice in the manufacture of Portland cement from blast- 
furnace slag. The slag is granulated in order to remove sulphur and 
to reduce the cost of crushing. The granulated slag is dried and mixed 
with about an equal amount of limestone. To the mixture is added 
about 3-J per cent of powdered slaked lime, and their intimate mixing 
and reduction are accomplished in ball mills and tube mills. About 
8 per cent of water is added, and the slurry is then made into bricks, 
which are dried before charging into the kiln. A ring kiln is used, 
with coke as fuel. The clinker is moistened, stored for six weeks, 
and reduced in ball and tube mills. 
Analyses of limestone, slag, and finished cement at << typical plant. 
Constituent. 
Limestone. 
Slag. 
Cement. 
SiO, 
1.6 
1.0 
30 -35 
10 11 
23. 70 
A1 2 3 
6. 14 
Fe 2 3 
1.80 
FeO . 
0.2- 1.2 
3. - 4 
MnO 
CaC0 3 
97.0 
CaO . . 
46 -49 
0.5- 3.5 
0.2- 0.6 
59. 08 
MgO 
0.5 
0.06 
1.40 
S0 3 _. 
1.30 
Loss on ignition . . 
5.70 
SLAG BLOCKS. 
Slag, run into molds on issuing from the furnace, furnishes blocks 
which have been used for paving, notably in Philadelphia. These 
slag blocks are very durable, but objectionable because of their slip- 
periness. This difficulty has been overcome, in English practice, by 
casting the blocks in a double-sized mold, with a projection which 
results in a notch passing around the slag block. The two halves of 
the block are then split apart at this notch, and the rough fracture 
surface of each is laid uppermost in paving. 
SLAG BRICK. 
The manufacture of slag brick can hardly be considered as being 
more than a specialized phase of the manufacture of slag cement. 
Slags, approximately of the same composition as those usee! in cement 
making, are granulated, dried, and pulverized. Sufficient slaked lime 
is added to bring the calcium oxide content of the mixture up to about 
55 per cent, the mixing being carefully and thoroughly done. Dur- 
ing or after mixing, a small amount of water is added, and the moist- 
ened material is then fed to the brick machine. On issuing from this 
the bricks are placed on racks to dry. The drying takes from six to 
ten days, at the end of which time the bricks are ready for use. 
