360 CEMENT MATERIALS AND INDUSTRY. [bull. 243, 
Prost, at a later date, investigated the subject, using for experinienl 
several commercial slags and also a series prepared from pure CaO. 
Si0 2 , and Al 2 O s . He decided that the hydraulic properties (both as 
regards rapidity of set and ultimate strength) of the slag increased as 
the proportions of lime and alumina increased, and failed to find anj 
indication that a high alumina content causes disintegration. His best 
results were obtained from slags having the compositions respective J 
of 2Si0 2 , A1 2 3 , SCaO and 2Si0 2 , A1 2 3 , 4CaO. 
Mahon in 1893 made a series of experiments to determine the value 
(for cement manufacture) of a large series of the slags produced by 
the furnaces of the Maryland Steel Company, and found that the sladB 
giving the best results were two, having respectively the following.; 
compositions: 
(1) Si0 2 , 30 per cent; A1 2 3 , 17 per cent; CaO, 47.5 per cent; S,\ 
2.38 per cent; and (2) Si0 2 , 25.3 per cent; A1 2 3 , 20.1 per cent; CaO,), 
48 per cent; MgO, 3.28 per cent; S, 2.63 per cent. 
The ratios of 7 ^ T1 - and _* 3 , calculated for these sla^s are — 
Si0 2 Si0 2 ' 
/^ Ca0 , KO A1 A n l n , /ox CaO ln A1,0, „*„ 
^SiOT 1 ' 58 ; Srb7=°- 57 5 and (2) gjjj^l.9; ^=0.79. 
At the close of the experiments Mahon recommended that slags be 
used even slightly higher in alumina than those above quoted. 
The specifications under which slag from the furnaces is acceptedi 
by the cement department of the Illinois Steel Company are as follows: 
(1) Slag must analyze within the following limits: 
Si0 2 +Al 2 3 not over 49 per cent; A1 2 3 , from 13 to 16 per cent;; 
MgO, under 4 per cent. 
(2) Slag must be made in a hot furnace and must be of a light-gray 
color. 
(3) Slag must be thoroughly disintegrated by the action of a large 
stream of cold water directed against it with considerable force. This-j 
contact should be made as near the furnace as is possible. 
A series of over 300 analyses- of slags used by this company in their 
slag (puzzolanic) cement, show the following range in composition: 
Si0 2 , 29.60 to 35.60 per cent; A1 2 3 and Fe 2 3 , 12.80 to 16.80 per 
cent; CaO, 47.99 to 50.48 per cent; MgO, 2.09 to 2.81 per cent, 
The requirements of the Birmingham Cement Company as to the 
chemical composition of the slags used for cement are as follows: The 
lime content shall not be less than 47.9 per cent; the silica and lime 
together shall approximately amount to 81 per cent; and the alumina 1 
and iron oxide together shall equal from 12 to 15 per cent. 
Analyses of a number of slags used in cement manufacture are 
shown in the table below. The analyses of foreign slags are quoted 
from various reliable authorities and the five analyses of the Illinois I 
