el.] PUZZOLAN CEMENTS. 369 
Srier Hill Iron and Coal Company, of Youngstown, Ohio, under 
which license this company manufactures its "Brier Hill Portland" 
semen t. 
The process, as practiced in the slag-cement plant of the Illinois 
>tecl Company, Chicago, 111., is as follows: The quicklime used is 
obtained from the calcination of Marblehead or Bedford limestone, 
,nd carries less than 1 per cent MgO. On its arrival at the mill it is 
inloaded into bins, beneath which are placed two screens of different 
lesh, the coarser at the top. A quantit\ r of lime is drawn upon the 
tpper screen, where it is slaked by means of the addition of water con- 
aining a small percentage of caustic soda. As the lime is slaked it falls 
hrough the coarse screen onto the finer screen, through which it falls 
nto a conve/yor which carries it to a rotary drier. After heating, the 
esulting slaked and dried lime is carried by elevators to hoppers 
bove the tube mills, where it is mixed in proper proportions with 
he granulated slag, which has been dried and powdered. 
COMPOSITION AND PROPERTIES OF SLAG CEMENT. 
Slag cement when ready for sale is a mechanical mixture of lime 
ydrate(Ca 2 (OH) 2 ) and a calcium-aluminum silicate (.rSi0 2 , Al 2 3 ,?/CaO). 
n addition to the essential ingredients noted above, certain others of 
ess amount usually occur. The most important of these in the effect 
t produces on the quality of the product is sulphur, which is 
stained from the slag in the form of sulphides of lime or iron. To 
he presence of these sulphides is due, in large part at least, the disin- 
egration of slag cements when used in dry air. If the cement be 
ised for construction in water, their presence is of much less impor- 
ance, and the total sulphides may run as high as 5 per cent without 
eriously impairing the quality. Several per cent of iron oxide obtained 
rom the slag are commonly present. Magnesia also occurs, derived 
rom the slag or the lime. It is inert, if not positively detrimental, 
uid the amount therefore should be kept as low as possible. 
In addition to the ingredients mentioned above, a percentage, usually 
mall, of other compounds may be found, which have been added by 
he manufacturer during some stage of the process for the purpose of 
ncreasing the rapidity of set of the cement. 
The table below contains the analysis of a number of American and 
European slag cements, as given by various authorities. It will be 
een that, despite the apparently great variations in practice, the ulti- 
nate composition of the finished cement falls within quite narrow 
Units. The range in composition of a good slag cement may be eon- 
idered to be about: Si0 3 , 22 to 30 per cent; Al 2 3 +Fe 2 3 , 11 to 16 
>er cent; CaO, 49 to 52 per cent; MgO, less than 4 per cent; S, less 
ihan 1.5 percent; ignition loss, 2.5 to 7.5 per cent, 
Bull. 243—05 24 
