UNIVERSAL PORTLAND CEMENT CO. 
Just as the available supply of limestone and coal 
required to convert iron ore into pig iron for the manufac- 
ture of steel has contributed toward making the Pittsburgh 
District the world’s largest steel center, so has the available 
supply of the same materials enabled the Keystone State 
to take a leading position in the manufacture of cement. 
In the making of pig iron, one of the by-products is slag. 
For years, no wide uses for this were found. It was waste 
material. It cost money to get rid of it. But back in 
the 90’s, it was discovered that the silica, alumina and lime 
found in blast-furnace slag, the principal chemical ingre- 
dients required in the manufacture of portland cement, 
could be used to make this modern material, and today 
large quantities of granulated slag are used by the Universal 
Portland Cement Co. in the steel centers of Pittsburgh. 
Chicago and Duluth. 
INGREDIENTS OF PORTLAND CEMENT 
Portland Cement consists principally of silica, alumina 
and lime obtained from (a) cement rock and limestone; 
(b) clay or shale and limestone; (¢) clay and marl; or 
(d) blast-furnace slag and limestone. Any of these com- 
binations in various proportions provide the required 
chemical constituents for portland cement. The im- 
portant requisites for the manufacture of portland cement 
are: 
The cement mixture must be composed of properly 
proportioned materials. 
These raw materials must be finely ground and 
intimately mixed before burning. 
I'he burning must be conducted at the proper 
cemperature to obtain a chemical combination 
© ¢ burning, the resulting clinker must be finely