40 CEMENT MATERIALS AND INDUSTRY. [bull. 243. 
tity — say 1 per cent or less. If the limestone is a clayey limestone, 
or "cement rock," the proportion between its silica and its alumina 
and iron should fall within the limits 
AlA+FeA ' AlA+FeA 
A clay or shale should satisfy the above equation, and should be free 
from sand, gravel, etc. Alkalies and sulphates should, if present, not 
exceed 3 per cent. 
(2) Physical character. — Economy in excavation and crushing 
requires that the raw materials should be as soft and as dry as possible. 
(3) Amount available. — A Portland-cement plant running on dry 
raw materials, such as a mixture of limestone and shale, will use 
approximately 20,000 tons of raw material a year per kiln. Of this 
about 15,000 tons are limestone and 5,000 tons shale. Assuming that 
the limestone weighs 160 pounds per cubic foot, which is a fair aver- 
age weight, each kiln in the plant will require about 190,000 cubic 
feet of limestone a year. As the shale or clay may be assumed to 
contain considerable water, a cubic foot will probably contain not over 
125 pounds of dry material, so that each kiln will also require about 
80,000 cubic feet of shale or clay. 
A cement plant is an expensive undertaking, and it would be folly 
to locate a plant with less than a twenty years' supply of raw material 
in sight. In order to justify the erection of a cement plant, there 
must be in sight at least 3,800,000 cubic feet of limestone and 1,600,000 
cubic feet of clay or shale for each kiln. 
(4) Location with respect to transportation routes. — Portland cement 
is for its value a bulky product, and is therefore much influenced by 
transportation routes. To locate a plant on only one railroad, unless 
the railroad officials are financially connected with the cement plant, 
is simply to invite disaster. At least two transportation routes should 
be available, and it is best of all if one of these be a good water route. 
(5) Location with respect to fuel supplies. — Every barrel (380 pounds) 
of Portland cement marketed implies that at least 200 to 300 pounds of 
coal have been used in the power plant and the kilns. In other words, 
each kiln in the plant will, with its corresponding crushing machinery, 
use up from 6,000 to 9,000 tons of coal a year. The item of fuel cost 
is therefore highly important, for in the average plant about 30 to 
40 per cent of the total cost of the cement will be chargeable to coal 
supplies. 
(6) Location with respect to markets. — In order to achieve an estab- 
lished position in the trade, a new cement plant should have (a) a local 
market area, within which it may sell practically on a noncompetitive 
basis, and (b) easy access to a larger though competitive market area. 
