74 
GEOLOGY AND MINERAL "RESOURCES OF MISSISSIPPI. 
It will be seen that the usual mixtures cany from 75 to 77 percent of lime carbonate. 
With this in mind, it will be obvious that there is a great advantage in using, as one of the; 
raw materials, a limestone of about this degree of purity. 
PHYSICAL COMPOSITION. 
Economy in excavation and crushing requires that the raw materials should be as soft as 
possible. This condition is admirably met by t he chalky limestones of the Tombigbee River 
district, and they should show a considerable saving in crushing costs as against the hard 
limestones used in many northern plants. 
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 per year per kiln. Of this about 
15,000 tons are limestone and 5,000 tons shale. Assuming that the limestone weighs 16(1 
pounds per cubic foot, which is a fair average weight, each kiln in the plant will require' 
about 190,000 cubic feet of limestone per 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 one with less 
than a twenty years' supply of raw material in sight. This would require that, to justify 
the erection of a cement plant on any property, for each kiln of the proposed plant there 
must be in sight at least 3,800,000 cubic feet of limestone and 1,000,000 cubic feet of clay or 
shale. 
LOCATION WITH RESPECT TO TRANSPORTATION ROUTES^ 
Portland cement is, for its value, a bulky product, and its economic manufacture is there- 
fore much influenced by the subject of transportation routes. To locate a plant on only one 
railroad, unless the railroad officials are financially connected with the cement plant, is siml 
ply to invite disaster. At least two transportation routes should be available, and it is ber| 
of all if one of them be a good water route. 
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 0,000 to 9,000. 
tons of coal per 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. 
The fuel most commonly used in modern rotary-kiln practice is bituminous coal pulver- 
ized very finely. Coal for this purpose should be high in volatile matter and as low in asa 
an 1 sulphur as possible. Russell gives the following analyses of West Virginia and PennH 
sylvania coals used at present at various cement plants in Michigan: 
Analyses of kiln coals. 
1. 
2. 
3. 
4. 
I i se I carbon 
56.15 
35.41 
6.36 
2.08 
1.30 
56.33 
35.26 
7.06 
1.35 
1.34 
55.82 
39. 37 
3.81 
1.00 
.42 
51.69 
Volatile matter. ... 
39.1 
Ash 
fi. 13 
Moisture 
1.40 
Sulphur 
1.46 
