378 CEMENTS, LIMES, AND PLASTERS. 



Cost of Raw Materials at Mill. 



The most natural way, perhaps, to express the cost of the raw 

 materials delivered at the mill would be to state it as being so many 

 cents per ton or cubic yard of raw material; and this is the method 

 followed by quarry men or miners in general. To the cement manufac- 

 turer, however, such an estimate is not so suitable as one based on the 

 cost of raw materials per ton or barrel of finished cement. 



Loss on drying, etc. In the case of hard and comparatively dry 

 limestones or shales, it may be considered that the raw mixture loses 

 33 3 per cent in weight on burning. Converting this relation into pounds 

 of raw material and of clinker, we find that 600 pounds of dry raw material 

 will make about 400 pounds of clinker. Allowing something for other 

 losses in the process of manufacture, it is convenient and sufficiently 

 accurate to estimate that 600 pounds of dry raw material will give one 

 barrel of finished cement. These estimates must be increased if the 

 raw materials carry any appreciable amount of water. Clays will fre- 

 quently contain 15 per cent or more of water; while soft, chalky lime- 

 stones, if quarried during weather, may carry as high as 15 to over 20 

 per cent. A Portland-cement mixture composed of a pure chalky lime- 

 stone and a clay might, therefore, average 10 to 20 per cent of water, and 

 consequently about 700 pounds of such a mixture would be required 

 to make one barrel of finished cement. 



With marls the loss on drying and burning is much greater. 

 Russell states * that according to determinations made by E. D. Camp- 

 bell, 1 cubic foot of marl as it usually occurs in the natural deposits 

 contains about 47 pounds of lime carbonate and 48 pounds of water. 

 In making cement from a mixture of marl and clay, therefore, it would 

 be necessary to figure on excavating and transporting over 1000 pounds 

 of raw material for every barrel of finished cement. 



From the preceding notes it will be understood that the cost of 

 raw materials at the mill per barrel of cement will vary not only with 

 the cost of excavation, but with the kind of materials in use. 



Costs of quarrying or mining. In dealing with hard, dry materials 

 extracted from open quarries near the mills, the cost of raw materials 

 may vary between 8 cents and 15 cents per barrel of cement. The 

 lower figure named is probably about the lowest attainable with good 

 management and under favorable natural conditions; the higher figure 



* 22d Ann. Rep. U. S. Geol. Survey, pt. 3, p. 657. 



