37 



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 raiw material carry any 

 appreciable amount of water. Clays will frequently contain 15 

 per cent, or more of water ; while soft chalky limestones, if 

 quarried during wet weather, may carry as high as 15 to over 

 20 per cent. A Portland cement mixture composed of a pure 

 chalky limestone 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 ce- 

 ment. 



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

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

 natural deposits, contains about 47 1-2 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 ex- 

 cavating and transporting over 1,000 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 ma- 

 terials in use. 



[IT dealing with hard dry materials, extracted from open 

 quarries near the mills, the cost of raw materials may vary be- 

 tween 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 is probably a maximum for fairly careful management 

 of a quarry under eastern labor conditions. Whem it is neces- 

 sary to mine the materials, the cost will be somewhat increased. 

 Cement rock has been mined at a cost equivalent to 10 cents 

 per barrel of cement; but the figure is attained under particu- 

 larly favorable conditions. The cost at mining and transpor- 

 tation may reach from this figure up to 20 cents per barrel. 



*22nd Ann. Kept., U. S. Geol. Surv., pt. 3, p. 657. 



