MANUFACTURE OF NATURAL CEMENTS. 



229 



at times, and apparently gives almost as good results as the bituminous 

 slack alone. About 10 per cent of the total product is underburnt, or 

 clinkered. This record is about equivalent to a fuel consumption of 

 40 Ibs. per barrel, or 15.1 per cent, on the weight of cement produced. 

 This is rather high fuel consumption for natural cement, but, on the 

 other hand, the product is of peculiarly high grade, passing most Portland 

 standards. 



The natural-cement kilns at one of the prominent Lehigh district 

 plants are about 30 feet in height and of circular cross-section. In- 

 ternally they are almost exactly cylindrical, being 10 feet in diameter 

 at the top and 9^ feet in diameter at the base. The cement rock and 



FIG. 41. Kilns and coal-conveyor of the Speed plant, Speeds, Ind. 



fuel are fed in alternate layers, the fuel being anthracite coal broken 

 to about -inch size. From 35 to 50 Ibs. of coal are required to burn 

 one barrel (300 Ibs.) of cement, corresponding to a fuel consumption of 

 11.6 to 16.7 per cent of the weight of cement produced. 



Two styles of kiln are in use in the Louisville district. The older 

 and smaller kilns are 36 feet in height, 8 feet in diameter at the top, 

 enlarging to 12 feet at a point 24 feet above the base and again con- 

 tracting to 4 feet at the base. These are drawn from a chute by use 

 of a swinging gate or apron. Coal and rock are charged in alternate 



