234 



CEMENTS, LIMES, AND PLASTEBA 



TABLE 103. 

 FUEL CONSUMPTION IN AMERICAN NATURAL-CEMENT PLANTS 



Hard and soft clinker. When a natural-cement kiln is drawn, part 

 of the product will consist of hard, clinkered material, part of softer, 

 porous, moderately burned stuff, and part of cores and masses of prac- 

 tically unburned rock. The relative proportions in which these three 

 grades are present will be determined by the type of kiln and the 

 care with which the burning has been conducted. The differences in 

 burning are of course due to some extent to the fact that the masses 

 of rock fed into the kiln differed among themselves in composition; but 

 they are mostly due to the different extent to which the masses have 

 been exposed to the heat of the fuel. 



The facts above stated are obvious enough, and the matter might 

 be passed over without further notice if it were not the case that with 

 some rocks the clinkered product will give the best cement, while with 

 other rocks the medium-burned part of the product is the best. This 

 fact certainly requires both consideration and explanation. 



The facts themselves are beyond question. In the Rosendale dis- 

 trict, for example, from 10 to 20 per cent of the output of the kiln is 

 clinkered material. This clinker is thrown away, for experiments 

 have shown that it does not give a cement nearly as good as the mod- 

 erately burned product. In the Akron-Buffalo district, on the other 

 hand, the hard, clinkered parts of the product are carefully separated 

 and ground; for experience has shown that these clinkers give a much 

 stronger cement than the softer, more porous masses. These separate 

 facts have been noted by many writers, but no explanation has been 

 offered. 



