50 



Analyses of cement mixtures. 



1234 



Silica 12.62 13.46 13.85 11.77 



Alumina and iron oxide 6.00 ? 7.20 4.35 



Carbonate of lime 75.46 73.66 73.93 76.84 



Magnesia 2.65 ? ? 1.74 



BURNING THE MIXTURE. 



After the cement mixture has been carefully prepared, as de- 

 scribed in preceding pages, it must be burned with equal care. 



In the early days of the Portland cement industry a simple 

 vertical kiln, much like that used for burning lime and natural 

 cement, was used for burning the Portland cement mixture. 

 These kilns, while fairly efficient so far as fuel consumption 

 was concerned, were expensive in labor, and their daily output 

 was small. In France and Germany they were soon supplanted 

 by improved types, but still stationary and vertical, which gave 

 very much lower fuel consumption. In America, hcwever, 

 where laibor is expensive while fuel is comparatively cheap, an 

 entirely different style of kiln has been evolved. This is the ro- 

 tary kiln. With the exception of a very few of the older plants, 

 which have retained vertical kilns, all American Portland ce- 

 ment plants are now equipped with rotary kilns. 



The history of the gradual evolution of the rotary kiln is of 

 great interest, but as the subject can not be taken up here, ref- 

 erence should be made to the papers cited below* in which de-- 

 tails, accompanied often by illustrations of early types of rotary 

 kilns are given. 



*Duryee, E., The first manufacture of Portland cement by the 

 direct rotary kiln process. Engineering News, July 26, 1900. 



Lesley, R. W., History of the Portland cement industry in the 

 United States. 8 vo. pp. 146, Philadelphia, 1900. 



Lewis, F. H., The American rotary kiln process for Portland ce- 

 ment, in The Cement Industry, pp. 188-199, New York, 1900. 



Matthey, H., The invention of the new cement burning method. 

 Engineering and Mining Journal, vol. 67, pp. 555, 705; 1899. 



Stanger, W. H., and Blount, B., The rotary process of cement 

 manufacture. Proc. Institution Civil Engineers, vol. 145, pp. 44- 

 136; 1901. 



Editorial, The influence of the rotary kiln on the development 

 of Portland cement manufacture in America. Engineering News, 

 May 3, 1900. 



