CHAPTERS ON THE CEMENT INDUSTRY 883 



The tests of the natural cements are of considerably less value, 

 as they are based on a much smaller number of samples. The 

 diagrams show very well the fine grinding practised in the Rosen- 

 dale region. PL 94 shows the abnormally high tensile strength for 

 cements of that class obtained during 1900 from the natural 

 cements manufactured in Erie co., N. Y. 



