UTILIZATION OF CLAYS FOR PORTLAND CEMENT. 201 



siliceous clays or limestones are undesirable, the materi- 

 als used often contain ferric oxide, magnesia or alkalies. 



Their afifect according to Shewberry is as follows: 

 Ferric oxide combines with lime at a high heat and acts 

 like alumina in promoting combinations of silica and 

 lime. For practical purposes the presence of ferric oxide 

 in a clay need not be considered in calculating the 

 amount of lime required. 



Alkalies so far as indicated by the behavior of soda, 

 are of no value in promoting the combination of silica 

 and lime, and probably play no part in the formation of 

 cement. 



Magnesia though possessing marked hydraulic pro- 

 perties when igniled alone, yields no hydraulic products 

 when heated with clay, and probably plays no part in 

 the formation of cement, and it is incapable of replacing 

 lime in cement mixtures. 



The following analyses taken from the 1897 Mineral 

 Industry will give an idea of the composition of clays 

 used in portland cement, while following them are several 

 Alabama occurence that could no doubt be used in ce- 

 ment manufacture. 



