474 grim. CERAMICS AND CLAY COMPOSITION [Ch. 25 



thorough mixing of the clay before processing to distribute the silt 

 uniformly solved the problem. 



Frequently such processing problems are far more complicated, and 

 the cause begins to appear only after very thorough analysis of all 

 factors of the composition of the clay. 



Plant Control for Uniformity of Material 



It is obvious from the foregoing discussion that both producers and 

 users of clay are interested in clay with uniform properties. They are, 

 therefore, interested in tests, which usually must be rapid, to detect 

 variations in properties and, if possible, the cause of the variation in 

 properties. Simple determinations of properties are, of course, used in 

 plant-control work, but frequently a test to show variation in com- 

 position is more satisfactory because it shows something of the cause 

 of the variations in properties in addition to the simple facts of property 

 variation itself. Again an example will suffice to illustrate the point. 

 Differential thermal analysis (Grim, 1942) has been found to be an 

 excellent instrument for plant control because it provides information 

 about several factors of the composition of a clay, so that, in addition 

 to showing that a clay sample has varied, it reveals the nature of the 

 variation. 



REFERENCES 



Casagrande, A. (1932). Research on the Atterberg limits of soils: Public Roads, 



vol. 13, pp. 121-130. 

 Grim, R. E. (1942). Modern concepts of clay materials: Jour. Geol., vol. 50, 



pp. 225-275; III. Geol. Survey, Rept. Inv. 80. 

 (1944). Differential thermal analysis of clays and shales; a control and 



prospecting method: Jour. Amer. Cer. Soc, vol. 27, pp. 65-76; III. Geol. Survey, 



Rept. Inv. 96. 



(1948). Some fundamental factors influencing the properties of soil ma- 



terials: Proceedings of Second International Conference on Soil Mechanics, 

 Rotterdam, vol. III. 

 , and Cuthbert, F. L. (1945, 1946). The bonding action of clays, Part I, 



Clays in green molding sands: III. Geol. Survey, Rept. Inv. 102; Part II, Clays 

 in dry molding sands: III. Geol. Survey, Rept. Inv. 110. 

 White, W. A. (1947). The properties of clays: Master's thesis, University of Il- 

 linois. 



