Firing behavior of Missouri plastic fire clay

There are two districts in Missouri in which plastic fire clay occurs. The oldest and least significant of these deposits is the Cheltenham , in the St. Louis area. The most prominent area in which plastic fire clay occurs is generally termed the east central district. Included in this district are Calloway, Montgomery, Audrain, Warren, Boone, Monroe, Pike and Lincoln Counties. The clay as tested in this report occurs in Boone County, near Columbia. A plastic fire clay does not have as high a P.C.E. (pyrometric cone equivalent) as the ordinary flint and semi-flint clays, but its high plasticity warrants its use in the manufacture of refractories as an aid in the forming process. Plastic fire clays are also used in the production of second-grade refractory products. The chief difference between plastic fire clay and semi-flint clay is that the plastic fire clay contains more impurities and has a higher alkali content --Introduction, page 1