CLAY 3,3 



refractoriness; but if present as a component of feldspar, it 

 serves the purpose of a flux and somewhat increases the 

 plasticity. The advantage of the rational analysis is that it 

 resolves the clay into its mineral components, affording an 

 insight into the physical properties — as fusibility, refractori- 

 ness — of the material. This is frequently a matter of far 

 greater importance than the chemical composition; for in- 

 stance, two clays of the same rational composition will behave 

 much alike if burned under the same conditions, even though 

 they may differ in chemical composition. 



Kaolin is a white burning, nonplastic, highly refractory 

 residual clay used in the manufacture of china and other 

 white wares; it must be practical^ free from iron, as a very 

 small quantity would cause the ware to become discolored 

 in burning. The chief producing states are Pennsylvania, 

 Delaware, North Carolina, and South Carolina. 



Ball clay is a white burning, plastic, sedimentary clay, 

 used with kaohn to afford plasticity to the body in the manu- 

 facture of white ware, and often incorrectly called kaolin. 

 The distinguishing characteristic of this clay is its plasticity. 

 The chief producers of ball clay are Florida, New Jersey, 

 and Kentucky. 



The term fire clay is a rather broad one, embracing not 

 only the high grade clays used for the manufacture of refrac- 

 tory material of all kinds, but also the more or less impure 

 varieties used for stoneware, terra cotta, and yellow and 

 Rockingham ware. Glasshouse supplies, which must be high- 

 ly refractory, are made from an especially high grade of this 

 clay. Fire clay is subdivided into flint, or nonplastic, and 

 plastic clay. The mining of fire clay for sale is most exten- 

 sively carried on in New Jersey, Missouri, Pennsylvania, and 

 Ohio. 



Clays for vitrified wares, such as sewer pipe, electric 

 conduits, and vitrified paving brick, are those in which the 

 proportion of fluxing impurities is sufficient to allow the clay 

 to vitrify at a moderately low temperature, but not to cause 

 the w'are to become soft under the pressure of a column of 

 some height and considerable weight. 



Brick clays are divided into those used for common and 



