A feldspar and a potter's flint (crushed quartz) of commercial grade were separated by means of an air elutriator into four fractions.Each fraction con- tained particles grading from the finest originally present to maximum diameters of 10, 20, 35, and 75 microns, respectively.In addition, fractions containing particles varying from 35 to 75 microns were separated and a portion of the original feldspar was reground to produce a material composed of particles of 35 micron maximum diameter.The specific surface in cm 2 /g was calculated for each fraction from data obtained by microscopic count.Various combinations of the several fractions of flint and of feldspar were incorporated in whiteware bodies.Specimens of these bodies were heated at 1150°, 1200°, 1250°, 1300°and 1350°C, and tested for linear shrinkage, apparent porosity, strength in bending, and linear thermal expansion.Shrinkage and porosity results were compared with the specific surface values of the flint and feldspar in the respective bodies.6. Fusion and solution (a) Specimens heated at 1350°C (6) Specimens heated at 1250°C (c) Specimens heated at 1150°C _ IV.
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Geller et al. (1933) studied this question.