AbstractThe particle‐size variations of eleven shipments of commercial flint and of fifteen shipments of feldspar have been investigated as a possible cause of production variations in electrical porcelain. A correlation of sieve data with specific surface calculations based on sedimentation determinations was made on six grades of commercial flint. The Andreasen pipette sedimentation method was used for all tests except those in which the hydrometer method was employed for comparison purposes. Either of these sedimentation methods had adequate accuracy to control particle size. The percentage remaining on the 325‐mesh sieve, however, could not be correlated with the specific surface values. Particle‐size distribution was determined for each sample. To facilitate comparisons, specific surface values were calculated from a plot of the distribution data on log‐probability graph paper. The investigation included the effect of various liquid suspending media and electrolytes on the settling characteristics of flint and feldspar. Neither flint nor feldspar could be adequately dispersed in non‐polar liquids. Feldspar apparently has surface‐active characteristics that permit it to be flocculated or deflocculated, depending on the nature of the ions present in solution. An anomalous peptizability of some feldspar samples in the particle‐size range below 3 microns