POWDER DISPERSIBILIT¾ 339 Table IV Particle Size, Specific Gravity, and •-Potential of Powder Samples Particle Diameter Size Specific Sample (u) Gravity Carbon black Iron oxide (A) Iron oxide (B) Iron oxide (C) Iron oxide (D) Iron oxide (E) Titanium dioxide (A) Titaniron dioxide (B) Titanium dioxide (C) Colloidal kaolin Mica Talc (A) Talc (B) Zinc oxide (A) Zinc oxide (B) Zinc oxide (C) Calcium carbonate Lake Red C Permanent Orange Zinc laurate 0 01 0 06 0 08 0 08 011 0 50 0 14 0 12 0 17 0 20 0 24 0 29 0 53 0.21 0.24 0.29 0.71 0.04 O. 39 I. 42 1.77 •, 4.03 4.73 5.79 5.18 5.25 4.35 4.40 4.04 2.69 2.92 2.86 2.81 5 87 5 74 5 66 2 64 2 11 1 57 1.18 •-Potential (mY) 37 12 36 67 72 42 37 28 47 86 53 78 83 17 36 19 2(} 82 83 ß . . "The specific gravity of carbon black was measured by pycnometer and other powders ere measured by Beckman's apparatusß Table III shows the measured values of SN2and Smo and the hydro- philieity (•$'n._,o/SN•) for the 20 selected samples of powder. Measurement of Speci•c Gravity Measurements of spedfie gravity were repeated three times using Beckman's spedfie gravity meter. The mean values are shown in Table IV. Measurement of Particle Size The particle size (d,,,,.) of Table IV, which is called the diameter of spedfie surface area, is obtained by the equation: where K p d. = K/p. SN• = shape factor of powder = density of powder = specific surface area of powder.

340 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Distilled water Cock 1' Deaeration Cock Powder sample Figure 2. Apparatus for mixing powder and water in vacumn Values of apparent particle size (d,•.) in Table IV were calculated by taking K = 6 corresponding to the spherical shape of the powder grain. For p, we used the values measured by Beckman's specific gravity meter and for SN2, the values obtained by adsorption of nitrogen gas by the BET method. Measurement of g-Potential Velocity of movement of powder grain in water was measured by electrophoresis, and the g-potential was calculated according to the equation below. The values obtained are shown in Table IV. No measurements were taken of zinc laurate because it floated on the sur- face of water. where 4•rlv velocity of movement of powder g-potential dielectric constant of dispersion medium distance between electrodes voltage applied viscosity of dispersion medium