Sample A HA B HB C HC D HD
median diameter (μm) 3.79 4.99 2.89 3.08 0.99 0.83 0.68 0.58
number average particle diameter  (μm) 5.43 5.27 4.34 4.52 2.31 2.22 1.10 1.15
% diameter: 90.0% (μm) 8.09 8.95 6.71 6.92 2.95 2.84 1.39 1.08
number per unit weight (/μg) 6650 6780 9255 9285 55286 56143 340500 412500
ratio of  number per unit weight (1 : 1.020) (1 : 1.003) (1 : 1.016) (1 : 1.211)
Table 1: Particle diameter and number per unit weight of silica samples.