Fine particles of calcium carbonate (1.4μm), metallic silicon (0.4μm) and talc (7μm) are dispersed in air by use of a mixer type disperser, a fluidized bed or a capillary pipe. Calcium carbonate powder is almost completely dispersed by the mixer type disperser. It is difficult, however, to disperse metallic silicon powder. On the other hand, talc powder seems to be broken up and agglomerated in the dispersers, and becomes to have a wide size distribution.
Effects of dust concentration in feed suspension on the dispersion are also experimentally studied, and discussed based on a simple model.

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Shirasu is a kind of volcanic ash covering widely the area of South Kyushu. The mineral components of Shirasu consist of 60-80wt% volcanic glass and 40-20wt% crystalline minerals. The volcanic glass is porous and irregular and has small apparent density.
For the purpose of using the volcanic glass contained in Shirasu as filter aid and filter medium, the authors carried out the compression permeability tests and measurement of porosity in case of loose and tight packings and surface factor on three samples: Shirasu A, B and C. The range of particle size of Shirasu B and C was 1190-37μ. Shirasu A was obtained by crushing Shirasu B and the particle size was in less than 44μ.
The experimental results obtained are as follows.
1) Shirasu B which is raw volcanic glass powder, has much porosity and irregularity in the region of more than about 300μ, and Shirasu C which is crushed volcanic glass powder, has the same properties in the region of more than about 200μ. Furthermore, Shirasu C is more porous and irregular than Shirasu B.
2) Shirasu B and Shirasu C are more porous and irregular than sand. Therefore, it is considered that Shirasu is superior to sand as a filter medium.
3) The compression permeability characteristics of Shirasu A are between those of Kaolin and Cement material and those of filter aids.
The experimental equations of equilibrium porosity, ε_x, and permeation resistance, α_x, are as follows.
ε_x=0.613-0.578p_s^0.0536 α_x=0.280×10¹¹+0.337p_s^1.28
Where p_s is compressive pressure.

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Adhesive forces generated at a contact point between spherical and plate specimens made of the same material due to water vapor adsorption on them were measured for four samples by using an electrobalance. The samples used here are commercial soda-lime glass bead, granulated urea and potassium halides, i.e. KCl and KBr. The values of the adhesive forces were collated with the amounts of adsorbed estimated from adsorption isotherms of water vapor on the above particle samples.
The adhesive forces appeared at relative water vapor pressures of 0.25, 0.30, 0.30 and 0.17 for the glass bead, the granular urea, KCl and KBr, respectively. At this time, the thicknesses of adsorbed water layers were less than two layers for all the samples. Concerning the above results, this adhesive force can not be a binding-force due to a liquid bridge formed near the contact point. Therefore, the force which occurred in the early stage of a caking process is considered to be generated by the hydrogen bond induced between the two samples being attached with water layers. On the other hand, the force which increases considerably in high water vapor pressure range will be due to a liquid bridge between the two specimens. Moreover, it is concluded that the adsorbed water molecules less than 2 or 3 layers are influenced by surface properties of the solid, whereas the adsorbed more than 4 or 5 layers is no longer influenced from the solid surface. Thus, multi-layers of water molecules are thought to acquire an inherent property as the liquid water.

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