In this Paper, the chemical mixing, that is the random rearengement of Powder particles and also of chemical elements in their particles, was investigated with the raw materials of silico-alumina or silico-magnesia catalysts, which were mixtures of silica gel and alumina gel or silicagel and magnesium hydroxide precipitate. The extent of the chemical mixing was examined by measuring of solid acidity and also was compared with that of homogeneous mixture of the same chemical compositions prepared by the super homogeneous coprecipitation method. The characteristics of the chemical mixing phenomenon in the presence or absence of water were investigated with mixtures of two crystalline powders, MoO₃ and V₂O₅.
From these investigations, the following results were derived.
(1) Silico-alumina or silico-magnesia catalysts are prepared with a mixture of two hydrogels obtained by the method of ball-milling and kneading etc. The one hour mixing was generally not enough for the chemical mixing of these raw materials. Their surface acidity, that is the solid acidity per unit surface area were less than that of the super homogeneous co-precipitates with the same chemical compositions.
(2) For the preparation of silico-alumina catalyst by the mixing of its raw materials, it is better to use the hydrogels than to use the dried or calcined xerogels.
(3) In the course of the preparation of silico-alumina catalyst by the mixing method, the surface acidity increased with the proceeding of the chemical mixing while the surface area decreased. It was further found the optimum mixing time which gave the maximum solid acidity per unit weight.
(4) When the calcined xerogel powders of silica and alumina are mechanically mixed and groud well with batch bowl kneader, the chemical mixing proceeded and the acidic “silico-alumina” was produced.
(5) The rate of the production of the surface acid by the chemical mixing of silica and alumina gels in the presence or absence of water could be shown by the following equation, dH_T/d_t=m(1/√t)³
(6) Following results were obtained by the experiments of the chemical mixing of two crystalline powders, MoO₃ and V₂O₅.
a) The dry grinding-mixing brought the sharp decrease im the sizes of crystallite of these particles, while the wet mixing did not.
b) The wet mixing brought the sharp decrease of the amount of these crystalline materials while the dry mixing did not.
c) These results induce that the dry grinding-mixing prefers the body breaking, but the wet mixing prefers the surface grinding, thus giving the quite different mechanisms of the grinding-mixing of solid particles.

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