The present authors have been studying on the sintering reaction of the mixture of dolomitic limestone and serpentine, and already reported the availability of the calcind mixture remarkably increased for the forming of soluble silicates in their reaction system at about 1100°C, in Gypsum & Lime No. 30 7-14 (1957).
On CaO-SiO₂ system, MgO-SiO₂ system and CaO-MgO-SiO₂ system compounds expecting to form in the sintering process of the mixture of dolomitic limestone and serpentine, many researches were reported connecting with the sintering mechanism of magnesia clinker, of dolomite clinker and their depression of slaking and dusting. Otherwise, though those compounds are the principal constitution of byproduced slags from iron and another metals industries showing great effect in the neutralisation of acidic soil and the improvement of soil wanting in magnesia and silica, the researches on the relationship between constitution and availability of them have been scarcely reported.
If the constitution of the compound having a high availability for fertilizer is made clear, the sintering condition of the mixture of dolomitic limestone and serpentine will be necessarily decided and the forming condition of metallurgical slags taking variable composition improved.
The purpose of this paper is to analyse the available constitution of some magnesium calcium silicatic fertilizers, the calcined fertilizer prepared in previous paper and the commercial fused fertilizers.
The procedure is first to synthesize 10 kinds of pure minerals, 3 CaO·SiO₂, 2CaO·SiO₂, 3 CaO·2 SiO₂, CaO·SiO₂, 2 MgO·SiO₂, MgO·SiO₂, 3 CaO·MgO·2 SiO₂, CaO·MgO·SiO₂, 2 CaO·MgO·SiO₂ and 2 CaO·MgO·2 SiO₂ from pure chemicals, secondly to examine the availabilities of them by 3 dissolution tests, boiling N/2 HCl soluble, shaking N/2 HCl soluble and 2% citric acid soluble, after confirming their constitution by X-ray powder patterns.
The results are summerized as follows ; the availabilities of the synthetic minerals prepared are different from each constitution of them. In these systems, CaO-MgO-SiO₂ system compounds have the highest availabilty, the next are CaO-SiO₂ system compounds and MgO-SiO₂ system compounds are the lowest. In each system, the higher the basicity of mineral becomes the more the availability increases.
Basic CaO-MgO-SiO₂ system minerals or the eutectic crystals of basic CaO-SiO₂ system mineral and periclase are often found for the available constitution of magnesium calcium silicatic fertilizer, the former are very effective for the availing of silica above all.
By the X-ray powder patterns, we can know the presents of 2 CaO·SiO₂, merwinite and periclase in the calcined mixture of dolomitic limestone and serpentime, akermanite in the blast furnace slag and in the electric furnace slag of pig iron by slow cooling method, and 2 CaO·SiO₂ and periclase in the magnesium manufacturing residue by Pidgeon process for the available constitution.

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We prepared various masonry cements by blending normal portland cement with one or more of fine powdered limestone, Keisan-hakudo and fly ash etc, and examined their soundness, plasticity and water retentionability to know the most proper materials, mixing ratio and their fineness. Summarizing these results;
(1) On the side of the color, powdered limestone and Keisan-hakudo are suitable, but the latter causes crack when it occupies too large part in the cement.
(2) The proper mixing ratio is thought to be 30-40% cement, 55-65% limestone powder and 5% Keisan-hakudo.
(3) The higher fineness gives the better plasticity and water retentionability but inclines to induce crack. On this point, there remains more to research.
(4) From the various procedures we tried for crack test, it seems to give the better judgement to cover 1 : 3 mortar foundation plate with wet cloth for having it contained some constant water and then coat it with the sample paste.

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This work has been conducted to determine the optimum conditions for the calcination of so-called chemical gypsum obtained as by-products from various chemical industries. Fluidized bed for calcination (8 cm I. D.) with a rod for agitation (Fig. 1 and 2) has been maintained in the state of complete mixing by the agitator rotating at the constant rate determined from the data of backmixing experiments. Assuming the controlling step in calcination is the diffusion process of water vapor in solid particle, the relation between particle diameter and reaction time has been derived, and the theoretical values of the rate of calcination have agreed satisfactorily with the experimental data (see Fig. 8 and Table 2). It might be guessed that the rapid calcination at relatively low temperature would become possible by fluidization.

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