The authors studied on the fluidity of particles of gypsum series such as dihydrate, hemihydrate as well as anhydrite and contributed these results to the fundamental problems concerning with the manufacturing process of various gypseous products such as plaster of Paris or Keene's cement etc.
As samples the authors used gypsum of by-product from salt manufacture and natural gypsum of Rasmallap Island by origin as well as the latter calcined for each 30 min. at 180°, 500° and 800°C respectively. The above samples were sieved between 0.0300-0.0147, 0.0147-0.0104, 0.0104-0.0074cm and finer than 0.0074cm particle sizes. Then, for comparison, the Normal Sand (JIS R 5201) was used at the same procedure. As fluidizing apparatus the authors used a tube of glass, with dimensions of 5cm diameter and 1m hight. The results were as follows.
The particles of gypsum series between 0.0300-0.0074cm sizes showed a good fluidization. However, they were less fluid than the Normal Sand, and dihydrate especially by-product one had very worse fluidity than hemihydrate or anhydrite. It is considered that these results were caused by the difference of particle shapes and of formation process. All finer particles than 0.0074cm (200 meshes), except the case of by-product gypsum, showed “channeling.” Moreover, it was recognized that slugging was observed for all samples when the hight of fixed bed reached to the amount more than twice of diameter of fluidizing tube. The hight of fluidizing bed was larger as the amount of samples was smaller, and also, with some exceptions, as the particle sizes larger. For the particle of gypsum series the bed hight increased as its specific gravity increased, namely, in the order, from dihydrate, himihydrate to anhydrite. But it appears that this fact was influenced by the kinds of particles. The necessary air velocity to obtain good fluidity was u>0.15u_m, and at this time the bed hight expanded to about 1.5-3.0 times of the hight of fixed bed.

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In order to study the origin of yellow spots usually found in thin section of fired bodies, size and amount of pores, uniform glassy like spheres and the yellow spots developed in the bodies were microscopically observed. The specimens set for the experiment consisted of 97% feldspar with 3% quartz fired at 1150-1450°C. Regular relationships were found between the size and firing conditions, but not between the amount and firing conditions (Figs. 1-6).
Distribution of the yellow spots and pores are microscopically compared and found that they show a marked similarity in the followings; (1) the lowest temperature at which they are detected in the thin section, (2) the aspect of the variation of their size and shape with firing schedule, and characteristics of their distribution, (3) irregularity between their amounts and firing conditions.
Furthermore, (4) in the case of total amounts of the pores and yellow spots, regular relationship between their amounts and firing condition can be found (Figs. 7, 8).
(5) Volume changes of the yellow spots with rising temperature and holding time are of the same order with that of pores which contain water vapour, air and other gases.
(6) Size of small yellowish brown particles included in the yellow spots is not changed with firing conditions, but rather with grinding conditions of the thin section. Moreover, their compactness to fill up the yellow spots is highly irregular. Appearance of the small yellowish brown particles closely resembles with that of the abrasive powders used in grinding the thin sections (Photo 4).
(7) Yellow spots can not be found in the powder of the specimens observed with oil immersion method.
(8) Content of Fe₂O₃ in the raw materials used for this experiments, is too low to produce such a number of dark yellowish spots. There are no conditions to produce carbon deposits on the specimens during firing schedule.
From the results mentioned above, following is to be concluded: The yellow spots are not actually present in the fired bodies, but derived from a part of the pores, which are filled with abrasive matters such as carborundum or emery powders, used during grinding the thin section.
In order to corroborate these conclusions, yellow spots are artificially produced in optical glass, FaK, which is ground into a thin section. Photo 5 shows the very one.
Besides the yellow spots which forms the chief subject of this paper, we rarely meet with similar ones, such as yellowish brown glasses, in the fired bodies. The writer also briely refers to them.

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(1) The existence of a linear relationship between the peak area in the differential thermograph, A, and the heat of reaction, ΔH, was discussed, and it was deduced that the ratio, A/ΔH, should change little with temperature. (2) This deduction was confirmed by the measurement of the heat of inversion for several salts, and it was noted that the correction term due to the difference in heat capacity could be large. (3) The differential thermograph for titania-opacified enamel was explained quantitatively by this theory. The heat of precipitation of titanium oxide in the frit was estimated to be about 11 kal/M, and also it was numerically confired that the broad peak found between 550° and 800°C was due to an apparent endothermic reaction accompanying the change in packing of the specimen.

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Oxidation tests on powdered green silicon carbide, mainly of the Type 6 H with 13.4μ or 21.6μ diameters, were carried out in dry oxygen of one atmospheric pressure for about 50 hours in the range of temperature from 810° to 1400°C. The result show that the oxidation increases with temperature.
An empirical equation for the rate of oxidation of silicon carbide powders is given as follows;
{R₀ (I→√I-X)}^N=Kt,
Where X stands for the oxidation rate, t for time, R₀ for mean radius, and N and K are constants.
At temperatures below 1200°C N was in the range of 1.7-1.5, while at temperatures from 1300° to 1400°C it was nealy 2.
From the studies of X-ray powder method, silica liberated by oxidation was found to take the form of cristobalite at the temperature above 1350°C, but below 1200°C the gel-like structure.
A discusion is given on the empirical equation.

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