Hot-pressing of alumina was caried out at 1700°-1900°C and 200-250kg/cm² for 5-60 min in graphite molds heated by high-frequency induction. Three types of structures were microscopically observed in hot-pressed specimens, depending on hot-pressing conditions. Temperature increase under constant high pressures from low to high temperatures tended to give the layered-typed bodies consisting of the structures varied near outer surfaces and in central parts. Application of pressure subsequent to temperature increase gave comparatively homogeneous structures in hot-pressed alumina, in which noticeable orientation was observed under microscope and by X-ray diffraction method. In the oriented-typed specimens, the c-axes of alumina crystallites tended to be parallel to the hot-pressing direction. The orientation degree was determined by X-ray diffraction method in comparison with a standard specimen with an at-random structure. In the cases where temperature was increased by about 50°C during hot-pressing under the conditions which should give the above-described homogeneous oriented-typed structures, enhanced grain growth tended to be caused in alumina specimens which contained 0.6% Na₂O, while the alumina with 0.08% Na₂O showed no enhanced grain growth. The lengths of grain growth were often observed to be about 1mm. The bending strengths of grown-typed specimens were about one forth of those of oriented-typed ones.

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The pottery stone called “Tôseki” is not defined mineralogically. And the process of rock-alteration to pottery stone is not studied yet.
In San-in district, there are several localities of pottery stone which may be classified into following three types:
I. Deposits produced by rock-alteration of pitchstone, which intrused into rhyolite-represented by Izushi pottery stone deposit in Hyôgo prefecture.
II. Deposits produced by rock-alteration of quartz porphyry-represented by Tanokouchi pottery stone deposit, Tottori prefecture.
III. Deposits produced by rock-alteration of rhyolite-represented by Amabe pottery stone deposit, Kyôto prefecture.
This paper concerns the geological and mineralogical studies of above three deposits stating in detail on the process of rock-alteration and also the mineralogical significance of pottery stone:
(1) Pottery stone deposits are the products of the replacement and metamorphosis under the influence of epithermal solution rising up along the weak line of mother rock.
During the process of deposition alkalies changed their position; Na₂O being generally leached out because of its smaller molecular volume, while K₂O codeposited with Fe on the circumference of pottery stone due to chemical migration giving lower quality ore so-called “Toraishi”.
(2) Pottery stone, Tôseki, is composed of SiO₂ and Al₂O₃ as chief ingredient, whose analysis is 75-82% SiO₂, 12-16% Al₂O₃, and 1-5% alklies (K₂O+Na₂O). It is white fine ore consisting mainly from quartz, sericite, halloycite and kaolinite, etc.

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Three kinds of forsterite batches of molar ratios, MgO:SiO₂=2.00:0.82 (specimen M), 2.00:1.00 (specimen F), and 2.00:1.05 (specimen S) were calcined at 1300°C, added 5% of Kaolin and fired at various temperatures.
Firing shrinkage, apparent specific gravity, water adsorption, dielectric loss, insulation resistance and bending strength of the fired specimens were measured to discuss the relation between the properties and the microstructure.
Above physical properties gave the maximum or the minimum values at certain firing temperatures. The specimen M fired at 1550°C, F at 1390°C, and S at 1370°C gave the maximum values of firing shrinkage, apparent specific gravity, T_e values of volume resistivity, and bending strength, and the minimum values of water adsorption and dielectric loss.
At these maximum or minimum points each specimen showed a similar microstructure being composed of the forsterite crystals of about 10μ. The texture was dense but not yet the perfect mosaic structure which came out by firing at higher temperature through the rapid aggregation of forsterite crystals.
In such a specimen cracks were observed in crystal and matrix which leads to the lowering of many properties.
Comparing the three specimens the aggregation of forsterite crystals by overfiring and concequently the fall of properties was the most remarkable in the specimen S.
The electrical properties of the specimen M were the best, but the proper firing temperature were considerably high.
It was suggested that the best composition for forsterite porcelain should lie between M and F.

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Using 9 base glasses given in Table 1 in the text a series of experiments was made to know the influences of the composition of base glass, melting atmosphere, heat treatment as well as the temperature at the observation.
It was confirmed that the titanium containing glasses may be colorless, blue and yellow to brown; they often become turbid or deep color during the heat treament; some of them change the color reversibly at the temperatures 300°-500°C.
From the observation of the spectral transmission curves the following conclusions were obtained:
(1) In glass coexist both Ti³⁺ and Ti⁴⁺.
(2) Melting in reducing atmosphere raised the concentration of Ti³⁺ giving blue color to glass. In this case the co-ordination number of oxygen is 6.
(3) There are two formes of Ti⁴⁺, one the network modifier in the form (TiO₆), and the other network former in the form (TiO₄) or (TiO₄)_n, the former gives colorless glass, while the latter the glass of the color changing from yellow to brown according to the increase of n.
The equilibrium such as
(TiO₆)→←(TiO₄)→←(TiO₄)_n
may be considered.
(4) It may be considered that the equilibrium (TiO₆)→←(TiO₄) goes towared (TiO₄) with the increase of the basicity of glass, and also with the elevation of temperature; and that (TiO₄)→←(TiO₄)_n goes toward (TiO₄)_n with decreasing temperature.
Based on these relations the change of color and turbidty of the glass may be explained.

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An experimental investigation of the etching of the surface of ceramic materials was carried out by means of electric dischage machning method.
It was conformed that the surface of ceramic materals may be etched in electrolyte solution by superposing the effect of electric discharge, and that the solutions thus activated attack the grain boundary and the grain itself with the different rate of erosion owing to the different energy levels.
Test were carried out using sintered alumina, petalite, cermet (cobalt-bonded tungsten carbides), barium titanate and ferrite (nickel system) as samples.
It was observed that 1) the sintered alumina in 33% HaOH solution or 20% HF solution, 2) the petalite in 25% NaOH solution or 35% HCl solution, 3) the cermet in 20% HF solution, 4) the barium titanate in 25% NaOH solution, 5) the ferrite in 25% NaOH solution gave the good results.

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It was confirmed that the area of the glass forming region of the system Sb₂O₃-Al₂O₃-R₂O (Na₂O+K₂O) increases with the addition of SiO₂ or GeO₂.
The glasses containing 5% SiO₂ or GeO₂ melted under oxidizing condition (o. glass) gave a different infrared transmission from those melted under neutral condition (n. glass). Also the difference in such properties as the color, density, softening point, and density were observed.
O. glass has better infrared transmittance and chemical durability than n. glass which gave broad absorption band between 750 and 1000cm^-1 and 1520cm^-1. These two absorption bands at 1420cm^-1, and sharp absorption bands at 1420 and 1520cm^-1. These absorption bands at 1420 and 1520cm^-1 appeared when o. glass is devitrified.
AlSbO₄ crystal has the absorption band at 1420cm^-1. After heating with Na₂O the crystal gave a broad absorption band between 750 and 1000cm^-1.
It was, therefore, concluded that n. glass contains the crystallite region, and the chain segments composed of Al³⁺Sb⁵⁺O tetrahedra are built up more easily in o. glass than in n. glass; also it may be assumed that SiO₂ or GeO₂ bridges the chain segment of AlSbO₄ tetrahedra.

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