The single component bodies of chlorite, pyrophyllite, and sericite, as well as those made from the mixture of chlorite-quartz, pyrophyllite-quartz, and pyrophyllite-sericite were fired to measure shrinkage and absorption. The addition of a small amount of alkaline earth oxides on their physical properties, colour and the degree of vitrification were also noted. The measurements of dielectric loss and insulation resistance were also made using the specimens having smaller porosity values.
In general, the chlorite and chlorite-quartz bodies showed high insulation resistance and low dielectric loss, but they had high shrinkage. Chlorite body, and some bodies in the series of pyrophyllite-chlorite had also low dielectric loss, but they were of low insulation resistance. The bodies in the series of pyrophyllite-sericite had high loss factors and low, although some of them had low dielectric loss.
Large variatin in the properties such as the range of vitrification, dielectric loss, and insulation resistance etc. followed from the variation in the amount, and the property of the alkali earth oxides added to the body. Bodies having high insulation resistance were not necessarily those having a low dielectric loss.

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Alumina-chromium cermet bodies containing 20 to 70 vol. % Cr were hot-pressed at 1400°-1470°C and 150kg/cm² for 20-30 min., in argon atmosphere using graphite molds having a circular hole of 8mm in diameter, or a rectangular hole of 4×15mm.
From the results of this study it was concluded that:
(1) In hot pressing, increase in the chromium content decreased the press-temperature, for instance, 1400°-1430°C for 60 vol. % of chromium, being about 300°C lower than the hot-pressing temperature in hydrogen atomosphere (Table 1).
(2) Measuring the hardness distribution along the center line of hot-pressed bodies whose hight to dia. ratio was 2:1 the method of pressing was studied, and the best result was obtained when the pressure was applied with a plunger moving downwards in a floating die. (Table 2 and Fig. 3).
(3) The distribution of hardness in hot-pressed bodies of complex shape was studied with a result that there are some regions giving lower hardness values caused by the lack of the flowability of the mix, which suggests the necessity of three directional pressing (Photo. 2).
(4) The transverse rupture strength of hot-pressed bodies of the size 4×4×15mm were 55-72kg/mm² at room temperature.
(5) The microstructure of hot-pressed bodies was characterized by the occurence of smaller corundum crystals of the order 1-3μ, and by the more rough boundaries between the alumina and chromium phase than those in the bodies sintered in hydrogen atmosphere. Continuous metallic phase was observed in the hot-pressed bodies containing more chromium than 60-70 vol. % (Photo. 3).
(6) Fractures in the tension side of the specimens of bending rupture test passed through the crystals. of corundum, chromium as well as their phase boundary, and consequently, both chromium and corundum phases were appeared in the electron microphotographs (Photo. 4-5).

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The swell by heating of obsidian from Wada pass in Nagano prefecture, Japan, and some other natural glasses caused by the evolution of gases were studied with the following results:
(1) The total weight loss by heating the grains of obsidian increases with time approaching gradually to a definite value which in turn is dependent on the grain size and the temperature. The finer the grain and the higher the temperature the more rapidly proceeded the change to a higher value of the loss of weight (Fig. 2 and 3).
(2) The time of starting the change and for reaching to a maximum volume were reduced remarkably with the increase of heating temperature, giving rise to the sudden expansion of the grains (Fig. 4).
(3) The grain size had only a slight influence on the delay of the start of swell, whereas the time for reaching to a maximum was influenced rather remarkably (Fig. 5).
(4) The volume expansion increased with increasing grain size, at first rapidly and then gradually, tending to a cirtain value depending on the heating temperature. In the final stage only a slight volume increase was observed (Fig. 6).
(5) The higher the heating temperature the greater will be the expansion (Fig. 7).
(6) Passing through a maximum the grains began to shrink with the rate increasing rapidly with the heating temperature (Fig. 9).
Following successively after the change of the structure of obsidian grains under a microscope it was observed that;
(7) when the grains were heated with a constant rate they suddenly began to bubble which increase in number and size with time, and thus giving a honycumb structure.
(8) after full expansion, occured the burst of the bubbles from the outermost layer leading to the formation of a crust around the grain growing gradually until its thickness checked the further collapse of the pores.
The author was thus able to find out the necessary conditions for producing the strong expanded grains of obsidian.

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Flame length, flow patterns, and the degree of mixing of Jets in furnaces were studied by liquid model experimants.
The dilute solutions of caustic soda, and of hydrochrolic acid were used to stand for, respectively, fuel gas and air in the model. The former was coloured by phenolphthalein to visualize the end point of the neutralizing reaction between the solutions supplied in two separate streams. The point at which the colour of the caustic soda solution just vanishes indicates the position of the tip, and thus the length of flame. In Fig. 2 and 3 are plotted the flame lengths under various excess air rates. The curves make it clear that the flame lengths decreases with an increasing excess air rate. The flame length was also affected by the relative port velocity as shown in Fig. 5. Some examples of liquid model flames in a scale model were shown in Fig. 6.
A series of experiments was carried out to observe the flow patterns from the photographic records of the tracks of tracer particles moving in the illuminated area of the water jets in a box. When there is a difference between the velocities of two jets one having a lower velocity is drawn into the other, so that, after a little while, both flow as a single unit as it is seen in Fig. 7 b. The intensity of turbulence in the jets was evaluated from the records of the tracks described by the tracers.

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Magnesium and zinc titanium spinels are the white compounds with the basic formulas 2MgOTiO₂ and 2ZnOTiO₂, in which Mg²⁺ and Zn²⁺ can partly or wholly be replaced by other bivalent ions such as Co²⁺ and Ni²⁺. The ternary and the quarternary compounds thus obtained are coloured producing a great variety of hues.
For the purpose of studying the properties of such pigments each constituents were mixed by dry process, calcined at the temperatures 1000°-1350°C. The reflectance between 400-750mμ were measured by a photo- electric spectrometer to represent the result by C. I. E. colour specification, and also X-ray analyses were made. The results are summarized as follows:
(1) CoO-MgO-TiO₂ system showed a wide variety of hues, ranging from light blue, through greenish blue, to medium and dark green. Pigments in this series had good brilliance, and the samples calcined at a temperature higher than 1200°C had the spinel structure.
(2) NiO-MgO-TiO₂ system gave no spinel structure in the samples heated at 1200°C, indicating that the formation of spinel was more difficult to occur than in the systems MgO-TiO₂ and CoO-MgO-TiO₂. The spinel structure was not found in NiOMgOTiO₂ calcined at 1400°C, but NiOZnOTiO₂ gave a light green pigment by calcining at 1200°C.
(3) The spinel structure was not found in the system NiO-CoO-MgO-TiO₂ when heated at 1200°C, but at 1350°C, and with increasing content of CoO, spinel was observed in the pigment whose colour changed from yellowish to brilliant green.
(4) Pigments of the system CoO-ZnO-TiO₂ gave colours ranging from light to dark yellowish brown, so that in NiO-CoO-ZnO-TiO₂ series a clean brilliant hue could not be obtained with increasing amount of CoO.

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これまで真空管の外囲器としてはほとんどガラスが使われてきたし, 今もなお大部分のものはガラスを使用している. しかしこれはガラスが長年にわたる技術の進歩によって種々の封着用金属や封着技術が発達し, 大量生産によって価格も廉くなり, 加工が容易で気密であって絶縁抵抗もかなり高い, 内部が透視できるなどの点ではこれまでの習慣からすれば, たしかに便利で今後とも大いに使われることと思われる. しかし一面ガラスは脆くて壊れやすい, 熱の急変に対して弱い, 高周波で絶縁がよくない, 安全使用温度が低いなどの欠点があり, 最近発達してきた超短波大電力送信管のような特殊なものになるとその構造材料としてはもはや使用に耐えなくなってきた. たとえばガラスが強力な超高周波電界内におかれた場合に, その誘電体損失のために温度が昇り, ついには軟化して外気圧に耐えなくなり破壊するという具合である. このような高度の負荷と高周波に対する要求を満たすためにはその構造材料としては次のような条件があげられる.
(1) 気密であること
(2) 高周波においても誘電体損失の小さいこと
(3) 安全温度が高く, 熱衝撃に対する抵抗が大きいこと
(4) 機械的強度が大きいこと
(5) 電気抵抗が高くその温度係数が小さいこと
(6) 金属との封着が可能なこと
以上のような点でセラミックがガラスに優ることは明らかで, 寸法精度の点でも機械研磨が可能で寸法精度がよくでき形状も割合広い範囲で定められるなどの. 利点がある. なおこの外セラミックを使用すれば真空管の設計上非常に有利となる点が多い. たとえばセラミックは外囲器として絶縁ブッシング型にして使われるのが普通であるが, この場合セラミック自身が治具となり, また金属との封着部分が電極として使用できるなどその構造が単純化され, その設計にも無理がきくので同一出力に対して小型となり超高周波特性も改善される.
以上いろいろ述べたような理由でセラミックが使われるようになったが, これはガラスと違ってガス焔で熔かして金属と封着するというわけにはゆかないので, これには新しい独特の封着技術が必要となった.
そこで以下セラミック真空管に使用する各種セラミックの諸性質とこれに必要な金属との封着技術や封着機構などについてその概略を述べて見たい.

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