The most predominat causes of the wide varieties of unfired kaolins in their physical properties seem to depend on the degree of crystallinity and particle size.
For the sake of more reliable deduction of the degree of crystallinity and particle size of kaolins, admixtures were made and their influences on the D. T. A. curves were examined. On admixing an inert substance, only a diluent effect was found in thermal peaks of kaolins, whereas in the case of the mixtures of 2 sorts of kaolins, a mutual influence between the each original exopeaks was detected. The results obtained are summarrized as follows.
(1) In accordance with the increasing replacement of kaolins by α-Al₂O₃, the interval between the endo- and exopeak became wider. By the same degree of the replacement, the shifting of exopeak towards higher temperature amounted to the 1/10 order of that of the endopeak towards lower temperature.
(2) It seemed that the “slope ratio” differed with the kaolin content. The interval between the starting and top temperature of endo-peak largely changed with the kaolin content, however, the interval between the top and final temperature of the peak was not so much affected.
(3) The complicated shape of exopeak which appears in rare cases on the D. T. A. curve of a kaolin seems to be caused by an ifluence of acompanied montmorillonite or other sort of kaolin having an exopeak which differs more than about 30°C from that of the main component mineral.

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In a previous paper one of the authors, A. Naruse, formulated the relation between the dimensions of the throat of a glass tank furnace and the maximum velocity of the current passing through it. And the present one contains the result of a series of model experiments carried out in order to built up a sound experimental background for the theory postulated before, and if necessary, to modify it.
A transparent plastic model throat, 6cm long, 5cm wide, and variable height 1-4cm, having the dimensions as a whole which satisfy the similarity conditions to actual tank as far as possible, was used for the experiments. The model was immersed in a water bath which was composed of three compartments so that the temperature of either one of both end-sections may be fixed at a desired point. Furthermore, in order to set up the necessary temperatures at the principal points, the melting chamber was heated electrically with a hot plate, while the working chamber was cooled with water.
As a liquid medium was used 83% glycerin, and as the traces for observing the flow of liquid were used the coloured oil droplets having the specific gravity well matched with that of the medium. At regular time intervals a fine line of coloured oil was drawn through the liquid, which immediately afterwards disperse into minute droplets. The velocity of flow at every level was determined from the photographic records taken at regular time intervals. The observations were carried out under the conditions both with and wothout pull.
A fairly good agreement of the experimental values with those calculated by Peychès' formula was proved. And, if the correction for the friction at the side walls was introduced, the agreement became excellent.
As long as the throat is not too high the velocity distribution in existence of pull was also in good agreement with the theory.
The co-existence of the convection and the pull currents in a throat makes the forward current stronger, while it makes the backward current to run down gradually until it finally vanishes.
This limited velocity Wc may be expressed as
Wc=1/72⋅ρ₀ρbgk/η⋅Δθ/l⋅fh⁴
When the height of the throat is changed keeping the pull velocity constant the limiting height having the same meaning as above may be represented as follows:
f^1/4h_c=2.91(Wηl/ρ₀ρbgkΔθ)^1/4
The symbols used in those equations are referred to the table of nomenclatures in the text.
From the technological point of view the authors maintain their opinion that both figures give the corresponding optimum values which reduce the velocity of erosion of refractories to the minimum.

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The construction and the operation of the automatic recording dilatometer which was developed for measuring the thermal expansion of glass is described. The sample, 10cm long and 1.5-2.0mm in diameter, was heated at a constant rate, and the temperature was recorded by an automatic temperature recorder. The expansion of the sample was magnified by an optical lever having the effective length of about 5mm, and was traced by a tracer mechanism. This mechanism drived therecording chart of the recorder, and as the result, the expansion curve of the sample was drawn on the chart.
Several improvements were also made on the dilatometer to increase its accuracy.
Results of the measurements for three kinds of glass are described briefly.

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真空管の外殼 (外囲器) には, 一般にもっぱらガラスが使われている. ガラスは一般に (1) 加工が楽である, (2) 封着が容易である, (3) 内部が透視出来る, (4) 絶縁がよい, (5) 価格が安い, (6) 気密である等の理由で始めから真空管や電球に用いられて来たが, まだまだその用途は絶えないのみか, 将来とも大いに用いられることであろう. しかしガラスにはまた (1) 脆弱で破損し易い, (2) 高温度に使用出来ない, (3) 高周波では絶縁がよくない, (4) 熱の急変に対して弱い等の欠点があるために一時的の現象ではあったが, 金属真空管というのが現われ, 真空管が大いに小形化され, Tin Can Tubeなど量産的のものも現われ受信管がすべて金属管になるのではないかとさえ思われた. 金属管によって強度は改良されたが, 高周波用には限度があり不選当なことが判って来たので, 高周波の世界からはだんだん忘れ去られ, 真空管の構造, 材料の研究, 発達により再びガラス管時代となり, 今日ではガラスで極めて小形のサブミネチュア管等が容易に作られるようになった. そしてさらに高度の負荷と, 高周波に対してはセラミック以外に求めるものがなくなった. セラミックが真空管の構造材料として用いられ始めたのは40年も前になるが, 真空管の外殻としても既に20年前には試作が行われている. 両者とも, ドイツで始められた技術であった. 戦後アメリカで完成したセラミック真空管も実はこの技術に学んだものである. われわれが7ケ年の歳月をかけて試作完成したセラミック真空管も大いにこれらを参考とした.
セラミックがガラスに比して如何なる特徴を持つかといえば, (1) 耐熱性が優れている, (2) 機械的の強度が大である, (3) 高周波特性がよい, (4) 成形正度が大である, (5) 熱の急変に対して強い等列挙される. しかしセラミックにも種々あり, しかもガラスと異なり焼成収縮という現象があるために成形, 焼成にはガラス工業にない一つの技術が必要である. しかしある程度機械的強度が大なるため研磨仕上げが容易である. これらはセラミックの技術者にとっては常識である. そこでセラミック真空管の技術は第1がセラミックの選択, 第2は金属の選択, 第3はセラミックと金属の封着の技術となるが, さらに大切なことは真空管の設計と構造である. これによって第1, 第2, 第3の事項が順次決定して来る. これらについて述べて見たいと思う.

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