Ii freshly mixed plaster is allowed to set, a part of water, which is it excess of the theoretical amount requuired to bring about the chemical change, evaporates.
The set mass attains the maximum strengtn, when the mixed plster has dried completely. It is inevitable that the set mass becomes incompact to some extent. The maximum hardness and strength attained after setting, however, depends mainly upon the compactness of the set mass and, therefore, varies inversely with the proportion of water used.
If compressed, the cracked set mass slips along the slip plan. If more water is used in maxing, the set mass will be more incompact and slips easily. Therfore, its strength is abated.
I tried to set forth this relation of stregth and compactness of strength and compactness of gypsum in formulae. In woaking out the formulae, it was assumed that the set mass is homogeneous, has no air bubbles in it and that the volume does not change in the process of setting.
The theoretical formulae are given as follows:
logσ_x1/σ_x0=n logρ₁/ρ₀ or logσ_x1=n logρ₁-logσ_x0/ρ₀ⁿ
Where σ_x1 &ρ₁: compressive strength and apparent specific gravity of set mass
n: experimental constant
σ_x0 & ρ₀: compressive strength and apparent specific gravity of the ideal set mass for which only the theoretical amount of water required to bring about the chemical change is used.
apparent gravity=weight of specimen/volume of specimen
Specimen were tested after seven days. The theoretical formulae indicate a straight line. The logρ₁-logσ_x1 curves obtained from the experiments endorsed this anticipation.
It is concluded that n is affected by conditions of crystallization of plaster. Therefore, qualities of plaster is detrmined by the value of this constant.

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(1) TiO₂-CaO系磁器の誘電體力率は添加大理石量の増加と共に急激に減少し, 大理石添加量が45.5%) 重量百分率, 以下同じ) のところで最小値を示し更に大理石を添加すると燒成磁器化不能となり, 誘電體力率は再び増大する。しかして高周波蓄電器用誘電體として使用出來るものと考えられる範圍は添加大理石量が29.4-45.5%の間にあるものである。
(2) 本系磁器の誘電率は大理石添加量6-8%のところに最小値を示す點があり, それより添加大理石量を増加すると共に誘電率は漸次増大し, 大理石含有量45.5%の所で最大値を示し, それより更に大理石を増すと燒成磁器化不能となり, 燒成試料は多孔質となり, 見掛の誘電率は急激に減少する。しかし, 氣孔率の高い割にその見掛誘電率は大きな値を持つている。
一般に酸化チタン磁器の誘電率は添加物の量が多い程減少するものと考えられてきたが, 本系磁器では全く逆で大理石添加量の増加と共にその誘電率は益々増大し, ルチル状酸化チタンの平均誘電率114より大なる値を持つものがこゝに得られた。この値は又B. M. vul氏等の得たカルシウムのチタン酸鹽の誘電率の値よりも更に大であり, A. von Hippel氏等の得た値に匹敵するものである。なおこの誘電率と調合比との關係は燒成牧縮率と調合比との關係と酷似している。
(3) 各種調合組成における誘電體力率と燒成温度との關係は添加大理石量23.8%迄は大體燒成温度の高い方が誘電體力率は大となる。又添加大理石29.4%と34.9%の試料では燒成温度を高めてゆくに從い誘電體力率は初め減少し次いで増大する傾向を持つ。
(4) 各種調合組成における誘電率と燒成温度との關係は, 燒成温度上昇と共に誘電率は初め増大し, 最大値を示し, 次いで減少する樣な傾向を持つ。このことは燒成收縮率と嵩比重の燒成温度に對する關係と類似し, かつ吸水率, 見掛氣孔率および耐急熱急冷性の燒成温度に對する關係と對照的である。
(5) 充分に燒成磁器化した試料の嵩比重は, 大理石含有量10.0-29.4%で最大値を示し, 又耐急熱急冷性は4TiO₂・CaOなる組成で最大値を示す。
終りに本研究は戰時中, 當時の住友通信工業株式會社でなされたもので丹羽保次郎, 小林正次, 釜范善一吉田梅次郎の諸博士より御懇切なる御指導と御鞭達を賜つた。又東京工業大學教授山内俊吉博士よりも種々御指導を頂いたもので, 以上の方々に對して衷心より厚く感謝の意を表する次第である。

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As it is well known, for the calculation of the additive rule of glass properties, (e. g. thermal expansion coefficient) we must know the oxide composition of the glass. If we, however, declare the algebric relations between the weight ratio of raw materials and the oxide ratio of the glass formed. We could calculate directly the additive properties from weight ratio of raw materials without knowing oxide-compositions of the glass.
Under this view-point, the author, using Winkelmann and Schott's factors, determined new factors calculating expansion coefficient from raw materials but not from oxides. And he appointed that, using this new calculation, we could realize speedy corrective action in glassbatch preparation, during the quantity-control of glass.
Several examples in glass-factory were given.

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Alumina cement is commonly produced by melting in an electric furnace from raw mixture of bauxite and lime. But, in the present paper, the special manufacturing method was devised and fully discussed. The new method is the sintering to clinker, without melting. The proper mixture of aluminous raw material and lime or limestone was ground, kneaded with water, moulded to briquette, dried and sintered to clinker by the single or tunnel kiln as in the potte ry or refractory industry. This method is especially suited for the making of alumina cement from alumina (residual) ash from aluminium remelting or reclaiming factory and slaked lime. Some samples of the special alumina cement produced by this method, were tested and proved to be of good quality. It is now further being studied to compare this special sintering method to the common electric melting one, by using the same raw materials, e.g., aluminous shale or almina (residual) ash and lime, which result will be reported in the next report.

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