Aluminous cement or high alumina cement as “Ciment fondu” in France, “Lumnite” in America, or “Citadur” in Hungary, can never be manufactured in Japan, owing to the want of raw materials containing large amount of alumina as Bauxite. But recently it became to be able to obtain special raw material of large alumina content from Manchoukuo, North China, etc. (S. Nagai and J. Katayama: “On Some points of High Aluminous Clayey Substances”, This Journal, 1937, 45, 66). The Osaka Yogyo Cement Co. has started in this year the manufacturing of alumina cement by using this high aluminous clay. The present author tested several samples of this alumina cement first produced in Japan and reported here the main results, which are briefly abstracted from the original Japanese paper, as following:
(1) The chemical compositions were analysed and observed to be specially high alumina cement, i.e., SiO₂: ca. 6-8%; Fe₂O₃: ca. 1-3%; CaO: ca. 36-38% and Al₂O₃: ca. 50-55%. The content of Fe₂O₃ is specially very small, owing to the manufacturing method of electric furnace melting and the low content of Fe₂O₃ in the raw material.
(2) The specific gravity is small (2.93-2.98) and the time of setting is a little too wuick, owing to the small content of Fe₂O₃ and the large content of Al₂O₃.
(3) The strength test of this high alumina cement was carried out by two ways, (1) the ordinary non-plastic (or earth-wet, or moist-earth) mortar and (2) the special plastic mortar, and observed to be considerably early high strength cement.
(4) The relation between strength and the curing temperatures (20°C, 50°C and 75°C) was tested and the strength was considerably damaged by the high temperature curing, as those of foreighn alumina cements.
(5) The relation between strength or time of setting and fineness of cement was studied and the ordinary degree of fineness (residue on 4900 meshes/cm²-sieve: 3.5-10%) is to be necessary and the extremely high fineness (0.5% residue on 4900 meshes/cm²-sieve) or too low feneness (25% residue on 4900 meshes/cm²-sieve) is not suitable to obtain the alumina cement of superior quality.
The author will hereafter report further studies on this specially high alumina cement first produced in Japan.

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The author made a preliminary discussion which may be followed by a report of the researches on the above subject.
The so-called bentonite and acid-clay (fuller's earth), at least those of Japanese origin, have quite many points in common each other, being similar in distribution and geological condition of occurrence, in chemical composition and concluded formula, etc.
Arguing against the known results and conclusions, the author showed the very similar points mentioned, and he tried a further discussion to the effect that the natural bentonites might mainly be composed of both montmorillonite and beidellite or one of them, and that each of them should theoretically have a molecular formula equivalent to that of pyrophillite, which is now clearly distinguished from kaolinite minerals by the X-ray study. It seems, therefore, quite reasonable to conclude that the principal constituent of acid-clay might have the pyrophyllite structure too.
In the end, the author arrived at this conclusion that is seems resonable to say that there remains much more yet to be studied, as well as in bentonite itself, in both. K. Kobayashi's formula of acid-clay and the new mineral “Kanbaraite” proposed by H. Isobe and T. Okazawa.
The discussions were made according to the following heads: (1) Introduction, (2) Definition of bentonite, (3) Definition of acid-clay, (4) Chemical composition of bentonite, (5) Acidity of clay, (6) On the origin, (7) Specific density of acid-clay, (8) Empirical formula of acid-clay, (9) Empirical formula of bentonite, (10) Clay and its related minerals, (11) Crystal structure of bentonite, (12) Conclusion.

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