On the basis of many analytical data the author concluded that both bentonite and acid-clay or fuller's earth are quite the same clay material and they must have at least two common end minerals, montmorillonite and beidellite, in the pure sides. In other words, the BENTONITE as well as the ACID-CLAY are nothing but a rock name. Therefore they have no definite meaning in the strict mineralogical sense.

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A study has been made on the inversion of dicalcium silicate. Specimens for the experiments have been prepared by heating an intimate mixture of 2 mol. of c. p. calcium carbonate and 1 mol. of c. p. silica for 2 to 8 hr. at temperatures ranging between 1400 and 1700°C. They have been quenched in ice-cold mercury and have been examined for microstructure, X-ray diffraction, thermal changes, etc. with the following results:
(1) Specimens made at 1500° and up have dusted less than those prepared at lower temperatures. All specimens quenched in ice-cold platinum crucible or in similar way have been mixtures of α-and γ dicalcium silicates.
(2) when the temperatures have been raised gradually over 1500°, the products quenched as said above have become poorer in γ modification and richer in α one, almost pure α dicalcium silicate being obtained at about 1700°.
(3) On cooling naturally, the products have to change completely to γ form, since α and β are only stable at 2130 to 1420° and 1420 to 675° resp. However, in facts, they have contained α form and pure γ form has never been given.
(4) Pure γ dicalcium silicate can be obtained from its mixtures with α form (a) by screening the products to collect dusted minute powder, (b) by reheating the products long at temperatures therein γ form is stable, say over 300 hr. at 550°, and also (c) by dissolving the α form off with water.
(5) As to thermal analysis, γ dicalcium silicate has indicated a strong endothermic reaction at 720±5° in heating up and a strong exothermic one at 690±5° in cooling down. These changes are probably due to γ_??_β inversion α 2CaO⋅SiO₂ and 3CaO⋅2SiO₂ have shown slight exothermal changes at temperatures between 600 and 700°; they owe probably to γ_??_β inversion of γ dicalcium silicate contamimated in the specimens.
(6) It may be concluded that α β and α γ transformation are sluggish inversions while β γ changes are very quick and are therefore high-low inversions.
(7) It is likely that synthetic 3CaO⋅2SiO₂ contain some γ dicalcium silicate and also that we have to investigate further on the problem whether tricalcium disilicate exists or not?.

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[in Japanese]

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