In order to study more on the solid solutions existing in the system CaO-Al₂O₃-Fe₂O₃, whose Al₂O₃: Fe₂O₃ molar ratios are greater than 1, the author has investigated by microscopic and X ray methods the minerals which exist in the fired samples of xCaO: 2Al₂O₃: Fe₂O₃ and yCaO: 4Al₂O₃: Fe₂O₃(x=5, 6, 7, 8, 10, 15; y=6, 8, 10, 12, 15, 20, 30).
The experimental results are as follows:
(1) In the xCaO: 2Al₂O₃: Fe₂O₃ of x=5 and above, the solid solutions contained in those fired products, are the same with the principal mineral of 6CaO: 2Al₂O₃: Fe₂O₃ that was described in the author's previous report (part II).
(2) In the yCaO: 4Al₂O₃: Fe₂O₃, the solid solutions, which are contained in those fired products, increase those miscibilities according to the increase of y, and, in y=12, the miscibility reaches to the utmost limit.
The solid solution having this maximum miscibility in this series has a higher miscibility than the solid solution of 6CaO: 2Al₂O₃: Fe₂O₃.
(3) In the high lime mix consisting of CaO-Al₂O₃-Fe₂O₃, the addition of SiO₂ has no effect on the composition of the ferric oxide series solid solution that is made by firing the mix.
(4) Accordingly, it can be known that the miscibility of the ferric oxide series solid solutions, which exist in the firing products of the high lime mixes of CaO-Al₂O₃-Fe₂O₃-SiO₂, increases gradually according to the increase of Al₂O₃: Fe₂O₃ molar ratio. And the composition of the ferric oxide series solid solution having the maximum miscibility must be approximately 6.2CaO: 2.2Al₂O₃: Fe₂O₃.
(5) Therefore, it is expected that, in the high lime cements, the celite part changes its composition with the variation of the iron modulus; that is to say, in the high lime cements of the iron modulus 1.4 and above, the composition of the ferric oxide series solid solution existing in the cements is approximately 6.2CaO: 2.2Al₂O₃: Fe₂O₃, and also, in the iron modulus 1.4 and under, the more decreases the iron modulus, the more decreases the miscibility of the ferric oxide series solid solution existing in the cement.

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Continuing the previous studies (This Journal, 1936, 44, 531; 1937, 45, 605), the present authors reported here the results of further studies on the various reactions of alkali to kaolin in wet and dry methods. The following is the brief abstract from the original Japanese communication, as following:
(1) Three kaolin samples were used; (1) Zettlitz kaolin, (2) German kaolin and (3) Hongkong kaolin. They were compared on their chemical compositions by the ordinary total analysis and also by the rational analysis.
(2) These kaolin samples were treated by (a) water, (b) 5% NH₄OH, (c) 5% NaOH or (d) 5% KOH solution for two hours by heating on water bath. The products were compared by their chemical analysis and proved that water and 5% NH₄OH did not react but 5% NaOH and 5% KOH reacted clearly on kaolin.
(3) Concentrated ammonia cal water (28%) was used to heat with kaolin for 1-3 hours under high pressures of 20-70 atmospheres, but it was not observed any clear effect or reaction by ammonia.
(4) Nextly, kaolin samples were heated with 10% or 20% solution of NaOH or KOH on water bath for 5-10 hours, and the products were proved to be nearly (0.4-0.6.)R₂O⋅Al₂O₃⋅(1.9-2.1)SiO₂⋅nH₂O from (1) Zettlitz kaolin and (0.8-0.9)R₂O⋅Al₂O₃⋅(2.7-2.9)SiO₂⋅nH₂O from (2) German kaolin. So that, the reaction was not complete, but it is clear that alkali kaolin hydrate xR₂O⋅Al₂O₃⋅ySiO₂⋅zH₂O can be easily obtained by alkali solution of propper concentration even under ordinary pressure, which fact was already observed and reported by one of the present author in foregoing reports.
(5) These products were tested on the point of dehydration by heating from 110°C to 700°C or 800°C. The curve of weight decrease-heating temperature was clearly different between the products (a) and (b) treated by water and 5% NH₄OH and those (c) and (d) treated by 10% NaOH and 10% KOH solutions. The latter samples of alkali hydrokaolin or alkali kaolin hydrate as abtained in the former section (4) lost some part of their combined water even by warming at 25-110°C and then completely, heating at 200°-300°C but the former samples (a) or (b) obtained by treating with water or NH₄OH solution lost difficultly their combined water by heating at 400-500°C.
(6) These calcined product and alkali kaolin were tested their solubility by the soluble analysis with dilute (10%) HCl solution and then dilute (5%) NaOH solution, and the dissolved part was proved to be R₂O⋅Al₂O₃⋅2SiO₂⋅nH₂O or artificial nepheline type compound.
(7) The mixed powder of kaolin and sodium carbonate was heated at 950°C, the sintered mass was powdered and then extracted by warm water on water bath for excluding completely the excess and free alkali (Na₂O). The final product was proved to be Na₂O⋅Al₂O₃⋅2SiO₂⋅H₂O, which is completely equal to that obtained by heating kaolin and alkali solution as above mentioned in the section (4).
(8) The authors are now further studying on these products for various points and objects, which results will be reported hereafter.

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The auther investigated the thermo-physical properties of the magnesia bricks, 2 of those are made in Germany, 3 of them are made in Japan, and the other 2 are made in the authers Laboratory.
The chemical composition of the bricks are as follows: by other small content and by the microstructure, considered possible minerals in the minerals are considered Tested thermo-physical properties are as following:
Specific gravity. porosity, absorption, coef. of thermal expansion, crushing strength normal and under heating, Softening pt, under the load. thermal conductivity, difusibility, specific heat.
The most inportant test for magnesia brick, the slake test is also made.
After examined these proper-ties, & compared with the literatures. The auther proposed the normal properties for the magnesia brick with will be used in open Hearth steel fr.
1. Chem. component. MgO 87-88% enough; CaO small as posible, SiO₂ under 2% Fe₂O₃ under 7%
2. Specific gr. above 2-8, porosity under 23%
3. Crushing strength will be 1000kg/cm², at & heated 1000°C. 500kg/cm² at least,
4. Thermal expansion coef. 1000°C 1.35%, 1300°C 1.95%, 1500°C, 2.1%; and at 1600°C it will be no contraction.
5. Softening pt. under load will be above 1450°C under the load of 2kg per. squar cm.
6. Sp. heat is at 400°C, 0.2241, at 600°C, 0.2448 at 1000°C, 0.2554: thermal conductivity is at 400°C 0.01024, at 650°C 0.00968, at 800°C 0.00939.
7. For spalling under sudden cooling, when tested by crushing strength 500kg/cm² after heating 1hr. at 1500°C and droped in the water at 18°C.
8. For slake test in the vapour press. of 1.5 atcs. it must hold the original figure at least 6hrs.

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