The authors reported, on continuing the previous reports part I-IV, the further results of various studies on the fine refractory and electric insulating material of magnesium silicates “steatite”. The main points were abstracted from the original Japanese paper, as sollowing:
(1) The raw material of talc sample (E) in the report part IV was used to mould under various moulding pressures 200-600kg/cm² without water and burned at 1400°C for several hours from 2 hours to 6 hours. The transverse and compressive strengths, apparent and true densities, and porosities of the specimens were compared in the following table 1.
As seen from the table, the strength and porosity were considerably improved by the moulding conditions under higher pressure (600kg/cm²) and without water, but the longer heating was not so effective.
(2) Dead burned magnesia and quartz were ground and mixed in molecular ratio: (I) 3MgO: 4SiO₂ as talc-(TB), (II) 3MgO: 2SiO₂ as serpentine-(SB) and (III) 2MgO: 3SiO₂ as meerschaum (MB). These three mixtures were moulded by adding 3% of boric acid powder under several moulding pressure 300-600kg/cm² and without moulding water, and then burned at 1400°C for 6 hours. The specimens were tested on their several physical properties as before and obtained the following results.
It is seen from these results that these steatite specimens obtained from the three mixtures of dead burned magnesia and natural quartz sand were not of so good properties as those from natural talc in the foregoing experiments. So that, these speciments must be burned at a little higher temperature then 1450°C to obtain the specimens of properly sintered and having higher strength and smaller porosity.
(3) Talc powder (E) was mixed with small percentage (about 3-5%) of dead burned magnesia, lime or alumina, moulded under high moulding pressure 600kg/cm² with or without water, and then burned at serveral temperatures 1300, 1400 or 1450°C for 2 hours. The specimens thus obtained were tested on their properties as before and the following results in the table 3 were obtained.
As seen from these results, the strengths of the specimens I-1 (magnesia added) and II-a (lime added) are not so good as those of talc without admixture, but the other specimens III-2 and III-3 (3-5% alumina added) have very good results. This good effect by the addition of alumina or aluminium hydroxide is now further systematically being studied on, with the object of obtaining the new modified steatite of good quality.
(4) The sample “Shuganseki” (A) in the report I, having the rational formular 3MgO·2SiO₂·2H₂O and obtained in Manchukuo, was used directly or after calcining at 700°C, moulded with 5-20% water or starch solution under pressure 600kg/cm², and burned at 1450°C for 2 hours. The specimens had large strengths, large densities and small porosities, but on the contrary the burning shrinkage was very large, which is only one defect. These results are tabulated in the following table 4.
It is seen from these results that, when the steatite of very large strength and small porosity will be desired, the raw material of “Shuganseki” is to be first moulded under very large pressure with some moulding medium, preliminarily burned at about 1200-1300°C, cut out to the desired dimensions, and then again burned at about 1450°C.
(5) The present authors are now further studying on various points of steatite, e. g., heat conductivity, electric resistance, chemical resistance, etc., which will be hereafter reported in the next reports.

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Four extremely intimate mixtures were prepared of c. p. calcium carbonate, and silica. and magnesiumhydroxide. They were composed of 100 parts of 3CaO+SiO₂ and 0, 2, 4, and 6 parts of MgO when ignited thoroughly. 1/3 mol of SiO₂ was added to each mol of MgO in order to leave a part of the latter in free state, if any chemical reaction occur between the two oxides. The mixtureswere heated at 1500°C for 90 minutes once, twice, thrice, and four times, the heated products having been pulverized very fine each time.
Sixteen samples thus prepared were examined for the chemical composition, microstructure, and X-ray diffraction to find the influence of magnesia upon the formation of tricalcium silicate. Meanwhile, an investigation was carried out for the determination of free magnesia in the samples.
The results of the chemical analyses indicate that the formation of tricalcium silicate is accelerated by the presence of magnesia, that the effect of magnesia increases as its amount increases, and also that the repitition of the heating and pulverization favors the formation of the silicate. The results were verified by microscopic examinations and X-ray analyses.
Exactly speaking, the attempt of determining free magnesia by the combination of the Rathke's method of determining free lime and the method of N. A. Tananaeff and L. M. Kuehlberg for the determination of free lime and magnesia was not very successful. However the combined method seems to be promising.

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Integral cooler of “Unax” type is better than any one of “under cooler” type, both in its cooling effect and heat economy.
It is due to the peculiar construction of this integral type and its chain curtain hanging in it, I think. But it is wanted to some improvements of its mechanical construction.

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