The softening behavior under load of 5 series of siliceous bricks prepared experimentally with usual factory processes at a silica-brick plant has been examined by means of an Endell's apparatus. The first series consisted of semi-Dinas bricks made of soft quartzite of Buzen and Fukushu clay and containing 96.6 to 44.1% of silica; test-pieces for the load-test were small cubes cut from the bricks; besides load-test, linear expansion up to 800°C, residual expansion shown on heating at cone 19 to 20 for 4 hours, and refractoriness have been measured. The second series comprised silica bricks made of 7 different quartzites and fired to cone 17; testpieces were cubic as above; P. C. E. has also been determined. The third series contained small cylindrical silica refractories which were made of Dairen quartzite ground to varying fineness but were prepared with fixed amounts of lime and water, a same forming pressure, and a same firing temperature, i.e. cone 17; also true sp. gr., porosity, and compressive strength have been tested. Test-pieces of the fourth series were small cylindrical silica bricks made of “Akashiro” quartzite of Tamba with addition of 0 to 8% of lime; P. C. E., porosity, true sp. gr., and compressive strength have been determined. The fifth series comprised small cylindrical silica bricks made of the Tamba quartzite with forming pressures varying from 50 to 400kg. per sq. cm.; they have also been examined for bulk density, porosity, and compressive strength. The results of the experiments seem to justify the following conclusions:-
(1) The softening temperature of semi-Dinas bricks rises with increasing contents of silica. Although an increase of silica causes an increase of thermal expansion, it serves in reducing residual contraction.
(2) Owing to only slight variation in silica contents of usual silica bricks made of different quartzites and also to the intricate influences of impurities of quartzites, silica bricks with high contents of silica don't have always high softening temperatures.
(3) The influence of the variation in the fineness of quartzite-grain upon the softening temperature of silica brick under load is not intense except when the grain is so fine as for instance its mean diameter is 0.25mm.
(4) The softening temperature of silica brick made of sole quartzite is strikingly higher than that of the brick bonded with any amount of lime. However there is no remarkable difference among the softening temperatures of the bricks containing 1 to 4% of lime. It has also been ascertained from an experiment of the present paper and from former experiments made by a silica-brick plant that silica bricks with up to 4% of lime give almost similar results in refractoriness-test, slag-corrosion test, and open-hearth furnace test. In other words, it is likely that any addition of lime up to 4% is not detrimental to the quality of silica brick.
(5) Any low forming pressure results a silica brick yielding at a low temperature under load. However the pressures over 150kg. per sq. cm. are only slightly effective in improving the softening behavior and moreover give no particular superiority in porosity, bulk sp. gr., and mechanical strength at ordinary temperatures. 150kg. per sq. cm. are probably the most economical forming pressure for commercial products.

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In the preceding paper (III) the author proposed a new tablet-swelling method which can be opplied to grade natural bentonites. The present paper is a supplement to the previous one. 1) The author revealed that the above-mentioned method can well be opplied to many Japanese bentonites from several different districts, and that the testing method is of good use as a general practical method. (2) The mode of swelling or the swelled form: of original cylindrical pieces of most natural bentonites is normal, that is to say, a cylinder gradually passes into a single swelled cone. In an electrolyte solution, however, normal forms readily turns into various anormal ones. The author made a distinction between them. In the following figur, No. O shows a normal type and the others five (or six) anormal ones respeetively.

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The author reported, in continuing the previous studies (This Journal, 1933, 41, 623; 1934, 42, 273, 628, 688; 1935, 43, 215, 572; 1936, 44, 22, 617; 1937, 45, 8), the results of further studies on mixed Portland cements. The report of the present paper is the continued tests of high silica mixed Portland cements, which were already studied on their common physical properties and chemical compositions. The brief summary is abstracted from the original Japanese paper, as following:
(1) The paste of neat cement was kneaded with the amount of water of normal consistency for determining the time of setting, and moulded to small cylindrical test pieces (Dia.: 5cm and Ht.: 10cm). These test pieces were cured in four serie-(a) in water for 7 days, (b) in water for 28 days, (c) in water for 7 days and then in warm (50°C) water for 7 days, and (d) in water 7 days and then in warm (50°C) water for 28 days. The compressive strengths of these four series of cured specimens, were tested and the hardened samples were quickly taken from the fresh part of the crushed pieces after strength tests and dried in desiccator. The chemical compositions were determined and the amounts of free lime or hydrated lime were specially determined and compared for these four series of curing (a), (b), (c) and (d), which are tabulated in the table 1.
Table 1 Amounts of Free Lime in Hardened Cements
From these results, it can be clearly observed that the amount of free calcium hydroxide increses in Portland cement and on the contrary decreases in mixed Portland cement. This fact shows that the high siliceous admixture used in mixed Portland cement combines with calcium hydroxide set free by the hydration, which owes to clinker part 60-75% of cement.
(3) The strengths of dry (or non-plastic) and wet (or plastic) mortars of these cements were tested in the longer curing ages (3, 6 and 12 months) than the standard curing ages 3, 7 and 28 days, which strengths were already reported in the foregoing report (This Journal, 1937, 45, 8). The increase of strength is greater in high silica mixed Portland cements than in the common Portland cements, which owes to the same reason with the combination of siliceous admixture and calcium hydroxide produced in set cement.
(4) The expansion or contraction of mortars were tested by the prismatic (4×4×16cm) test pieces moulded by wet mortars and cured in water for 3, 7, 28, 91 (3 months), 182 (9 months) and 364 (12 months) days. The results show the fact that the contraction or expansion was not greater in the case of high silica mixed Portland cement than in the case of common Portland cement, which is quite contrary in air curing.
(5) The corrosion, expansion or contraction, and decrease or increase of strength by curing in water, 10% NaCI solution and 10% Na₂SO₄ solutions were fully studied by using the prismatic test pieces of wet mortar, which were vertically dipped in water or salt solutions for 4, 8, 12, 16, 20 and 24 weeks. The expansion crack and then disintegration were seen in the test pieces dipped in 10% Na₂SO₄ solution and especially considerable in common Portland cement and blast furnace slag cement. This result owes to the large amount of alumina in the cement, and the formation of xCaO⋅yAl₂O₃⋅zCaSO₄⋅nH₂O (so-called cement bacillus). This results were clearly shown by the photographs of the disintegrated test pieces, and coincide quite well with those recently reported by G. Haegermann (Zement, 1937, 26, 210).
(6) The strengths were tested b these corroded test pieces after expansion test for 24 weeks curing above described. The decrease of strength was most remarkable in the specimens cured in 10% Na₂SO₄ solution, and then followed by those cured in water and 10% NaCl

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[in Japanese]

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