Some preparatory experiments were made of glost warping of feldspathic faience. The temperatures of biscuit and glost firing were 1200° and 1100°C resp. As, in most cases, only one test piece was used for each member of every experiment, no conclusion is deduced from the results which are more or less interesting as follows: (1) The warpage increased with an increase of the time of glost firing, the thickness of glaze, and the fluidity of molten glaze, and decreased with an increase of forming pressure. (2) Indications were that plastic kaolin and pyrophyllite in the body acted to decrease the warpage, while kaolin, quartz and feldspar in the body intensified it. (3) A rectangular rod glazed on 3 surfaces was elongated by glost firing. (4) A glaze colored with cobalt oxide diffused into the body on prolonged firing.

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An investigation was carried out to verify the preveious report on the same subject (J. Jap. Ceram Assocn., 40, 769, 1932) in which it was concluded that the content of MgO of portland cement can safely be allowed up to 8%. Five commercial raw materials, i.e. limestone, dolomite, shale, soft quartzite, and pyrite cinder, were proportioned so as to give 3 clinkers which should contain 3, 5, and 8% of MgO and have a same hydraulic modulus, silica modulus, and iron modulus of 2.15, 2.70, and 1.50 respectively. Small brickets were made of the raw mixture pulverized wet to pass through a 10000-mesh sieve. They were fired in a gas-fired muffle kiln at 1360°C for 2 hours. The clinkers thus prepared were analyzed with the following result:
The clinkers were ground with 3% of gypsum and the products were tested for the crushing strength of 1:3 mortar. The test-pieces measured 2cm in diameter and 3cm in height. A set of them was tested after aging for 4 weeks in water and then heating at 140°C for 6 hours in an autoclave. The results are shown in Table 2.
The results indicate that MgO is harmless and rather beneficial up to 5%.

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Durability in water of the glass Na₂O (1-x) CaO, x MgO, y Al₂O₃ 5.3SiO₂, in which x=0-1.0 and y=0-0.2, was determined by the powder method at 95°C (by water bath) and at 170°C (by autoclave)
When y was constant the durability decreased with the increase of x, but the amount of decrease was not so much and became smaller and smaller with the increase of y and at last it became almost insignificant. When x was constant the durability increased with the increase of y
The glass which had greater durability at 95°C had also greater durability at 170°C.

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Taking that the general glass composition is 72% SiO₂, (12-x) CaO, xFe₂O₃, 16K₂O, I have chosen glasses in which the content of x being varies from O to 12, and studied about the variation of the state of oxidation of iron oxide, of the color presented by glasses and of forms of transmission curves.
The process of melting and amount of batches are simila to what I have described in my third report but owing to a difficulty of melting potash glass more than the soda glass the melting temperature applied for the said glass in the experiment has been higher than the normal of 1450°C.
(A) The amount of ferrous oxide contained in the glass and the amount of total oxide expressed in ferric oxide have been obtained by analysis which being as follows: -
The relation between the percentage ratio of FeO/FeO+Fe₂O₃ and the total iron oxide in the glass, appeared in the above table has a tendency similar to that shown in the previous report with the case of soda-lime-silica glass. However, comparing glasses containing same amount of said substance these is formed such a trend that the dissociation of iron oxide in potash-lime-silica glass is less than that in soda-lime-silica glass.
(B) The color and transmission curve of the glasses have been determined.
As to the color those having exceedingly small iron oxide centent present faint bluish green; the color is gradually thickened as the content of iron oxide increases. When the content of total iron oxide reaches as much as 0.5% the glass becomes greenish, along with the increase of iron oxide content yellowish and greenish color are intensified materially and the resultant is that it varies to brownish green until it becomes darkblack glass as the iron oxide content is considerably increased.
Next, colors of soda-lime-silica glasses and potash-lime-silica glasses, both containing approximately same amount of iron oxide, have been compared. In case of thé content of iron oxide is small the color in potash-lime-silica glass is found lighter and clearer and when the said iron content is increased more, and more there is no distinction between the two.
Further, limit wave length which transmit these glasses have been determined from transmission curves obtained through experiment. The re'ation between the iron oxide content and the limit wave length that transmit the glass is quite similar with the soda-lime-silica glass.
Finally, when transmisaion curves of the soda-lime-silica glass and the potash-lime-silica glass are compared it has been formd in general that the transmission in the latter is higher than the former, and this shows the fact that the potash glass is clearer than the soda glass. (Glass research laboratory of The Tokyo Electric Co.)

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