The object of this research is to synthesize the crystaly pure crystals of the 2CaO⋅SiO₂ modifications and to certificate them by the way to explain results of X-ray analysis. The following method were most suitable for synthesis of each modification.
(1) γC₂S: The mixture of CaCO₃ and silica gel, charged in theoretical ratio, was fired at 1550°C for 1hr in Pt crucible and then cooled down for dusting.
(2) βC₂S: γC₂S was re-heated up to 1000°C and then cooled down to the room temperature.
(3) α′ C₂S: 4.5 weight % of B₂O₃ were added to the mixture (1). And then this mixture was heated at 1550°C for 1hr. in Pt crucible and cooled down rapidly.
(4) αC₂S: 5.0 weight % of P₂O₅ were added to the mixture (1). And then this mixture was heated at 1550°C for 1hr. and cooled down rapidly.
The X-ray diffraction patterns of the specimens thus obtained were exactly indexed as the function of the following lattice constants. Thus the lattice constants and the spacing of the 2CaO⋅SiO₂ crystals given in this paper seem to be of very high accuracy

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Forty parts of bonding materials composing of equal parts of gairomé-, kibushi-, roseki-clay and kaolin (Table 1) were mixed to 60 parts of various chamottes (totaling 80 kinds in Table 2) previously graded and weighed-out as 21 parts of coarse, 6 parts of fine and 33 parts of very fine, and the drying, burning and spalling tests were made. The results are summerized as follows.
(1) At the burning temperature of chamotte within the range of this experiment, added alumiua scarcely sintered with kaolin and added quartzite aided sintering only when burned at high temperatures, but a remarkable sintering occured at lower temperatures in mixed chamotte of kaolin and feldspar.
(2) Amount of water required for the same fluidity of casting slips with the same bonding material, but differing in kinds and in burning temperature of chamotte, increased linearly with the water absorption of the chamotte used. The amount of the drying shrinkage water of bodies cast from these slips remained nearly constant irrespective of kinds and burning temperatures of chamottes.
(3) Between the bulk density of dried or burnt bodies and that of chamottes, a hyperbolic relation was found.
(4) Bodies of as small porosity as necessary for a practical use could not be made by chamotte of kaolin mixed with more than 20% of alumina, nor with quartzite unless they were burned at very high temperatures. Chamotte made of kaolin with each 5% of quartzite and feldspar gave, on mixing with bonding materials and burning at high temperature, more dense bodies than those with addition of 10% feldspar.
When the same mixture of 4 kinds of clays was used both for chamotte preparation and bonding material, more dense body was obtained than in cases when chamottes were made from single clay.
(5) Resistance against spalling was tested at two temperatures, that is the temperature at which glass batches are thrown-in and the other is that of withdrawal of pots from furnace. Addition of feldspar to raw clays for chamotte preparation decreased spalling resistance, whereas addition of alumina or quartzite gave rise to no definite tendencies but these were dependent on the composition of mix and the temperature at which the chamotte was burned.
(6) Spalling resistance seemed to be chiefly dependent on the physical properties of chamotte grain themselves, because adherence between chamotte and bonding material was not promoted by the use of the same raw material for the both of the two.
(7) When pot shell, which had been used repeatedly, was quenched or cooled slowly and used as chamotte, no denser bodies were obtained than the chamottes from single clay. The difference in the cooling manner of the pot was not reflected on the obtained bodies.
(8) Dense but spalling-resistant bodies could be easily obtained by selection of the proper chamotte. Chamotte made from roseki- or kibushi-clay was found to be good.

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False set of Portland cement is one of so complicated phenomena, that it has not been yet apprehended and controlled perfectlly.
In the present paper the authors explained the mechanism of false set of cement at the view-point of hypothesis based upon the hardening of hemihydrate contained in cement. Although its mechanisim now could not be fully clarified by this hypothesis, by introducing the idea of hardening time of hemihydrate the authors solved distinctly several features of false set, which had not been made clear.
That is, false set of cement only takes place, when the hemihydrate content is in the following certain amount in cement and its hardening occurs in certain period (1-5 min. after mixing by the test procedure of American Federal Specification).
From the authors' experimental series, it will be concluded as follows;
(1) In the specimens of powder prepared by grinding the silicious sand together with a small amount of hemihydrate, false set took place when the SO₃ content is above 0.5% in weight and above 1.2% initial set of cement also was very quick.
But in the same specimens, false set can be eliminated by prolonged mixing or by shortening the hardening time of hemihydrate with additional dihydrate, or by aerating at high humidity, -in the last case a portion of hemihydrate changes into dihydrate, and consequently the hardening of hemihydrate is so shortened, that false set can be eliminated by dead-mixing. On the contrary, false set is induced more severe by reducing the mixing time or by adding such reagents as alkali carbonates which can retard the hardening of hemihydrate.
(2) In the case of cement, false set is not so simple as in above-mentioned case of silicious powder, but nearly the same tendency is recognized. It seems that the hardening time of hemihydrate in cement is considered to be affected by hemihydrate itself, and also by dihydrate, calcium sulfoaluminate, several alkali salts, calcium hydroxide and by many others. As direct measurement of hardening time of hemihydrate in cement is very difficult, the determination of initial set during the hardening time of 1:1 mixture of hemihydrate and cement according to the test method of plaster of Paris is able to indicate the degree of hardening of hemihydrate.
(3) False set of fresh cement direct come from cement grinding mill takes place hardly, because the hardening of hemihydrate in this case is almost very rapid and therefore the dead-mixing is carried out. Hence the grade of false set of this cement occurs undirectly against to SO₃ content. By aeration, however, hardening of hemihydrate is prolonged, and accordingly false set appears, and its degree is generally dependent on the amount of SO₃ in cement. According to Federal Specification, if the hemihydrate efficiency is defined as the quotient of the amount of hemihydrate, which can harden within 1-5 min. after mixing, divided by hmihydrate, it can be regarded that the intensity of false set is proportional to the product of total amount of hemihydrate and hemihydrate effcieney.
(4) In the case of additional dihydrate on the false setting cement or of aeration at high humidity, the reasons of disappearing of false set in cement is seemed to be in quick hardening of hemihydrate in cement. Especially in the latter case the decreasing of hemihydrate is proceeded by its transformation into dihydrate or sulfoaluminate, therefore the hardening of hemihydrate would be fastened by these after-formed compounds.
(5) In cement aerated at low humidity, false set continues unchangeably for a considerable period. It is believed that the hemihydrate at this state exists under the stable condition.
(6) In cement prepared by mixing powder of clinker aerated at high humidity and hemihydrate, false set usually takes place strongly. However in cement composed of above clinker powder and dihydrate instead of hemihydrate, it does not take place. And in

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