The authors investigated in detail the reducing reaction processes of gypsum in the nitrogenous atmosphere without oxygen. Then we clarified the effect of oxygen by introducing air on the samples in order to study the reaction in the industrial process, and tried some experiments to get some suggestions on the conditions favourable to the industrial process.
(1) The reactions are as follows;
CaSO₄+2C→CaS+2CO₂…(1)
3CaSO₄+CaS→4CaO+4SO₂…(2)
2CaSO₄+C→2CaO+CO₂+2SO₂…(A)
There are two steps in the reducing processes of gypsum. The first reduction step (1) begins near 750°C, proceeds quickly between 800° and 900°C and completes almost at 1000°C. The second step begins near 900°C, proceeds quickly between 1000° and 1200°C and completes almost at 1250°C.
Sulphur is formed by the reaction (3) which occurs simultaneously with the reaction (2), but the reaction (3) is not so active as the reaction (2).
CaSO₄+3CaS→4CaO+2S₂…(3)
The following reactions did not occur in this experiments.
CaSO₄+4C→CaS+4CO…(4)
CaSO₄+CO→CaO+CO₂+SO₂…(5)
(2) The amount of CaS formed in the first reduction step is proportional to the amount of the reducing agent. We discussed the appropriate amount of the agent in order to promote the reaction rate effectively and to make the reaction (2) complete.
(3) Pressing of raw mixtures decreases the loss of the reducing agent due to the combustion and promotes the reactions.
(4) It is observed that burning of sulphur with the introduction of air reduces sulphur trouble in the process and promotes the reaction (2) with the production of sulphur dioxide.
(5) Anthracite and coke were used as the reducing agent in this experiments. Anthracite showed a better results rather than coke.
(6) In the first reduction step, when CaSO₄ was used CaS is formed much more than CaSO₄⋅2H₂O was used. But in the second decomposition step there is no obvious difference in the two cases.

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The formation of 15 R-type SiC in the Lely's procedure has been studied experimentally with the method of steplike nitrogen doping, and the thermal stability of the 6 Hand the 15 R-types are discussed through heating experiments of the colourless single crystals of both types in a small graphite capsule. The results obtained are summarized as follows:
1) The 6 H-type has the higher thermal stability than the 15 R-type in the range from 2100°C to 2600°C.
2) Structural change is not recognized in the single crystals of 4 H, 15 R and 6 H after heating at 2100°C for 500 hours.
3) The 15 R-type has marked tendency to grow from the twinning (the angle between basal plane; ca. 70°30′) of 6 H-type.
4) This type twinning of 6 H is explained as the developed feature of spinel type twinning of β-SiC which formed in the initial stage of recrystallization.
5) The effect of nitrogen to the relationship of the thermal stability among polytypes is discussed. It is negligible small at 2500°C, if the partial pressure of nitrogen is in the order of 60mmHg or below.

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The thermal decomposition of MgCO₃⋅3H₂O was studied using T. G. A. and X-ray powder diffraction.
Calculation of thermogravimetric curves showed that the decomposition processes consisted of four stages. The dehydration processes were superimposed in part, but each of the effects were separated by calculation. The energy of activation and the order of reaction were derived as,
X-ray patterns of heated samples showed the intermediate phase of the dehydration process to be MgCO₃⋅2H₂O and coincided with T. G. A. data.

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