In our previous studies^{1), 2)} , it had been made clear that the volue of calcium sulfate dihydrate as the raw material of calcium sulfate hemihydrate plaster depend markedly upon the crystal state there of and pointed out that the crystal state as well as the chemical impurities were the important factors for controlling raw materials. Thus, the crystal state of calcium sulfate dihydrate is not only significant materially, but also readily, supposed to be effective on the behavior of water molecule in crystalline itself. However, a number of studies on the transition by the dehydration of calcium sulfate hydrate, which were introduced in the previous report³⁾ , had scarecely clarified this problem, e.g., Keayss and Jorns⁴⁾ had found the difference in dehydration behavior, but they attributed it to the influence of origin. The authors also had pointed out the difference in the dehydration behavior of calcium sulfate hydrate from the same point of view⁵⁾ . Although the investigators in foreign countries has been not interested in such prablem presumably because of the difference in circumstances of raw material, in Japan, besides the authors, Hayashi and Sato⁶⁾ , Machida⁷⁾ , Murakami and Tanaka⁸⁾ had studied on this prablem. From these investigations, it had boon found that the dehydration behavior of chemical gypsums is particularly different each other, being due to the producing origin. It may be pointed out the factors for it are above all the crystal shape and the chemical imprities. Aforesaid three reports gave enough suggestions and phenomena concerned to this view point, but separate affecting factor is not yet clarified satisfactorily. Consequenty, intending to clarify the effect of the separate factor on the dehydration of calcium sulfate dihydrate, in this paper together with another paper⁹⁾ Calcium sulfate dihydrate of various shapes of crystal (Figs. 1, 2, 3) were synthetized arifiicially and chemically (Table 1) and then the effects of crystal state on the dehydration were examined.
D. T. A. curves for variovs samples of calcium sulfate dihydrate are shown in Figs. 4 and 5. As is seen these results, both the first and the second dehydration temperature of calcium sulfate dihydrate varies with the crystal state there of notwithstanding the synthetic conditions, producing origin or reproduction conditions, and the high crystallinity tends to raise these dehydration temperature but little affects on the third peak corresponding to the tramsition from hemihydrate to anhydrite II (SGX-5, Exception-the inffluence of the residual salts). Furthe, as is seen from the D. T. A. curves which show the influence of crystal states, the higher the apparent crystallinity is, the longer the first dehydration period becomes-that is-the more needle shaped and minute crystal seems to dehydrate more rapidly. Howerer, it has been found that the crystal particle and shape distribution affect the occurrence of the first and second dehydration curve, and consequently the unifrom shape readily gives its characteristics on the curve as well as the dehydration temperature and occures the second peak, but to the contrary, wide distribution of shape gives wide peak and extinguish readily the second peak.
Experimental resulte obtained by the heat balance are shown in Figs. 6, 7 and 8. It can be concluded that these results about the influence of crystal shape of calcium sulfate dihydrate on the dehydration coincides with those obtained by aforesaid D. T. A. curves. For the calcium sulfate of higher crystallinity, the cnic on the weight-decrease curve becomes more indistinct. This fact has been found, from the consideration combined with the dehydration-temperature interval curve, to be due to the delay in dehydration period of crystal water of 3/2 mol. in the case of tabular crystal.
Eeah peak temperature in both D. T. A. curves and

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We studied plasticity figure of slaked lime for plaster and the effect of some factors on this property with Emely plasticimeter.
The results obtained are summarised as follows.
1) Plasticity figure of slaked lime for plaster showed 111-150 (for finishing coat) and 110-135 (for first coat).
2) The effect of water ratio to plasticity figure was specific and not similar with samples.
3) Plasticity figure of slaked lime for plartes at same aging time decreased in accordance with the rising of aging temperature.
4) The effect of aging time to plasticity figure of slaked lime for plaster decreased with the rising of aging temperatur.
5) If we expect good effect of aging to plasticity figure of slaked lime for plaster, we must avoid high aging temperature.

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The Kurosawa mine is a Tertiary Miocene Black-ore-Type gypsum mine, and mining gypsum and pyrite. In this report we have researched into original chemical working of gypsum mine, its inner structure and slender vein gypsum. And then we have caught some interesting facts, about them so we report as follows;-

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