Nothing has been reported yet conerning the fluidity in relation to the state transiton where the plaster of Paris is set with hydration. Taking advantage of the opportunity given to the authors to consider this problem from the practical view of point, we tested the fluidity of the Plaster of Paris alone and also together with saw-dust, using the simple apparatus to determine fluidity (Burr's method). The effect of several addition agents was studied in this experiment.

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The effects of wet and dry conditions to the volume, weight, surface hardness, and strength of hardened gypsums were studied. (1) The weight changes of samples under 100 % relative humidity and under water were very different, but the linear expansions of both samples were almost equal. The quantities of water required to expansion were little. (2) The strengths under alcohol were equal or a little superior to those of 45°C dry samples, but strengths under water were decreased to the half of the former. (3) Dry strengths and expansions under wet conditions were in inverse proportion to the mixed water. The decline in strengths under wet conditions and the coeff. of water absorption were proportional to the mixed water. The surface-hardnesses of the same samples were also tested. (4) The compressive strengths under 10 % solutions of Na₂B₄O₇·10 H₂O, Na₂C₂H₃O₂·3H₂O, KNa C₄H₄O₆·2H₂O, AlK (SO₄) ₂·12H₂O and Cu SO₄·5H₂O were not so different from the strengths under water. The decline in strengths under Benzol and CCl₄ were small and nearly close to the dry strengths.

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The thermal analysis of some lime-stones abroad were studied already but not of those from Japan proper. We picked up 59 samples of lime-stone and dolomite from various places of this country, considering several conditions about them, and report here these results of thermal analysis together with chemical analysis.

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