It is very important in the manufacture of phosphoric acid from phosphate rock and sulphuric acid to produce the phosphoric acid concentrated as possible and the CaSO₄-H₃PO₄ slurry having a high filtration rate. In accordance with increasing the concentration of P₂O₅ and the temperature of the reaction in order to produce directly the concentrated phosphoric acid over 40 per cent by weight P₂O₅ without evaporating, the calcium sulphate formed in the course of the reaction is deposited substantially as CaSO₄ with CaSO₄·1/2H₂O. Because the operation of filtration becomes very difficult and the utility value of gypsum becomes lower, the process of anhydrous gypsum has not so been developing in our country wanting in the resources of crystalline gypsum.
The present authors studied on the hydration rate, the filtration rate and the conversion effect to crystalline gypsum of the anhydrous gypsum slurry deposited in a concentrated phosphoric acid, with the object of preparating the anhydrous gyusum slurry having the suitable nature for the successful operation of the process.
The process has the particularities as follows, difficult soluble and easily separative slurry as the mixture of CaSO₄ and CaSO₄·1/2H₂O in H₃PO₄ containing 40 per cent by weight P₂O₅, the first filtrate containing 43 per cent by weight P₂O₅ and yield of about 97 per cent. The anhydrous gypsum slurry easily converts to crystalline gypsum in the dilute solution of H₃PO₄ or H₂SO₄ at ordinary temperature. The semi-stability of CaSO₄ in the stable zone of CaSO₄·1/2H₂O is found in the considerable large extent.

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The properties of the byproduct gypsum, - “Sengo-gypsum” -which is yielded by concentrating the sea-water or brine at the salt-making plant, were studied on the stand point of view to use as the raw material of calcined gypsum. In this object the sample were then examined by differential thermal analysis, thermo-gravimetric analysis, X-ray analysis and setting. In this paper we were reported the result as follows ;
1. The setting of this byproduct gypsum was slower as that of the natural gypsum, because of the impurities such as the oil contaminated mechanically in the multiple effect evaporators and the ocean soluble or double salts due to the components in the sea water.
2. The setting time was normalized by the operations as follows :
(1) Washing the raw “Sengo-gypsum” by the petroleum-ether and removing the oil.
(2) Calcinating the raw “Sengo-gypsum” up to the temperature 200°C and burning the oil off.
(3) Boiling the raw “Sengo gypsum” in the 2% HCl solution for 1hr, resolving the soluble inorganic salts, destroying the double salts, etc. and removing the oil.
3. In the “Sengo-gypsum, ” same hydrated salts but crystal gypsum were detected in the D. T. A.

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It has been made clear in the previous paper that the dehydration characteristics of dihydrated gypsum under pressure differs greatly from those in an atomsphere. This present paper extends previously reports and deals with the preparation method as well as the general characteristic of semihydrated gypsum so prepared, which is being summerezed as follows;
(1) In an atomsphere, the primary dehydration temperature of natual dihydrated gypsum used as a test sample is 133°C while its secondary dehydration temperature being 192°C. Under pressure of saturated water vapor, the same sample is primarily dehydrated at 142°C without the secondary dehydration and is directly lead to the natural anhydrit as the temperature increases without the second dehydration's endothermic region.
(2) Under pressure of 99.5% ethyl alcohol saturated vapor, the primary dehydration temperature is raised to 162°C and semihydrated is obtained by heating the sample of dihydrated gypsum at 230°C without the secondary dehydration. The primary dehydration temperature becomes higher as the partial pressure of ethyl alcohol in H₂O-EtOH vapor system is increased.
(3) Under the pressed nitrogen gas, there obsereved three distinct endothermic regions in thermal analysis map which are identified as being due to the primary dehydration, boiling of water and the secondary dehydration respectively in the order of increasing temperature. The pressure-temperature relationship in the second endothermic region is identical with that water vapor. The temperature of the secondary dehydration increaes with increasing the pressure of gas enclosed in autoclave according to the experimentally obtained relation T=65 log P+192 for the pressure up to 15 ata. Thus, under pressure the results are entirely different whether the dehydration is performed in the saturated vapor of water, ethyl alcohol or in the inert gaseous surroundings such as nitrogen
(4) Semihydrared gypsum in prepared in saturated vapor of water or ethyl alcohol as well as in the liquid with varying condition, and the properties of the resulting products are examined. As a result, it is become known that the measurment of true specific gravity is the convenient and practical means for the estimation of the state of semihydrated gypsum so produced. In general, the true specific gravity of semihydrated gypsum produced by dehydration under pressure is greater than that produced at normal pressure.
(5) Semihydrated gypsum prepared under pressure of nitrogen in unsaturated water vapor is found to be a well developed form of α-semihydrated gypsum. Therefore it is possible to prepare α-semihydrated gypsum which is easier to dry that made by hitherto known hydro-thermal method.

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A automatic apparatus for d.t.a., which have a automatically controlled electric furnace to follw the programs of temperature elevation of 3 or 8°C per minute and the photographic recording devices for temperature of differential and heating of sample, have arranged newly, and approved as same as Borshad done.
The possibilities of quantitative analysis of CaSO₄·2H₂O and CaSO₄·1/2H₂O from the area of d.t.a. curves of dehydration which obtained using this apparatus was searched, and there was the linear proportion between the mass of CaSO₄ and the area.
Various states of hydration of CaSO₄·1/2 H₂O produced on H₃PO₄ making, have been researched by d.t.a. and. been found that there exist a small endothermic peak between two dehydration ones.

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Effects of the addition of Asbestos-tailing to plasters and cement on the quality of the wall, was reported by Dr. S. Nagai, his assistant Y. Hukumori and the same author (this journal No. 23, 17-26 (1956)), as the following abridgements.
(1) Shrinkage-cracks are reduced.
(2) Workability to coat is so good.
(3) Appearance of the mortar-surface is very lustrous.
(4) Water retention of the mortar is increased.
(5) Ideal mixing proportion of Asbestos-tailing is 10% to cement and 30% to plasters.
Then, the writer studied the same tests on the large samples, and the extensive actual places, so the addition of small amount (10-30%) of Asbestos-tailing to plasters and cement, was proved to give good effects on the mixed wall as the previous paper.

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