The quality, crystal form and amounts of combined water of the chemical gypsum byproduced from salt making are very variable with the crystallization condition of calcium sulfate in a concentrated solution of brine and therefore the utilization of the gypsum is often limited.
The raw gypsum materials generally contain dihydrate and hemihydrate of calicum sulfate for the principal constituent, and also sodium chloride and alkalline double salts for impurities. These hemihydrate and anhydrate are easily hydrated to dihydrate by water or sea water, and the most of impurities are easily soluble in water, it is probable to improve crystal form and develop crystal size with dissolving the impurities by aging simply in water.
The present authors studied on the most brief, effective and economical purification process of these raw gypsum materials and the physical properties of the calcined gypsum prepared from the purified crystalline gypsum. Sample gypsum materials are a scale rakaed out from multiple effect evaporator and a pan scale deposited in the concentrating pan over the hot spring heater. For the purification process, washing by and steeping in cold water, hot water, boiling water, a dilute solution of sodium chloride and of sulfuric acid are taken alone or together. Microcrystals of sodium chloride are almost removed by washing, and hemihydrate and anhydrate completely convert to dihydrate. Crystal size of gypsum makes difference to each process and is developed to the gross prismatic crystal by steeping in water firstly and washing with a dilute solution of sulfuric acid secondly.
The physical properties of the calcined gypsum prepared from salt making process are far superior to them of the calcined from the double decomposition of rock phosphate and sulfuric acid to phosphoric acid and gypsum, but it has tendency to hasten the initial setting time for a little sodium chloride remained within crystalline gypsum.

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Magnesium carbonate reacts with potasium chloride in the presence of CO₂:
2KCl+3MgCO₃·3H₂O+CO₂=2 (KHCO₃·MgCO₃·4H₂0)+MgCl₂This hydrated double salt of KHCO₃ and MgCO₃ is insoluble and can be washed free from MgCl₂with water. If this double salt is decomposed with hot water, the products are K₂CO₃ solution and a precipitate of magnesium carbonate.
2KHCO₃·MgCO₃·4H₂0=K₂CO₃+2MgCO₃+9H₂O+CO₂If decomposed at temperature below 20°C with a suspension of magnesium hydroxide or oxide, the magnesium is precipitated as the trihydrate, and can be re-used.
2KHCO₃·MgCO₃·4H₂O+Mg(OH)₂=K₂CO₃+3MgCO₃·3H₂O+H₂O The authors utilized these reactions to prepare K₂CO₃ and MgCO₃ from bittern. In this report, the fundamental conditions of these reactions were investigated.

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The purpose of fhe present papaer is to examine fundamentally the separation and recovery of gyp sum by means of the flotation process from the so-called“Scale”obtained in the salt-making plants.
The wettability of the saturated solutions of the gypsum together with or without the other salts for the gypsum particles, at first, are studied qualitatively to determine the most suitable collector and experimental conditions when the flotation is applied. From the experiments in which the various surface active agents was tested as the collector, it was indicated that oleic acid was the best collector for the crystal gypsum and “Auxide”(alkyl pyridinium salts) for the gypsum in the scale.
The simple flotation tests with an apparatus described by Knoll & Leaf were carried out for the two cases; the one is the mixture of NaCl and CaSO₄·2H₂O (both commercial grade), and the other being the scale. In the former, it was observed thet the rate of flotation upon the CaSO₄·2H₂O became greater if the ratios of amounts of initially presented CaSO₄·2H₂O to those of NaCl were made smaller. In the latter, moreover, it was acertained that the rate of flotation was up to arround 86%, with the results that the concentrate contained about 40-48% gypsum, in which dihydrate was 88.3%, and NaCl and magnesium salts as the remainder.
According to the results abovementioned, the possibility on the separation of gypsum by the flotation process could be expected. Especially, from the views of separation and recovery of gypsum, the following treatment would be recommended which the concentrates risen by flotation were well washed by water, because of the greater solubility of such coexisting salts as NaCl, MgSO₄, MgCl₂ and so on than that of gypsum in water.

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Generally light basic magnesium carbonate has the composition of “MgO: CO₂: H₂0=(4:3:n) -(5:4:n)” mole-ratio. There is, however, another light basic carbonate of “2.0:1.2:2.1” mole-ratio, which was found by authors and made by passing CO₂ gas into the aqueous suspension of Mg (OH) ₂ at 90°C.
In this report, the relation between the bulkiness and crystal property of the above carbonate was studied by means of the X-ray analysis and the electron nticroscopy. The result is as follows:
1. The bulkiness of basic magnesium carbonate depends on the factors, such as the size and the lyophility of particles.
2. The single particle of “2.0:1.2:2.1” mole-ratio is composed of the flaky crystals of “5:4:5” moleratio, and each of these crystals are covered and sandwiched by the film of amorphous basic carbonate. Furthermore, the surface layers of these particles are more carbonated than the inner part, having the less hydrophilic property.
3. In order to be in the highly bulky state, therefore, the aggregates of fine flaky crystals must be dispersed, and also their surfaces must be less hydrophilic. Such conditionings are possible not only by the mechanical stirring, but also by the controlling of the CO₂-adsorption in the process above mentioned.

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By the direct electrolysis of magnesium salt solution or bittern, several studies that magnesium had been separated as basic magnesium hypochlorite are found.
The mechanism in this method depends on the reaction between anodic oxidation products of chlorine and magnesium hydroxide as cathode deposit.
On the other hand, magnesium is separated as hydroxide according to the electrolytic conditions. In this report, from the view point of removing completely magnesium from the sea water, to select whether to employ the mechanism of reaction which is suitable to preparation of basic hypo-chlorite, or hydroxide, and to illustrate the mechanism in these reactions, the effects of factors to the removal ratio of magnesium and calcium, oxidation current efficiency, and decomposition ratio of chloride were studied by means of statistical methods.
Factors that had been employed were composition and temperature of electrolytes in the concentration of magnesium, calcium and chlorine equaled with each ion concentration in the sea water, current density, running hour, diaphragm, and agitation.
A process which used a diaphragm, and precipitated magnesium ion as hydroxide was better to complete removal of magnesium. Under the same conditions, calcium was removed, but it would be necessary to increase moreover the quantity of electricity to remove a quite quantities of calcium as hydroxide.
It might be estimated that using electrolytes in chlorine ion concentration such as in sea water was not suitable for the preparation of basic magnesium hypochlorite owing to the low concentration of oxidation products of chlorine which diffused to the cathode.

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In our previous papers, it was shown that the results of foundamental and practical experiment on the scale-prevention in the way of the addition of crystal seeds had been investigated. This new repot is concerned with the relations between the condition of evaporation and properties of the seed itself, and five experiments were carried out with the following results. Exp. I: the effect of suspended amounts of seeds-the results showed that the amounts of calcium sulfate crystal were adequate to 20g per liter in brine for the pratical use. Exp. 2: about the size of crystals-the smaller is the more eminent, and then the crystals made by crushing large one were also usable for seed. Exp. 3: the influence of dihydrate in anhydrite-it was found that the contents of dihydrate might be permitted up to 20% in weight. Exp. 4: the effect of temperature of the mo ther liquor and water of crystalization-the transition point was influenced by the seed, and in the temperature range from 90 to 65°C, hemihydrate one was effective relatively. But after long running, the evaporation was disturbed with the scale formation. Exp. 5: the effect of velocity of liquid circulated in heating tube-the quantities of adhered scale increased inversely to the velocity of the liquid flow and as the result of this examination, good data were obtained in the case of 0.25m/sec.

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Sakito salt manufacturing factory completed on May 1956 and has been worked moothly.
This foctory has a following salt producting method: Sea water in concentrated in the thermo compressive evaporator driven directly by the back pressur turbine in the triple effect vacuum pan heating by the turbine evacuation. Low quality coals are used for producting the original vaper.

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We studied on various problems occured in Mitsui Salt Manufacturing Factory which completed on June of last year. Especially the blower (axial type) has been one difficulty in this factory, and therefore we put stress on this blower.

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