In Japan, the salt manufacturing method from sea-water was completely changed on January 26th, 1971. The traditional and time-honored salt-making fields were all abolished, and a new salt-making method by electrodialysis with ion-exchange membranes was adopted instead.
Those ionic brines obtained from the new method have special compositions. Namely, they contain little SO₄^2-, and the proportion of each ion vary from another. So, it is quite difficult to find out regular relations among them. If the small content of SO₄^2- be neglected, however, they may be treated with the five-component system Na⁺, K⁺, Mg²⁺, Ca²⁺||Cl^--H₂O.
The five-component system already reported at various temperatures, contains relative few kinds of crystals as the solid phases, and at least it does not cause serious super-saturations till the saturation of KCl.
On the other hand, the brine produced from the traditional salt-field contains almost the same proportion of salt as in the sea-water. It must be treated with the five-component system of oceanic salts; Na⁺, K⁺, Mg²⁺||Cl^-, SO₄^2--H₂O. This five-component system contains SO₄^2- which is liable to yield many hydrated salts and compound salts, often causing serious super-saturation. Therefore, it is hard to do the graphical calculations, and the results obtained often differ from the experimental results.
From the above-mentioned points, the author came to the conclusion that the electrodialysis method was most suitable for the graphical treatment with the phase diagrams. In the present paper, a study was made on the reliability of such treatments.
The evaporations of four ionic brines at the three different temperatures of 110°C, 70°C and 45°C were calculated in a graphical way. For such calculations upto the saturation of KCl, trian-gular coordinated diagrams of Jänecke type simplified to be always saturated with NaCl, were used. The concentrations of NaCl and H₂O were not shown on such diagrams. To get the concentrations of these components. therefore, an interpolation method was used by presuming that the contents of NaCl and H₂O would change linearly on the straight lines of the diagrams. For the calculation of their evaporations upto NaCl saturation, the orthogonal projection of diagrams on the tetrahedron coordinate were used. The contents of water were calculated by the interpolation method as mentioned above. Also, the calculation of the same evaporations was done by the empirical formula developed by the Japan Monopoly Corporation. The results of the above two calculations were shown in Table 3. The calculated items were as follows: Water evaporated to the saturation of NaCl:E_s, the quantity of NaCl saturated brine:W_s, water evaporated from NaCl brine to KCl brine:E_b', NaCl deposited:Sb', the quantity of KCl saturated brine:Wb', and the total water evaporated to the KCl saturation: E_s+E_b'.
The study of Table 3 showed that the graphically calculated E_s was larger than the empirical formula value by several percents. Because of this fact, the graphically calculated W_s and Eb' were several percent smaller. However, both the values of S_b' and E_s+E_b' coincided very well. Accordingly,S_b' and E_s+E_b' were considered the most important values for the salt-making factory. The fact that the results of the two methods coincided in these important values, indicated that the graphical method was as reliable as the empirical formula method authorized by the Japan Monopoly Corporation.

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The quality of salt produced by ion-exchange method was examined from the amount of impurities contained on and in the crystals of the salt, and a comparative study was made with the quality of the salt produced by salt-field method. Also, there was made a study on the powder properties of the both salts.
1. The analytical data of the salts produced during the recent seven years indicated the following facts: The content of sodium chloride of common salt had gradually increased from 96.4% to 97.4%. The content of water, magnesium, and sulfate ions had also increased, respectively. However, there had been little change in the purity of kitchen salt. Since the year of 1972 when the traditional salt-making method by salt-fields was replaced by the ion-exchange method, there has been an increase in the content of potassium for both common salt and kitchen salt, but some decline in the content of sulfate ions.
2. As compared with the salt produced from the salt-field, the total quantity of impurity ions except sodium and chloride ions had increased from 0.045-0.13% to 0.07-0.23%. In more detail, potassium, calcium and sulfate ions had increased, but magnesium ions and water-content in cavities had shown a decrease.
3. About the salt produced by the ion-exchange method, potassium or sodium sulfate (and/or double salt containing those single crystals) was supposed to crystallize in vacuum pans and enter the crystals of sodium chloride, and potassium ions to enter the crystals of sodium chloride in place of sodium ions as in the case of the salt produced by salt-field method.
4. The critical humidity of the salt produced by the ion-exchange method was 68-73% R. H. at 25°C for common salt and 37-38% R. H. at 25°C for kitchen salt. The pH values of these two salts were 5.3 8.5 and 7.4 8.5, respectively, when 10 grams of the salts were dissolved in 30 ml pure water.
5. The powder properties of the common salt were mean particle size 280-400μ; apparent densities 0.75-0.86g/cm³ (coarse), 1.21-1.31g/cm³ (dense); and angles of internal friction 36-40°. Those of the kitchen salt, on the other hand, were mean particle size 290-390μ; apparent densities 1.25-1.41g/cm³ (coarse), 1.37-1.46g/cm³ (dense); angles of repose 41-45°; and angles of internal friction 33-40°.

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In the process of sea water distillation, the concentration of the dissolved oxygen (DO) in the circulating brine is decreased, in ordinary cases, to be 10μg/l in order to prevent the corrosion of metallic materials in the plant. Trace amounts of DO are usually determined by Winkler method. This chemical method is interfered by the oxidizing and reducing substances of samples.
In the present study, the influence by ferric, ferrous, cupric, nitrate, and nitrite ions on this analysis and the preventive measures for them were examined in deionized water samples. The results obtained were applied to sea water samples.
The interferences caused by ferric, ferrous, and nitrite ions could be eliminated by adding phosphoric acid,o-phenanthroline hydrochloride, and sodium azide, respectively. The influences of cupric and nitrate proved to be negligible. An apparatus was developed for the preparation of water and sea water samples containing trace amounts of DO.

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This study was conducted to examine the validity of phase diagrammatical method on the separation and utilization of oceanic salts in sea water.
There are various methods for the separation and utilization of oceanic salts which are complicated salt solutions. However, it must be considered that the multiphase equilibria in salts and water systems such as mixed salt solution treatments are accompanied by phase transition.
Therefore, the author devised the method of surmising various qualitative and quantitative relations in the case of solution treatment, under a phase rule analysis by drawing the equilibrium diagrams of the five-component system in oceanic salts and by making graphical calculations including the samples and conditions. The validity of this graphical method was confirmed by experiments.
The drawing of the equilibrium diagrams, the graphical calculations and the experiments were carried out on the preparation of potassium chloride from carnallite and on the preparation of potassium sulphate from bitter, especially for the purpose of recovering potassium salts.
As the result of the study, the author found theoretical relations on the optimum conditions, yields, etc., which have not been made clear yet by the oceanic salt industry depending on just experiences.
The results of the author's diagram-drawing, graphical calculations and phase rule analysis coincided fairly well with the values actually determined. Thus, the method proposed by the author was proved to be valid and useful.
The conclusion of the author was that the method was fairly reliable and could be used for making judgements, estimations and fundamental operation in the case of planning of factory manipulation, investigation, etc.

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