The experiment of desalination of sea water has been made in Okinawa Island by using multieffect, direct solar, thermal diffusion stills. These solar stills have shown much higher efficiency than ordinary basin solar stills. General evaluation of these solar stills were reported in other papers. In this report, the relation between temperature of solar radiation absorptive plate and volume of distilled fresh water was explained in detail and proved theoretically.

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Mercurometry (ISO 2481), potentiometry (ISO 6227), and argentometry (JTS) for determination of chloride in common salt were studied as mutual comparison regarding the operation, error, time required and cost. Mercurometry was effected by pH and quantity of diphenylcarbazone. Excessive addition of nitric acid caused a decrease in repeatability because of an increase in blank value and unstable color at the end-point. Too little addition of nitric acid gave too little determination value. So addition of 0.5 to 1.0ml of 2 N-nitric acid and preparation about pH 2 were recommended. The color of the end-point was changed by the quantity of diphenylcarbazon, but determination value was not affected. A serious disadvantage in mercurometry was a disagreement of color with the color-matching solution, and the instability of end-point color gave frequently some anxiety to, the operator.
Repeatability in potentiometry in the ruled six combinations of electrodes was not different from others, but a combination of silver-ion selective electrode and calomel electrode gave relatively good accurate results. Repeatability of titration was 1: potentiometry, 2: argentometry, 3: mercurometry in the other of excellence. But each standard deviation in the total operation of determination was nearly equal because the dilution error was greater than the titration error. The comparison of accuracy of each method was obtained from the deviation from the standard value of the International Standard Seawater. The argentometry was the most accurate, the mercurometry gave lower value, and the potentiometry gave higher value.
Time required for making a sample was about 25 min in mercurometry, about 30min in potentiometry, and about 20min in argentometry after pipetting the sample solution. The reagent cost, apparatus cost and personnel expenses were estimated, and the total cost of argentometry was more reasonable than mercurometry in spite of expensive reagent cost because the weight of personnel expenses was greater than reagents and apparatus cost.

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By using an electrodialysis cell with 4 chambers of which effective membrane area was 12.6cm<USP>2</USP>, between 10 to 40A/m<USP>2</USP> of current density was measured selectivity of multivalenced metal cations (B) such as Co<USP>2+</USP>, Cr<USP>3+</USP> and Fe<USP>3+</USP> to Na<USP>+</USP> through two types of commercially available cation exchange membranes CMV and C66-5T, and two types of self made heterogeneous cation exchange resin membrane and chelating resin membrane. (T<USP>B</USP><USB>Na</USB>)<USB>i=0</USB> at zero current density wascalculated by using the concentration of each metal cation in the membrane equilibriated with aqueous solution of mixed metal ions and transference of each metal ion calculated based on membrane potential between two aqueous mixed solutions of different concentrations.
T<USP>B</USP><USB>Na</USB> for Co<USP>2+</USP> and Fe<USP>3+</USP> may be expressed by the following equation:
T<USP>B</USP><USB>Na</USB>(i)=(T<USP>B</USP><USB>Na</USB>)<USB>i=∞</USB>+ {(T<USP>B</USP><USB>Na</USB>)<USB>i=0</USB>-(T<USP>B</USP><USB>Na</USB>)<USB>i=∞</USB>} e<USP>-βi</USP>
where (T<USP>B</USP><USB>Na</USB>)<USB>i=∞</USB> is a ratio of mobility of ion B to that of Na<USP>+</USP> in aqueous solution.

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Based on design of uranium recovery process from sea water, total cost for uranium production was estimated. Production scale of 1,000 ton-uranium per year was supposed, because of the big demand for uranium in the second age, i. e., fast breeder reactor age.
The process is described as follows: Fluidized bed of hydrous titanium oxide (diameter is 0.1 mm, saturated adsorption capacity is 510 μg-U/g-Ad, adsorption capacity for ten days is 150 μg-U/g-Ad) is supposed, as an example, to be utilized as the primarily concentration unit. Fine adsorbent particles can be transferred as slurry in all of the steps of adsorption, washing, desorption, washing, regeneration. As an example, ammonium carbonate is applied to desorb the adsorbed uranium from titanium oxide. Then, stripping method is adopted for desorbent recovery. As for the secondary concentration, strong basic anion exchange method is supposed.
The first step of process design is to determine the mass balance of each component through the whole process system by using the signal diagram. Then, the scale of each unit process, with which the mass balances are satisfied, is estimated by detailed chemical engineering calculation. Also, driving cost of each unit operation is estimated. As a result, minimum total cost of 160,000 yen/kg-U is obtained. Adsorption process cost is 80 to 90% of the total cost. Capital cost and driving cost are fifty-fifty in the adsorption process cost. Pump driving cost forms a big part of the driving cost.
Further concentrated study should be necessary on the adsorption process design. It might be important to make an effort on direct utilization of ocean current for saving the pump driving cost.

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The oxidation of ferrous hydroxide Fe (OH) ₂ was investigated by using an experimental apparatus. When the precipitates of Fe (OH) ₂ in the brine was oxidized by the air injected, iron compounds produced at various temperatures of oxidation had different forms, e. g., Fe₃O₄ at high temperature and γ-FeOOH at low temperature. And the boundary of formation of γ-FeOOH was extended to higher temperature stage, as the ratio of iron concentration in the brine to air flow rate through the brine decreased.
The data on the chemical compositions of the iron sludge formed in the two plants, each of which had a capacity of 100m³/d and 2,000m³/d respectively, were obtained. In these plants, the iron compound was oxidized by the dissolved oxygen in the brine. The concentration of the iron compound and the dissolved oxygen in the plants were very low in comparison with the experimental data, so the oxidation condition of the iron compounds in the plants differed from the condition of the fundamental experiment. However, the forms of the iron compounds produced in the plants were similar to the ones experimentally produced. In the 100m³/d plant, in which the ratio of iron to oxygen was large, the formation of Fe₃O₄ was observed in the wide range. On the other hand, in the 2,000m³/d plant, in which the iron concentration in the brine was low, the most of the iron sludge had the form of γ-FeOOH.

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The analysis conducted on the sea water and sea-bottom sediments at Otozu-Hakuchi in Beppu Bay showed polluted inflow spread into the surface portion of the sea water, with minor mixing in the vertical direction owing to the density difference between polluted inflow and authentic sea water. This stratifying phenomenon appeared more clearly in summer. The COD and sulfide content in the sediment were almost identical to those in more polluted estuary, irrespective of the degree of pollution of the sea water above the sediment, which indicated pollutants accumulate into the bottom sediment. A good correlation between the number of sulfate-reducing bacteria in the sediment to sulfide content in the sediment was observed in summer season.

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