The reserch reported in this paper have been done in the concentrator of fishing-net system, the shijoka and splinkling system concentrators at Hofu Salt Experiment Station for the purpose of theoretical and experimental investigation in natural evaporation of general concentrators.
In consequence of some calcurations about measured data of surface-area, the water-surface-area per unit volume of the equipments were conjectured as follow:
Net System 1.2m²/m³
Shjoka 5.1m²/m³
Splinking System 0.007 m²/m³
We made some characteristics of these concentrators clear comparing the evaporation velocity of field test with the water-surface-area of the concenrator.

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As polyvinyl alcohol (P.V.A.) is very (unstable) for hot water, it is difficult to elute boric acid adsorbed in P.V.A. with hot water.
Then the insoluble polyvinyl glycerin acetal (P.V.G.A.) has been prepared from P.V.A.
The quantity of boric acid adsorbed in P.V.G.A. is larger than in P.V.A., and the quantity adsorbed in P.V.G.A. or P.V.A. is affected by the addition ratio in stationary method. The adsorption velocity for P.V.G.A. increases with the concentration and the temperature, and is nearly equal to the adsorption velocity for P.V.A. The elution velocity of boric acid from P.V.G.A.-boric acid complex is also nearly equal to the velocity from P.V.A.-boric acid complex in stationary method. The elution of boric acid from P.V.G.A. with distilled water increases with the temperature and decreases with the addition ratio. In column method, P.V.G.A. can be used as ion exchanger.

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The quantity of iodine adsorbed in P.V.G.A. increases linearly with the acetal value.
When P.V.G.A. of higher acetal value is synthesized, the quantity of iodine adsorbed in the P.V.G.A. will, perhaps, greatly increase. The adsorption velocity increases with the concentration of iodine solution. On the other hand, it falls suddenly as the concentration decreases, The quantity of iodine adsorbed in P.V.G.A. in the same addition ratio varies according to the “Freundlich adsorption isotherm”.

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(Supplement to part 3). On the manganese content of evaporating salt.
The Mn contents of various home product salt were determined colorimetrically by the periodate method after being collected by coprecipitation with ferric hydroxide.
Analysis showed that the Mn content of 12 samples is far little than that of the solar salt (8.3 p.p.m. on the average as reported already), and lies from 0.5 to 1.67p.p.m.(0.80p.p.m. on the avevage).
The manganese is distributed rather in the insoluble matter than the water soluble part.
(part 4). Colorimetric determination of iron in common salt with O-Phenanthroline.
Colorimetric determination of iron with O-Phenanthroline were made on the analysis of common salt, and the following results were obtained.
(1) This method is superior to the thiocyanate method as the color is stable and the procedure is simple.
(2) Iron in common salt can be determined directly as little as few microgram.
(3) Iron content and the tendency of distribution between the water soluble and the insoluble part of common salts was similar to the results already reported in this journal.
(part 5) On the lead content of common salt.
The lead contents of various solar and evaporating salt were determined colorimetrically by the dithizone method.
It was found that the Pb content of solar salt variedl from 0.4 to 7.1p.p.m.(2.3p.p.m. on the average of 17 samples), and lead is distributed mostly in the water soluble part.
The Pb content of evaporating salt manufactured in Japan is far little and is varied from 0.1 to 1.7p.p.m.(0.47p.p.m. on the average of 14 samples) and lead is distributed similarly both in soluble and insoluble matter.

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Ion exclusion is a process that chromatographically separates ionic from nonionic water-soluble materials by the use of ion exchange resins. In this paper, the separation of boric acid from sodium chloride was investigated. The resins employed were chromatographic grade resins, 100 to 200 mesh in particle size, named respectively by CG-120, a strongly acidic resin and CG-400, a strongly basic resin. Mixed solutions of sodium chloride and boric acid followed by water as eluant, were passed through the resin beds in the sodium form or the chloride form, at room temperature and at the rate of about 1 cc per minute. The effluent was collected in 10cc fractions and each fraction was analyzed for sodium chloride and boric acid. When 20cc of tha mixed solution containing 0.05N of sodium chloride and 0.05N of boric acid, is passed through 15 cc of the resin bed, separation is nearly complete. Sodium chloride is eluted from 50 to 80cc at the maximum concentration of 0.044N and boric acid from 90 to 120cc at 0.043N.

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Reaction between dilute phosphoric acid and magnesium hydroxide gave a dimagnesium phosphate (MgHPO₄·3H₂O). Specimen which was manufactured from phosphoric acid by wet process and magnesium hydroxide produced from sea water was soluble in 2% citric acid solution and its chemical compositions were as follows; T-P₂O₅ 39.75%, C-P₂O₅ 39.67%, T-MgO 22.43%, C-MgO 21.58%. These were agreed with theoretical value of dimagnesium phosphate (MgHPO4·3H₂O) and its X-ray diffraction also shows MgHPO₄·3H₂O.
Hygroscopic degree of this phosphate was as well as ammonium sulfate at ordinary temperature and is possible to use as fertilizers.
Finally magnesium phosphate mixed with superphosphate and could have made magnesian superphosphate comparable to serpentine superphosphate. And for the purpose of feeding B₂O₃ as the trace element, borax or boric acid adding to this magnesian superphosphate. These all fertilizers remained a high water soluble phosphate and good results were obtained, and some results are shown in the following tables.

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