The author reports in this paper the results of his study conducted on the change in chemical composition and the potassium content of the crystallized salt and on the equilibrium of the system during the crystallization of the mixture of salt-field and ion-exchange membrane brines.
1. Mother liquid in the crystallizer was in 20-70Mg mol/1000 mol H₂O, where the liquid was in the range between a₁ and a₂(saturated with sodium chloride) or in the range over a₂. The concentrating process of the brine indicated a tendency of containing more sulfate ion than the concentrating of sea water.
2. Potassium chloride crystallized in all the crystallizing pans over a₂.
3. The potassium content of salt produced from mixed brine was greater that from salt-field brine.
4. A comparison was made between the calculated and observed values of a₁ and a₂, and the result was in a good accord with a₁ but in a poor accord with a₂.
5. NS·A (Na₂SO₄·2MgSO₄·Mg (OH)₂·4H₂O) crystallized in all the pans and polyhalite (K₂SO₄·MgSO₄·2CaSO₄·2H₂O) crystallized in the second and third pans.
6. Magnesium ion and potassium ion showed the phenomenon of “fed back to the crystallizers” in the process of concentrating the ion-exchange membrane brine and the mixed brine, respectively. This phenomenon was not observed in a laboratory test.
7. The concentrate began to saturate with sodium chloride in the order of the ion-exchange membrane brine, the mixed brine and the salt-field brine according to the content of sodium chloride to the total salt.

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While the gravitationally drained bed of ice crystals was washed, a part of the crystals melted in the upper part of the liquid which was unsaturated. As the washing proceeded, a part of the washing water froze on the surface of the crystals in the lower part of the liquid which was saturated.
However, under such experimental conditions as those that temperature of the washing water was lower than 5°C, the flow rate was less than 0.22 cm/sec and the room temperature was around 1°C, those effects to be exerted by the melting of the crystals and the freezing of the washing water upon the apparent axial dispersion number were so small that the displacement type washing of the ice-crystal bed could be done in the same treatment as that of the bed packed with such inert particles as glass beads.

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The height of the saturation zone ane permeability of the ice-crystal bed were measured in the gravitational field, and the following results were obtained:
1. The height of the saturation zone of the ice-crystal bed was lower than that of the bed packed with such inert particles as the crushed quartz which was similar to that of ice crystals in average size. The permeability of the former bed was superior to that of the latter bed. These results could be understood on the assumption that the thin water film exist on the surface of ice crystal in the state of equilibrium.
2. The relation between the height of the saturation zone and the permeability of the bed was derived from the Yamaguchi's and Carman's equations as mentioned below:
ρmH (g K)^1/2/λcosθ= (1/5)^1/2_ε3/2/(1-ε)[m (1-ε)^-1/3-n]
where H is the height of saturaion zone, K is permeability,λ is surface tension,θ is contact angle (cosθ=1),ε is porosity,ρm is the density of solution, g is gravitational constant, and m and n are constants. The values of m and n for ice-crystal bed, in which the size of the crystals and the porosity of the bed were not uniform, were different from those of the bed uniformly packed with the crushed quartz of uniform size, indicating 0.446 and 0.433, respectively.

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A study was made to examine the behavior of fluoride in the process of concentrating sea water by ion exchange membrane method. The Alizarin complexon method was employed for carrying out an analysis of fluoride. However, it was necessary, especially in the analysis of concentrated solution, to add some sodium chloride to samples for avoiding errors to be derived from a change in the concentration of sodium chloride.
The permselectivities of fluoride to chloride T^F_Cl in sea water were as small as about 0.1, representing a half or one-third of those of sodium chloride solution. The differential permselectivity T^F_Cl in sea water was constant (about 0.17) in the region of less than 60% in degree of desalting for chloride. As for the small apparent permeability of fluoride in sea water, it seemed to be reasonable to consider that fluoride formed complex ion with a cation or cations in sea water. As the result of our examination on the effects of cations in sea water upon the permeability of fluoride, effects of magnesium were found to be great, but fluoride was found to be never concentrated as cations. The form of the complex ion was approximately MgF⁺, and the constant of its formation was about 10^1·8 at 20-40°C. Therefore, our conclusion was that most of fluoride contained in sea water existed in the form of MgF⁺ and seemed to hardly permeate through the cation exchange membrane in the form of MgF⁺, but F- which was in equilibrium with the MgF⁺ permeated through the anion exchange membrane.

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Hydrostatic phenomena in the diluting compartment and the concentrating compartment of electrodialytic apparatus of filter-press type was studied, and the following results were obtained.
1) The height of hydrostatic pressure balance point (θ) between the hydrostatic pressure of diluting compartment and that of concentrating compartment was found to be expressed by the following equatlon.
where
ρ_c: Specific gravity of concentrate
ρ_d: Specific gravity of dialysate
a: Height of diluting (concentrating) compartment
H_dl: Liquid level at the bottom of diluting compartment
H_du: Liquid level at the top of diluting compartment
H_cl: Liquid level at the bottom of concentrating compartment
H_cu: Liquid level at the top of concentrating compartment
ΔH_d=H_dl-H_du,ΔH_c=H_cl-H_cu
2) In case of up flow (in diluting compartment) system,θ was found to approach the value of a, as H_dl increased.

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