The authors designed an improved cell-type electrodialytic apparatus possessing rationalized bath structure and membrane pack structure, and equipped it with 306 unit cells of 115 dm² effective membrane area. In addition, this apparatus was equipped with two kinds of membrane cells (Membrane I-S'₂ and Membrane II), and a test was carried out for some ten thousand hours. The results obtained were as follows:
1. Throughout the test, no special problem was found in the bath and membrane pack structures. and the treatment of the membrane pack proved to be easy. Thus, it became promising that an apparatus of larger scale could be designed on the basis of the structure of this apparatus.
2. As the result of an increase in the ratio of effective electrizing area of the end plate of the membrane pack from 74% to 94%, the overall electric resistance of the electrodialytic bath seemed to decrease by about 2 or 3%.
When the membrane cells were inspected after the long-term test, the “projection” of frame figure of the end plate of the membrane pack, which was probably formed by the interruption of electric current by the frame, was observed on the membrane of the end cell next to the end plate, but the “projection” was not clear on the cell next to the end cell.
3. In the initial period of the long test, troubles were caused by stagnant brine in membrane cells of Memb. I-S'₂, but in all cases this was found to be caused due to the imperfect preparation of membrane cells.
4. During the long test, large wrinkles were formed on the membrane cells of Memb. I-S'₂ and small wrinkles on the membrane cells of Memb. II. These wrinkles were found to be of obstacle to the operation, because they interrupted the flow of sea water.
5. The low-permselectivity for divalent cations of Memb. I-S'₂ was rapidly deteriorated in the initial period of the test, but almost no deterioration was observed in the low-permselectivity of some of those membranes of the same kind replaced in the midst of the test.
6. When sandfiltered sea water was fed, the amount of suspended matter deposited on the membrane surface was decreased by air-blow treatment. The electric resistance of electrodialytic bath decreased by about 5% for a time just after air-blow treat ment.
7. Little increase was observed in the flow resistance of the electrodialytic bath during the entire period of the test.
8. Anion membranes of Memb. II became fairly stiff during the operation, but it was found that their flexibility was restored by dipping them in acidic solution.

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In this study, we determined the permselectivities of Mg²⁺ and H⁺ in case of ion-exchange transfer and diffusion transfer. Results obtained were as follows:
The permeability of Mg²⁺ in case of diffusion transfer was very small as compared with that in ion-exchange transfer, while the permeability of Mg²⁺ was one twentieth to H⁺ However, the permeability of Mg²⁺ in diffusion transfer increased as the concentration of the original solution decreased, and the influence of the concentration was smaller than in ion-exchange trasfer. The values of permselectivity coefficient in ion-exchange transfer were about the same as those in electrodialysis.

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In our previous study, we carried out the electrodialytic concentration of sea water using ionexchange membrane, and as the result we found that the concentration of some cations contained in the brine did not indicate its normal tendency. This was considered to have been brought about by the chlorine added to the sea water for sterization.
In our present study, therefore, we used the sea water containing no chlorine and measured the concentration of each ion contained in the brine in the same way as in our previous study. As the result, we obtained appropriate values of permselectivities for characteristic cation exchange membrane, and the values of permselectivity coefficients Ca2+ and Mg²⁺ to Na⁺ were about 0.6 times as much as those of usual cation exchange membrane.

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