Systems NaCl-Na₄Fe(CN)₆-H₂O, KCl-K₄Fe(CN)₆-H₂O and 4NaCl+K₄Fe(CN)₆→4KCl+Na₄Fe(CN)₆were determined at 25° and 50°. And the data were presented in Tables 1-3 and Figs. 1-4.
Of the reciprocal salt pairs as mentioned above, a pair of KCl and Na₄Fe(CN)₆was found. to be stable at 25°C and 50°C.

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(1) The relation between the pH and the N/P (atomic ratio) of various ammonium phosphate solutions of concentration 2, 1,…1/8, 1/16 M/lwas studied.
When the N/P was, for instance, in the range of 1.2-1.4 (adequate range for synthesis), the pH of the solution was as follows:
in 1 M/lsolution 5.6-6.1
in 1/8 M/lsolution 6.1-6.5
The influence of temperature was negligible at 15-35°C in the range of 1.1-1.5 of the N/P.
(2) A series of syntheses using ammonium phosphate solution of 1/4 M/land N/P 1.2 were carried out by changing the reaction time between 5 minutes and 60 minutes for the purpose of investigating its influence.
The result of chemical analysis of the synthetic products showed that the reaction time had little influence on the component of the products.
This was due to the fact that as soon as the particles of magnesium hydroxide were added to ammonium phosphate solution, they turned into magnesium ammonium phosphate in a moment with the core unchanged, and then grew larger by aggregating with each other.

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For the purpose of electrodialytic concentration of potassium ion from sea water with ion exchange membranes, several experiments were carried out to find the effect of various current density or feed rate on the permselectivity coefficient, i. e. T^K_Naof potassium ion against sodium ion.
Also, the effects of total salt concentration or composition of the feed solution on the potassium permselectivity were examined with mixed solution of sodium chloride and potassium chloride.
The results were as follows:
1) The permselectivity coeff. T^K_Naincreased with a decrease in current density and an increase in feed rate, and the effect of the latter was found remarkable.
In the electrodialytic concentration of sea water, the value of T^K_Nawas about 2.6 at current density 1.0A/dm², and feed rate 40cm/sec.
2) The permselectivity coeff. T^K_Nawas exponentially related to feed velocity under the constant current density.
3) There was almost no effect as to the variation of the mol ratio of potassium ion to sodium ion on the potassium permeability, but the permselectivity coeff. T^K_Nadecreased with an increase in concentration of feed solution. These phenomena were caused due to the variation in concentration for the selectivity coeff. K^K_Naof the membrane.

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