It is necessary to maintain silica concentration at a minimum in boiler feed water, because the silica in a boiler, operating at higher pressure and temperature, not only tends to form complex scale causing lowering in boiler efficiency, but evaporates with steam and deposits on turbine blades resulting in many accidents.
Widespread procedures for removal of silica in water are the chemical treatment by the addition of chemicals such as aluminium hydroxide and magnesium oxide, by aluminium hydroxide being produced in water by the electrolysis of aluminium and the ion exchange treatment by the anion exchange resin. But, because there had been few basic studies on these procedures, the writer investigated here the silica removal in the sodium silicate solution containing 20ppm of silica and the tap water containing 18.7ppm of silica and according to the order of procedures aforementiond following results were obtained.
(1) The quantity of removed silica increased with the increase in quantity of aluminium hydroxide added and the Freundlich adsorption isotherm holds exactly between the residual content of silica and the quantity of removed silica.
The pH value of solution influenced the silica removal efficiency, The residual content of silica was minimum when the pH of solution was 11.
The content of silica in tap water became about 0.6ppm when the content of aluminium hydroxide was 600ppm and the pH of water was 11.
The quantity of removed silica decreased with the increase in temperature of operation.
(2) The magnesium hydroxide and two kinds of magnesium oxides prepared by the dehydration of magnesium hydroxide at 350°C and 1000°C were used as the removing agents.
Magnesium oxide being prepared by the dehydration of magnesium hydroxide at 350°C showed the greatest silica removal efficiency.
The higher the temperature of operation, the more efficient was the removal of silica and the necessary retention time was 15 minutes at 95°C.
The pH value of solution influenced the silica removal efficiency and the minimum content of silica was obtained at a pH of 7. In the case of tap water, the residual content of silica became 1.2ppm at pH value 7, the content of magnesium oxide being 600ppm which was prepared by the dehydration at 350°C, the operation temperature 95°C and the retention time 15 minutes.
(3) The quantity of silica removed was proportional to the quantity of aluminium hydroxide prepared by the passage of direct current through the sodium silicate solution.
The residual content of silica became 0.3ppm when the content of aluminium hydroxide was 100ppm.
When the alternating current was used, the aluminium hydroxide produced were small, hence the amount of removed silica was small.
The residual content of silica in tap water became 0.3ppm when the content of aluminium hydroxide was 300ppm.
(4) When the sodium silicate solution was passed through each column of anion exchange resins namely Amberlite 410, Dowex-2 and Duolite A-40 the content of silica in effluent solution was reduced to 0.05ppm-0.07ppm.
In the same process, the content of silica in the tap water became 0.2ppm-0.3ppm.
The content of silica in the tap water was reduced to 0.2ppm when the tap water was passed through a column in which Amberlite 410 and Amberlite 120 were mixed.
Finally, the silica removal efficiency of four kinds of procedures that had been studied was compared and it was concluded that the ion exchange treatment and the process of electrolysis were recommendable.

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From the view point of removing magnesium and calcium dissolved in sea water as basic hypochlorite, an electrolytic separation process with no diaphragm was used.
Factors that had been employed in this report were quantity of electrolytic current, current density, and agitation at 10°C.
The effects of these three factors on the variation of magnesium, calcium and chlorine ion concentration, the removal ratio of magnesium and calcium, adhessive ratio of magnesium and calcium to the cathode, oxidation current efficiency, decomposition ratio of chloride, and the pH value in electrolyte were studied. And the relations between above characteristic values and the quantity of electrolytic current were determined.
It was difficult to remove magnesium ion completely by this method.
A small amount of calcium was deposited forming a thin layer of calcium hydroxide on the cathode plate.
The current efficiency for the preparation of hypochlorous acid and hypochlorite was affected significantly by the above three factors, and increased with current density and showed high value under non-agitation, but decreased with increasing of quantity of electrolytic current.
The current efficiency for the preparation of chlorate was high in agitation.
Decomposition ratio of chloride increased with quantity of electrolytic current, and the total of chlorine ion which was a constituent of hypochlorous acid, hypochlorite, chlorate and chloride gave a constant value in electrolyte during electrolysis, so it was found that the chlorine which discharged on anode plate did not go away from the solution, but it was oxidized to its oxidation forms.

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In the previous paper, the equilibrium of five components system Ca(OH)₂-CaCl₂-KCl-NaCl-H₂O was studied, and it was found that the range to form the double salts of calcium hydroxychloride in this system. So, in this report, extraction of potassium chloride in bittern free from Mg²⁺ was investigated in the various conditions to find effective factors.
As the results, the reaction between bittern free from Mg²⁺ and calcium hydroxide was mainly decided by the amount of calcium hydroxide added, K/Ca ratio in the bittern was nearly increased proportionally to the amounts, for example, in the case of addition of 15% calcium hydroxide, the value of K/Ca was increased from 0.28 to 0.40.
This treated solution was evaporated at the boiling point to various degrees of concentration, and cooled down to 25°C to separate potassium chloride. The extraction rates of potassium chloride calculated with equilibrium diagram, were compared with the ones obtained experimentally.
As the results, it was found that the yield of potassium chloride from the solution treated with calcium hydroxide were some 15-20% more than the ones untreated, and in the best conditions, the absolute value of the yield reached 75-80% for the original bittern.

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Sea water was concentrated at boiling point, and artificial brines were prepared by dissolving NaCl, KCl, MgCl₂ and MgS0₄. After equilibrium was attained at 25°C in 3hr., the composition of these solutions was determined. The experimental results coincided with the calculated values in the previous paper (this journal, 11,305 (1957)). Composition of the brine saturated with NaCl was obtained; d²⁵₄=1.2136, Cl=15.55%.
The author's value coincided with that of MAEDA (1920), OKA (1944) and ICHIKAWA (1956). In these experiments, compositions of the brines saturated with NaCl were obtained by its analysis directly. On the other hand the results reported by USIGLIO (1849) and MURAKAMI (1950), which calculated from composition of deposited salts was 10-30% smaller in Cl % than that of the author.

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