In the salt-manufacturing process in Japan and desalination, scale formation and its prevention are the most important problem. This study has been carried out in an attempt to solve this problem.
On the scale formation, following studies were made:
1) The relationship between concentrating method of sea water and behavior of scale components of sea water or compositions of adhered scale.
2) Proceeding of scale formation of NS triple salt-A in the salt manufacturing process from the brine obtained by salt-field method.
3) Proceeding of scale formation of di-sodium pentacalcium sulfate in the salt manufacturing process from the brine obtained by ion-exchange membrane method.
4) Rate of dissolution and crystallization of calcium sulfate in the brine during transition stage.
5) Formation of alkaline scale in heating the brine obtained by ion-exchange membrane method.
6) Decomposition of condensed sodium phosphate in heating the brine obtained by ion-exchange membrane method.
On the scale prevention, following studies were made:
1) Effect of various additives on the formation of alkaline and calcium sulfate scale.
2) Effect of various seeds on the formation of alkaline and calcium sulfate scale.
3) Application of sodium hexametaphosphate to prevention of scale formation of brine-preheater.
4) Development of a new, preventing method of scale formation in salt manufacturing process by using sodium hexametaphosphate together, with hydrochloric acid.
5) Development of a preventing method of scale formation in multi-flash evaporater by using seeds (CaCO₃+Mg (OH)₂, CaSO₄·anh) together with slaked lime.
Bench and plant scale tests of the developed methods such as 3), 4) and 5) above mentioned were made in salt-manufacturing factories and desalination factories of 6-stage flash evaporator. And satisfactory results were obtained. Then, the methods of 3) and 4) have been applied successfully to salt-manufacturing factories.

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In the process of seawater distillation, the concentration of dissolved oxygen (DO) in feed seawater is reduced to about 10μg/lin order to prevent the plant from the corrosion of metallic materials. An electrochemical DO meter (model 6400) made by Electronic Instruments Ltd. is an on-line analyser of gas transfer type for measuring trace amounts of DO in μg/lunit, but this instrument was developed for pure water such as boiler feed water. The DO meter is equiped with the mechanism of zero point and 25μg/lchecks and the accuracy of the measurement is ±10%.
Previously, the authors had reported an apparatus for the preparation of water containing trace amounts of DO. This study was done with DO meter combined to the new preparating apparatus that was developed for this purpose. Measuring conditions were varied to investigate the influence on the measurement in a range of 0-60μg/lin pure water and seawater.
The measured values were proportional to the calculated ones, but measured values using seawater

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The caking tendency of common grade salt and kitchen salt made by ion-exchange membrane method was compared with that made by salt-field method. And the effect of palletized transportation system on the caking tendency during transportation was concurrently examined. For these purposes, piling test of common salt made by three salt-manufacturing factories (Z, W and P) was made at six warehouses of various environmental conditions, where blocks of three pallets of saltbags (30 and 36 piling steps for common grade and kitchen salt, respectively) were stored for three and six months. In previous paper, the results of common grade salt were reported and in this paper those of kitchen salt are reported. And the following results were obtained;
(1) The magnesium contents of piled kitchen salt of Z and W were very small and that of P was average. The mean particle sizes of Z and P were small and that of W was average. Variations of these values in three salt-manufacturing factories were very large and must be controlled within smaller range.
(2) The degree of caking of P in three and six months'storage was less than 1kg/cm², while those of Z and W were 2-5kg/cm²according to the environmental conditions and or duration of storage. Some preventing procedure must be taken in latter cases.
(3) The Water content of kitchen salt of all piling warehouses increased during three and six months'storage.
(4) Environmental conditions affected greatly on the caking tendency, when kitchen salt contained less magnesium ions. However, caking tendency could be kept smaller notwithstanding environmental conditions, in case kitchen salt contained more magnesium ions.
(5) The piling blocks of three pallets of 5 kg kitchen salt-bags of about 3,700mm in height sank 3.8% of their initial height in the manufacturing werehouses and 2.1% in the intermediate warehouses after transportation during three months'storage and 4-5% in the former and 2-3% in the latter during six months'storage.
(6) When the caked 5 kg kitchen salt-bags of 1.3-3.5kg/cm²degree of caking fell down from 1m height twice, more than 60% of the salt in a bag was normally crushed. No further e1ffect was expected by more falling-down.
(7) Generally kitchen salt made by an ion-exchange membrane method showed less caking tendency than that made by a salt-field method. This was estimated to be attributed to the difference of chemical composition of trace attached liquid and the fluctuation of amount of magnesium ions and particle size.
(8) The degree of caking of kitchen salt was less than 1.5kg/cm²before a palletized transportation system was adopted, while that of this experiment was 0.3-4kg/cm². Although caking

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A Gas chromatographic determination of organic acids added in common salt has been developed. Malic acid and citric acid added in sodium chloride were easily extracted with acetone. Then, this solvent layer was separated, and evaporated to dryness. After this treatment the sample was converted directly to trimethylsilyl derivatives withN, O-bis (trimethylsilyl) trifluoroacetamide (BSTFA), and this product was analysed on colomn (1m×3mm) packed with 2% of OV-17 on Chromosorb G (AW-DMCS){(60-80) mesh} and operated with temperature programing from 100°C to 230°C at 10°C/min. When tartaric acid was used as internal standard substance, the retention time and recovery rate of malic acid were 4.7 min and 105% and of citric acid were 9.1 min and 106% respectively. Working curve of malic acid or citric acid using tartaric acid as internal standard substance was rectilinear in the range of ratio from 0.02 to 0.08% in common salt. The reproducibility of the determination of malic acid within above range of concentration was 1.2% as coefficient of variation, and of citric acid was 2.2% respectively. Impurities like calcium, magnesium, potassium, iron, copper and aluminium which contained in common salt did not interfere.“Tsukemonoyouen” on the market was analysed by this method and its results showed 0.05% for malic acid and 0.04% for citric acid respectively.

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