We studied the compositions of various scales obtained from common salt making factories by chemical analysis and X-ray diffractive methods. Analysis were made on about fifty samples taken from the preheater and evaporator of vacuum system or thermocompression system equipments, and “Shijoka” or net type concentrating installation. We found that the principal component of scales from vacuum system evaporator or preheater is calcium sulphate, and that of thermocompression evaporator or preheater consists of calcium carbonate, magnesium hydroxide and calcium sulphate, but that of evaporator or preheater of vacuum system is calcium carbonate, when used the brine concentrated in flowing down salt field.

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With connection to the previous papers, we inform here the synthetic methods of polyhexyl and per properties. p-Mononitropolystyrene seported in the previous papers, is reduced by sodium sulfide an aut oclave about 150°C to p-aminopolystyrene and the latter condenses with picrylchloride in vridine forming Picryl-p-Aminopolystyrene. Still more picryl-p-aminopolystyrene is nitrated by a mixed acid of nitric and nitric fuming to polyhexyl. This compound or resin is refined by dealing with 0.2 N NaOH and 0.2N H₂SO₄ continuously. This absorbs almost 100 % potassuim ions of calculated values and the selectivity curve in Na-K-Cl system is shown in Fig-2.

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The trial to apply PVC sheet on sloping salt field in place of sea clay has been carried on for seveval years, for the purpose of increasing yield of brine by defencing the leakage of flowing sea water. At present PVC sheet is used in practice at Hayashida Salt Field (Kagawa pref.), Kirayoshida (Aichi pref.) and others, not yet decided how long to be used.
Part 1 “On Estimation of PVC Sheet for Salt Field in Laboratory and its Comparison with Practical Weathering Tast.”
As to 11 kinds PVC sheet which are in the market for miscellaneous articles, agriculture and salt field, were excecuted proofing tests against water and NaCl solution with various concentration in comparison with weatherometer test from a point of view for salt field. Durability of PVC sheet on salt field is to be attributed to the amount of migration of plasticizer and resistance of PVC resin itself agrainst weathering. The experimental results are as follows.
(a) Amount of plasticizer migrated from sheet into liquid is different not only in each sample, but also by concentration of solution, and it is most in 3% NaCl solution corresponding to natural sea water for all samples.
From the results of migration test, PVC sheet sample for salt field can be estimated by decrease of its weight after 30 to 50 days.
(b) All of PVC sheet samples were more stable in concentrated brine.
(c) Migration rate of plasticizer was accerated at higher temperature as in summer (30-40°C).
(d) Effect of ultravioletray on migration of plasticizer was not appreciated.
(e) Effect of contact material on the migration was different at each plasticizer, so that by selecting a suitable plasticizer, this influence would be avoided.
(f) Modulus strength and elongation are more important for the estimation of durability of PVC sheet than tensile strength.
(g) The limit of loss of plasticizer was about 15 wt.%. Destraction of PVC resin seems to become vigorous over this limit.
(h) Shrinkage of PVC sheet is proportional to the amount of loss of plasticizer, and available limit of the loss is to be less than 7-8% in practice.

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Copper, zinc, iron and aluminium contents of thirty samples of various evaporating salt (salts manufactured by vacuum evaporator, thermo-compression evaporator, closed pan, open pan and by hot spring heat utilization), were determined, and found that the average contents of copper, zinc, iron and aluminium is 0.17, 0.34, 1.99 and 0.36 milligram respectively per 100 gram of salt, and generally distributed more in the insoluble matter rather than in water soluble parts.
The greater part of these elements in original sea water is distributed in gypsum deposited by concentration.
But a majority of these elements in the salt is derived from the salt making plants, and these are a relation that the high zinc contents in the water soluble part of salt tend also to contain high copper contents in the insoluble matter.

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A rapid volumetric method suitable for potassium in common salt has been made with sodium tetraphenyl boron-mercuric chloride and obtained the following results.(1) The precipitation of potassium tetraphenyl boron is completed by standing for 10 minutes after the addition of the reaent more than 1.6 fold of the theoretical ammount of potassium.(2) For the determination of 0.2-5mg of potassium, the maximum deviation is 0.02mg.(3) The interference of Na ion (up to 1g) is prevented by the presence of a little AlCl₃. The presence of Mg 20 mg and Ca 10 mg cause not the interference. This method can be summerized as follows: The test common salt solution of 25 ml (within 5 mg of potassium) is acidified with 0.5 ml of 1 per cent acetic acid and added 5 drops of 0.01 N-AlCl₃. Five ml of a 2 per cet sodiumtetraphenyl boron solution is added with stirring and allowed to stand about 10 minutes, the precipitate is filtered throuth a glass filter, washed and dissolved with acetone. About 4 ml of saturated mercaric chloride solution, a little alcoholic solution of methyl red and a measured volume of 0.02 N-NaOH is added and the mixture is boiled for a short time. A 20 per cent solution of KI is added dropwise until the HgI₂ precipitate is dissolved. The mixture is titrated with 0.02 N-HCl to a strong red color, then boiled to expel CO₂ and backtitrated with the NaOH solution.

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