We studied on the contents of nitrite and nitrate in domestic salts produced in early September of 1966 by all 27 factories in Japan, as well as in solar salts and some rock salts imported from 21 areas of the world in 1965 fiscal year. Having been relate to the method of nitrate determination adopted, the nitrite was determined by the procedure of Rider and Mellon.
Some experiments were tried as to the influences of sodium chloride and heavy metals met little amount with. common salt such as copper, zinc, lead and manganese. From these results, there were no interferences if restricted amount of sample was taken.
The nitrite contents were generally very scarce ranging from 0 to 0.042 ppm (mean value 0.014 ppm) in domestic salts, and from 0 to 0.064 ppm (mean value 0.032 ppm) in solar salts, but in rock salts, it was found up to 0.13 ppm as in Chilean salt.
The nitrate was determined by the method of Mullin and Riley with some modifications. To adopt above method, following experiments were examined. These were the influences during reduction period of nitrate to nitrite, of temperature, pH, oceanic salts especially magnesium salts, and heavy metals. The results show those:
1) The influence of temperature was rather more remarkable than as Mullin and Riley stated in sea water analysis.
2) As to the pH, good results were obtained in the generous range of 10.0-10.4 compared with 9.58-9.69 of very severe control as in sea water analysis.
3) From the experiments onmain oceanic salts, it was found that Na⁺, K⁺and S0₄^2-had no influences, but Mg²⁺and Ca²⁺interfered at that order. The chloride influenced, but, when sodium chloride was used, maximum absorbance in optical measurment at 524mμ was found by the concentration of about 2.0g sodium chloride per 50 ml solution.
4) Heavy metals such as copper, zinc, lead and manganese caused remarkable influences in every case of the reduct reaction even contained only 10μg per 2.0g sodium chloride. If the contents increases, the effect was more severe, especially for copper and zinc.
For above problems, following procedures were adopted.
i) Reduction temperature was kept at standard 20±1°C.
ii) Magnesium could be removed by pretreatment with sodium hydroxide solution at pH 11.5 without loss of nitrate. However, as the content of magnesium or calcium salts in common salt were generally much less compared with that of. the solid matter of sea water, these treatments were not needed.
iii) Without any loss of nitrate, heavy metals were effectively removed with ferric hydroxide formed by addition of ferric chloride to solution containing common salt at pH 8 to 9.
iv) Copper ion as reduction catalyzer was newly added exactly 15μg per 2.0g of sample treated by above procedure, instead of 10μg which recommended by Mullin and Riley.
From above discussions we proposed a modified procedure for the purpose of common salt analysis, and determined the nitrate contents in various samples of common salts as the same samples as nitrite determination, as well as some byproduct salt. The nitrate contents ranging from o to 0.80ppm (mean value O.15ppm) were slightly more the nitrite contents in domestic salts, and 0-0.50ppm (mean value O.11ppm) in solar salts, but in rock salt the contents were generally much more as an example found 22.5ppm in Chilean salt. In byproduct salt from saltpetre manufactories, up to several thousands ppm were found.

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In this paper, a series of studies, which have been carried out since six years ago, are summarized, with emphasis on the separation of ice-crystals from brine and the formation of solid hydrates of the secondary refrigerant used in this process.
As for the former studies, several basic experiments were firstly perfomed using synthetic resin particles, quartz sand, and glass spheres, respectively, in place of ice crystals. The results suggested the possibility of countercurrent displacement-type washing for the bed of such floating particles as ice crystals in brine in a smoothly-lined column.
As regards to the latter studies, the equilibrium pressure-temperature diagram for the isobutane-water-sodium chloride system over the ranges of the temperature of -5° to +2°C and the pressure of 1.0 to 1.7 atm was firstly established and followed by the similar measurements for the isobutane-one of butene isomers-water system at a given temperature (-0.7°C, conveniently taken). Based on the results, a general drawing method for the approximate equilibrium pressurecomposition diagram was derived from theoretical considerations.

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