A new spectrophotometric method suitable for the determination of a small amount of chloride using iron alum solution in nitric acid solution, and mercuric thiocyanate solution in a mixture of dioxane and alcohol solution has been established.
The calibration curves conform to Beer’s law at concentrations up to 50 p. p. m. of chloride. The calibration curves are reproducible within ±1% for the range of 5-80 p. p. m. Cl− (Procedure A), and within ±0.05 p. p. m. for the range of 0.05-5 p. p. m. Cl− (Procedure B). As the calibration curves are affected by temperature, it is necessary to measure the absorbance always under the same conditions of temperature in order to achieve good accuracy.
The colored solution is stable. A very small volume of the sample solution such as 5 cc. or 2.5 cc. is good enough for the determination. Interfering substances are few, because this method is carried out in acid medium. Br−, I−, CN−, SCN−, S2−, S2O32−, BrO3−, [Fe(CN)6]4− and [Fe(CN)6]3− interfere, but usually they are not present in natural waters in concentrations that would give a serious error.
This simple method is suitable for rapid determinations, because it is unnecessary to control pH or filter the precipitate. It is suggested that this method can be widely applied to the determination of chloride in waters, rocks, etc.
The halogen contents of 49 Japanese volcanic rocks are; F: 50–1700 (average 410), Cl: 17–1220 (av. 270), Br: 0.09–8.10 (av. 0.85), I: 0.011–0.32 (av. 0.088) μg/g. The fluorine and chlorine were determined by usual photometric methods, and the bromine and iodine, by photometric methods based on their catalytic action, after decomposition and separation procedures suitable for each case. The bromine and iodine contents are appreciably lower than the values generally accepted for igneous rocks. The bromine content agrees with Sugiura’s value. The frequency distribution of each halogen content shows an approximate lognormality. The chlorine and bromine contents are strongly correlated, and the Br/Cl atomic ratio is in a narrow range (0.66–3.7)×10−3 (av. 1.5×10−3). No other correlation is observed among the halogen contents at all. Each halogen content has no marked relation to the type of rock. A regional difference is seen in the F/Cl and I/Br ratios. Three ultrabasic rocks have very low fluorine (≤20) and chlorine contents (≤50 μg/g). On the other hand, they have a slightly lower bromine content (0.15–0.34 μg/g) than, and almost the same iodine content (0.07–0.13 μg/g) as, the volcanic rocks.
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