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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.

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The authors have devised a new method for the determination of small amounts of sulfate. Sulfate is precipitated as barium sulfate using barium chromate suspension in an acid solution (0.5 M acetic, 0.01 M hydrochloric acid), and the excess of barium is almost completely precipitated as barium chromate by adding ammonia water (containing calcium ion) and ethanol. Finally the amount of chromate which is exchanged with sulfate is estimated. The proposed method may be applicable to the determination of 0.3–100p. p.m. sulfate with satisfactory results.

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