Abstract
The authors conducted a study on the properties of both the FAC which was available on the general market and the FAC which had been prepared by varying the compositions of iron and ammonium. The study aimed at investigating the colors of their aqueous solutions, the color of salt with FAC added, changes in habits of sodium chloride caused by FAC, and the anti-caking effects of the FACs. A further study was made on the decoloration of the commercially available FAC and changes in its anti-caking capacity. The following were the results obtained from these studies:
1. The aqueous FAC solution changed its color from yellowish green to dark brown in accordance with an increase in its pH. The absorbance of the solution at 520 mμ was the minimum at pH 5.
2. When a FAC having a greater absorbance at 520 mμ was used, the color of the salt with the FAC added developed in accordance with the increase of whiteness (ΔR).
3. When treated with active charcoal, the commercial FAC changed its color from brown to yellowish green. and the absorbance of its aqueous solution at 520 mμ became lower. However, no difference was observed in the white ness (ΔR) of the sait with 20-100ppm FAC added, between the treated and untreated ones. When the aqueous solution of the commercial FAC having little anti-caking effect was decolored, the pH of the solution showed a rise according to an increase in the anti-caking capacity.
4. When the aqueous sodium chloride solutions containing FAC at pH 8.5-9.0 were concentrated naturally on a slide glass, fine crystals of sodium chloride were produced. This showed that the TAC had an anti-caking effect of common salt changing habits by impurity. It was also shown by scanning electron microscopic observations that the fine crystals treated with ferrocyanide ions were different from those treated with the FAC.
5. The anti-caking effect of the FAC increased in proportion to the increase of pH, and the absorbance of its aqueous solution at 520 mp showed a rise making brown the color of salt with the FAC added.
