Abstract
Rapid routine analyses of free acid, ferrous-and ferric salts in iron pickling liquor have been investigated. For quantitative determination of the free acid, three methods a gravimetric method, a volumetric method of estimating the CO2 evolved, and a titrimetric method of determining the neutrality have been comparatively studied, among which the last method was improved by using a mixed indicator composed of Bromocresol Green-Methyl Red or Methylene Blue-Methyl Red. Interference by the iron was prevented by adding neutral KF or NaF in order to convert it into a colorless or white complex salt, and the titration was made rapidly and accurately with standard NaOH solution. The above method was applied to prepared sample solutions containing 620 % free acid (all in wt. /vol. ), 48% ferrous sulfate, and 14% ferric sulfate. The quantitative determination could be made in 1520 minutes within 2% relative error. Determinations of Fe2+ and Fe3+ were made by the usual KMnO4 method.
