K THE determination of the iron content of various fruit I products and materials utilized in their production, two methods have been used previously by the authors. With dried fruits (6) a dry-ashing was followed by a determination of the iron using the colorimetric thiocyanate method of Stugart (6). In early studies on fruit juices and wines (4) essentially the colorimetric mercaptoacetic acid method of Lyons (3) and Leavell and Ellis (a), with sulfuric and perchloric acid wet-ashing, was used. The latter methods were also used in a study of certain filter aids and asbestos filtering products.The dry-ashing and Stugart procedure require considerable time, so that where several hundred determinations are to be made, a more rapid and simple, yet accurate, method is desirable. For over 2 years an adaptation of the wet-ashing method of Leavell and Ellis has been successfully employed with the usual ashing times of 3 to 7 hours for wines and many fruit juices reduced to periods of 2 to 10 minutes for each sample.Because of the difficulty in color comparison with concentrations lower than 2 or 3 parts per million (p. p. m.) and the occasional fading of the mercaptoacetic acid colored complex, it appeared desirable to have a method of equal or greater sensitivity and accuracy, with a higher degree of precision. ExperimentalIt has been pointed out by Walden, Hammett, and Chapman (7) that the ferrous o-phenanthroline complex ion discovered by Blau (1) may be used as a reversible oxidation indicator of high potential. The ferrous complex gives an intense red color.The authors have observed that the color, when once formed in slightly acid to neutral solutions, is very stable and standards have been kept for over 4 months without exhibiting differences from freshly prepared standards, Solutions containing a final iron concentration of 1 to 10,000,000 give color of sufficient intensity for colorimetric comparison. For iron concentrations of the same magnitude, the intensity of the color is proportional t o the iron content. Concentrations of greater than 20 or 25 p. p. m. may be conveniently diluted by one-half, or smaller samples may be taken for analysis.As the iron in the strongly acid solution remaining from the wet-ashing is in the ferric condition, reduction to the ferrous condition before the addition of the o-phenanthroline is necessary. Several reducing agents were studied, the best being sodium hypophosphite or hypophosphorous acid, and sodium formate, which were discontinued because of the considerable iron content of these products and the necessary correction therefor. The use of a concentrated solution of iron-free hydroxylamine hydrochloride has been adopted.Numerous experiments were made to ascertain the most satisfactory procedure and conditions for the addition of the reagents, As a result it was observed that a treatment of the warm acid solution (remaining from the wet-ashing) with hydroxylamine, followed by the addition of o-phenanthroline and neutralization with concentrated ammonium

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