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CIRCULAR 205, U. S. DEPARTMENT OF AGRICULTURE 



value were few, the analysis of a large variety of common vegetables 

 and fruits was undertaken. 



This circular presents the results of the author's analyses of 237 

 specimens of 82 different forms, parts, or varieties of vegetables and 

 fruits, and also data from the literature which appear trustworth}^ and 

 representative. In presenting other data for purposes of comparison 

 and compilation, the author has included figures only when it was 

 apparent from the reports that the determination of iron was the 

 major concern of the analyst and that the work was conducted under 

 laboratory conditions adapted to precise iron determinations. 



METHOD OF ANALYSIS 



The technique of iron determination is exacting, and many of the 

 errors frequently attending the analysis lead to an overestimation of 

 the quantities present. Contamination of the samples with iron is 

 often a large source of error, as was emphasized by Bunge (4) many 

 years ago. All the analyses made by the author were conducted in a 

 new and specially equipped laboratory containing practically no iron 

 fixtures or apparatus. Special care was exercised to prevent con- 

 tamination of the samples. The laboratory was kept as free as pos- 

 sible from dust and currents of air, since laboratory dust is likely to be 

 very rich in iron. Only instruments and vessels made of silver, 

 nickel, platinum, silica, or glass, and thoroughly cleansed immediately 

 before being used, were used in contact ^Yith the samples. 



Approximately 50 grams of the fresh edible portion of each food 

 material was ashed without preliminary drying, at low red heat in 

 platinum or new siHca dishes. Extraction was made when necessar}^ 

 with hydrochloric or acetic acid to facilitate the access of air to the 

 last traces of carbon. Special care was taken to guard against 

 excessive temperatures in ashing which might permit volatilization of 

 iron as ferric chloride. Precautions were also taken to prevent con- 

 tamination mth iron from dust, and to prevent the inclusion of 

 minute amounts of platinum salts from the dishes used in burning the 

 samples. 



The ash was dissolved in hydrochloric acid and the iron deter- 

 mined by the Zinamermann-Reinhardt method, essentially as described 

 by Fales (8). Since the samples contained but small amounts of iron, 

 and the quantities of reagents used were small, the final titration with 

 a very dilute standardized solution of potassium permanganate was 

 carried out in a correspondingly small final volume (about 50 cubic 

 centimeters). The amount of permanganate required to oxidize any 

 traces of iron in the reagents, together with that requhed to give a 

 perceptible end point in the titration was determined, and allowed for 

 in the calculation of the result of each analysis. Each specimen was 

 analyzed in duplicate or in triplicate. 



The Zimmermann-Reinhardt method is rapid but requires con- 

 siderable care and some experience in manipulation. It is convenient 

 for use in analyzing the ash of vegetables and fruits in that the reduc- 

 tion and titration of iron are made in the presence of hydrochloric acid. 

 The methods used by other investigators for determining iron can be 

 learned from the references cited, except for that of Sheets, who 

 employed the method of Kennedy (11) modified to correct for the 

 variability in the acidity of solutions of oxidized products. 



