Estimation of Small Amounts of Bismuth, Antimony, Tin, and Molybdenum in Copper BARTHOLOW PARK,Michigan College of Mining and Technology, Houghton, Mich. NUMBER of methods for separating small amounts of bismuth from large amounts of copper have been proPosed- Those generally used depend upon separation of the bismuth as a basic salt, which may be nitrate, sulfate, chloride, or bromide in a slightly acid solution, or upon the formation of an insoluble carbonate or phosphate in ammoniacal solution. I n the latter case iron is Usually added to help collect the precipitated bismuth. Most of these methods work satisfactorily for comparatively large amounts of hismuth bu,t are not sufficientlysensitive for extremely small amounts.
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(about 30 minutes), allowed to stand until the precipitate settled out, and then filtered through a No. 4 Jena glass filter. The precipitate was washed with a little water, and the combined filtrate and washings were treated with potassium bromide and permanganate as before. After settling, the solution was filtered and the combined preci itates were dissolved with 50 CC. of hot concentrated hydrochzric acid. The pH of the filtrates varied between 2.0 and 2.6. The hydrochloric acid solution was concentrated to about 30 cc., neutralized with ammonium hydroxide, acidified with 1 cc. of concentrated hydrochloric acid, diluted to 100 CC., heated to boiling, and treated with hydrogen sulfide until precipitation was complete. The sulfides were filtered out on a glass filter, washed with water, and dissolved with 25 cc. of hot concentrated nitric acid, followed by 10 cc. of hot concentrated hydrochloric acid. The solution of sulfides was evaporated to about 5 cc., 10 cc. of hydrochloric acid were added, and the solution was evaporated to 3 or 4 CC. It was diluted to exactly 5 cc., and portions of this concentrate were used to impregnate graphite electrodes which were dried in an oven at 100" C. and subsequently arced to give spectrograms. These spectrograms were compared with others made from solutions containing known amounts of bismuth, tin, antimony, and molybdenum, according to the procedure described by Nitchie (8).
FIGURE1. SPECTROGRAMS OF STANDARD SOLUTIONS
In a previous paper (3) it was shown that antimony may be separated from copper by precipitating manganese dioxide in the slightly acid solution. During this work it was noticed that bismuth accompanied the antimony and manga-
Tin, antimony, and molybdenum are quantitatively precipitated along with the bismuth. Thif was proved in the following manner:
Three consecutive precipitations of manganese dioxide were made in a solution of 100 grams of refined copper. Practically all the antimony, tin, and bismuth were found in the first preci inese dioxide, but recent experiments have shown that its Pre- tate. Traces of antimony, tin, and bismuth were found in t i e cipitation is not quantitative. Bismuth was found spectro- second precipitate, but the third precipitate was spectroscopically graphically in each of three consecutive manganese dioxide free from all three elements. TOthe filtrate from the third precipitation was added 0.1 mg. of each of the four impurities, and precipitatesthrown out o f liter of copper nitrate solution three more consecutive precipitations were then made. The first t o which had been added 2 mg. of bismuth. precipitate contained all four elements. The second contained a Moser and Maxymowicz (1) have shown that the precipita- trace of tin but no trace of the other three. The third was spectrotion of bismuth oxybromide by means of potassium bromate- scopically free from all four. potassium bromide mixtures is capable of detecting about 0.3 mg. of bismuth [n 100 cc. of solution. They also have succeeded in separating 13 mg. of bismuth from about 13 grams of copper, although their error was large (13 mg. added, 20 mg. found). By combining the precipitation as oxybromide with a simultaneous precipitation of manganese dioxide it is possible to separate less than one part of bismuth from a million parts of copper. One hundred grams of copper were boiled with concentrated hydrochloric acid, washed with distilled water. and dissolved in 400 cc. of cencentrated nitric FIGURE2. SPECTROGRAMS FROM SAMPLES AND BLANK acid. The solution was evaporated to dryness on a steam bath, diluted with 1 liter of water, heated to boiling, and treated with 1 N sodium carbonate solution until This procedure was repeated with the addition of 2 mg. of each a slight permanent precipitate formed. This was dissolved by impurity. The results were practically the same. All the imthe addition of 1 cc. of concentrated nitric acid. To the clear purities were found in the first and second precipitates, but none boiling solution were added 10 cc. of 20 per cent potassium bro- in the third. mide solution (a precipitate of silver bromide usually formed at this Silver and arsenic precipitate along with the other elements, point), and 10 cc. of 3 per cent potassium permanganate solution. but no experiments were performed to ascertain whether or not At this oint manganese dioxide precipitated and bromine was the precipitation is complete. A little lead also was found in the liberatecf The solution was boiled until free from bromine final concentrate but experiments showed that precipitation was 89
190
ANALYTICAL EDITION
not quantitative. Lead was found in each of three consecutive precipitations brought down in the manner described above. I
A number of samples of refilled copper from various sources were analyzed, with the results shown in Table I. TABLE I. ANALYSISOF REFINEDCOPPER SAXPLE ANTIYONY
% 1 2
0.00013
TIN
BISMUTH
%
%
MOLYBDENUM % None None None None None 0.00015
0.00017 0.0045 0.0005 0.0015 0.00016 0.0013 0.0012 0.00015 0.0004 0.00007 0.0002 0.0003 0.00002 0.00018 < 0.00001 0.00018 0.00004 7a 0.00017 < 0.00001 0.00018 0.000025 8 0.00005 0.00005 < 0.00001 9 None 0.0001 10 0.00008 < 0.00001 0.00015 < 0.00001 11 0.00005 0.00001 Blank None None a An unmelted cathode deposited from a leached aolution.
3 4 5 6a
0.002
0.0005 None None None None None
Figure 1 shows a number of spectrograms of the standard solutions, using 0.1 cc. for each exposure. Concentrations are given in milligrams per 5 cc. Figure 2 shows spectro-
Vol. 6 , No. 3
grams made from the samples tested and the blank obtained by electrolyzing the filtrate from sample 9, dissolving the deposit in nitric acid, and treating as a sample. Some platinum was dissolved from the electrode in the process, as may be seen. The section of $he spectrum shown in the figures extends from about 2590 A. on the left to 3200 A. on the right, and includes the most persistent lines of all of the elements sought. ACKNOWLEDGMENT The author wishes to thank for their cooperation the Copper and Brass Research Association and the many copper refiners who furnished the samples. LITERATURE CITED (1) Moser and Maxvmowicz. Z . anal. Chem.. 67. 248 (1925-26). (2) Nitchie, IND.ENG.CHEM.,Anal. Ed., 1, 1 (1929). (3) Park and Lewis* RECEIVED December 9, 1933.
Determination of the Acids of Plant Tissue 111. Determination of Citric Acid GEORGEW. PUCHER, HUBERTBRADFORD VICKERY,AND CHARLESS. LEAVENWORTH Connecticut Agricultural Experiment Station, N e w Haven, Conn. It was obvious that a voluITRIC acid, when treated Citric acid is oxidized to pentabromoacetone metric method to d e t e r m i n e with potassium permanby potassium permanganate in the presence of pentabromoacetone w o u l d b e ganate and p o t a s s i u m potassium bromide. The oxidation product is n e c e s sa r y . Accordingly, the bromide under the proper conextracted by petroleum ether, dehalogenated by authors have studied s e v e r a l ditions, is converted into the sodium sulfide, and the bromide ion produced is procedures w h e r e b y this subinsoluble substance pentabromostance can be dehalogenated a c e t o n e . T h i s reaction was titrated with silver nitrate. Quantities of citric and the h a l o g e n determined. originally employed by Stahre acid of the order of 1 to 20 mg. can be determined Kometiani (b) has described a (6) for the qualitative r e c o g in this manner with a n accuracy of =t$ per cent. method for the dehalogenation n i t i o n of citric acid, but was Malic acid alone of the common organic acids of pentabromoacetone by warm placed upon a quantitative basis interferes in a n y way with the determination, alcoholic sodium iodide in the by the work of Kunz (4),and of presence of acetic acid. A careHartmann and Hillig ( 1 ) ; it is and the error introduced by the presence of this ful investigation of this reaction now widely used for the detersubstance is ordinarily so small as to be negligible. showed that quantitative results mination of citric acid in plant Inasmuch a s the conversion of citric acid to could be obtained only under the tissues. I n order to obtain trustpentabromoacetone is not quantitative, although most r i g i d l y controlled condiworthy results with the method in constant proportion under the conditions tions; in the authors’ hands the as described by Hartmann and conditions described by KometiHillig, it is desirable to subject described, it is necessary to employ a correction ani invariably yielded results a t least 50 mg. of citric acid factor in the calculation of the results. This from 30 to 40 per cent too high. to the oxidation; furthermore, factor is approximately 1.12. Furthermore it was observed the transfer of the precipitate that D e n t a b r o m o a c e t o n e is to t h e filter, a n d t h e s u b s e quent washing and drying, require the most careful attention unstable in ethyl alcohol solution. The reaction was not investigated in detail, but within 3 hours a t least 15 per cent of to details of technic. Although of great value for many types of analytical the pentabromoacetone in a 0.035 per cent solution of this studies, Hartmann and Hillig’s method is seriously limited in substance in alcohol had been converted to a product that usefulness for the investigation of citric acid metabolism was no longer dehalogenated by sodium iodide; after 72 owing to the large amount of citric acid required for accurate hours the conversion was greater than 75 per cent. Inciresults. Nevertheless the specificity of the oxidation re- dentally it was noted that pentabromoacetone is unstable in action upon which it is founded makes it the method of ether solution also, but it appears to be stable when dissolved choice for the determination of citric acid. The authors in chloroform or in petroleum ether. If a freshly prepared solution of pentabromoacetone in have therefore sought to improve the pentabromoacetone method so that the filtration, with its attendant and necessary alcohol is treated with silver nitrate, a precipitate of silver solubility correction, may be avoided and trustworthy results bromide separates in a few minutes a t room temperature. A study of this reaction showed that it was entirely unsuited may be secured on relatively small quantities of citric acid.
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