January 15, 1935
ANALYTICAL EDITION
involved. The action of these ions on cacotheline has been noted by Leuchs and co-workers (3, 6). A water solution of the bisulfite ion at concentrations above 0.0001 M decolorized 0.1 cc. of the cacotheline reagent, while in hydrochloric acid solution even at the maximum concentration (0.01 M ) no change of color was noticed until after 15 minutes, when a detectable amethyst color was observed. The hydrosulfite ion in water solution at concentrations below 0.0001 M caused no change in the cacotheline color, but from 0.0001 M to 0.001 M the cacotheline color was destroyed. From 0.001 M to 0.005 M a fu ‘tive amethyst color of 15 minutes’ duration developed, while %om 0.005 M to 0.01 M destruction of the cacotheline color again occurred. In hydrochloric acid solution at concentrations up to 0.0001 M there was no change in the cacotheline color. Above this concentration a fugitive amythyst color of approximately 15 minutes’ duration was produced and at concentrations approaching 0.01 M amorphous sulfur was precipitated. The sulfite ion in water solution produced no change in the cacotheline color. In hydrochloric acid solution a concentration of 0.01 M caused a detectable amethyst color after 15 minutes. Lower concentrations produced no change in color. Among the substances that interfere with the cacotheline test are oxidants, such as the mercuric, chromate, and chromic ions, and nitric acid. Reductants, such as the titanous, sulfite, hydrosulfite, and bisulfite ions, interfere when present in small concentrations. Colored ions, such as the cobaltous, cupric, cuprous, ferric, nickelous, and vanadate ions, interfere when present in sufficient concentrations. Certain other ions, such as molybdate, react with the stannous tin and prevent the test.
27
Where the maximum concentration used (0.01 M ) gave no interference, there was no indication that there would be interference in higher concentrations, except in the case of the antimonous and hypophosphite ions. CONCLUSIONS The cacotheline test for tin cannot be regarded as specific, although it should prove useful for the detection or confirmation of the presence or absence of small amounts of tin where the conflicting substances are either absent or have been reduced in concentration to below those noted in Table I. The presence of hydrochloric acid was found to increase the sensitivity of the test. The maximum sensitivity of the cacotheline test for tin was found to be from 1 to 2 parts per million. LITERATURE CITED Feigl, F., “QualitativeAnalyse mit Hilfe von Tupfelreaktionen,” Leipzig, Akademische Verlagsgesellschaft, m. b. h., 1931. Gutzeit, G., Helv. Chim. Acta, 12, 720 (1929). Leuchs and KBhrn, Ber., 55,724 (1922). Leuchs and Leuchs, Ibid., 43,1042 (1910). Leuchs, Osterburg, and Kahm, Ibid., 55,664 (1922). Leuchs, Winkler, and Leuchs, Ibid., 55,3936 (1922). RECEIVED July 16, 1934. Presented before the Division of Physical and Inorganic Chemistry at the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 to 14, 1934. The preliminary experiments in this investigation were carried out by the senior author at the laboratory of the Henry Souther Engineering Co., Hartford, Conn.
Spectrophotometric Determination of Manganese in Steel J. P. MEHLIG,Oregon State College, Corvallis, Ore.
A
NUMBER of methods have been worked out for the
colorimetric determination of manganese, based upon the oxidation of the manganese to permanganate and comparison of the color of the resulting solution with the colors of a series of standard permanganate solutions. The oxidation has been accomplished in various ways, the most important of which are by the use of sodium bismuthate (2), ammonium persulfate in the presence of silver nitrate (11,17), lead dioxide ( 1 4 , and potassium periodate (18). Permanganate color standards, with the exception of those made by the periodate oxidation, are not stable enough to permit making permanent standards which may be used day after day in routine analyses. Hence the writer proposed to avoid their use entirely by the development of a spectrophotometrie method for manganese. The spectrophotometric method depends upon the fact that the percentage transmittancy of light a t a given wave length for a permanganate solution is a function of the manganese concentration. If a reference curve is constructed by plotting the percentage transmittancy a t the given wave length of a series of standard permanganate solutions against the known manganese concentrations, it should be possible to convert the percentage transmittancy of an unknown permanganate solution into manganese concentration by use of the curve. Main and Locke (10) have determined protein nitrogen similarly by measuring the light absorption at a given wave length of the nesslerized solution and converting this value into milligrams of nitrogen per 100 ml. by use of their reference curve relating absorption with concentration. Davis and Sheard (3) have determined hemo-
globin in blood spectrophotometrically, and recently Sanford, Sheard, and Osterberg (16) have described an instrument called the photelometer, by use of which the intensity of the light transmitted by a colored solution is correlated with the concentration of the constituent responsible for the color. With it they have determined hemoglobin, blood sugar, and creatinine. Using a Pulfrich spectrophotometer in a somewhat similar manner, Pucher, Vickery, and Wakeman (16) have determined malic acid in plant tissues.
SEPARATION AND DETERMINATION OF MANGANESE In applying the spectrophotometric method to the determination of manganese in steel it was necessary to find a satisfactory procedure for separating the manganese from iron and other color-producing metals, since the color caused by the presence of these metals in the solutions would modify the transmittancy of the permanganate solution. Addition of phosphoric acid to decolorize the iron was not advisable, since this acid interfered with the bismuthate oxidation (7) and did not decolorize any chromium, nickel, or cobalt that might be present. Precipitation of the manganese as hydrated manganese dioxide by boiling with potassium or sodium chlorate in concentrated nitric acid solution (1, 4) proved to be very unsatisfactory, as much of the manganese was left in solution. A modification of this method as proposed by James (6) was likewise unsatisfactory, for in addition to incomplete precipitation of the manganese there was an unaccountable oxidation to permanganate. After slight modification, von Knorre’s method (6, 8) gave
Vol. 7, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
28
excellent results. It makes use of the fact that hydrated manganese dioxide is precipitated when manganous sulfate is boiled with a large excess of ammonium persulfate in 1 to 50 sulfuric acid solution. Zinc, chromium, nickel, cobalt, and moderate amounts of tungsten, molybdenum, or phosphorus I100
I
540, and 560 mp were determined on another portion of the permanganate solution in a 5-cm. tube using the Keuffel and Esser color analyzer described by Mellon and Martin (18) and used by the writer in previous work (12). All data were obtained by setting the instrument for the desired wave length and reading the percentage transmittancy direct. The value recorded for each setting represented the average of five readings, among which the greatest variation was not more than 0.5 per cent. By use of reference curves (Figure 1) the concentrations of manganese were read off and the percentage of manganese was calculated. The results are given in Table 11. TABLEI. RESULTS OBTAINIOD BY VON KNORRE-BISMUTHATE TITRATION METHOD BUREAUOF STANDARDS SAMPLE TYPEOF STEIBL
MANGANEBE Certificate value Found
10d 130
15a 16a
21a 23a 30a
DIFFERENCE
%
%
%
0.915 0,700 0.372 0.264 0.621 0.634 0.805
0.913 0.703 0.363 0.266 0.621 0.638 0.813
-0.002 +0.003 -0.009 +0.002 0.000 $0.004 +0.008
(1.02% Cr, 0.21 V) -0.001 A 0 H 08%z 0.501 0.500 -0.008 0.300 A: 0 : H:: 1% C 0.292 +0.002 0.437 B 0 H 03v C 0.439" 8c 0.381 0.000 0.381s 16b B: 0: H:: 1% Determination made by T P. Marsh, student at Oregon State College. Determination made by C.' M. Kelley, student at Oregon State College.
34s 35
6
0
b
OBTAINEDBY SPECTROPHOTOMETRIC TABLE11. RESULTS METHOD (Permanganate solution made up to 1000 ml. and second dilution made as shown when necessary) BUREIAU MAN- SOLD OF GANEBE TION AVEIRAGE STAND- CEIR- DILUTEID MANGANEIBEI OBTAINEDFROM MANARDB TIFICATEI TO 100 TRANBMITTANCY AT GANEBE DIFFEIRSAMPLEVALUE ML. 500 mp 520 mp 540 mp 560 mp FOUND ENCE
% 10d 130 15a Ma 21a 23a 30a 3423 35.
% irunsmhmcy FIGURE1. REFERENCECURVESRELATING OF MANGANESE AND TRANSCONCENTRATION MITTANCY OF LIGHTAT 500 AND 520 MP OF PERMANGANATE SOLUTION IN A 5-cM. TUBE
The ourvea for 540 and 560 mp are aimilar to those for 500 and 520 mp.
do not interfere (8). The modification consists in the use of two additional 5-gram portions of persulfate, followed by boiling periods of 5 and 10 minutes, respectively. Yon Knorre used a total of only 15 grams of persulfate, but this amount failed to give complete precipitation in the present work. The manganese dioxide precipitate after filtration on a Gooch crucible was dissolved by reduction with sodium bisulfite in nitric acid solution. The manganese was then oxidized to permanganate with sodium bismuthate in the cold, and, after filtration on a Gooch crucible to remove the asbestos and excess bismuthate, the permanganate filtrate was made up to 1000 ml. a t 25" C. To test the completeness of the separation of the manganese from the iron, the manganese was determined titrimetrically, using an aliquot of the solution, by adding excess standard solution of Mohr's salt and titrating the excess with 0.05 N solution of potassium permanganate. The results obtained on Bureau of Standards steel samples are given in Table I. The transmittancies of light at wave lengths of 500, 520,
0.915 0.700 0.372 0.264 0.621 0.634 0.805 0.601 0.300
M
L
50.03 50.03 None None 50.03 50.03 50.03 50.03 None
. 0.908 0.699 0,362 0.262 0,624 0.634 0.804 0.500 0.292
% 0.904 0.699 0.363 0.262 0.619 0.635 0.799 0.500 0.292
%
%
0.913 0.697 0.361 0.260 0.620 0.635 0.804 0.600 0.291
% 0.912 0.699 0.363 0.260 0.619 0.636 0.804 0.499 0.291
% 0.909 0.699 0.362 0.261 0.621 0.636 0.803 0.500 0.292
% -0,006 -0,001 -0.010 -0.003 0.000 +0.001 -0.002 -0.001 -0.008
PROCEDURE The procedure is a combination of the von Knorre (6) and bismuthate (9) methods. Weigh accurately about 2 grams of sample and transfer to a 500-ml. beaker (tall form preferred). Dissolve in 50 ml. of 1 to 9 sulfuric acid, warming to hasten solution. As soon as the steel has dissolved, dilute to 250 ml., add 10 grams of ammonium per' sulfate, cover with a watch lass, and boil on the hot plate 10 minutes, If neither pink coyor nor brown precipitate appears, keep adding small portions of persulfat,e and boiling. Let cool slightly, add 5 grams more persulfate, and boil 5 minutes, Let cool, add 5 grams more persulfate, and again boil 5 minutes. Let cool, add another 5 grams of persulfate, and boil 10 minutes. Cool to room temperature and filter on a Gooch crucible containing an extra thick pad of asbestos. If the filtrate is not absolutely clear, refilter it through the same pad. Wash the beaker and the residue thoroughly with a 2 per cent solution of ammonium persulfate and finally once with cold water. Transfer the asbestos pad with the residue to the beaker in which the precipitation was made, cover with water, stir, and add a few millimeters of 1 to 3 nitric acid and just enough solid sodium bisulfite to dissolve all the manganese dioxide. Place the crucible in the beaker and after any adhering Pecipitate has been dissolved remove and rinse the crucible. l d d 50 ml. of 1 to 3 nitric acid, followed by 0.5 gram of sodium bismuthate, and agitate. Let stand 3 minutes, add 50 mI. of 1 to 97 nitric acid, and filter on a Gooch crucible, washing the residue with the same dilute nitric acid (at least 50 ml.) until washings are entirely colorless. Transfer the filtrate to a liter volumetric flask, make up t o the mark at 25" C., and mix thoroughly.
ANALYTICAL EDITION
January 15, 1935
By means of the spectrophotometer determine the percentage transmittancy of this solution in a 54m. tube at 500, 520, 540, and 560 mp. If the permanganate solution contains more than 10 mg. of manganese per liter, it will be too opaque for a transmittancy determination and a measured portion of it must be suitably diluted at 25” C. From the respective reference curves read off the milligrams of manganese per liter corresponding to the transmittancies and calculate percentage of manganese for each case, taking into account any extra dilution that was made. Take the average of these values as the percentage of manganese in the sample. NOTES. 1. All free carbon left when the steel is dissolved is completely oxidized by the persulfate. 2. In dissolving the manganese dioxide by use of bisulfite care must be taken to insure complete solution. Any remaining brownish black particles should be disintegrated with a stirring rod. 3. Removal of the small excess of sulfur dioxide by boiling after the solution of the manganese dioxide is not necessary, since sodium bismuthate oxidizes it along with the manganese. 4. The 1 to 3 and 1 t o 97 nitric acid solutions must be free from nitrous acid, which interferes with the bismuthate oxidation (7). They are repared by dilution of concentrated nitric acid which has been \oiled for 1 minute, cooled somewhat, and then aerated by suction until perfectly colorless.
REFERENCE CURVES Data for plotting the reference curves were obtained by determining the light transmittancies in a 5-em. tube a t 500, 520, 540, and 560 mp of a series of solutions prepared by diluting to 250 ml. a t 25” C. various volumes of a solution of potassium permanganate that had been standardized against sodium oxalate of known purity. Each transmittancy was determined as soon as the solution had been prepared. Collins and Foster (2) state that, since sodium bismuthate oxidizes manganese perfectly to permanganate, a solution of potassium permanganate of known strength is as useful as a manganous sulfate solution for the preparation of standards and that there is no advantage in reducing the permanganate solution and using this reduced manganese for the preparation of standards with nitric acid and sodium bismuthate. Reference curves (Figure 1) were constructed from the data in Table I11 by plotting the milligrams of manganese per liter as ordinates against the transmittancies a t the given wave length as abscissas. These data are applicable to other spectrophotometers only in case the same values are obtained on similar, known solutions. TABLE111. DATAFOR CONRTRUCTION OF ~ F E R E N C E CURVXIS TRANSMITTANCY AT
MANQANESE
500 mp
520 mp
540 mp
Md1. 10.02 8.91 8.27 7.80 7.37 7.13 6.68 6.24 6.02 6.79 6.57 6.35 5.12 4.92 4.46 3.79 3.34 2.90 2.23
%
%
%
560 m p
%
4.0 5.9 7.4 8.2 9.5 10.1 12.4 13.3 14.1 15.1 17.8 18.3 19.8 20.8 23.7 27.8 31.9 35.8 47.1
1.0 1.8 2.2 3.0 3.6 4.0 5.0 5.6 6.0 6.9 7.9 8.7 9.2 10.1 12.9 16.8 21.1 24.2 34.1
1.2 2.0 2.4 3.2 3.8 4.2 5.2 5.8 6.3 7.1 8.4 9.0 9.5 10.5 13.3 17.1 21.7 25.1 35.1
5.3 7.7 9.2 10.3 11.7 12.3 14.3 16.1 17.0 18.0 20.6 21.1 22.0 23.0 26.0 31.7 35.7 39.9 49.8
As a further test of the sDectroDhotometric met od. the manganese was determined in-two series of solutions of potassium permanganate made by dilutions of a standard solution at 25” C. These results are shown in Table IV. Twentythree such solutions, in which the manganese concentration ranged from 2.93 to 6.69 mg. per liter, were analyzed with a precision of -0.07 to +0.09 mg. per liter. In six cases there was no deviation from the calculated value.
29
TABLE IV. RESULTSOBTAINED BY SPECTROPHOTOMETRIC METHOD MANQANESE
AVB:RAQE
MAN-
MAN-
QANESE
QANESE
AVERAGEJ MANQANESR
PRESENT FOUNDDIFFERENCE PRESENTFOUNDDIFFERENCE Mg./l. Me./1. Me. Mu./l. Mu./l. Mu. .. .. 2.93 2.94 +O.~Ol 6.97 6.96 -0.01 3.35 3.31 -0.04 7.25 7.25 0.00 3.63 3.63 0.00 7.66 7.64 -0.02 3.90 3.93 +0.03 8.36 8.44 +o.os 4.18 4.18 0.00 8.64 8.66 +0.02 4.46 4.45 -0.01 4.01 4.00 -0.01 4.74 4.75 $0.01 4.68 4.75 +0.07 5.02 5.02 0.00 5.01 5.01 0.00 5.30 5.28 -0.02 5.35 5.30 -0.05 5.58 5.53 -0.05 6.02 6.02 0.00 6.31 6.40 6.69 6.62 +0.09 -0.07 6.69 6.64 -0.05
SUMMARY Manganese can be practically completely separated from iron and the other metals usually occurring in steel by precipitation as hydrated manganese dioxide with excess ammonium persulfate in boiling 1 to 50 sulfuric acid solution. The spectrophotometric method when carefully carried out is capable of giving results for manganese in steel that are within kO.01 per cent of the correct value. For manganese in solution the precision is about *O.l mg. per liter. Although concentrations of manganese below 2 mg. per liter may be read directly from the curves, it is advisable either to increase the sample weight or to make the permanganate solution up to a volume less than 1liter that will call for use of the more nearly vertical portion of the curves. The method may be carried out in a comparatively short time and has the advantage over the colorimetric methods of requiring no color standards. However, it has no advantage over the volumetric bismuthate method; the two methods are to be regarded as alternate procedures. ACKNOWLEDGMENT The writer wishes to express his sincere appreciation to
M. G. Mellon, Department of Chemistry, Purdue University, in whose laboratory the greater part of this investigation was carried on, and to thank him for the use of the Purdue spectrophotometer. LITERATURE CITED (1) Beilstein, F., and Jawein, L., Ber., 12, 1528 (1879). (2) Collins, W. D., and Foster, M. D., IND.ENQ.CHEM.,16, 586 (1924). (3) Davis, G. E.,and Sheard, C., Arch. InternaE Med., 40, 226 (1927). (4) Ford, S. A., Trans. Am. Inst. Mining Engrs., 9, 397 (1881). (5) James, L. H., IND.ENQ.CHBM.,Anal. Ed., 3,31 (1931). (6) Xnorre, G. yon, Z. angew. Chem., 14, 1149 (1901); 16, 905 (1903). (7) Lundell, G. E. F., Hoffman, J. I., and Bright, H. A., “Chemioal Analysis of Iron and Steel,” p. 192, New York, John Wiley & Sons, 1931. (8) Ibid., p. 206. (9) Mahin, E. G., “Quantitative Analysis,” p. 509, New York, McGraw-Hill Book Co., 1932. (10) Main, E. R., and Locke, A. P., J . Biol. Chem., 64,75 (1925). (11) Marshall, H., Chem. News, 83,76 (1901). (12) Mehlig, J. P., with Mellon, M. G., J. Phys. Chern., 33, 3400 (1931). (13) Mellon, M. G., and Martin, F. D., Ibid., 31, 161 (1927). (14) Peter, S., Chem. News, 33, 35 (1876). (15) Pucher, G. W., Vickery, H. B., and Wakeman, A. J., IND.ENQ. CHEM.,Anal. Ed., 6, 289 (1934). (16) Sanford, A. H., Sheard, C., and Osterberg, A. E., Am. J . Clin. Path., 3, No. 6,405 (1933). (17) “alters, H. E., Chem. News, 84,239 (1901). (18) Willard, H. H., and Greathouse, L. H., J . Am. Chem. SOC.,39, 2366 (1917): J . Soc. Chern. Ind., 37,41A (1918). R ~ C E I V EAuguat D 26, 1834.
