159
V O L U M E 19, NO. 3, M A R C H 1 9 4 7 Table 11. Analysis of Allyl Sucrose and Allyl Starch Method 1-hour bromine method 2-hour bromine method 3-hour bromine method Rapid Wijs 1-hour Wijs Rosenmund a n d Kuhnhenn Iiaufmann
Allyl Sucrose Iodine KO. D.S. 268.3,268.1 6.25 270.6,269.6 6.32 271.0,272.2 6 . 4 2 273.0,274.0 6.45 272.1,271.3 6.42 269.1,264.3 6.30 6.10 231.3,233.8 4.95
Allyl Starch Iodine KO. D.S. 183.8,181.7 1.62 180.6,181.0 1.60 180.4,180.5 1 . 6 9 176.7,177.4 1.55 175.8,176.6 1.54 174.6,175.6 1.53 143.5,152.5 1.23
It is of interest that the Rosenmund and Kuhnhenn method gave results which differed from the theoretical values by approximately 1%, since Earle and Milner ( 2 ) found that this method gave results appreciably low for all vegetable oils having iodine numbers greater than 100. In all instances the Kaufmann method gave results approximately 10% lower than theoretical or the average of the other methods. The degree of substitution for triallyl glycerol as calculated from the iodine values varied between 2.90 and 2.96, with the rapid Wijs method giving the degree of substitution of 2.96.
In applying these methods to the determination of the degree of substitution of allyl starch and allyl sucrose the iodine values were in good agreement, as were the degree of substitution values. LITERATURE CITED
Official Agr. Chem., Official and Tentative Methods of Analysis, p. 90 (1940).
(1) hssoc.
Earle, T. R., and Milner, R. T., Oil & Soap, 16,69 (1939). (3) Hoffman,H. D., and Green, C. E.,I b i d . , 16,236 (1939). (4) Kaufmann, H. P., and Hartwig, L., Ber., 70B,2554 (1937). ( 5 ) McCutcheon, J. W., IND.ENG.CHEM.,AKAL.ED.,12, 465 (1940). (6) Xichols, P. L., Jr., Hamilton, R. >I., Smith, L. T., and Yanovsky, E., l n d . Eng. Chem., 37, 201 (1945). (7) KJichols,P. L., Jr., and Yanovsky, E., J . Am. Chem. SOC.,67, 4 6 (2)
(1945).
(8) Rosenmund, K. W.,and Kuhnhenn, TT., Z . C'ntersuch. S a h r . u . Genussm., 46,154 (1923) ; Analyst, 1924,105. (9) Skell, P. S., and Radlove, S. B., IND. EJG. CHEM.,ANAL.ED., 18, 67 (1946).
PRESESTED before the Division of Analytical and Llicro Chemistry a t the 110th Meeting of the A 3 f E R I c A x CHEMICAL SOCIETY, Chicago, Ill. Paper 73, Journal Series, General Mills, Inc., Research Laboratories.
Polarographic Determination of Vanadium in Steel and Other Ferroalloys JAMES J. LINGANE AND LOUIS MEITES, JR. Department of Chemistry, Hurvard University, Cambridge 38, Muss. A method is described for the polarographic determination of vanadium in steel and other ferroalloys, based on the removal of interfering elements by electrolysis with a mercury cathode from a dilute sulfuric-phosphoric acid solution, and subsequent measurement of the anodic diffusion current produced by the oxidation of C4 to 4-5 vanadium in a supporting electrolyte containing 0.5 to 3 N sodium hydroxide and 0.1 M sodium sulfite. Results obtained in the analysis of ten Bureau of Standards samples of ferroalloys, containing from 0.01 to 2% vanadium and large amounts of manganese, molybdenum, tungsten, chromium, nickel, copper, and other common alloying elements, were in excellent agreement with the bureau's values.
T
HE polarographic determination of vanadium in steel and
determination of vanadium in steel is that of Stackelberg
other ferroalloys described in this paper is based on the measurement of the anodic wave produced by the oxidation of f 4 to $ 5 vanadium in a strongly alkaline supporting electrolyte. The general characteristics of this wave have been described in a previous paper (6). Iron and other interfering elements are removed by electrolyzing a solution of the sample in a phosphoricsulfuric acid solution with a mercury cathode. Of the elements likely to be present in ferroalloys this procedure leaves in the solution, in addition to vanadium in the + 3 state, only molybdenum, tungsten, titanium, uranium, columbium, tantalum, aluminum, and a trace of manganese. Kone of these elements interferes in the determination of the vanadium. The residual solution is treated with hydrogen peroxide and then with sulfite (sulfurous acid) in excess to convert the vanadium to the +4 state, and is made up to a known volume. An aliquot portion of this solution is added to a known volume of air-free 1 N sodium hydroxide in a polarographic cell and the polarogram is recorded. 4 complete determination requires only about 90 minutes' elapsed time. Results obtained with a variety of Bureau of Standards samples demonstrate that the method is as accurate as the classical methods for steels containing a few per cent of vanadium, and with very small amounts of vanadium the polarographic method is probably more reliable. The only previously reported method for the polarographic
et al. (11). These authors used the classical sodium hydroxide
precipitation method for separating iron and various other elements from +?Ivanadium, and the latter was finally determined in an ammoniacal supporting electrolyte. This method is rapid, but it involves the danger of coprecipitation of some of the vanadium, particularly when much manganese is present, and the results quoted by Stackelberg et al. are less accurate than those obtained by the present method. I n preliminary work the electrolytic separation with the mercury cathode was carried out by the usual technique from a dilute sulfuric acid solution (1, 9), but difficulties arose when much manganese and molybdenum were present. Manganese was partially oxidized to manganese dioxide and permanganate ion a t the anode, and molybdenum tended to precipitate (probably hydrous hloO2) during the electrolysis. By adding phosphoric acid as recommended by Chlopin (2) these difficulties were avoided. EXPERIMENTAL TECHNIQUE
The cell used for the electrolytic separation was of the Melaven type (1,9,10); it had a capacity of about 200 cc. and the area of the cathode mercury was about 25 sq. cm. A coil of platinum wire served as anode. Stirring was accomplished by a glass propeller stirrer whose blades were partly immersed in the mercury, so that the mercury-solution interface was well stirred. A current of 3 to 5 amperes was used, a t a total applied e.m.f. of about
160
ANALYTICAL CHEMISTRY
10 volts. Electrolysis for 3 ampere-hours per gram of sample was usually adequate. Most of the polarographic measurements were made with a manual apparatus (S), but some polarograms were recorded with a Sargent-Heyrovsk4 Model XI polarograph. The galvanometer of the polarograph was calibrated a t frequent intervals by the usual technique (5). An H-type polarographic cell, with a saturated calomel anode (S), was used, and all measurements were made with the cell in a water thermostat a t 25.00' * 0.05" C. The dropping mercury electrode assembly, which included a stop-clock device for automatically measuring the rate of flow of mercury, was of the type previously described (j),except that the rubber pinchcock between the stand tube and the mercury reservoir was replaced by a very lightly lubricated glass stopcock. Purified hydrogen was used to remove dissolved air from the solutions. 0
-0.5
m
5
8,o
Electrolyze with a current of 3 to 5 amperes for a length of time corresponding to a t least 3 ampere-hours per gram of sample-Le., for 45 minutes if a 1-gram sample was used and the current is 4 amperes. If the amount of molybdenum in the sample is more than about 100 times greater than the amount of vanadium (a most unusual circumstance), the electrolysis should be prolonged for a time corresponding to 30 ampere-hours per gram of molybdenum present. (Molybdenum is only partially deposited in this procedure. As long as the amount remaining in solution is not more than about 100 times the amount of vanadium present it does not interfere, but larger amounts produce erratic results in the polarographic determination of the vanadium.) Transfer the residual solution to a Kjeldahl flask, add 2 to 5 cc. of 307, hydrogen peroxide to oxidize any + 3 vanadium, and boil gently for a minute or two. Then add 2 grams of sodium sulfite , t o reduce the vanadium to the $4 state, evaporate the solution to about 75 cc., cool, transfer t o a 100-cc. volumetric flask, add 1 gram of sodium sulfite, and dilute to volume. Add a suitable aliquot portion of this soll.ition-e.g., 10 cc.-to a suitable volume-e.g., 50 cc.-of air-free 1 N sodium hydroxide4.l M sodium sulfite supporting electrolyte in a polarographic cell, and measure the diffusion current a t 25' C. at -0.25 volt us. the saturated calomel electrode-Le., a t the middle of the plateau. Subtract the previously measured residual current from the observed diffusion current. Measure the drop time a t -0.25 volt, and the m-value of the capillary, and compute the concentration of vanadium from the relation C = i0i1.466 mzi3ti!6.
-1.0
i4
RESULTS AND
- 1.5
j'
/ I -e.io
I
I
I
-0.05 Ed... oa. S.C.E., Volt
-0.30
I
I -0.70
Figure 1. Typical Polarogram of +4 Vanadium in 1 N Sodium Hydroxide-O.1 M Sodium Sulfite Obtained with Mo-W-Cr-V Steel 134
Concentrations were computed from the relation C = i d / I r n z f L f 1 '9 millimoles per liter, where i d is the observed diffusion current (microamperes), m is the rate of mercury flow from the dropping electrode (mg. per second), t is the drop time (seconds) a t the po-
tential a t which the diffusion current is measure, and I is the diffusion current constant (4). The use of this relation is much more convenient than the repeated calibration of each dropping electrode with known concentrations of the substance being determined, but it must not be applied with capillaries whose drop time is smaller than about 1 second (7, 8). In 0.5 to 3 N sodium hydroxide containing 0.1 M sodium sulfite the I-value for the anodic wave of $4 vanadium was found to be 1.466 * 0.002 a t 25" C.,which agrees well with a previous measurement (6). The half-wave potential is -0.432 volt us. the saturated calomel electrode (see Figure 1). Alkaline solutions of $4 vanadium are very easily oxidized by atmospheric oxygen (6), and hence care must be taken to compose the final solution out of contact with air. A known volume of the $4 vanadium solution should be added to a known volume of the supporting electrolyte previously freed from dissolved air with hydrogen or nitrogen in a polarographic cell. To ensure the complete absence of oxygen, the supporting electrolyte should also contain about 0.1 M sulfite ion. Solutions prepared with these precautions were found to be stable for a t least 12 hours. The residual current of the supporting electrolyte alone should be determined before adding the vanadyl solution, and subtracted from the total current to obtain the corrected diffusion current. It is not necessary to record the entire wave, and it is sufficient to make single measurements of the residual current and thediffusion current a t -0.25 volt (compare Figure 1). PROCEDURE
Transfer a 0.5- to 2.5-gram sample to a small Kjeldahl flask, and add 20 cc. of 6 N (1 to 1) hydrochloric acid, 5 grams of disodium phos&ate dodecahydrate, and 3 cc. of concentrated nitric acid in small portions. When the action moderates, add 3 cc. of concentrated sulfuric acid and evaporate to fumes of sulfur trioxide to remove oxides of nitrogen and chloride. Disregarding any graphitic and/or siliceous residue, transfer the solution to a Melaven cell (IO)with water, and dilute to about 100 cc. This solution will be about 0.3 M in respect to sulfuric acid and about 0.14 Y in phosphoric acid:
DISCUSSION
Results obtained in the analysis of ten Bureau of Standards steels and ferroalloys, with percentages of vanadium between 0.01 and 2, are shown in Table I. In every case the polarographic values agree with the bureau's values to well within the probable uncertainty of the latter. In order to attain maximal precision in these analyses the measurements were made with the manual apparatus (S), rather than with the recording polarograph. To further increase the
Table I. Polarographic Determination of Vanadium in Bureau of Standards Steels and Ferroalloys Sample end Bureau of Standard6 Certificate Values Co-Mo-W steel 153 V 2.03 C 0.86, Mn 0.22, P 0.026 S 0.009, Si 0.19, Cu 0.10, Ni 0.12, 'Cr 4.14,Mo8.36,W1.58,Co8.43 (provisional) Mo-W-Cr-V steel 132 V 1.64 C 0.803, M n 0.252, P 0.027, S 0.004, Si 0.239, Cu 0.149, Ni 0.094, Cr 4.11, M o 7.07, W 6.29 >lo-W-Cr-V steel 134 V 1.13 C 0.810 h l n 0.155 P 0.016 S 0.006 Si 0.323' C u 0.114,'Ni 0.077: Cr 3.37: Mo 8.6& W 1.82 Cr-W-V steel 6Ob V 1.02 C 0 7 3 M n 0.32 P 0 0 2 9 S 0.00d. Bi 0.36, Cu 0.11,' Ni 0.09: C r 4.09, Mo 0.40, W 18.06, Sn 0.025 (provisional) Cr-V steel 30D V 0,190 C 0.363 U n 0.786 P 0.031 S 0.031 'Si 0.286,' &I 0.092,'Ni0.150: Cr 1.15: M o 0.034 18 Cr-8Si steel lOlB V 0.049 C 0.069 ?In 0.597, P 0.017, S 0.025,'Si 0.483: ku 0.168, S i 8.99, Cr 18.49 \ l o 0.078, Co 0.78, Cb 0.062, Sn 0.012: i- 0.021 Ferromanganese 68A V 0.045 C 6.83 \In 80.07 P 0.294 , s 0.014,'Si om', 'Cr 0.025,' co 0.02: -4s0.035 Spiegeleisen 66 V 0.012 C 4.05, M n 19.93, P 0.070, 9 0,016 'Si 2.22, Fe 73.45, C U 0.019 ;Uio.Olb, Cr0.009, M00.005, Ti 0.20: c o 0.01
h l n rail steel 100 V 0 011 C 0.617 Mn 1.38, P 0.023, S 0.021,'Si0.191,'CuO.124, Ni0.151, Cr 0.180, M o 0.005 Cu-Ni-Cr cast iron 115 V 0.009, C 2.42, M n 1.01, P 0.113. S 0.032, Si 1.60, Cu, 6.44, N1 15.89, Cr,2.17,Mo0.002,Ti0.021,As0.007, Co 0.08
Vanadium
%
Found,
2.00
1.635
1,133
1.009
0.190
0,0500
0.0432
0.0108
0.0111
0.0092
V O L U M E 19, NO. 3, M A R C H 1 9 4 1
161
Table 11. Typical Data Obtained in Analysis of Mo-W-Cr-V Steel 134 0.967-gram sample, electrolyzed 1.5 hours with 3 amperes, and residual solution finally diluted t o 100 cc. Initial volume of supportingelectrolyte = 49.86 cc. Diffusion current measured a t - 0 . 2 5 volt u s . the saturated calomel electrode, a n d corrected for the residual current (0.037 microampere). Temperature = 25.00° C. m2/stl’6 = 2.490 mg.213 s e c . - ’ / Z Sample Solution Added id (Corrected) Vanadium c c. Microamperes % 1.00 0.152 1.133 2 00 0.306 1,142 0.451 3.00 1,148 4.00 1.133 0.580 5.00 0.716 1.129 1,133 0.845 6.00 0.972 7.00 1.135 1.070 8.00 1.117 1.205 9.00 1.132 1,127 1.310 10.00 Av. 1.133 Av. deviation 1 0 . 0 0 5
precision ten successive 1-cc. portions of the vanadyl solution were added from a calibrated microburet to 50 cc. of the supporting electrolyte, the diffusion current was measured after each addition, and the measurements were averaged to compute the result. The precision attainable is illustrated by the typical data in Table 11, which were obtained in the analysis of the MoW-Cr-V steel 134.
The data in Table I1 demonstrate that a precision of about 0.5% (in terms of the average deviation from the mean) can be obtained under optimum conditions when special care is exercised in measuring the diffusion current and residual current. When measurements are made from recorded polarograms, as in routine analytical practice, results as precise as those in Table 11 cannot be expected. The precision also decreases, of course, ’ when the concentration of vanadium-i.e., the diffusion currentis very small, and the correction for the residual current is correspondingly large. LITERATURE CITED
(1) A.S.T.M. Methods of Chemical Analysis of Metals, American Society for Testing Materials, Philadelphia, 1943. (2) Chlopin, N. J., 2. anal. Chem., 107, 104 (1936). (3) Kolthoff, I. M.,and Lingane, J. J., “Polarography”, p. 215, New York, Interscience Publishers, 1941. ENG.CHEM.,ANAL.ED., 15, 583 (1943). (4) Lingane, J. J., IXD. (5) Ibid., 16, 329 (1944). (6) Lingane, J. J., J. Am. Chem. SOC.,67, 182 (1945). (7) Lingane, J. J., and Loveridge, E. A., Ibid., 66, 1425 (1944). (8) Ibid., 68, 395 (1946). (9) Lundell, G. E. F., Hoffman, J. I., and Bright, H. A., “Chemical
Analysis of Iron and Steel”, New York, John Wiley 8: Sons,
1929. (10) Melaven, A. D., IXD. ENG.CHEM.,ANAL. ED., 2, 180 (1930). (11) Stackelberg, M. v., Klinger, P., Koch, W., and Krath, E., Forschungsber. Tech. Mitt. K r u p p , Essen, 2, 59 (1939).
Polarographic Analysis of Mixtures of Maleic and Fumaric Acids BEYJ . WARSHOWSKY, PHILIP J. ELVING,
AND
JOYCE RIANDEL, Publicker Industries, Znc., Philadelphia, P a .
A polarographic study has been made of fumaric and maleic acids, and a method is described for the simultaneous polarographic determination of the two acids or their salts. Mixtures of the maleate and fumarate ions are analyzed by comparing the current readings at three applied potentials to those of a standard solution of the two ions at the same potentials, using an ammonium hydroxide ammonium chloride buffer solution of pH 8.2 as the supporting electrolyte. In the presence of interfering aubstances maleate and fumarate can be separated by precipitation of their barium salts in alcoholic solution; the precipitate is soluble in the base solution used.
A
S PART of a general program of examination of available
and possible methods for the determination of 1,3-butadiene the reaction of butadiene with maleic anhydride was extensively investigated. It is possible to remove butadiene from gaseous mixtures containing appreciable aniouiits of it by absorption in molten maleic anhydride and determination of the decrease in volume. However, for a number of reasons, this method cannot be advantageously applied to the determination of traces of butadiene in gaseous mixtures or in the presence of substances of appreciable physical solubility in molten maleic anhydride except by the use of rather elaborate apparatus and technique. A possible method for butadiene in gaseous mixtures would consist of passing a measured volume of gas through a known weight of molten maleic anhydride and then determining either the tetrahydrophthalic anhydride formed by the reaction of the maleic anhydride with the butadiene or the maleic anhydride which had not reacted. The unreacted maleic anhydride could be determined by dissolving the final reaction mixture in
water, converting the anhydrides to acids, and determining the maleic acid polarographically. The original sample of maleic anhydride could have been assayed for maleic acid content in the same manner. In connection with this method it was decided to investigate the polarographic behavior of maleic acid. Since fumaric acid might possibly be present and there are no satisfactory chemical procedures for differentiating between these two isomeric cis-trans unsaturated dicarboxylic acids, it was also decided to study the polarographic behavior of fumaric acid. Of additional interest was the fact that the polarographic method for the simultaneous determination of maleic and fumaric acids in mixtures was found to be deficient (1). Previously suggested methods for the analysis of mixtures of maleic and fumaric acids include, in addition to the use of polarography, differential neutralimetric titration based on the difference in magnitude of the primary ionization process for the two acids, the slight solubility in water of fumaric acid compared to maleic, and the formation of different esters. Various methods for the polarographic determination of maleic and fumaric acids in mixtures have been described in the literature. Vopirka (13) reported obtaining two distinct polarographic waves for maleic and fumaric acids in mixtures by polarographing the sodium salts of the acids in solutions which were 0.1 N in potassium chloride and 0.5 to 1 N in sodium acetate. When this procedure was attempted with a solution containing approximately gram per ml. of maleic and fumaric acids, no separation of the polarographic waves was obtained. Semerano and Rao ( 1 2 ) found that in exactly neutral or, a t most, slightly alkaline solution the waves due to maleic and fumaric acids can be resolved. They suggest using the calcium salts in an unbuffered medium of 0.5 N ammonium chloride for the determination of maleic acid in the presence of fumaric. Since maleic and fumaric acids show similar polarographic behavior in acid solutions (S),this medium is also unsatisfactory in that the resulting pH of the solution is approximately that of ammonium chloride
.
