V O L U M E 21, NO. 6, J U N E 1 9 4 9 P
GLASS HOOK
-5.5rnm.
677
Table 111. Polarographic Standards for Benzene Standard Code No. Nitrating mixture Aliquot treated, ml. Equivalent polarized, Y/d.
hmm.
A 62 K 2
(Sensitivity, X , 5 . Calibration standard curYe B) B C D E A-1 B-1 63 64 65 66 71 70 K K K K K-1 K- 1 4 6 10 8 3 2
4 12.1
8 30.9
12 51.2
16 77.3
20 99.0
4 13.0
€
E
Table IV.
0
0
I
Code KO. Nitrating mixture Aliquot, ml. Equivalent polarized, -,/ml, hmm.
33 L-2 10” 20 d.5
6 20.8
8 29.9
E-1 74 K- 1 10
D-1 73
K- 1 5
10 40.9
20 100.2
Polarographic Standards (Sensitivity, X ,5 ) 48 47 L-3 0-2 10b 100 20 20 30.8 1.0
Curve ... a Treated t o oxidize dinitrotoluene according t o procedure. b Untreated.
paring the standard curve. The 7.0 m m . wave steps obtained produced a DIAL(. curve which was not a straight line in itself, but could be Figure 3. Special Nistraightened out by plotting on tration Tube for Standlog-log paper. This phenomenon ardized Nitrating Conditions was not interpreted, as a calibration curve was to be prepared. The color of the solution prior t o extraction with petroleum ether but after addition of the sodium hydroxide will be that of dichromate orange if toluene is present, and chrome yellow if toluene is not present. Finally, the best polarographic technique (6) would require the use of an external calomel electrode, thereby assuring adequate cleaning of the polarographic cell. When this equipment is not immediately available, reproducible results may be obtained by filling the cell with the solution to be tested and using that solution to rinse the dropping mercury electrode, calomel electrode, and nitrogen tube. After thorough draining the aliquot to be polarized is admitted. Under normal drainage conditions, the residual volume will be small and not vary appreciably. The effect of temperature on half-wave potential and wave step was not determined, but in order to use standardized conditions the polarographic cell was jacketed in a water bath a t 20.0” C. and the solutions were polarized immediately after aerating, because they deteriorated rapidly after the addition of the polarographic base.
C-1 72 K-1 4
...
47-a 0-2 10b 20 3.0
...
60 L-3 50
31.1 C
58 DNT 4.OQ 40 17.9 C
49
DST 5.00 50 31.8
c
Table V. Polarographic Standards Code No. Nitrating mixture Aliauot treated, ml.
hmm.
CsHs calculated, 7; CmHa from curve A , Deviation, 70
y
32 N-2 2.0 11.3 4.84 4.60 4.1)
37 5-2 2 .0 11.7 4.84 4.80 0.1
A colorimetric procedure based on the selective oxidationdifferential solubility procedure indicated herewith is also being processed. LITERATURE CITED
(1) Baernstein, H. D., IND. ENG.CHEM.,ANAL.ED., 15,251 (1943). (2) Dennis, M. M., “Gas Analysis,” pp. 112-13, New York, Macmillan Co., 1929. (3) Ibid., p. 185. EBG.CHEM.,A x . 4 ~ED., . 1 5 , 2 4 2 (1943). (4) Dolin, B. H., IXD. (5) Hodgman, C. D., ed., “Handbook of Chemistry and Physics,” 24th ed., p. 1373, Cleveland, Ohio, Chemical Rubber Publishing Co., 1940. (6) Landry, A. S., J . Ind. Hug. Tozicol., 2 9 , 1 6 8 (1947). (7) Lingane, J. J., Office of Technical Services, PB 30,752 (1946). ( 8 ) Roubal. Jan, 6a;asopisLJkami C e s k w h , 85, 1002 (1946). (9) Schrenk, H. H., Pearce, S. J., and Yant, W. P., Bur. Minea, R e p t . Inrest. 3287 (1935). (10) Teisinger, J., AvMikrochemie oer. X i k r o c h i m . Acta, 25, 328 (1938). RECEIVEDAugust 24, 1948. Report of preliminary investigation presented a t annual meeting of New England Section, American Industrial Hygiene Association, Boston, Mass., Kovember 29, 1947.
Polarographic Determination of Tin in Steel W. E. ALLSOPP’ AND V. R . DARIERELL Western Reserue University, Cleveland, Ohio
T
HE standard method of Scherrer (6) for the determination of tin in steel is time-consuming, and offers many opportunities for indeterminate errors. It requires a hydrogen sulfide precipitation from a solution obtained from a 10-gram sample; this makes it awkward to use in the case of alloy steels high in molybdenum, because of the difficulty of filtering and washing such large amounts of molybdenum sulfide. Allsopp felt that this procedure might be shortened, and a smaller sample might suffice, if a polarographic method could be worked out. In a literature search, it was found that Lingane ( 4 ) had reported the reduction of stannic ions a t the dropping mercury electrode in a supporting electrolyte of 1 N hydrochloric 1 Proaent
address, T h e Cleveland Twist Drill Co.. Cleveland, Ohio.
acid, resulting in a wave a t -0.47 volt us. the saturated calomel electrode. Lingane also ( 5 )reported a well defined doublet wave for the reduction of chlorostannite ions with a half-wave potential of -0.25 and -0.52 volt us. the saturated calomel electrode in a supporting electrolyte of 1 N hydrochloric acid and 4 molar ammonium chloride at 25” C. However, no published work on the polarographic determination of tin in steel could be found. The following research was accordingly carried out with seven Bureau of Standards standard steel samples, six with tin certificate values. It was found that the polarographic analysis of steel is entirely feasible, and saves much time over the earlier method. Results can be obtained on a batch of six or eight steel samples, using the polarographic method described, on the second (&hour)
678
ANALYTICAL CHEMISTRY
A polarographic m e t h o d for the determination of tin in steel is described. Samples are treated either with sulfuric acid, followed by nitric acid a n d potassium permanganate, if they are tool steels, or with nitric acid followed by potassium p e r m a n g a n a t e if they are plain oarbon steels. The tin is separated as stannic chloride by successive steps involving hydrogen sulfide, potassium pyrosulfate, hydrochloric acid, ammonia, and hydrochloric acid again. After reduction of any iron with hydroxylamine, the tin is determined by measuring the wave with a half-wave potential of -0.58 volt, using a saturated calomel electrode a t 30' C. Percentages of tin are obtained by referring t o a standard curve.
day. Scherrer's present method for tin in steel is a t least twice as long. APPARATUS
A Model XXI Sargent pohrogmph with a dropping mercury electrode adjusted for a drop time of approximately 4 seconds per drop. H-type polarographic cells with a saturated calomel electrode
(8.
Tank nitrogen, after passage over copper turnings at 4509 C. to remove oxygen. A Fisher unitized constant temperature bath, used a t 30.0' + -.or. ".a u. A General Electric reflector drying 250-watt type infrared lamp for fuming the samples. The dropping mercury electrode was held with a holder previously described (0. Figure 1shows the entire setup of the equipment used for this work. PRELIMINARY RESEARCH
A calibration chart was first made using stannic chloride solutions from pure tin, which were also 1N with respect to hydrochloric acid and 4 molar with respect to ammonium chloride. It was established while using these that hydroxylamine, added in the analysis to reduce iron, did not affect the diffusion current, and that no tin is lost when dilui stannic chloride solution is boiled wit hydrochloric acid; this confirms hill^ brand and Lundell ( d ) . A straightline calibratiou curve resulted. After tin was in solution, It could readily be separated and made ready for the polamgraph in a series of steps involving hydrogen sulfide, potassium pyrosulfate, hydrochloric acid, ammonia, and hydrochloric acid again. The chief problem, apparently, was to have all the tin from the steel precipitated by hydrogen sulfide a t the start of the series. Treatment of the original samde with sulfuric acid
if the molybdenum and copper concentration will permit the sulfide precipitate to be easily handled. (If the steel contaius less than 0.5% molybdenum, add a solution of molybdic oxide in 1 to 4 sulfuric acid to bring the molybdenum concentration to that of a 0.5% molybdenum steel. The molybdenum sulfide acts 8s a collector precipitate during the hydrogen sulfide precipitation.) After the sample has dissolved, add 15 ml. of 1to 1 nitric acid; after the reaction has subsided add 10 ml. of 1.5% solution of potassium permanganate or add until manganese dioxide appears, boil for 10 minutes, and add 8% potassium nitrite dropwiise until the precipitate disappears. Boil the solution until salts appear and then carefully fume with the aid of gentle heat and an infrared lamp. Cool and dilute to approximately 100 ml.. with distilled water and add 10 grams of tartaric acid. Make the resulting solution ammoniacal and warm until all the tungstic acid is in solution. Dilute to 400 ml., add 24 ml. of 1 to 1sulfuric acid, and heat to boiling. Any insoluble chromium salts will go into solution a t this point. Pass hydrogen sulfide through the solution for 45 minutes. Let the precipitate digest in a warm place for another 45 minutes, then filter and wash i t with a 1% sulfuric acid solution saturated vith hydrogen sulfide. Ignite the precipitate in a 35-ml. porcelain crucible and fuse with 3 grams of potassium pyrosulfate. Cool and leach the fused mass with 2 N hydrochloric acid, keeping the volume less than 100 ml. Transfer to a 250-ml. beaker and add a slight excess of ammonium hydroxide. Boil for a few minutes to coagulate the precipitate ani of ferric hydroxide is present,
679
V O L U M E 21, N O . 6, J U N E 1 9 4 9
Dissolve a 1.5-gram Sam le in a 600-ml. beaker with 60 ml. of
Table I. Samplea
Type of Steel,
Sn A\,. Certificate Sn Deviation Value Detected of Mean
% 60a 60b 51a 55, 6%
1 to 4 nitric acid with the ailof heat. If the steel contains less than
Determination of Tin in Steel
Chrome-tungsten-vanadium 0,025 Chrome-tungsten-vanadium 0.025 Electric steel, 1.2% C 0.011 Open-hearth iron 0.007 Basic electric, 0.3% C 0.008 152 Basic open-hearth, 0.4% C 0.036 1.52 Basic oDen-hearth. 0.4% C 0.036 134 Molybdenum-tungsten-‘ chrome-vanadiu m 0.013d a S a t i o n a l Bureau of Standards. b Average of three determinations. C Alternative procedure. Determined with d S o certificate value reported. e Average of six deternunations.
c7
/C
70
0.0271, 0,028b 0.009b 0.007b 0.007b 0.028b 0.035bvC
0.0017 0.0020
O.Ol5e
0.0012
0.0012 0.0006 0.0008 0.0060 0.0009
0.5% molybdenum, which is likely, add a solution of molybdic oxide in nitric acid to bring the molybdenum concentration to that of a t least a 0.5% molybdenum steel. Warm the mixture to facilitate solution and then boil to remove oxides of nitrogen. Add 10 ml. of 1.5%potassium permanganate solution, boil the mixture for 10 minutes, and add 8% potassium nitrite solution dropwise until the permanganate color disappears. Continue boiling for a few more minutes to remove oxides of nitrogen again. Dilute the resulting solution to 300 ml., heat to boiling, and then pass hydrogen sulfide through the solution for 45 minutes. Filter and wash with 1% sulfuric acid solution saturated with hydrogen sulfide. Handle the resulting precipitate, consisting of the group I1 sulfides and a large quantity of sulfur, as in the procedure for tool steels.
method of Scherrer.
The results are shown in Table I. DISCUSSION OF RESULTS
add ferric ion as a collector. Wash the precipitate well with 2% ammonium hydroxide and twice with water. Dissolve the precipitate from the paper with 50 ml. of 2 A’ hydrochloric acid and catch the filtrate in the original 250-ml. beaker used in the ammonia precipitation. Wash the paper twice with water. Add 0.75 gram of hydroxylamine hydrochloride and boil gently for 5 minutes. Transfer the warm solution to a 100-ml. volumetric flask that contains 21 grams of ammonium chloride. Add 2 ml. of a O.5y0 gelatin solution and dilute to the mark with water. Remove the dissolved oxygen from the solution with pure nitrogen and obtain a polarogram over the range 0 to - 1.4 volts us. the saturated calomel electrode. Measure the height of the polarograph wave occurring a t a half-wave potential of -0.58 volt us. the saturated calomel electrode a t 30” C., using the method of Taylor ( 7 ) , and relate this to concentration of tin. ALTERNATIVE PROCEDURE FOR DETERMINATION OF TIN IN PLAIN CARBON STEEL
In an effort to make the proposed procedure more versatile, and so include a greater number of types of steel, National Bureau of Standards standard sample KO. 152 was dissolved in nitric acid as recommended by Scherrer (6) and the tin was precipitated from the resulting nitric acid solution with hydrogen sulfide. It was found necessary to add a solution of molybdic ion to the dissolved sample before precipitation to act as a collector during the sulfide precipitation and to ensure the complete recovery of tin.
Results obtained with Bureau of Standards steels fall within, or very close to, the results accepted by the bureau for certification of the steels, and never differ more than 0.001% from the extreme values used for calculating certification. The authors feel that the proposed polarographic method will yield satisfactory results for tin in steel. ACKNOWLEDGMENT
The authors are deeply grateful t o the Cleveland Twist Drill Company of Cleveland for the equipment and laboratory space used in this research, and to chief metanurgist J. V. Emmons and chief chemist W.L. Emerson of that company for their helpful interest. LITERATURE CITED (1) Allsopp, W. E., ANAL.CHEM.,21,428 (1949).
(2) Hillebrand, W. F.,and Lundell, G. E. F., “Applied Inorgania Analysis,” p. 234,New York, John Wiley & Sons, 1929. (3) Kolthoff, I. hl., and Lingane, J. J., “Polarography,” p. 215,New York, Interscience Publishers, 1941. (4) Lingane, J. J., IND. ENQ.CHEM.,ANAL.ED.,15,583(1943). (5) Lingane, J. J., J . Am. Chem. Soc., 67, 919 (1945). (6) Scherrer, J. A., J . Research Natl. BUT.Standards, 8,309-20(1931)1 Research Paper 415. (7) Taylor, J. K.,ANAL.CHEM.,19, 478 (1947). RECEIVEDJuly 7, 1948.
Improvement in Precision of Polarographic ROLF K. LADISCH AND CLIFFORD E. BALMER Quartermaster General Laboratories, Philadelphia, Pa.
S
INCE the photorecording system was introduced in polarography, numerous papers have interpreted photorecorded polarograms, but no definite conclusion has been reached as yet with respect to the degree of accuracy that can be expected in measuring these curves. Buckley and Taylor (2) estimated that the value of id (diffusion current) is reproducible within the limits of 0.5 and 4%, whereas Mueller (11) believes that an accuracy of A 1%can be reached by using averages of several polarograms of the same solution. To minimize these errors Jablonski and Moritz (6) suggest the use of an accurate measuring microscope for determining the wave height, and Baumberger and Bardwell (1) recommend the draw-
ing of abscissas on the photographic paper by the help of an additional lamp, in order to facilitate a direct reading of the applied voltage. Probably as a consequence of these uncertainties, Kolthoff and Lingane (?‘), Zlotowski and Kolthoff (14), and Lingane and Meites (10) depart from the use of the more convenient polarograph and prefer manual measurements, in order to attain maximum precision. It appears that sufficient emphasis has not been placed on errors arising from the photorecording of polarograms and their measurement. Continuous dimensional changes of the photographic paper itself under the influence of changes in the relative
