and refer to a 1-gram sample. The last two values were determined in final volumes of 50 and 25 ml., rather than in 100 ml. as were the remaining determinations. There is a possible discrepancy in the current values, but as the author no longer has access to the equipment or his records, it cannot be checked. I n application, the method is used with a n external standardization procedure ( 3 ) . More recent data on different equipment give Ks,,/Kcd = 1.07, where K's refer to expressions of the form id = K x concentration (moles per liter). The standard deviation of the quantity idper mg. per ml., based on the first ten measurements, is 0.50. The results of the determination of three samples of Zircaloy 2 are presented in Table 11. The tin content for alloy A had been determined chemically as 1.&yo. I n the course of analyzing a large set of Zircaloy 3 samples, duplicate determinations were carried out on 12 samples, six having tin contents of about 0.250j, and six containing o.5y0 tin. The standard deviation computed from this data was 0.008%. Comparison of this value with those for Zircaloy 2 (Table 11) indicates that in this range the relative variation is more nearly constant than the absolute. To test the validity of eliminating the iron powder reduction by dissolving the sampleunder astream of nitrogen, tinwas determined in a Zircaloy 2 sample using both procedures. Because the concentration of zirconium in the final solution represents a significant contribution to the composition of the supporting medium, there was a possibility that sample size might affect the diffusion current constant through an effect on the
Table 1. Polarographic Results on Synthetic Solutions of Tin in Zirconium
Tin Tin in Added, Mg. id" idlMg.lM1.a 1.43 22.0 6.50 0.65 1.48 22.8 6.50 0.65 2.97 22.8 13.00 1.30 19.50 1.95 4.63 23.8 1.50 23.1 6.50 0.65 3.07 23.6 13.00 1.30 4.53 23.2 1.95 19.50 23.1 0.13 0.300 1.30 0.610 23.5 2.60 0.26 0.300 23.1 0.650 0.06 0.26 20 0.325 0.03 Current units arbitrary.
Table
111. Analyses of a Zircaloy under Varying Conditions
Method of Reduction Iron powder Soln. under nitrogen
Sample Size, Gram 0.254 0.246 0.242 0.240 0.247 0.284 0.240 0.240 0.108
0.109 0.102
Tin Found,
%
1.46 1.43 1.43 1.49 1.45 1.47 1.48 1.44 1.44 1.41 1.48
0
Table 11.
Alloy A 1.44 1.46 1.52 1.50 1.50 Av.
1.48
Analyses of Zircaloys tin)
(%
Alloy B 1.39 1.44 1.42 1.47 1.44 1.44 1.43
Alloy C 1.56 1.56 1.53 1.58 1.60 1.63 1.58
supporting electrolyte. Therefore, this sample was also analyzed using different sample sizes. Table I11 indicates that the method can be carried out omitting the iron reduction without affecting the diffusion current constant. All determinations were made with the same calibration constant. The change in sample size had no significant effect. Determinations of the alloy in Table I11 were not affected by additions of chromium and nickel.
I n applying Zircaloy t o reactor fuel element development, determination of tin in the presence of uranium may be required. Two samples of the alloy in Table I11 were determined in the presence of the equivalent of 7.5Y0uranium. Vranium was added as uranyl sulfate and reduction was carried out using iron powder. The results were 1.43 and 1.46% tin. Because samples containing high uranium concentrations will require nitric acid for complete solution, the use of the iron reduction procedure will be mandatory. LITERATURE CITED
(1) Bryson, T. C., Goward, G. W., Mc-
Cay, J. R., Perrine, A. W., Rogers, J. F., Wilson, B. B., TT-estinghouse Electric Corp., Atomic Power Div., Rept. WAPD GTA(GLA) - 172 (1956). (2) Nucleonics 14, KO. 2, 45 (1956). (3) Porter, J. T. 11, ANAL. CHERI.29, 1638 (1957).
-
RECEIVEDfor review June 26, 1957.
Accepted December 26, 1957. Work carried out under contract W-31-109 Eng-52, U. S. Atomic Energy Commission.
Pola rogra phic Determination of S ma I I Amounts of Tin SILVE KALLMANN, ROBERT LIU, and HANS OBERTHIN Research Division, ledoux & Co., 359 Alfred Ave., Teaneck, N. I .
b Steam distillation with hydrobromic acid effectively separates tin from all accompanying elements, except antimony and arsenic. The subsequent polarographic determination of tin in a bromide-chloride medium is not affected by arsenic. Antimony has a slight repressing effect.
D
of small amounts of tin in complex materials frequently is difficult. Of the methods using organic reagents, the dithiol method (8, 9, I 4 is enjoying increasing ETERMINATION
popularity. Unfortunately, it requires prior removal of arsenic and antimony, and destruction of the bromide was more time-consuming and involved than had been anticipated. The silicomolybdate blue spectrophotometric method (6) has not always yielded consistent results. Allsopp and Damerell ( I ) suggested a polarographic procedure for determination of tin in steels, which is considerably faster than the method suggested by Scherrer ( I S ) , but requires prior collection of the tin as the sulfide and is not directly applicable to other materials.
Lingane (11) reported the reduction of stannic ions a t the dropping mercury electrode in a supporting electrolyte of 1N hydrochloric acid, resulting in a wave a t -0.47 volt us. the standard calomel electrode. He ( I d ) also reported a well-defined doublet wave potential of -0.25 and -0.52 volt os. the saturated calomel electrode in a supporting electrolyte of 1N hydrochloric acid and 4N ammonium chloride. According to Lingane, stannic tin also produces a well defined double wave in 4N ammonium bromide as supporting electrolyte. VOL. 30, NO. 4, APRIL 1958
485
As Lingane observed that both arsenic(V) and antimony(V) are not reduced a t the dropping electrode from any of the supporting electrolytes studied, it was hoped that bromide distillation of tin without prior removal of arsenic and antimony could be used in a rapid polarographic procedure,
FUSIOKWITH SODIUM CARBONATE SODIUMPEROXIDE. Tin occurs in most minerals and ores in the form of AND
A
DISTILLATION OF TIN
During this investigation it was discovered that tin can be efficiently and rapidly distilled by a procedure similar to the conventional steam distillation of ammonia, in a modified Kjeldahl apparatus (7) (Figure 1). Table I indicates the efficiency of the tin distillation when 40- and 20-ml. portions of hydrobromic acid are introduced in the form of hot vapor into sulfuric acid a t about 250" C. Polarographic Characteristics of Stannic Bromide. Lingane (11, 12) investigated the reduction of stannic ion a t the dropping mercury electrode in various supporting electrolytes. However, as the investigation reported here involved the use of a mixed hydrobromic acid-ammonium chloride medium, the polarographic characteristics of tin were further investigated. It was found that reduction of stannic ion in a supporting electrolyte of 1.8N hydrobromic acid and about 1-Y ammonium chloride yields a well defined wave with a half-wave potential of about -0.25 volt 1's. S.C.E. A 0.1% solution of sodium carboxymethylcellulose was used as a maximum supressor. SUGGESTED PROCEDURE
Apparatus. Model XXI Sargent polarograph with a dropping mercury electrode adjusted for a drop time of approximately 3 seconds per drop. Reference electrode, H-type polarographic cell with a saturated calomel electrode. Alternatively a pool of mercury was used. The distilling apparatus (Figure 1) is essentially a Kjeldahl apparatus with the addition of a suitable means of passing hot hydrogen bromide vapor through the solution in the flask. For rapid distillation of tin in samples requiring a preliminary fusion with sodium peroxide in a nickel crucible, a specially constructed 11ide-mouthed flask allowed direct transfer of the melt without the use of water. A 0.1% solution of sodium carboxymethylcellulose was used. Procedure. DECOJIPOSITIOX WITH HYDROFLUORIC ASD SITRIC ACIDS, Xiobimi, tantalum, titanium tungsten, and zirconium and their ferroalloys are decomposed with nitric a n d hydrofluoric acids. Weigh a sample to provide a minimum of 0.2 and a maximum of 50 mg. of tin into a platinum dish or beaker. 486
ANALYTICAL CHEMISTRY
Figure 1. A.
E.
Tin-distilling apparatus
Hydrobromic acid generating flask, 500 ml. Distilling flask, 300 ml.
Table I. Efficiency of Steam Distillation of Tin with Hydrobromic Acid
Tin Used, R'Ig.
0.10 0.50
1.0
2.0
...
5.0 ...
Tin Recovered, M g . 2nd 1st Fraction fraction, 40 ml. 20 ml. 20 ml. ... 0.10a ... ... 0.510 ... ... 1.01a ... ... 1.985 ... ... 1.99a ... ... 4.935 0.105 5.0=
10.0
10.2a 9.98b
20.0
20
...
...
50.0 100.0
3a
19.w
49.9ib
...
...
... ... ... ... ... .. .
...
... ...
0.20"
...
0.42a
99.92b 1.2a 248.30b 1.755 Tin determined polarographically by procedure described. Standardization with known concentrations of stannic brcimide without distillation. Tin determined iodometrically. 250.0
Decompose with nitric acid, with the dropwise addition of hydrofluoric acid (4) or hydrofluoric acid plus nitric acid (2). When solution is complete, add 10 ml. of sulfuric acid for sample weights u p to 1 gram, or 20 to 25 ml. for sample weights up to 5 grams. Evaporate t o light fumes of sulfuric acid. Cool, wash down the sides of the platinum vessel with a little n-ater, and again evaporate to fumes. Refume once more after addition of a little water. Dissolve the cold sulfates in 40 ml. of water, and heat, disregarding any cloudiness or precipitate. DECOMPOSITION WITH KITRIC ACID. Copper, nickel, zinc, and lead and their alloys are decomposed with nitric acid. Dissolve a sample to provide a minimum of 0.2 and a maximum of 50 mg. of tin in concentrated or dilute nitric acid. Add sulfuric acid and evaporate to fumes. Expel residual nitrogen compounds by refuming and dissolre sulfates in water.
cassiterite @no2), which is insoluble in acids and acid fluxes. A fusion with sodium carbonate and sodium peroxide not only renders the tin soluble but also effectively decomposes the rest of the sample. Fuse a sample to provide minimum of 0.2 and a maximum of 50 mg. of tin, in sodium carbonate and sodium peroxide (3). Either iron or nickel crucibles may be used. When the crucible containing the fusion has partly cooled, place a tight-fitting nickel cover on it and t a p the crucible several times on a n iron plate to loosen the melt in a solid cake. Transfer the melt to a dry 400-ml. beaker, and add 70 ml. of 18N sulfuric acid. Rinse the crucible with 5 ml. of the sulfuric acid and water and add to beaker. DECOMPOSITION WITH OTHER ACIDS. Dissolve alloy steels and aluminum alloys in aqua regia. Decompose iron and steel in dilute sulfuric acid. Decompose organic substances with nitric and sulfuric acids. To determine tin in miscellaneous solutions, collect the tin with ferric hydroxide cupferron (10), or manganese hydroxide (6) and obtain a sulfuric acid solution by wet-ashing the paper containing the tin with nitric and sulfuric acids. DISTILLATION OF TIN. Transfer the sulfuric acid solution of the sample to the distilling flask and evaporate the solution to light fumes (about 250" C.). Connect the apparatus as outlined in Figure 1, placing in flask B about 100 ml. of hydrobromic acid. With B heated to boiling and A maintained near 250' C., collect 40 f 4 ml. of hydrogen bromide in a 100-ml. graduate containing 30 ml. of water. (If the tin content is suspected or known to be above 20 mg., collect an additional 20 ml. of hydrobromic acid in a second graduate. For larger amounts of tin, increase the volume of the first distillate and take a n aliquot for the polarographic measurement. Alternatively, transfer a larger distillate to a correspondingly larger volumetric flask. For trace amounts, a 20or 10-ml. distillate frequently is sufficient and a smaller volumetric flask may be chosen.) Transfer the distillate containing 40 ml. of hydrobromic acid to a 200-ml. volumetric flask and the 20-ml. distillate to a 100-ml. flask. Add to the 200ml. flask just enough hydroxylamine to destroy any yellow coloration in the distillate, 10 grams of ammonium chloride, and 10 ml. of 0.10% sodium carboxymethylcellulose, and dilute almost to the mark. Add to the 100-ml. flask half of all reagents. Warm the solution for 15 minutes on a steam bath, cool to 20" C., dilute to the mark, and mix. Transfer a suitable portion of the solutions to the electrolysis cell and bubble nitrogen through the solution for 5 minutes to remove oxygen. Obtain a polarograph over the range -0.15 to - 1.50 volts, adjusting the sensitivity of the circuit to obtain a curve of optimum
step height. Measure the height of the polarographic wave which occurs approximately at a half-wive potential of -0.25 volt. Compare the wave height, which is directly proportional to the concentration of tin with the wave height of standards. RESULTS
The method was applied to the determination of tin in various samples of known tin content (Table 11). Interferences. T h e distillation step separates tin effectively from most elements with which i t is usually associated in minerals, metals, a n d alloys. Only arsenic and antimony of t h e more common elements accompany t h e tin into t h e distillate. While Lingane states (11) that arsenic(V) and antimony(V) are not reduced a t the dropping mercury electrode, his experiments were carried out in chloride solutions while the present investigation involres a mixed chloride-bromide medium. The use of hydroxylamine hydrochloride undoubtedly causes a t least partial reduction of both the antimony and arsenic to the + 3 state. The results in Table I11 indicate that arsenic does not interfere in concentrations u p to 10 times those of tin; antimony affects the polarographic wave to some extent. Although this effect is insignificant for concentration of antimony u p to five times those of tin, larger quantities slightly repress the polarographic wave of the tin. This negative effect of the antimony can be compensated by the addition of equivalent amounts of antimony to the standard.
Table II.
Accuracy
of Proposed Method
Marks NBS 164 NBS 62C XBS 37B NBS 53C NBS 50.4 NBS 170 NBS 152 NBS 55A w.4 44
Material Mn-41 bronze Mn bronze Sheet brass Lead-base bearing metal Cr-W-V steel Open hearth steel Open hearth steel Open hearth steel Ti-alloy Zircaloy 2 Zircaloy 2 Zircaloy 3 Ferroniobium Ferroniobium tantalum Tantalum ore Tungsten ore Tungsten ore a Average of duplicate determinations.
Table 111.
Interference of Arsenic and Antimony
Tin, Mg. Present Found 1.0 1.00 1.02 0.99 5.0 4.99 5.03 1.0 1.00 0.99 0.96 5.0 5.02 4.80 10.0 9 65
Present, Mg. Arsenic Antimony
.. 5
10
20 50
..
.. ..
.. .. ..
...
... ... ...
...
2
5
10 20 50
100
LITERATURE CITED
(1) Allsopp, W. E., Damerell, V. R., ANAL.CHEJI.21, 677. (1949). (2) Am. Soc. Testing Materials, Philadelphia, L‘ASTMhlethode for Chemical ‘Analysis of hfetals,” p. 182, 1956.
(3) (4) (5) (6)
Tin Preeent, yo Tin Founda, 0.61 0.63 0.40 0.39 0.98 0.99 5.12 5.17 0.029 0.025 0.020 0.018 0.033 0.036 0.009 0.007 2.52 2.67 1.32 1.32 1.24 1.24 0.23 0.24 0.19 0.17 1.31 1.32 0.65 0.65 0.18 0.17 0.F5 0.87
70
Ibid., p. 186. Ibid., p. 187. Ibid., p. 339. Baker, I., Miller, M., Gibbs, S., ISD. ESG.CHEM.,ANAL. ED. 16, 269
(1944). (7) Beeghly, H. F., Aiv.4~. CHEJI. 21, 1,513 11949). Clark, R. E. D., A n a l y s t 61, 242 (1936); 62, 661 (1937). Farnsworth, M.,Pekola, J., AKAL. CHEM.26, 735 (1954). Hillebrand, W,F., Lundell, G. E. F., Bright, H. A., Hoffman,. J. I., “Applied Inorganic .4nalysis,” pp. 287, 289, Wiley, Sew York, 1953. Lingane, J. J., IND.ESG. CHEW, AXAL.ED. 15, 583 (1943). Lineane. J. J J Am. Chem. SOC.67, 9T9 (1945): (13) Schemer, J. -4.,BUT.Standards J Research 8 , 309-20 (1931). (14) Stone, I., ISD. ENG.CHEM.,ASAL. ED.13, 791 (1941). RECEIVEDfor reviem- August 21, 1957. Accepted December 26, 1957.
Apparatus for Automatic Controlled Potential Electrolysis Using an Electronic Coulometer LYNNE L. MERRITT, Jr., ERNEST 1. MARTIN, Jr.l, and RAM DEV BED1 Department o f Chemistry, lndiana University, Bloomington, Ind. An electronic instrumental circuit has been constructed, tested, and used in automatic controlled-potential coulometric electrolyses. It includes a constant-current source to supply current to a large capacitor, an electronic tripper circuit to limit the potential range of the working electrode, and a signal generator-scaler circuit for measuring the total time during which the capacitor i s charged. The capacitor serves as the current source for the electrolysis cell. By measuring the time that the constant current is applied to the capacitor and thus the total number of coulombs used for the elec-
trolysis, the concentration of electroactive species can b e calculated from Faraday’s law. Oxidation of iodide ion to iodine, reduction of dichromate ion to chromic ion, and deposition of silver and copper have been successfully carried out. Possible sources of error are discussed and several methods of improving the instrumental system are proposed.
A
of instruments for carrying out electrolyses a t controlled working-electrode potentials are reviewed by Lingane ( 6 ) and Delahay ( 2 ) . These SUMBER
instruments hare bcen combined with chemical coulometers or mechanical or electrical current-time integrators (1, 6 , 8) to measure the number of coulombs required for the electrolysis. However, chemical coulometers are inconvenient to use and most of the mechanical and electrical integrators developed up to the present time leave much t o be desired in precision and range of currents oyer which they operate. The current integrator described by ILIeites ( 8 ) is precise and accurate t o 1 Present address, Shell Chemical Co., Houston, Tex.
VOL. 30, NO. 4, APRIL 1958
487
