V O L U M E 2 6 , NO. 8, A U G U S T 1 9 5 4
1371
been obtained by increasing the ratio of buffer mixture to sample and multiplying the result by the proper factor. EFFECT O F LITIIIU.11 I Y COAL ASH
During the preliminary investigation of the method, many coal ashes and fireside deposits mere examined qualitatively for lithium. In no case v a s the lithium 3232.6 line detected and it was estimated from a synthetic standard that the limit of detection w-as 0.05% lithium as Li20.
Table 111.
Comparison of Spectrographic and Chemical Results K20,%
NanO, % Spectrographic Chemical
Sample
Spectrographic
Chemical
However, variable amounts of lithium oxide a t the conccntration level recently reported hy Headlee (6) would cause small, variable errors in the sodium dctermination. In t,he event that the coal contains significant am Iurits of lithium, the method is modified by ( a ) adding 0.20’34 lithium oxide to the standard and ( b ) doubling the amount of lithium carbonate used in the sodium buffer. PRECISION AND ACCURACY
The standard deviation for the method, as determined from data selected a t random over a period of 3 months, was 4.1% for the potassium and 4.301, for the sodium determination. The accuracy of the method is somewhat difficult to determine because there is a lack of standard samples of these materials
in Table 111. There is a tendency for the spectrographic results to be consistently lower than the chemical values. However, in view of the difficulty in obtaining agreement on the chemical sodium and potassium determinations on silicate rocks which as reported recently ( I O ) , the comparison appears adequate. SUMMARY AND CONCLUSIONS
.4 spectrographic method for determining sodium and potassium that is applicable to the analysis of coal ashes, tapped slag. fly ash, nnd tube deposits has been developed. It was advisable to det’ermine each element on a separate sample, so that the influence that’ potassium exerted on the sodium determination could be minimized. The cyanogen and iron interferences with potassium and rubidium lines mere eliminated by using lithium carbonate as a buffer. Rubidium \vas found to be an excellent internal standard for potassium, and the potassium-rubidium ratio was apparently independent of the sodium content. The time requirement of 1.5 hours for the determination, in duplicate, of both elements represents a substantial saving in time over the classical chemical methods for these elements. The accuracy of the method, as nieasurPd from a comparison of spectrographic and chemical results, ia -.:Ltisfactory. LITERATURE CITED
(1) Churchill, J. R., I s n . ENG.C H E x , A k ~ . kEo., ~ . 16, 653 (1944). (2) Duffendack, 0. S., Wiley, F.H., and Owem, ,J. S., Ibid.,7, 410 (1036).
( 3 ) Fassel, V. A , , J . Opt. SOC.A m e r . , 39, 187 (1949). (4) Fast, E., ANAL.CHEX.,22, 320 (1950).
(5) Harrison, G. R., Ed., “M.I.T. Wavelength Tables,” p . xis, New York, John TViley & Sons, 1938. (6) Headlee, A. J. TV., Mining Eng.. 5 , 1012 (1953). ( 7 ) Helz, A., J . Research Natl. Bur. Standads, 34, 129 (1945). ( 8 ) Helz, A , , and Scribner, B. F., Ibid., 38, 439 (1947). (9) Hunter, R . G., and Headlee. A. J. W., A X ~ L CHEY.,22, 441 (1950). ( I O ) Schlocht, W. G., I b i d . , 23, 1568 (1951).
Rapid Photometric Determination of Chromium In Alloy Steels and Bronzes MORLEY
D. KAHN
and FRANK J. MOYER
Specialloy, Inc., Chicago, 111.
THE
need for a more rapid, accurate, routine photometric determination of chromium in ferrous alloys of all compositions has long been recognized. There is a particular need for a determination applicable to stainless steels (8 to 30% chromium), alloy cast irons (0.5 to 15% chromium), and chromium-bearing bronze alloys (0.5 to 10% chromium). Fowler and Culbertson ( I ) have developed a photometric method based on the absorption of the orange-red sexivalent chromate ion. However, the presence of a number of colorproducing ions and the necessary provisions required therefore limited application for the purposes of this work. It has been suggested by Vredenburg and Sackter ( 3 ) that the aqua-colored chromic ion complex in a solution of nitric, sulfuric, and phosphoric acids will lend itself to photometric measurement. The presence of molybdenum and copper in the alloys investigated constituted a source of interference. The time required for decomposition further restricted the use of this method on alloys studied in the experiments.
Trace concentrations of chromium can be determined by photometric analysis through the use of s-diphenyl-carbazide ( 2 ) . The alloys investigated had chromium contents of such magnitude as to render this reagent unsuitable. METHOD
d number of experiments were made by dissolving and aubsequently oxidizing the selected alloys through the use of perchloric acid. The resultant sexivalent chromium was reduced with metallic zinc to an aqua-colored complex, and the solution was boiled to stabilize this complex in the trivalent state. The absorbance of this solution was measured in acid media on a Brociner-Mass photometer a t a wave length of 585 mfi. Cupric ion was reduced by the zinc to elemental copper. Hydrogen peroxide mas added to prevent interference in the presence of molphdenum. Phosphoric acid was then used to decolorize
1372
ANALYTICAL CHEMISTRY
ferric ion and to dissolve any intermediary products that may have been formed by the action of hydrogen peroxide. Sickel increased the absorbance of the solution. However, the increase ( a t 585 mp) was constant over a wide range of nickel content. This nickel effect was compensated by using a calibration curve standardized from nickel-bearing material?. I t was found that one curve suffices for nickel concentrations from approximately 5 t o 400 mg. per 200 ml., x-hich range inrludes all the alloys investigated.
Table I.
Results on National Bureau of Standards Iraterials
c h ro 111e Prewnt.
Chrome Found,
'ample S B S 121.4
1s 69
18.70 18.70 18 32 18.45
0.01 0.01 0.37 0.24
S B S 161
lti.90
17 05 17.06 17.OR 17.05
0.15 0 16 0 . lfi 0.15
KBS 30.4
2.41
"35 2 35 2 41 2 38
5
PROCEDURE
Apparatus. Brociner-Mass photometer; cell size, 17 nun. Lumetron No. 400 photometer; cell size, 17 mm. Procedure for Chromium in Alloy Steels. Weigh sample so that 10 t o 150 mg. of chromium will be present, and place in a 600-ml. beaker. Decompose with 10 ml. of concentrated nitric acid and 10 ml. of concentrated hydrochloric acid. Heat on a hot plate until actmioncommences; then warm gently until decomposition is complete. .4dd small amounts of acid as required. Add 10 ml. of perchloric acid (70%). and cover the beaker with inverted watch glass to allow refluxing acid to run down sides of the beaker. Fume until the chromium is completely oxidized, indicated by the formation of red sexivalent chromium salts. Cool, from 1 to 2 minutes, and cautious1)- add 70 ml. of distilled water without removing the watch glass. Swirl salts into solut,io n . If the solution is free of tungsten ( a t this stage present as the dense precipitate of tungsten trioxide) and contains less than about 0,75y0 silicon (present as silicon dioxide a t this point), i t may be filtered through Whatman KO. 41-H paper into a second 600-ml. beaker. If either tungsten or more than about O.i5% silicon is present, it is advisable to filter with suction through Whatman S o . 41-H paper.
S B S 153
4.14
XBS 132
Deviation,
70
70
4.11
0.06 0.06 0.00
0 03
4.14 4 10
0.04
-1.16 4,14
0.05 0.03
0.00
Procedure for Bronzes. Weigh the sample so that 10 to 150 mg. of chromium will be present, and place in a 600-ml. beaker. For each 2 grams of sample, decompose by the addition of 20 mt. of nitric acid ( 1 to 1) and 10 ml. of perchloric acid (70'%). Cover the beaker with an inverted watch glass and fume until t h e chromium is complet'ely oxidized, indicated by the formation of red sexivalent chromium salts. Cool, from 1 to 2 minutes, and cautiously add 70 ml. of distilled water without removing the watch glass. Swirl salts into solution. .Idd approximately 10 ml. of concentrated sulfuric acid and 15 to 30 grams of metallic zinc. Keep the beaker covered with a watch glass during the reduction in order to maintain a reducing atmosphere over the solution. Allow the reaction to continue from 12 to 17 minutes, adding small quantities of zinc only to replenish the metal consumed by the reaction. Raise to a strong boil, coagulating copper into a mass filterable condition. Filter through Whatman No. 41-H paper into a second beaker. Wash n-ith distilled water twice, adding washings to filtrate. Raise solution to a boil. Boil for 3 minutes. Filter a second time, using Whatman N o . 41 paper which has been treated with a small amount of macerated filter pulp, into a 200-ml. volumetric flask. Wash the paper twice with distilled water, alloir-ing washings to go int,o the f l a n k . Cool to room temperature, fill t o mark, and shake. ~
-__
~
Table 11. Results on Synthesized Standards M Q . CHROYIUU/'LOOML
Figure 1. Absorbance us. JIilligranis of Chromium per 200 M1. 1. 2.
Calibrated for nickel-bearing material Calibrated for nickel-free material
Kash the paper with distilled water until it is clean. a,lding n-sshings to the filtrate. Add to the filtrate approximately 10 ml. of concentrated sulfuric acid and 15 t o 30 grams of metallic zinc. The zinc used must be any form of electrolytic grade having a large surface area. Keep the beaker covered with a watch glass during the reduction in order to maintain a reducing atmosphere over the solution. .illon- the reaction to continue from 12 to 17 minutes, adding small quantities of zinc only to re lenish the metal consumed by t,he reaction. Filter through atman No. 41-H paper into a second beaker. K a s h wit!i distilled water twice. adding n-ashings to filtrate. -1dd 4 nil. of hydrogen peroxide ( 3 0 % ) , and raise to a boil. Boil for 3 minutes. Remove from hot plate, add 4 ml. of concentrated phosphoric acid and mix. Filter through Whatman S o . 41-H paper into a 200-ml. volumetric flask. Wash the paper twice again with distilled water, allowing washings to go into the flask. Cool to room temperature, fill to mark, and shake. Measure absorbance a t 585 mp. Record the measurement against water blank and calculate the chromium content by using the formula
\&
%Cr =
grams of chromium/200 ml. (from curve) Weight of sample
x
100
Samplea. Specialloy No. 1224-4x
Chromeb Present, c;b 4.21
Chrom? Found,
Deviation,
4.22 4.22 4.21
0.01 0.01 0.00
1224-5x
5.03
5.03 5.09 5.04
0.00 0.06 0.01
1224-6x
6.17
6.15 6.15 6.13
0.02 0.02 0.04
1224-7x
7.10
7.07
0.03 0.03 0.05
%
7.07 7.05
%
Made by research department of Sixcialloy. Ine. Determined by ferrous ammonium sulfate titrations. Determined by method described.
Measure absorbance a t 585 nip against a \I ater blank. the chromium content using the foImula
%Cr
=
grams of chromium/200 nil. (fiom curve) Weight of sample
Calculate
x
100
Preparation of Standard Reference Curves. The first curve constructed was for ferrous alloys bearing no more thnn 5 mg. of nickel per 200 ml. National Bureau of Standards 363 (2.4170 chromium) was used as the base material for calibration. Samples of this standard, 0.3 gram, were weighed into each of several beakers and varying aliquots of ferrochrome standard solution were added so as to construct a curve that covered the chromium range from 0 to 200 mg. of chiomium per 200 ml.
V O L U M E 26, NO. 8, A U G U S T 1 9 5 4
1373
Ferrochrome standard solution was prepared b y fusing a 0.5gram sample of NBS No. 64a with 8 grams of sodium peroxide in an iron crucible. After the melt was cooled, it was dissolved in 150 ml. of water and acidified with sulfuric acid, treated with an excess of potassium permanganate, and boiled for 10 minutes. T h e potassium ermanganate was then destroyed with a minimum of hydrocfloric acid and the resulting clear solution was made up t o volume in a 250-ml. volumetric flask. A second curve, applicable to nickel-bearing ferrous alloys, was constructed in precisely the same manner, except t h a t for each plotted point an increment of a solution containing nickel ions was added. T h e amount of nickel added was the arbitrary value of 200 mg. (equivalent to a nickel content of 40% based on a 0.5-gram sample). This solution was prepared b y dissolving electrolytic nickel in nitric acid and fuming with sulfuric acid. T h e curve derived in this manner is for use in chromium determination of nickel-bearing ferrous alloys in the range of approximately 5 to 200 mg. per 200 ml.
Table 111.
Effect of Concentrations of Nickel in Steel Sickel,
70
Chrome Present,
Chrome Found,
Sample
S B S 121.4
20.00 (added) 40.00 (added) 64.3
18.69 18.65
18.69 18.69
S B S 161
q
16.90
B
17.06
results obtained for standard samples manufactured by Specialloy, Inc. The effect of varying concentrations of nickel in steel was studied and the results are shown in Table 111. I n addit.ion to the metals mentioned above carbon, manganess, phosphorous, sulfur, vanadium, titanium, tin, lend, zinc, aluminum, cadmium, niobium, tantalum, and selenium do not affect the absorbance of the solution. C o h l t does not interfere if present in concentrations under 0.5%. Tungsten is removed as the trioxide by filtration following the perchloric acid fuming. The trivalent chromium comples was stable for a t least 6 hours, as indirated by observing a constant absorbance over this period. CONCLUSION
The method exhibits the degree of reproducibility and speed n-hich was sought, together with the degree of accuracy required. Furthermore, in practice a large number of samples could be handled conveniently a t one time. This simplicity of operation results in relatively low analysis costs. The results of this study indicate that the application of this procedure exhibits a high order of efficiency, in that one procedure covers a wide range of chromium-bearing materials. ACKNOWLEDGRIENT
-1 t,hird curve, for bronzes, TTW constructed b y using alloy standards prepared by the research department of Specialloy, Iiic. This special processing was required, since S B S standard samples of chromium-bearing copper-base alloys Tvere not available. The chromium content of these special standards was determined by classical methods, while the procedure followed in calibrating the curve was that described by this work. DISCUSSION OF RESULTS
Table I summarizes the results obtained on various SBS standards of ferrous materials tested. Table I1 summarizes the
The authors gratefully acknowledge the advice and assistance of Bernard Hauscr and Mitchell Silverstein. LITER4TURE CITED
(1) Culbertson,
J. B., and Fowler, R. M.,Steel, 122,
S o . 21, 108 (1948). ( 2 ) Sandell. E. B.. “Colorimetric Metal Analysis.” DQ. 191-3, Kew York. Interscience Publishers. Inc.. 1944. (3) T-redenburg, 11. >I,,and Sackter, E. A,, Can. Chcm. Process Inrls., 34, 119-21 (1950).
R E C E I ) F Dfor review June 10, 1553
Accepted May 4, 1954.
Formation of Bromate in the Oxidation of Iodide by Bromine PHILIP W. J E N S E N ’ and A. L. C R I T T E N D E N D e p a r t m e n t o f Chemistry, University o f Washington, Seattle, W a s h ,
I
S THE oxidation of iodide to iodate for iodometric titration, aqueous bromine is used in a number of procedures. There is some disagreement regarding the pH range suitable for the oxidation of iodide and for the removal of excess bromine by boiling. I n some methods ( 1 , 2 ) bromine is added to weakly acidic solutions of iodide and the solutions are boiled. I n other procedures (4,6 ) bromine is added to alkaline solutions which are then acidified before boiling. Under these conditions a slox return of the end point is observed after liberation of iodine from potassium iodide and titration with sodium thiosulfate. Waters and Beal ( 5 ) have attributed the return of the end point to the use of too much bromine. Heim ( 2 ) has reported that if the solution is made weakly acidic before the addition of bromine ( p H of 1.2 to 3.2), no return of the end point, occurs. Heim mggcsted that compounds of bromine in higher oxidation states are formed in alkaline solution and that traces of these are slowly reduced by iodide, causing return of the end point. It is \vel1 known t h a t bromate is not readily reduced by bromide un1 l’rewnt a d d r e r a . Film D t - i m r t n r n t . E I Inc , Biiffalo. S . I-.
dii
Pont de S r i i i o u r s R: C o . ,
less the acidity is high (3). Results reported here confirm Heim’s suggestions. EXPERIMENTAL
Solutions of potassium carbonate (6.5 grams in 50 nil.) were treated with 3 ml. of saturated bromine water then acidified to known pH with concentrated phosphoric acid. T h e solutions \yere boiled for 20 minutes, then cooled. These solutions, corresponding roughly to those obtained in the United States Pharmacopoeia XIT- method ( 4 ) ,were transferred to an H-type polarograph cell. Oxygen was removed by bubbling with nitrogen and polarograms were obtained with the dropping mercury electrode. Similar experiments were made adding bromine only after acidification. Polarograms were compared with those obtained nTithout the addition of bromine, and without the addition of bromine but with addition of known amounts of potassium bromate after acidification. I n some rases 3 ml. of 5% aqueous phenol was added after boiling. I n a series of experiments similar t o those above, the solutions !r-ere acidified strongly with 25 ml. of 6.U sulfuric acid after boiling. Sitrogen gas was bubbled through the solutions to remove bromine and the expelled gases were passed through a drying tower filled with anhydrous magnesium perchlorate. T h e dried gases were mixed with ethylene gas and passed into a trap in a dry ice-acetone bath. Excess ethylene and nitrogen were pumped off and the material remaining in the trap was introduced into
