ANALYTICAL CHEMISTRY
1496 together with the colors observed and the limits of detection. The colors reported correspond t o those found on the hlulliken color standard (8). The limits of detection were obtained by successive halving of the concentrations of the nitro compounds and are defined as lying between the concentration a t which the test was questionable and the next higher concentration. Of the compounds listed, only 2-chloro-5-nitrobenzenesulfonic acid failed t o give the test. A large number of substances other than aromatic nitro compounds were also tested. Of importance is the fact that hydroxylamine, amyl nitrate, amyl nitrite, benzoquinone, hydroquinone, nitroethane, and nitrocyc.lohexane all gave negative tests. Many of these compounds interfere with other test.s for aromatic nitro groups. Phenylacetonitrile gave a positive test, presumably because of a reaction involving its alpha-hydrogen, as octanenitrile and benzonitrile gave negative tests. p-Dimethylaminonitrosobenzene and azosybenzene, as was expected, gave positive tests. Carefully purified hydrazobenzene also gave a positive test. All substances, such as 8-quinolinol, which are capable of forming colored complexes with aluminum ion will also be expected to give positive tests. Michler’s ketone (p,p’-bisdimethylaminobenzophenone) gave a negative test. If, however, the reaction mixture of Michler’s ketone and lithium aluminum hydride is hydrolyzed and then oxidized, various shades of blue and green are obtained depending on the concentration of hydride (IO). I n contrast t o some other color tests, colored compounds can be tested by this procedure because a change (but not a disappearance) of color constitutes a positive test. It is, of course, advisable to compare the color of the tested solution with that of a solution having an equivalent concentration of the unknown. The test described here is both simple t o perform and sensitive. It is given by those compounds which can be reduced to
azo compounds by lithium aluminum hydride-Le., aromatic nitro, aromatic nitroso, and azoxy compounds. hliphat,ic nitro compounds, nitrates, and nitrites do notjnterfere. LITERATURE CITED
(1) Bost, R. W., and Nicholson, F., ISD. ESG. CHEM..AXIL. ED., 7, 190-1 (1935).
(2) Cheronis, N. D., and Entrikin, J. B., ”Semimicro Qualitative Organic Analysis,” p . 135, Xem York, Thomas Crowell Co., 1947. (3) Gilman, H., and Goreau, T. N., J . A m . Chertt. Yoc., 73,293940 (1951). (4) Hearon, W. M., and Gustavson, R. G., IND.ESG. CHEDI., ~ A L ED., . 9, 352-2 (1937). ( 5 ) Kamm, O., “Qualitative Organic Analysis.” p. 69. New York, John Wiley & Sons, 1923. (6) Ihid., p. 72. (7) AlcElvain. S. AI.. ”Characterization of Oiaaiiic Comi,ounds.” p. 145, Sew York. Macmillan Co., 1945. (8) hlulliken, S. P., “Identification of Pure Organic Compounds,” Vol. I, Xew York, John Wiley & Sons, 1904. (9) Mulliken, S. P., and Huntress, E. H., “Identification of Organic Compounds,” p. 162, Cambridge, ~ ~ I s s s .Cummings , Co., 1937. (10) Systrom, R. F., and Brown, ST” G., J . Am. Chem. Soc., 70,373840 (1948). (11) Olivier, S. C. J., Rec. trac. chim.,37,241-1 (1918). (12) Porter, C. W., Stewart, T. D., and Branch, G. E. K., “Methods of Organic Chemistry,” p. 203, Boston, Ginn & Co., 1927. (13) Shriner, R. L., and Fuson, R. C., “Systematic Identification of Organic Compounds,” 2nd ed., p. 73, Sew York, John Wiley &Sons, 1940. (14) Ibid.,p. 75. (15) Vogel, -4.I., ”A Text-Book of Practical Organic Chemistry,” p. 930, London, Longmans, Green & Co., 1948. RECEIVED February 17, 1951. Presented before the Division of Organic SOCIETY. CleveChemistry a t the 119th Jfeeting of the AXERICASCHEMICAL land, Ohio.
Colorimetric Determination of Phosphorus in Steel U S 0 T. HILL Inland Steel Co., East Chicago, Ind. determination of phosphorus in steel bv COLORIMETRIC the molybdenum blue method generally requires either elimi-
nation of all nitric acid from the solution prior to reduction of the bound complex (1,S), or a separation by estraction with an organic solvent (4, 5 ) . This work m s undertaken t o eliminate these steps and if possible t o speed up the method for control purposes in steel manufacture where rapid determinations are a necessity. I n a previous paper ( 2 )it was reported that, by the addition of a fluoride to the silicomolybdate complex in a solution of ferric and ferrous salts, the bound molybdenum is reduced t o the blue, the color being proportional to the silicon present. Apparently after the ferric ions are removed from solution as the fluoride complex, the ferrous ions are capable of reducing the bound molybdenum under the described conditions. Further study of the complexing action of the fluoride ion has resulted in a rapid colorimetric method for the determination of phosphorus in steel based on the molybdenum blue color in a nitric acid medium. EQUIPMENT
The Coleman Model 11 spectrophotometer with 18-mm. matched cylindrical tubes \vas used. EXPERIMENTAL
I t was found that a stable molybdenum blue color proportional to the phosphorus present could be formpd in an oxidized nitric
acid solution of steel by complexing the ferric ions and auppressing the ionization of the nitric acid with a fluoride. Potassium permanganate as an oxidant and dtannous chloride as a reductant proved to be the most reliable reagents for the production of the blue color. Excess permanganate was removed with either sodium nitrite or sulfite. Where a colorimetric manganese determination is to be made on the same solution of sample, ammonium persulfate may be used as an oxidant, but the excess must be destroyed as in the permanganate ouidation. Hydrochloric acid in any appreciable amounts produced color instability and the use of stannous chloride dissolved in hydrochloric acid was abandoned, although a fairly accurate method based on its use was a t first developed. As stannous chloride is readily soluble in solutions of a fluoride, it became convenient t o incorporate it in the complexing reagent. The small amount of chloride introduced in this manner has little effect on the color stability. A spectral transmittance curve obtained with the Coleman instrument indicated a maximum absorption a t 780 mp. I n order to obtain a suitable range, a working curve was constructed a t 650 mp. Some interference has been noted a t this wave length iyith a filter instrument, but none Ivith the narrower band of the instrument used in this work. SOLUTIONS REQUIRED
Nitric acid, 1.20 specific gravity Potassium permanganate, 2.5% Sodium nitrite or sulfite, 10%
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1
1497
Table 1. Analysis of Standard Steels by Method for Low Bur. Stds. Sample 1?e 8g
21d 13e 129, 55h 10e 16c 22b 15d llf
1311
125 111 100
Alloys T. Type Basic open hearth Bessemer Acid open hearth Basic open hearth High sulfur Open hearth iron Bessemer Basic open hearth Bessemer Basic open hearth Basic open hearth Basic open hearth High silicon Ni-Mo M n rail
650 mu 78 3 28 0 54 8 72.0 27 5 91 9 32.2 60. .5 30.6 76 0 80 0 77 8 89 0 69.3 68 0
P
P
Present,
Found,
0.014 0,093 0.041 0.020 0.094 0.003 0.083 0.033 0.084
0.015 0,092 0.041 0.021 0,093 0.003 0.081 0.034 0.085 0.017 0.013 0.015 0.005 0.024 0.025
470
0.018
0.015 0.016 0.008 0.022 0.023
70
Deviation,
% +0.001 -0.001 0.000
+o
001 -0 001 0 000
Bur. Stds. Sample 121a Bob 134
+o
19e
2%
630 mu 70.5
Present,
Found.
ation,
61.0
0.023 0,029
0.021 0.031
-0,002 +0.002
77.j 57.8 29.5
0,016 0.083 0.083
0.015 0.035 0.08'2
-0.001 $0.002 -0.001
%
%
E F F E C T O F VARIABLES
001
-0 001 -0 002 -0 001 -0 003 +o. 002 t o 002
4nal: si- of Standard Steels by 1Iethod for i11 T>pes of Steel Pa DeviP T.
Type 18 Cr, 10 Si 4 Cr, 1 V. 18 W 9 M o , 2 W, 4 Cr, 1v Acidopenhearth Bessemer
Tables I and I1 show the values obtained on National Bureau of Standards samples.
-0.002 J-0 001
a Calculated from formula 7 ' % P = (1.980 - l o g T)/5.80, obtainedfrolnabove d a t a b y method of least squares. Average is t h a t of three determinations, n o determination dmiating from another b y more t h a n 2 ~ 0 . 0 0 2 % .
'Tahle 11.
monium molybdate solution and 80% by volume of the 2.4% sodium fluoride containing 0.2% stannous chloride. To a suitable aliquot of 25 ml. or less, add an equal volume of this solution. Heat for 3 minutes in boiling water, cool, and measure the transmittancy a t 650 mu against water. From a curve of phosphorus versus transmittancy based on Bureau of Standards samples determine the per cent phosphorus.
7c
fl Calrulatedfromformiila, OC P = (1.980 - loo T)/6.22, obtained b y method of least squares. Average is t h a t of three det&minationa. no determination deiiating from another by more t h a n *0.002%.
Ammonium molybdate, 8%. Dissolve 80 grams of aninionium molybdate tetrahydrate in 900 ml. of warm wat,er and dilute to 1 liter. Sodium fluoride, 2.4% containing 0.1% stannous chloride. Dissolve 24 grams of sodium fluoride and 1 gram of stannous chloride dihydrate in 950 ml. of water and dilute to 1 liter. Sodium fluoride 2.4% containing 0.2% stannous chloride. Dissolve 24 grams of sodium fluoride and 2 grams of stannous chloride dihydrate in 950 ml. of water and dilute to 1 liter. Sulfuric acid, 5.1-. METHODS
For Low Alloy and Carbon Steels. Weigh a 0.5-grain sample into a 250-ml. wide-mouthed Erlenmeyer flask bearing a 250-ml. calibration mark. Add 25 ml. of 1.20 specific gravity nitric acid and put in solution on a hot plate. After the oxides of nitrogen have boiled out, add 2 ml. of 2.5% potassium permanganate solution or until an escess persists and boil for a minute or two. Reduce the excess permanganate with 2 ml. of 10% sodium nitrite solution and boil for ahout 30 seconds. Dilute to the mark and mix. Immediately before use, mis 20% by volume of the ammonium molybdate solution and 80% by volume of the 0.1% stannous chloride-sodium fluoridr solution and, to a suitable aliquot of 25 ml. or less, add an equal volume of this solution. Heat from 2 to 3 minutes in boiling water. Cool and measure the trnnsmittancy against water at 650 mu. From a previously prepared curve based on Bureau of Standards samples of phwphorus versus transmittancy obtain the per cent phosphorus. I t is possible to add the reagents separately to the aliquot, the molybdate following the fluoride addition. For All Types of Steels. Weigh a 0.5-gram sample into a 250-nil. wide-mouthed Erlenmeyer flask bearing a 250-ml. calibration mark. .4dd 25 ml. of aqua regia for most alloy strels. Stainless steels are conveniently placed in solution by first -a-etting the sample with 30y0 hydrogen peroside, followed by the addition of 25 ml. of 1 to 1 hydrochloric acid. "hen in solution add 5 ml. of concentrated nitric acid, if not already present, and 10 ml. of 5 -V sulfuric acid. Take to fumes of sulfuric acid, cool, and dissolve salt3 in 15 nil. of 1.20 specific gravity nitric acid and 15 ml. of xater. Add 2 ml. of 2.5% potassium permanganate, boil, and reduce with 2 ml. of 10% sodium nitrite solution. Boil for 30 seronds, dilute to the mark, and mis. Filter off any turbidity. Immediately before me, mis 20% by volume of the 8% ani-
Acid Concentration. Lon acidity will cause precipitation of the colored complex and turbidity, while high acid concentrations will produce low values for phosphorus. Variation up to 1Oc7, of the amount specified may be tolerated. Fluoride Concentration. Unless the fluoride concentration is maintained within 2.5% of the amount specified, erratic results ill be obtained. Molybdate Concentration. The molybdate concentration may be varied widely without affecting the accuracy. Potassium Permanganate. Large excess has little effect, but a sufficient amount must be added to effect complete oxidation of the phosphorus. Sodium Nitrite. Large ncess may result in unstable colors. Variations up to 50% are permissible. Temperature. The color formation is greatly accelerated by heating and can be destroyrd by high temperatures over a long period of tinic. After proper heating and cooling, color stability up to 20 hours has been observed. Interfering Elements. No interference from elements commonly present in low alloy and carbon steels has been observed. Phosphorus Concentration. The method will accommodatc values up to 0.12% phosphorus. I n case of higher phosphorus samples, an aliquot may be diluted with a solution of phosphoruefree iron prepared like the sample to bring the phosphorus within limits of the curve. An aliquot is then processed m described in the procedure. Stability of Reagents. All the reagents are stable for a week or more, escept the sodium fluoride-stannous chloride solution. Tin is slowly oxidized and results will become erratic if a solution more than two days old is used. -4ttempts to stabilize this solution were unsuccessful. By dispensing the sodium fluoride-stannous chloride reagent from under an atmosphere of carbon dioside it has been possible to extend the life of this reagent greatly. Carbon dioxide may he generated in small quantities as needed by siphoning a water solution of dilute sodium carbonate into 50% sulfuric acid, the siphoning action being actuated by the withdrawal of the reagent. By connecting the flasks in series with only the sodium carbonate flask open to the atmosphere, the reagent flask mav be kept near atmospheric pressure of carbon dioside. DISCUSSIOY
A modification of the method has been used to analyze over ten thousand samples in a combined colorimetric procedure for phoqphorus and other elements. Satisfactory speed comparable to the output of other rapid methods of analysis has been realized b r the use of autoniatir pipets. Single samples may be analyzed in 10 minutes or leas. LITERATURE CITED
(1) Hague, J. L., and Bright, H. A , , ,J. Research Natl. Bur. Standards, 26,405-13 (1941). ( 2 ) Hill, U. T., ANAL.CHEY.,21, 589-91 (1939). (3) Xatz, H. L., and Proctor. K. L.. IND.ENG.CHEM.,A N . ~ LED.. .
19,612-14 (1947). (4) Matveeva, K. A , , Zaaodskaya Lab., 13, 1136-7 (194i) (5) Rainbow, C., S u t u r e , 157,268-9 (1946). RECEIVED J u l y 31, 1950.
