V O L U M E 2 8 , N O . 11, N O V E M B E R 1 9 5 6 rcsult v-as used. This indicated the superiority of the method over the chloroplatinate method. The volumetric procedure of Rudorff and Zannier (6) has been desciibed. The determination of the ammonium ion and potasium in the same aliquot has not been tried; but the method should be most satisfactory, since the formaldehyde determination of ammonium is a very accurate method. Although the alkalinity of the test solution due to the addition of sodium hydroxide should conceivably eliminate any ammonium ion on heating, a large excess of formaldehyde ensures quantitative elimination of the ammonium ion. The ammonium ion is known (3) to react quantitatively with formaldehyde to form hexamethylenetetramine. Rudorff and Zannier reported higher than theoretical results if a large excess of formaldehyde were not present or if the solution were only weakly alkaline. The ptvimetric procedure was preferred to the volumetric procedure only from the standpoint of the analyst’s time. Both procedures require precipitation and filtration. Once the precipitate
1773 is filtered, an analyst need only reweigh after the drying period is completed. A conductometric method using lithium tetraphenylborate t o determine potassium in the presence of sodium, magnesium, calcium, strontium, or barium has been developed by Raff and Brotz (4). The method is very rapid and possibly could be adapted t o the determination of potassium in the presence of the ammonium ion. LITERATURE CITED
(1) Findeia, A. F., Jr., De Vries, T., ASAL. CHEX.28, 209 (1956). ( 2 ) Flaschka, H., Holasek, d.,Amin, A. JZ., 2. anal. Chem. 138,
161-71 (1953).
W.,ISD. EXG.CHEM.,ANAL.ED. 18, 70910 (1946). (4) Raff, P., Brotz, W., 2. anal. Chem. 133, 241-8 (1951). ( 5 ) Rudorff, W., Zannier, H., I b i d . , 140, 241-5 (1953). (6) Sporek, K., Williams, A. F., Analyst 80, 347-54 (1955). (3) LMarcali, K., Rieman,
RECEIVED for review March 26, 1956. Accepted July 9, 1956.
Polarographic Determination of Aluminum and Zinc in Magnesium Alloys D. G. GAGE N a v a l Research Establishment, Defence Research Board of Canada, Dartmouth, N o v a Scotia, Canada
A method for polarographic determination of aluminum in alloy steels has been adapted to permit simultaneous determination of zinc and has been applied to analysis of magnesium-base alloys. An illustration of the effectiveness of this method in studying inverse segregation in magnesium alloys is given.
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S T H E course of an investigation of segregation of aluminum
and zinc in magnesium alloys, the need arose for a rapid and reasonably accurate method for determining these elements. A gravimetric method for aluminum ( 7 ) was unsuitable by reason of both the time required and the fact that zinc could be detected in the ignited residue. Gull ( I ) reported a polarographic method for aluminum, lead, zinc, and manganese in magnesium alloys. This method Tvas suitable for zinc determinations but in the case of aluminum there was some difficulty due to masking of the aluminum wave by a hydrogen wave a t p H 3 or less. A similar method has been reported by Heller and Zan’ko ( 2 , S ) , who also found difficulty with the aluminum determination. Unfortunately, buffer solutions cannot be used to overcome this difficulty (5’. Willard and Dean (9)have described a method for polarographic determination of aluminum in limestone, iron ores, copper-base alloys, and alloy steels containing 0.1 to 1% of the metal. The present paper deals Tvith the adaptation of the Willard and Dean method to the determination of both aluminum and zinc in magnesium-base alloys. 4PPAR4TUS AND REAGENTS
A Sargent Model XI1 polarograph was used in this work. S o other specialized apparatus was involved. Pontochrome Violet S W (sodium salt of 5-sulfo-2-hydroxybenzeneazonaphthol), obtained from E. I. du Pont de Nemours & Co., was used in 0 . 0 5 7 aqueous solution. Samples of the same
compound (designated Solochrome Violet) can be obtained from Imperial Chemical Industries, Ltd. STANDARD SOLLTIONS
The standard solutions of aluminum and zinc >\-ereprepared by dissolving the reagent grade metals in 5M perchloric acid and diluting with water to give each standard a concentration of 10 grams per liter. The magnesium standard was prepared from magnesium perchlorate and made up to contain 20 grams of magnesium per liter. PROCEDURE
A 0.5-gram sample of the alloy was dissolved by careful addition of 10 ml. of 5 M perchloric acid and diluted stepwise to give a final concentration of 5 mg. of magnesium in 50 ml. of the solution containing the dye. iYeutralization and buffering were carried out as outlined in the original work (9, and by Kolthoff and Lingane ( 5 ,6). A portion of the final solution was transferred to a polarographic cell, the dissolved air removed with nitrogen, and the polarogram recorded. The standard solutions were treated in the same way and the aluminum content of the unknown was determined by comparison of the heights of the second waves a t -0.5 volt us. S.C.E. Zinc content could be determined by comparison of height of the waves a t -1.2 volts us. S.C.E. but in cases where the aluminum-zinc ratio was greater than 1, this wave was too small for accurate measurement. In such cases, zinc was determined from the polarogram of an aliquot of the original solution equivalent to a 0.1-gram sample diluted to 50 ml. RESULTS AND DISCUSSION
The polarograms show the typical double wave reported by Willard and Dean (Q), the second wave (-0.5 volt os. S.C.E.) being that used for determination of aluminum. Diffusion currents of a series of standard solutions of aluminum plotted against their concentrations gave a calibration graph identical to that of Willard and Dean. A similar graph can he prepared for zinc, using the height of the third wave a t -1.2 volts us. S.C.E. This also applies when zinc is determined on a separate aliquot of the original solution. The high sample dilution used was made necessary by the limited solubility of the dye. Possible substitute dyes are Super-
1774
ANALYTICAL CHEMISTRY
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the original perchloric arid solution, thus avoiding the necessity of weighing out a separate s:tmple. The comparative method (graphic measurement and comparison with a standard) was used in all cases in calculating the aluminum or zinc concentration of u n k n o m solutions. Taylor (8) has examined the comparative and absolute methods and concluded that the former is more suit,able for routine analytical application, as it is not necessary to exercise a rigid control over conditions if standards are run with each series of samples. Polarographic maxima v-ere not seen in any of the polarograms recorded. Methyl red and bromophenol blue are acting as maximum suppressors as xvell as indicators in t’his case. The use of methyl red as a maximum suppressor has been discussed by Kolthoff and Lingane (4). This met,hod was intended for use in the study of segregation of major constituents in magnesium alloys. S n illustration of the effectiveness of this method in showing differences in the composition of adjacent samples is given in Figure 1. Drilling8 were taken from a magnesium casting and analyzed according t o the above procedure. In this figure, the results of these analyses are plotted against the posit’ionof the sample in the casting. The percentage of magnesium as determined by difference is included and s h o w a typical inverse segregation effect. Results of the colorimetric manganese determination are also shon-n. ACKNOWLEDGMENT
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This work was carried out a t the Naval Research Establishment of the Defence Research Board of Canada as part of Project Kumber D12-75-35-02. The permission of the board to publish this work is gratefully acknowledged.
0.5 1.5 2.5 DISTANCE THROUGH CASTING ( INCHES) Figure 1.
Segregation of major constituents in a magnesium casting
chrome Garnet 1-m d Pontochronie Blue Black R. The latter is often supplied in the form of a zinc salt and a polarogram of the pure dye qhould be checked for a zinc wave before proceeding with the determination of this element. I n the cource oi this 11-ork, it was found that manganese can be determined toloi imetrically with periodate in an aliquot of
LITERATURE CITED
(1) (2) (3) (4)
Gull, H. C., J . SOC.Chem. Ind. 56, 177 (1937). Heller, B. A., Zan’ko, 8 . AI., Za.~odsizayaLab. 8 , 1030 (1939). Ibid., 9, 513 (1940). Kolthoff, I. RI., Lingane, J. J., “Polarography,” vol. 1 , p. 162, Interscience, Xew York, 1952. ( 5 ) I b i d . , vol. 2, p. 515. (6) Zbid., p. 617. (7) Stenger, V. il., Kramer, W. R., Beshgetoor, d. ti-., ISD. EX. CHEW, ANAL.ED. 14, 797 (1942). (8) Taylor, J. K., Awat. CHEU.19, 368 (1947). (9) Willard, H. H., Dean, J. A , , Ibid., 22, 1264 (1950). RECEIVED for review February 27, 19.56.
Accepted June 25, 1936.
Spectrochemical Analysis of Fabricated Steel with the Rotating Electrode J. P. PAGLIASSOTTI Research Department, Standard
Oil Co. (Indiana), Whiting, lnd.
h simple. rapid, and accurate procedure for the spectrochemical anal?=isof steels in acid solutions has been deieloped. Condensed-spark excitation is used w-ith a rotating graphite electrode. Chromium, copper, manganese. inol?bdenuni, nicLe1, silicon, and vanadium are determined with a precision within 2 to 4qc. The procedure is particularly suited to the needs of the steel consunier, because he cannot control the physical form or metallurgical history of his samples. The steel producer may find the procedure useful for classifying scrap. Extension to the analysis of samples of other metals an dalloy is possible.
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OXVENTIONAL spectrochemical methods, in which the sample itself serves as one or both of the electrodes, are often of little use for analyzing fabricated steel. Serious problems arise because the steel consumer is not able to control the physical form or metallurgical history of his sample. The steel producer may encounter similar difficulties in the classification of scrap. A method that analyzes steels in solution would not suffer these disadvantages. Several methods have been described for introducing metal solutions into the excitation zone. Electrode carbons have been impregnated with steel solutions (7), a continuous flon- of metal solution has been fed through a capillary
