1806
ANALYTICAL CHEMISTRY
ference betlyeen the total c:tthotlic diffusion current and the anodic diffusion current. The rate of accumulation of the chloro cuprous complex is shown by curve C in Figure 14. The data in this figure were obtained at a pH of 5.3 a t 25". Fiom the difference between curve A (the total cathodic diffusion current) and curve R (the cathodic counterpart' of curve C) thr equilibrium concentration of the cupric tartrate complex is calculated t o he 1.13 millimolar compared to its initial value of 2.66 millimolar, and the equilibrium concentration of the chloro cuprous complex was 1.53 millimolar -i.e., 5i.5yO reduction. At a higher p H value the reduction proceeds more rapidly and more cornpletely, and when the copper concentration is greater than about 5 millimolar cuprous chloride precipitates. From the observed diffusion currents the id/Cm2/3t' l 6value for the cupric tartrate complex under the conditions of Figure 14 is 2.:38 and that of the chloro cuprous complex is 1.i5. Correspondingly, from these data and the Ilkovic' equation, the diffusion coefficient of the cupric complex is 0.39 X 10-5 and that of the cuprous complex is 0.83 X 10-5 sq. cm. per second. The niuch larger diffusion coefficient of the cuprous complex accounts for about a third of the greatly enhanced current observed when copper is deposited on a platinum cathode from a solution containing both hydrazine and chloride. SURZMARY
The optimum conditions for the separation and successive determinations of copper, l)isniutli, lead, and tin from a tartrate
solution by controlled potential deposition onto :I plntinu~ncathode have been established. The influence of such impoitant variables as pH, total tartrate concentration, temperatut e, and cathode potential have been investigated systematically. All four metals may be determined without any intermediate treatment of the solution, except acidification for the determination of tin, in a total elapsed time of about 4 hours (1 hour actual operator time). Very few other elements interfere. The beneficial effect of hydrazine and hydroxylamine as addition agents has been investigated, and theii oxidation products a t a platinum anode have been identified. Hydrazine in the presence of chloride ion is a much more efficient anodic depolarizer than hydroxylamine, and it plays an even more important role by reducing + 2 copper to a chloro cuprous complex which greatly accelerates the copper deposition. LITERATURE CITED
Kolthoff, 1. hI., and Sandrll, E. B., "Textbook of Quantitative Inorganic Analysis," p. 602, Sew York, hfacmillan Co., 1947. (2) Kolthoff. I. M., Sandell, E. B., and hloskovitz, B., J . Am. Chem. (1)
SOC.,55,1454 (1933).
(3) Lingane, .T. J., Anal. Chim.Acta, 2, 584 (1948). (4) Lingane, J. J., IND. ESG.CHEM., ASAL.ED.,16, 147 (1944). (5) Ibid., 17, 640 (1945). (6) Lingane, J., J . Am. Chem. Soc., 67, 1916 (1945). (7) Lingane, J. J., and Jones, S.L., A N ~ LCHEM.. . 22, 1169 (1950). (8) Sand, H. J. S., Trans. Chem. SOC.,91,373 (1907). RECEIVED March 19, 19.51.
Rapid Photometric Determination of Aluminum in Zinc and Steel LUTHEK C. IKENBERRY AND tRBA THOMAS, Armco Steel Corp., Middletown, Ohio
It is frequently necessary to determine small of acid-soluble aluminum amounts (0.002 to 0.10~"c) in zinc and steel. The conventional gravimetric methods are long and tedious. -4 simple photometric method has been developed based on the reaction of aluminum with eriochromecyanin R to form a \ iolet-red colored complex. Its reproducibility is at least equal to that obtained with the gravimetric method. Aluminum may be determined in zinc in 20 minutes as compared to 4 hours by the gravimetric method. .4 determination of acid-soluble aluminum in steel requires on11 3 hours as compared to 8 hours by the gravimetric method.
T
HE increasing use of sm:ill additions of aluminum t o zinc in the production of zinc coatings and the ever-increasing uee of aluminum in the production of steel has made it. highly desirable that a simple, rapid method be developed which would givr accurate values. The gravimetric methods are long and t ctlious and must be carpfully performed by a n-ell-t'rained analyst in order t o obtain accurate values, especially when the nluminum content is under 0.05%. The literature contains numerous references-nIanJ- of which are given by Sandell (6)-on the use of organic reagents for the colorimetric determination of aluminum. Most of these are I)ased on the formation of a st,rongly colored lake x i t h a suitable organic reagent. These lakes have been regarded as internal complexes of aluminum that esist in colloidal solution or as
colloidal aluminum hydroxide on Tvhich the organic compound is adsorbed with a pronounced change in color. Some of the more common reagents which have been used are ammonium aurintricarboxylate commonly known as "aluminon," alizarin S, eriochromecyanin R, and hematoxylin. The most widely used reagent in this country is aluminon (4, 7 , fl), while eriochromecyanin R has found great favor in Europe ( 1 , 2 ) . The simplicity and ease of developing the color with eriochromecyanin is advantageous, but the dark color of the dye itself in the alisence of aluminum is the greatest handicap in its use. I n the development of the colored lake with eriochromecyanin R most investigators (1, S) have added the dye t o the solution containing the aluminum, adjusted the acidity, added the buffer solution, and then allo\yed from 15 t o 30 minutes for color development. Seuthe (8) found that if the dye were added to .a dilute acid solution containing the aluminum and allowed to react for 5 minutes, the maximum color would develop ininiediately when the solution was buffered a t a pH of 6. The final pH of the solution affects the color of the dye as well as the intensity of the aluminum lake. Khile most investigators have used a pH of 6, some have used a lower pH (4.6-5.6). APPARATUS
The Kromatrol photometer was employed in most of this ~ o r k , using the test tube supplied with the instrument as the absorptiorl cell. The absorption cell has an effective light path of approximately 12 nim. Bromatrol filter KO. 5 , vihose maximum transmission is 525 millimicrons, was used. The industrial model of the Klett-Summerson photoelectric photometer with Klett filter KO. 54, whose maximum transmission is 540 millimicrons, was also used.
V O L U M E 23, NO. 12, D E C E M B E R 1951
1807
Table I. Reproducibility of the Photometric Methods for Determining Aluminum in Zinc and Steel No. of Sample Values Zinc (spelter) (0.012%Al) 10 Zinc (spelter) (0.09% Al) 6 Zinc (spelter) (0.16% Al) 6 Steel standard KO.4 (0.050% AI) 24
Range, % A1
AY.
U
0.0113-0.0118 0.076-0.090
0.0117 0.086
0.0002 0.0051
0.155-0.168
0.165 0.044-0.056 0.050
0.0055 0,0022
SOLUTIONS
Standard Aluminum Solution (1 M1. = 0.01 Mg.). Dissolve 0.1760 gram of analytical reagent or C.P. grade KzAlz(S04)4.24HzO in distilled water. Add 10 ml. of dilute (1 to 1) hydrochloric acid and dilute with distilled water to exactly 1 liter. Eriochromecyanin R (0.10%); Dissolve 1.0 gram of eriochromecyanin R (Harleco color index No. 722) in 1 liter of distilled water. Store in a brown bottle. Sodium Acetate Solution (40%). Dissolve 400 grams of SaCzHa02.3H20 in distilled water and dilute to 1liter.
rinsed thoroughly with acid and distilled water. Wash 3 to 4 times with cold water and discard the residue. Heat the filtrate to boiling and evaporate to less than 100 ml. Add 5 to 10 ml. of concentrated nitric acid, 5 ml. of perchloric acid (70 to 72y0), and evaporate the solution to perchloric acid fumes. Cover and continue to fume gently for 1 to 2 minutes with the perchloric acid refluxing on the sides of the beaker. Cool, add 50 ml. of water, and boil to remove chlorine. Transfer to a 200-ml. volumetric flask, cool, dilute to the mark with water, and mix. Transfer a 5-ml. (for 0.06 to 0.12% aluminum), 10-ml. (for 0.02 to 0.06% aluminum), or 25-ml. (for 0.002 to 0.020% aluminum) aliquot to a 200-ml. volumetric flask. Dilute to 100 to 150 ml. and continue with the color development as directed in the zinc method. Use 10 ml. of buffer solution for a 5-ml. aliquot, 15 ml. for a 10-ml. aliquot, and 35 ml. for a 25-mI. aliquot.
CURVE FOR 5 AND 10 M L . ALIQUOTS
/
0.03 004
0.05 0.06
600 -
PROCEDURE
Determination of Aluminum in Zinc. Transfer a 1.0-gram sample to a 250-ml. beaker and add 15 ml. of dilute (1 to 1) hydrochloric acid. Cover and place on a low temperature hot plate until the evolution of hydrogen is complete. Filter to remove the metallic residue (mainly lead) and collect the filtrate in a 200-ml. volumetric flask. Wash the paper and residue with cold water. Dilute the filtrate to the 200-ml. mark with cold water and mix thoroughly. By means of a pipet transfer a 5-ml. (for 0.08 to 0.24% aluminum) or a 10-ml. (for 0.025 to 0.08% aluminum) aliquot to a 200ml. volumetric flask. Dilute to 100 to 150 ml. with water. add exactly 5.0 ml. of eriochromecyanin R solution and allow to stand for 5 to 7 minutes. Then add 15 ml. of buffer solution for a 5-ml. aliquot or 20 ml. of buffer for a IO-ml. aliquot. Dilute to the 200-ml. mark with water, mix thoroughly, and within 5 minutes determine the transmittancy or the absorbancy a t approximately 530 millimicrons. Determine the amount of aluminum present from a predetermined calibration curve. The calibration curve (Figure 1)is prepared from data obtained by adding various amounts of standard aluminum solution to aliquots taken from Bureau of Standards zinc spelter samples No. 108 or 110 which contain less than 0.002% aluminum and developing the color as directed in the above procedure. For very small amounts of aluminum (
