ANALYTICAL EDITION
October 15, 1943
621
Summary
Literature Cited
A procedure is proposed for the colorimetric determination of fluoride in natural waters containing not more than 1000 parts per tnillion of any one of the common ions. BY applying small Corrections, results may be obtained to 0.1 part per million of fluoride phosphate and with the use of a 1 0 ( ) - ~ lsample. . interfere, but their presence may be recognized in the course of the determination. The method excels previous colorimetric methods in speed, accuracy, and stability of reagents.
(1) Lamar, W. L., and Seegmiller, C. G., IND.ENO.CHEM.,ANAL. ED., 13,901 (1941). (1941). (2) McClendon, J. F., and Foster, Wm, c.,Ibid.,13, (3) Merwe, P. K.van der, Onderstepomt J. Vet. Sei. Animal Id.. 14,359 (1940). (4) Sanchis. J. M., I N D . ENG.CHEM., ANAL.ED.,6, 134 (1934). (5) Scott, R. D.,J . Am. Water Works Assoc., 33, 2018 (1841). (6) wdpole, &,&aJ , . , 5, 207 (1911). (7) Weiser, H.B.,“Inorganic Colloid Chemistry”, Vol. 11, pp. 273. 360,New York, John Wiley & Sons Co.,1935. ( 8 ) Willtird and Winter, IND. ENG.CHEM, ANALED.,5, 7 (1933).
Modified Basic Succinate Estimation of Aluminum in Magnesium Alloys A. J. BOYLE AND D. F. MUSSER Laboratories of Basic Magnesium, Incorporated, Las Vegas, Nevada
The modification of the Willard and Tang basic succinate procedure described is rapid, simple, and accurate and is advocated as a routine as well as a referee method for aluminum. The accuracy obtained is equivalent to, or, in certain cases, greater than, that obtained with the benzoate-oxine procedure. Procedure8 are given for avoiding interference from iron, silicon, and copper.
T
HE purpose of this investigation is to establish a rapid and accurate routine method for the determination of aluminum in magnesium alloys and to compare it with the recent benzoateoxine method (2), which involves preliminary separation of aluminum as henzoate from most bivalent metals. The basic succinate method submitted is o, modification of the Willard and Tang procedure (4) for the determination of aluminum by precipitation with urea. In the modified procedure as used by the laboratories of Basic Magnesium, Incorporated, the alloy is dissolved in dilute hydrochloric acid, to which ammonium chloride, succinic acid, and urea are subaequently added. This solution, diluted to the proper volume, is made just alkaline to methyl orange by the addition of dilute, freshly filtered ammonium hydroxide or a solution of ammonium carbonate. Boiling the solution gently for 90 minutes results in the quantitative precipitation of aluminum 119 basic succinate. This procedure for aluminum is believed by the authors to be the most rapid accurate method available. It requires only a modicum of analytical skill and is advocated as a routine as well 9s referee method to establish the aluminum content of magnesium alloys. The precipitate of basic aluminum succinate is extremely dense, so that filtration is rapid. One precipitation is sufficient for effective separation from bivalent metals commonly occurring in magnesium alloys. This separation ip not quantitatively possible by the ammonium hydroxide procedure for aluminum, particularly in the presence of zinc (1).
Reagents Succinate reagent. 10 grams of urea, 5 grams of ammonium chloride, and 5 grams of succinic acid, diluted to 300 ml. Hydrochloric acid, c. P.; perchloric acid, c. P.; ammonium hydroxide, filtered; ammonium carbonate, c. P., 5 per cent solu-
tion. Phenylhydrazine, c. P.; hydroxylamine hydrochloride, c. P.; and ammonium bisulfite, 10 per cent solution.
Procedure Weigh a 1-gram sample of the alloy into a 600-ml. beaker. Treat wvith 50 ml. of distilled water and 10 ml. of concentrated hydrochloric acid. After the alloy is dissolved, filter to remove metallic copper. The interference due to appreciable amounts of iron is prevented by adding to the heated filtrate a few drops of a 10 per cent solution of ammonium bisulfite and 2 ml. of phenylhydrazine. This treatment serves to reduce the iron and to maintain it in a ferrous state during the precipitation of aluminum as basic succinate. Dilute with 300 ml. of succinate reagent and boil gently. Make the solution just alkaline to methyl orange with freshly filtered 1 to 1 ammonium hydroxide or a solution of ammonium carbonate. Continue boiling gently for 90 minutes, precipitating the aluminum as basic succinate. Gentle boiling is very effective and does not reduce the total volume quickly. No special care need be given the solution during this period. Filter through a paper of loose texture. Dissolve the small amount of precipitate which adheres to the beaker in 20 ml. of 1 to 4 hydrochloric acid and reprecipitate by addinq 1 to 1 ammonium hydroxide until just alkaline to methyl red. Boil the solution for one minute and filter through the paper containing the major portion of the precipitate. Wash the precipitate six times with hot 1 per cent ammonium chloride made alkaline to methyl red with ammonium hydroxide. Ignite the precipitate a t 1300’ C. for one hour to form nonhygroscopic Corundum, cool, and weigh as oxide. Unglazed porcelain crucibles appear to be best for this purpose since they show no change in weight. For long life of the crucible it is advisable to dry the crucible and precipitate in a standard oven before ignition. For rapid routine analysis, i t is preferable to brush the precipitate out of the crucible and weigh directly as oxide. If silicon is present in uantities greater than 0.2 per cent dissolve the alloy in 30 ml. 1 to 2 perchloric acid. Evaporate the solution on a hot plate to copious fumes of perchloric acid. Cool, dilute to 50 ml. with distilled water, and filter through B fast paper. Wash the precipitate six times with hot distilled water and discard. Copper is dissolved by this procedure. I n order to eliminate the error due to this element, add 20 ml. of the ammonium bisulfite reagent to the solution (0,or (if iron is absent) 1 gram of hydroxylamine. Add 300 ml. of the succinate reagent and continue as described previously.
01
Discussion For a comparison of the basic succinate method with the benzoate-oxine method and with precipitation by ammonium carbonate (used ~ W R W it is silica-free), a standard solution of aluminum chloride was prepared by dissolving aluminum metal
622
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 15. No. 10
Table IV illustrates the error introduced due to silica con-
TABLEI. ANALYSESOF STANDARDSOLUTIONOF ALUMINUM tamination in the aluminum precipitation by both benzoate and CHLORIDE succinate procedures. Each sample contained 51.80 mg. of Aluminum Determination As oxine by bensoate-oxine precipitation hoxidebyammoniumcarbonate precipitation
h oxide by basic succinate precipitation
A1 Present A1 Found Me. Mg. 51.55 51.28 51.55 51.30 51.55 51.49 51.55 51.32 51.55 51.43 51.55 51.48 51.55 51.59 51.55 51.59
Error
&e:
Mg. -0.27 -0.25 -0.06 -0.23 -0.12 -0.07 +0.04 +0.04
5.3 5.3 5.5 7.1 8.8 6.8 5.2 5.2
aluminum aa chloride. The aluminum precipitates were analyzed colorimetrically for silica.
TABLE IV. ERROR Dm Aluminium Precipitation As benzoate
TABLE 11. ANALYSESOF STANDARD SOLUTION OF ALUMINUM CHLORIDECONTAININQMAQNESIUM,NICKEL,MANGANESE, AND IRON CADMIUM, Aluminum Determination
A1 Present Mg. 51.80 51 .SO 51.80 51.80 51.80 51.80
oxine.by benzoate-oxine precipitation
A8
Ai oxide.by basio succinate precipitation
AI Found
TO
Si02 Added as Sodium Silicate
By succinate
SILICA SiOs Found in Precipitate
Mg.
io.
1.0 2.5 5.0 1 .o 2.5 5.0
0.045 0.254 0.468 0.000 0.000 0.027
Error
Mo.
Mg*
52.32 52.21 52.25 51.80 51.75 51.88
+0.52 +0.41 +0.45 0.0 -0.05 +0.06
of 99.99 per cent purity in a sufficient quantity of dilute hydrochloric acid. This was diluted to 1 liter, from which 25-ml. aliquots were taken containing 51.55 mg. of aluminum m chloride. A second solution was later prepared containing 51.80 mg. of aluminum as chloride per 25 ml. of solution. To each of 6 samples of aluminum chloride solution containizg 51.80 mg. of aluminum, the following substances were added as chlorides: 1 gram of magnesium, 5 mg. each of nickel, manganese, and cadmium, and 2 mg. of iron. As indicated in Table 11, the samples were analyzed for aluminum by both the benzoate-oxine and modified basic succinate procedures. The interference of iron was avoided in the precipitation of aluminum as basic succinate with ammonium bisulfite-phenylhydrazine treatment, as described in the Procedure. The bisulfite-phenylhydreeine treatment wan used in various unsuccessful attempts to reduce the iron error in the benzoateoxine method. Stenger, Kramer, and Beshgetoor (8) suggest the removal of iron by treatment with hydrogen sulfide before precipitation of aluminum with oxine. This refinement was not made. Since the concentrations of contaminants present in these six samples greatly exceed those normally found in magnesium alloys, the figures in Table I1 should not be taken as typical of benzoate-oxine iesults on ordinary alloys. They do show, however, that no interference occurs in the basic succinate procedure.
In a few instances magnesium alloys may contain as much as 0.5 per cent silicon. Chloride solutions were prepared containing 1gram of magnesium, 50 mg. of aluminum, and 5.5 mg. of silicon aa sodium silicate. Dehydration by the use of perchloric acid (3) resulted in the recovery of the silicon without measurable loss of aluminum from solution. Hydrofluoric-sulfuric acid treatment of the insoluble residue from perchloric acid dehydration is unnecessary for the amounts of silicon usually present in magnesium alloys.
TABLE V. DUPLICATE ANALYSESOF MAQNESIUM ALLOYSCONZINC(3%), ALUMINUM (6%), AND MANQANESE (0.3%)
TAINING
Sample 1 la 2 2a
3 3a 4 4a
5 5a
Succinate A1.b
A1 by Benzoate-Oxine
%
%
5.98 5.98 5.36 5.36 5.94 5.94 5.76 5.73 5.71 5.70
6.00 5.99 5.32 5.35 5.93 5.95 5.82 5.83 5.85 5.72
Summary
A modification of the Willard and Tang basic succinate procedure is advocated m a rapid and accurate routine method m well as a referee method for duminum. The accuracy attained is equivalent to, or, in certain cmes, greater than, that given by the benzoate-oxine procedure. One precipitation is sufficient to separate aluminum effectively as basic succinate from most SOLUTION OF ALUMINUM bivalent metals. The resulting precipitate is extremely dense, TABLE 111. ANALYSESOF STANDARD CHLORIDE CONTAINING MAGNESIUM, ALUMINUM, AND ZINC so that filtration and washing are rapid. It is essential to ignite Aluminum Determination Series A1 Present AI Found Error the precipitate at 1300" C. in order to convert it completely to MR. Me. Me. nonhygrosoopic Corundum within one hour, For this purpose As oxide by bensoatepreoipitation A 51.80 52.54 +0.74 (ignition temperature 1300°C.) B 51.80 52.70 +0.90 a Hevi-Duty muffle, Model HDT 5610, was used. A temperaAs oxide, by basic succinate preA 51.80 51.75 -0.05 ture of 1200" C. may be used if a sufficiently long ignition period cipitation B 51.80 51.86 +0.08 is allowed. Procedures are given for avoiding interference from iron, silicon, and copper. ~~
~
In order to establish the relative tendencies to coprecipitate zinc in the determination of aluminum by both the basic succinate and benzoate procedures, the latter not followed by oxine precipitation, synthetic solutions were prepared containing magnesium, aluminum, and zinc. Series A contained one gram of magnesium, 51.80 mg. of aluminum, and 40 mg. of zinc. Series 3 contained the same concentrations of magnesium and aluminum with 80 mg. of zinc.
Literature Cited (1) Hillebrand, W. F., and Lundell, G. E. F., "Applied Inorganic Analysis", p. 390, New York, John Wiley & Sons, 1929. (2) Stenger, V. A., Kramer, W. R., and Beshgetoor, A. W., IND.ENQ. CHEM.,ANAL.E D . , 14, 797 (1942). (3) Willard, H. H., and Cake, W. E., J . Am. Chem. Soc., 42, 2208 f19201. (4) Willard, H. H., and Tang, N. K., IND. ENG.CHEM.,ANAL.ED.,9, 357 (1937). \----,
