VOL. 9, NO. 11
INDUSTRIAL AND ENGINEERING CHEMISTRY
518
ing flasks and filter the extracts through crucibles in which a layer of Hy-Flo-Supercel (from the Johns-Manville Co.) is placed over a layer of ignited asbestos. The filtrates are received in 200-ml. Erlenmeyer flasks placed under bell jars; in a hole in the top of each jar a cork stopper is inserted for the stem of the Gooch holder and a glass tube to which suction is applied. Wash the flasks and Gooch crucibles with ether, combining the washings with the filtrates. Remove the ether in each Erlenmeyer flask rather completely under reduced pressure by inserting in the flask a one-hole rubber stopper and applying suction. Hasten the removal of the ether by rotating the flask in a pan of hot water not exceeding 50' C. Discontinue when the "rapid boiling" stops. Add 75 ml. of petroleum ether (Skelly solve F) and 5 ml. of ethylene glycol to each flask. Mix by rotating the flask and let stand overnight. Filter through a Gooch crucible (prepared as above) in order to remove the material precipitated by the petroleum ether, Wash the precipitate with a small amount of petroleum ether, receiving the washings in the filtrate. In order to prevent further precipitation of the insoluble material by the decrease in temperature and the addition of the washings during the process of filtration, place the flasks containing the filtrates in a pan of water a t about 35' C. In order to precipitate the ossypol as a dianiline compound, add 2 ml. of aniline and shafe thoroughly. Digest 1 to 1.25 hours by placing the flasks in pans of hot water (50" to 55" C.)
not over 2 om. (0.75 inch) deep, exercising carenot to exceed 60" C. When the digestion is completed, add sufficient petroleum ether, if necessary, to make a total volume of 50 to 60 ml. If the volume should fall to approximately 25 ml. before the digestion is completed, add an equal volume of petroleum ether (Skelly solve B or F). Lighbly stopper the flask and let stand overnight. When the precipitate is small (10 to 15 mg.), let stand 36 hours or longer. Filter through a tared Gooch crucible and wash the precipitate of dianiline gossypol with petroleum ether (Skelly solve B or F). Followwith four washings of water, then with 5 ml. of 95 per cent alcohol, and finally with a few milliliters o,f etroleum ether. Multiply the Dry the precipitate to constant weight at 100 weight of dianiline gossypol by 0.775 to obtain 'the equivalent weight of gossypol.
8
Literature Cited (1) Baskerville and Hamor, J. IND.ENG.C H ~ M3, . , 387 (1911). (2) Halverson, J. O., and Smith, F. H., Ibid., Anal. Ed., 5,29 (1933). (3) Marqueyrol, M.,and Goutal, E., Mdm. poudres salpetrea, 19, 368-80 (1917). (4) Smisniewicz, T., and Zielinski, R., Przemysl Chem., 16, 35 (1932).
RECEIVED September 14, 1937. Published with the approval of the Director of the North Carolina Agricultural Experiment Station as Paper 100 of the Journal Series.
Determination of Chromium in Chromite A New Procedure Employing a Mixture of Phosphoric, Sulfuric, and Perchloric Acids G. FREDERICK SMITH AND C. A. GETZ, University of Illinois, Urbana, Ill.
T
HE determination of chromium in chromite has until
now been made following solution of the sample after a sodium peroxide fusion (1). The highly refractory nature of chromite ores eliminates the possibility of solution following acid treatment with 72 per cent perchloric acid, 95 per cent sulfuric acid, or mixtures of both. The nearest approach to a suitable single acid is concentrated perchloric acid, but it would be desirable to be able to increase the temperature at which i t could be used and simultaneously to increase the solubility of chromic acid, which forms an insoluble protective coating on the surface of the undissolved ore. Using a mixture of phosphoric and sulfuric acids, solution of all available types of chromite ores is rapid. The conditions for the subsequent oxidation of chromium in this mixed acid solution of the sample are described here. The resulting complete method is very rapid, accurate, and economical. The complete analysis of chrome ores has been described by Cunningham and McNeill (1). The determination of chromium follows solution after fusion with sodium peroxide. The determination of iron and aluminum can be made after solution in a mixture of sulfuric and perchloric acids, or for samples not soluble by such treatment, after fusion in a mixture of sodium carbonate and borax. Willard and Thompson (6)recommend sirupy phosphoric acid as a solvent for refractory materials such as iron ore and bauxite, but this procedure was found to be unsuited to the solution of chromite. Smith and Getz (8) have used phosphoric acid as a solvent for ferrochrome, followed by the addition of perchloric and sulfuric acid for the oxidation of ohromium. A somewhat similar process has been described by Smith and Smith (4) for the determination of chromium in stainless steel after solution in a mixture of sulfuric and perchloric acids.
TABLEI. ANALYSISOF BUREAUOF STANDARDSCHROME REFRACTORY 103 Sample
Q& 0.1132 0.1526 0.1843 0.1285 0.1568 0.1576 0.1936 0.1441
0.06019 N FeS04 Required MI. 32.99 44.30 53.47 37.36 46.60 46.70 66.94 41.95
CrrOa Found
%
% 37.07
36.91 36.88
36.96
36.97 36.88
36.73"
37.02
Av. 36.96 4
Error CriO:
+o.
10 -0.06 -0.09 -0.01 0.0
-0.09
-0.245 $0.06 0.05
Excluded from the averages.
Materials Used The chromite solvent consists of a mixture of 8 parts of 95 per cent sulfuric acid and three parts of 85 per cent phosphoric acid. The oxidizing solution is made up with 2 parts of 72 per cent perchloric acid and one part of distilled water. A standard 0.05 N solution of ferrous sulfate and a standard 0.05 N solution of ceric sulfate are prepared and standardized by procedures often previously described. Ferroin (0- henanthroline ferrous ion), a 0.025 M solution, is used as the incfkator. Finely ground crystals of potassium permanganate, dilute (1 to 3) hydrochloric acid, and dilute (1 to 1) sulfuric acid are also required.
Special. Laboratory Apparatus The technic employed in the solution of samples, oxidation of chromium, and subsequent preparation for titration is greatly simplified by use of a few special items of laboratory equipment which have been described in a previous paper (2). While the determinations can be carried out successfully without the modified Rodgers ring burner and digestion flask
519
ANALYTICAL EDITION
NOVEMBER 15, 1937
still head therein described, the work is much simplified by their use.
Analyzed Samples for Evaluation of Procedure The B~~~~~of Standards chrome refractoryN ~ 103 . was the most valuable analyzed sample available. A sample of chromite ore having a complete, accurate analysis was supplied through the courtesy of H. H. Willard. A series of chromite ores was furnished by E. J. Lavino and Co., Norris-
part of the hexavalent chromium is reduced. Add 3 drops of ferroin indicator and titrate to complete reduction of chromium, as indicated by the appearance of a definite pink coloration. About 0.05 ml. of the ferrous sulfate is required after the first appearance of an orange color in the blue-green reduced solution. From the measured volume of standard ferrous sulfate required, the per cent of chromic oxide present may be calculated. The potassium permanganate is used in this procedure to eliminate the effect of hydrogen peroxide, known to result (3) during oxidations using perchloric acid at or near 200' c.
Analyses
town, Pa., with the works analysis for Crz03given through the kindness of G. E. Seil. Other samples were supplied by the Chromium Mining and Smelting Corporation, Sault Ste. Marie, Ontario, The samples were from such varied sources
For the following analyses the ceric sulfate was found as the mean of 9 consecutive comparisons with Bureau of Standards NazCz04 t o be 0.03541(1) N with a n average deviation from the mean of one part in a thousand. The ratio of ceric sulfate to ferrous sulfate was 50/35.28, giving a ferrous sulSAMPLES OF CHROMITE OF CriOa IN COMMERCIAL TABLE11. DETERMINATION fate normality of 0.05018(6) N . Average No. of
-
Duplicate Sample Analyses No. Averaged
Source
E. J. Lavino
University of Michigan Canadian Canadian (beneficiated)
9 10 11 12
3 3 3 5
CrlOs Found
Deviation from Average
% 32.56 31.86 33.35 30.96 30.90 31.79 31.44 31.64 26.63 31.92 27.12 26.72
0.01 0.06 0.02 0.04 0.02 0 02 0.02 0.03 0.06 0.05 0.04 0.10
that the new procedure is probably applicable to any chromite ore t h a t may be encountered. The samples had a range of 26 to 37 per cent of chromic oxide, 8 to 22 per cent of silica, and 16 to 22 per cent of magnesium oxide. The beneficiated sample supplied by the Canadian firm was low in Crz03 and high in calcium oxide. Detailed Procedure Grind samples to pass a 100-mesh sieve and dry 2 hours at 105' to 110' C. Transfer weighed 100-to 150-mg. samples from a weighin bottle to a clean, dry 500-ml. Erlenmeyer flask. Add IO-mf. of chromite solvent and swirl flask vigorously at once to get the sample in suspension and prevent a strong tendency to form a cake and stick to the bottom of the flask. Adjust the refluxing still head in the neck of the flask and heat to gentle boiling temperature, continuing the swirling motion for 5 to 15 minutes or until the sample is seen to be entirely dissolved. Allow to remain on the burner without swirling 5 minutes longer. Samples which are not all dissolved in the time given should be ground finer. The solution at this point is grayish green in color and only a very small amount of insoluble silica is found suspended in the solution. In swirling the hot flask, a laboratory metal clamp is conveniently employed. Allow the contents of the flask to cool for a minute and add through the still head 12 ml. of the oxidizing solution. Place a small Anschutz thermometer, suspended from a small platinum wire, within the solution in the flask, retaining the refluxing still head in position. Heat to 215" C. during a 5-minute interval. The droplets of condensed acid on the flask walls should all be undergoing rapid reflux down the flask walls at the end of this period. Remove the flask and contents from the source of heat and add 60 to 70 mg. of powdered potassium permanganate, after partially removing the still head and allowing the flask contents to cool to 210' C. Readjust the still head and swirl the flask contents to disperse the permanganate. With continued swirling of the flask contents, dip the flask into cold water. After 8 to 10 seconds add 125 ml., cautiously at first, of distilled water, pouring it through the refluxing still head. Remove and rinse the still head and thermometer. Rinse the flask walls and add 25 ml. of dilute (1 to 3) hydrochloric acid and a Filter-Cel boiling chip. Heat to a gentle boil and continue t o boil 5 minutes after disappearance of potassium ermanganate and manganese dioxide to ordinary temperature, and add to remove the chlorine. 40 ml. of dilute (1 to 1) sulfuric acid. Titrate, using a standard solution of approximately 0.05 N ferrous sulfate, until the greater
8001
CrrOg Present
Difference CriOs
%
%
...
..
BUREAU OF STANDARDS CHROMERE103. E i g h t c o n s e c u t i v e analyses of chrome refractory 103 (corFRACTORY
retted for its content of 0 . 0 8 p e ~ c e noft
vanadium) were carried out and the results are given in Table I. The cer... .. tificate value for this sample is 36.97 per ... .. cent CrzO,. Theaverage of the absolute ... .. 26168 +0:05 errors shows that the determinations ... .. agreed with the certificate value to ... .. within less than 2 parts per thousand. T o check the extent to which the finely ground samples of chromite ore adsorb moisture upon standing, three analyses of undried sample 103 were made and 36.75, 36.78, and 36.79 per cent of chromic oxide were found. This indicates the importance of drying before sampling. CHROMITE FROM COMMERCIAL SOURCES. T o test further the general applicability of the new process to samples of chromite from a wide variety of sources, 12 additional samples were analyzed and the results are given in Table 11. The values shown are the average of 3 to 4 individual determinations of each ore. The complete analysis of sample 10 was: CrzO3, 26.58; SiOz, 22.04; FeO, 14.93; Al103, 9.01; MgO, 21.38; SO3, 0.38; P, 0.39; loss onignition, 4.77 per cent. The beneficiated sample, No. 12, was found to be the most resistant of all to the solvent action of mixed phosphoric and sulfuric acids. 33:39 30.86 30.88
-0:04 -0.10 -0.02
Summary A new and rapid method for the solution of all types of chromite ore, using a mixture of phosphoric and sulfuric acids, is described. The chromium, after solution in mixed phosphoric and sulfuric acids, is oxidized, using concentrated perchloric acid at 215' C., followed by treatment for a brief time with potassium permanganate. I n the determination of hexavalent chromium, standard ferrous sulfate is used with ferroin as indicator. The new process was used for the analysis of 13 samples of chromite and chrome refractories from a wide variety of sources and no exceptions t o its applicability were found. The method is rapid, accurate to within less than 2 parts per thousand, and not costly.
Literature Cited (1) Cunningham and McNeill, IND.ENG. CHEM.,Anal. Ed., 1, 70 (1929). (2) Smith and Getz, Ibid.,9 , 3 7 8 (1937). (3) Smith, MoVickers, and Sullivan, J. SOC.Chem. Ind., 54, 369T (1935). (4) Smith and Smith, Ibid., 54, 185T (1935). (5) Willard and Thompson, IWJ. ENG.CHBIM., Anal. Ed., 3, 399 (1931).
R E C E I V ~July D 22, 1937.
