Volumetric D etlermination of Tungsten A Study of the Method Proposed by Dotreppe M. LESLIEHOLT,University of Wisconsin, Madison, Wis.
A
LTHOUGH it has been quite generally accepted that a satisfactory volumetric determination of tungsten based on a reduction and subsequent oxidation is impracticable (g), the method proposed by Dotreppe (1) appears simple and very accurate. The present author, having need for a rapid determination of tungsten, thought it worth while to repeat the work and investigate its possibilities. The method of Dotreppe involves reduction of an alkali tungstate by zinc and concentrated hydrochloric acid in an atmosphere of carbon dioxide, oxidation with ferric alum, titration of the resulting ferrous iron by permanganate, and calculation based on an apparent reduction of WOS to WaOr. The results reported show that 99.6 per cent of the tungsten, the average of the nine values included, was recovered. Table I presents results obtained when the method cited above was followed as exactly as possible. TABLE I. RESULTS USINQTHE DOTREPPE METHOD SAMPLE.
VARIATION IN NUMBER TUNQ~TSN OF TRIAL@ REICOV~RED
AVB~RAQS R~COVBRY
%
%
86 t o 94 74 to 94 79 to 98
86 84 93
tried. A sharp end point was obtained by reduction of the tungstate in the presence of a small amount of phosphoric acid and titration of the ferrous iron with potassium dichromate, using diphenylamine sulfonic acid indicator prepared and used as suggested by Sarver and Kolthoff (3). Phosphoric acid prevents the precipitation of tungstic acid, but still has no influence on the reduction or on the reduced compound (1). Table I1 presents results obtained by using this modified method. TABLE 11. RESULTSUSINGTHE DICHROMATE METHOD SAMPLS KzWO4+ KC1 KaWO4 NanWOc
NUMBER TRIAL^
OF
12 6 12
VARIATION IN TUNQBTEN AVSRAQB RB~COVEIRB~DRB~COVIORT
%
%
71 to 97 88 to 98 76 to 90
88 93 80
These again were very poor, even though the end point was quite clearly defined. CONCLUSION This proposed volumetric determination of tungsten has been found unsatisfactory mainly because of the apparent impossibility of obtaining consistently identical reductions of
MODIFIED PROCEDURE
WOS.
These poor results were apparently due to difficulties in the reduction of the tungstate and to a lack of sharpness in the permanganate end point. The end point was obscured by a flocculent precipitate of pale yellow hydrated tungstic acid which appeared when the solution waa diluted before being titrated. Conditions of reduction were kept as exactly alike as possible, although variations in time, temperature, concentration of the acid, and amount of zinc were
LITERATURE CITED (1)
Dotreppe, G., Chimie
& Industrie, Special No. 173-8 (March,
1931).
Hildebrand and Lundell, “Applied Inorganic Analysis,”
p. 551, John Wilev & Sons. N. Y . .1929. (3) Sarver, L. A., and Kolthoff; I. M., J . Am. Chem. SOC.53, 2902, 2906 (1931).
(2)
RECEIVEID September 16, 1934.
A Simple Laboratory Apparatus for Vacuum Distillation ALBERTW. STOUT AND H. A. SCHUETTE, University of Wisconsin, Madison, Wis.
A
LL the current types of receivers for collecting the successive fractions of a condensate from a vacuum distillation without interrupting the operation apparently trace their origins to one of two p r e c u r s o r s : One is t h e T h o r n e “ t r i a n g l e ” (6),the other is e i t h e r t h e Gorboff-Kessler v a c u u m desiccator (4) with r e v o l v i n g table, or its modification, t h e Bruhl apparatus (2), which appears to have been accepted to the exclusion of its predeFIGURE 1 cessor. It in turn seems to have inspired the less cumbersome, compact Bredt “star” device (1) or its antecedent, a receiver described by Gautier (3). The triangle types are not well suited for sharp
separations where quantitative analyses are involved. For this purpose the Briihl and star receivers are superior. The need, arising during the course of the fractionation of methyl esters of fatty acids in the analysis of oils, for a small receiver with tubes not too large to be weighed on an analytical balance, yet readily stoppered for storage, led to the construction of a device (Figure l), patterned after the von Wechmar (6) apparatus, from one 250-cc. and six 50-cc. Erlenmeyer flasks and a ground-glass joint. Because of its simplicity of construction and efficiency of operation-a 3-mm. vacuum can easily be maintained in the system and a recovery loss of less than 0.3 per cent is not unusual (Table I) -it is described here, in the hope that others may find it a useful tool in the analysis of fatty oils or in other fields. An outlet tube, throu h which the system is evacuated, is sealed into the side of t%e Erlenmeyer flask. Equally spaced around the eriphery of its base are sealed six 10 X 40 mm. outlets to whicg the receivers are subsequently attached by means of rubber stoppers. One is not necessarily limited to six o enings, and ground-glass joints may be substituted for rutber sto pers. The receivers are made by givin the neck of a 50-cc. Erinrneyer flask a 90’ bend. Into the ne& of the large flask a
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November 15,1934
I N D U STR I AL AN D E N G I N E E R I N G C H E M I ST R Y
female 0.75-inch (1.9-cm.) ground-glass joint, is fitted by means of a rubber sleeve, or, if preferred, joint and flask may be sealed together. The male joint is similarly treated with respect to the condenser, but in any case the system is 80 assembled that the end of the delivery tube is brought directly over one of the individual receivers SO that the droplets of distillate fall directly into the receiver without wetting the sides of the neck. TABLEI. FRACTIONAL DISTILLATION OF METHYLESTERSOF FATTYACID^^ FRLCTION BOILINQ POINT AT 3 MM.
WEIQHT c. Crams 1 165-166 2.8352 2 165-169 2,9516 3 169-172 3.1822 4 172-183 3.1690 1.4704 183t Taken 13.6370 Recovered 13.6984 Loes 0.0386 Percentage loss 0.30 Courtesy of Thelma Garvin.
477
This apparatus has given most satisfactory service in a 3-year trial in the hands of advanced students. It is rugged, requires the SerViceS Of no expert in its construction, is not costly to make, and takes up little space on the desk. Its dimensions and number of receivers can be varied to suit the needs of the operator. LITERATURE CITED (1) Bredt, J., Ann., 367, 354 (1909). (2) BriiN, J. W., Ber., 21, 3339 (1888). (3) Gautier, H., Bull. SOC. chim., [3] 2, 676 (1889). (4) Gorboff, A.,and Kessler, A., Ber., 18, 1363 (1885). (5) Thorne, L. T., Ibid., 16, 1327 (1883). (6) Wechmar, Houben-Weyl, “Die Methoden der organischen Chemie,” Vol. I, p. 568, Georg Thieme, Leipzig, 1921. RECEDIVBD September 10, 1934.
Ceric Sulfate for Estimating Tin in Bearing Metals L. G. BASSETT AND L. F. STUMPF, Rensselaer Polytechnic Institute, Troy, N. Y.
I
N THE usual method for estimating tin in bearing metals, the stannous tin is oxidized in hydrochloric solution with standard iodine solution which must be standardized against pure tin and checked frequently. H. H. Willard, N. H. Furman, and others in a series of papers in the Journal of the American Chemical Society from 1928 to 1934 have pointed out the advantages of ceric sulfate as a standard oxidizing agent., It may be used in hydrochloric acid solution and retains its original concentration over a long period of time. I n the present investigation the procedure as described by Hallett (2) was followed except that 0.1 N ceric sulfate was used as the oxidizing agent, using as indicator 5 ml. of a solution made by dissolving 1 gram of soluble starch and 10 grams of potassium iodide in 100 ml. of distilled water. It was also found that better results were obtained if 0.1 gram of antimony was dissolved with the sample. Runs were made on pure mossy tin with the results shown in Table I. TABLHI. ESTIMATION OF TIN TIN SAMPLE Gram 0.1032 0.1003 0.1080
TINFOUND Gram 0.1027 0.1001 0.1084
TINSAMPLI Gram 0.1082 0.1362 0.0996
TIN FOUND Gram 0.1080 0.1363 0.1003
In order to test the validity of the method on actual bearing metals containing possible interfering elements such as copper and arsenic, runs were made on Bureau of Standards bearing
metal samples, Nos. 53 and 54. No. 53 is a lead-base bearing metal containing 10.94 per cent of tin, and No. 54 is a tinbase bearing metal containing 88.24 per cent of tin. The results obtained are given in Table 11. TABLE11. ESTIMATION OF TININ BEARINQ METALS SAMPLE No.63 Weight of Tin sample found Gram % 1.0027 10.89 1.0010 10.87 1.0018 10.94
SAMPLB No. 64 Weight of Tin sample found Gram % 0.1904 88,23 0.1017 88.68 0.1927 88.06
From these results it appears that ceric sulfate may be used as the standard oxidizing agent in the analysis of tin in bearing metals with results precise to from one to four parts per thousand. The theoretical titer obtained by standardizing against anhydrous sodium oxalate (1) may be used. The solution does not have to be restandardized over a long period of time. In the authors’ work, extending over a period of 3 months, the solution did not change appreciably.
LITERATURE CITED (1) GFS Chemical Co., Cleveland, Ohio, BulIetin, “Ortho-Phenanthroline,” Method B, p. 22. (2) H d e t t , R. L.,J . Soc. Chem. In& 35,1087(1916). RECEIVBDJune 28,1934.
Cyclohexanol in Colorimetric Determination of Molybdenum LORENC. HURDAND FREDREYNOLDS, University of Wisconsin, Madison, Wis.
D
URING the course of a study of the variables involved in the colorimetric determination of rhenium it was found that the presence of small amounts of ether exerted an appreciable influence upon the development of the color. Ether is generally used to extract the thiocyanate-rhenium complex and it was thought that perhaps the erratic results often obtained might be due to an interaction of the ether and the rhenium thiocyanate or to an alteration accelerated by the ether. Accordingly a search was made for more inert extraction media. It was found that cyclohexanol exerted
practically no influence upon the reaction and that the colored complex was unusually soluble and stable in this solvent. Inasmuch as the conventional colorimetric method for molybdenum is identical with that for rhenium, it seemed probable that the same factors which contributed to the unreliability of the rhenium determination might account for some of the peculiarities often encountered with molybdenum. Cyclohexanol, like butyl acetate, is a better solvent for t h s thiocyanate than ether or ether mixtures. Consequently
