174
INDUSTRIAL AND ENGINEERING CHEMISTRY
beryllium,, ignite the precipitate in a tared platinum crucible and finally weigh as aluminum oxide. I n the presence of beryllium, separate aluminum using 8-hydroxyquinoline. Acknowledgment
The writer must give due credit to Walker & Whyte, Inc., New York, N. Y., where he carried out part of the above investigation while he was associated with Herbert H. Khite, now chief chemist of the Tin Processing Corporation, Galveston, Texas. To him and to W. C. Bowden, L. Cudroff, and E. H. Turner, all of Ledoux & Co., 155 Sixth Ave., New York, N. Y., the writer expresses grateful appreciation for valuable suggestions in connection with the preparation of this paper. Literature Cited (1) Allen, W. S.,and Bishop, N. B., 8th Intern. Congr. Appl. Chem., 1-2, 48, 1912. (2) Eng. Mining J . , 142, No. 2,48 (1941). (31 Gesellschaft Deutscher Metallhutten-und Bergleute. Berlin, “Mitteilungen des Chemikerfachausschusses der Gesellschaft
Vol. 15, No. 3
Deutscher Metallhutten-und Bergleute, Bd. I, Ausgewaehlte Methoden fur Schiedsanalysen und kontradiktorisches Arbeiten bei der Untersuchung von Erzen, Metallen und sonstigen Hiittenprodukten”, 2nd ed., p. 208. Ibtd., pp. 347-51. Hillebrand and Lundell, “Applied Inorganic Analysis”, p. 573, New York, John Wiley & Sons, 1929. Ibid., p. 575. Ibid., p. 679. Ibad., p. 580. Kallmann, S.,IND.ESG. CHEM..A x ~ LED., . 13, 897-900 (1941). Low, “Technical Methods of Ore Analysis”, p. 49, New York, John Wiley & Sons, 1922. Mantell, C. L., “Tin”, A. C. S. Monograph Series, p. 351, New York, Reinhold Publishing Co., 1929. Mellon, M. J., “Methods of Quantitative Chemical Analysis”, p. 123, New York, Macmillan Co., 1937. Richards, T. W., and Parker, H. G., Proc. Am. $cad. Arts SCZ.,31, 67 (1895-96). Roush, G. A., “Strategic Mineral Supplies”, p. 198, New York, McGraw-Hill Book Co., 1939. Ibid., p. 199. Scott, W. W., “Standard Methods of Chemical Analysis”, pp. 970-1, New York, D. Van Nostrand Co., 1939. Smoot, A. M., Eng. Mining J., 94, 412 (1912).
Determination of Iodate in the Presence of Bromate and Chlorate I. M. KOLTHOFF AND DAVID N. HUME, School of Chemistry, University of Minnesota, 4linneapolis, Minn.
T
HE method of van der Meulen ( 2 ) for the volumetric
determination of iodate in the presence of bromate, while accurate, involves a long and rather complicated procedure. I t has been found that by carefully buffering the reaction mixture it is possible to determine iodate by means of a n ordinary iodometric titration without interference from bromate or chlorate. After the titration of iodate, bromate can be titrated in the same mixture by adding a n adequate amount of hydrochloric acid and a fe\\- drops of a molybdate solution as a catalyst (1). Preliminary experiments indicated t h a t the reaction between iodate and iodide was rapid and complete in phthalate buffers between p H 4 and 5 . Under the same conditions the reaction between bromate and iodide is slow. At p H 5 it is slow enough to be disregarded during the time required for a titration unless the concentration is high. The rate of the reaction is more rapid a t p H 4. By proper choice of buffer it is possible to have all the iodate present in a
TABLE 1. TITRATIOX OF IODATE (Titration of 25.00-ml. samples of 0.1 N KI03 with 0.09791 0.1 S KBr08 NazStOa Added Biphthalate UsedU AWL Grams M1. .. 2 25.54 .. 2 25.54 .. 3 25.55 25.53
5 Xa?S:Os) Error
5% +0.04 +0.04
f0.08
0.00
mixture react without appreciable interference from the bromate. The buffer added has two functions. It supplies the hydrogen ions necessary for the iodate-iodide reaction. It also adjusts the p H of the medium to a value a t which the iodate reaction is rapid, whereas the bromate reaction is slow, though measurable. The p H of the buffered solution increases during the reaction between iodate and iodide, since hydrogen ions are used up. Thus the p H is raised t o a value at which the rate of reaction between bromate and iodide is negligibly small.
T.4BLE
s
11. TITRATIOSS OF IODATE-BROMATE MIXTURES WITH 0.09713 S SODIUM THIOSULFATE
0.1 KI03
0.1 s KBr03
Biphthalate
Ml. 25 25 50 50 5 5 5 5
M1.
Grams
M1.
M1.
5%
2.0 2.0 4.0 4.0 2.0 2.0 0.5 0.5 0.5 1.0 1.0
25.750. 25.75’” 51.45 51.48 5,210 5,240 5,153 5,153 5.148 10.30 10.30 10.30 25,74 25.74
25.74 25.74 51.48 51.48 5,148 5.148 5.148 5.148 5,148 10.30 10.30 10.30 25.74 25.74
+0.04 +0.04 -0.06 0.00 f1.2 fl.9 fO.l
5b
10 c
100 100
25 25 25 25 25 25 0
0
10 10 10 1.0 10 25 Od 2.0 25 Od 2.0 4 E n d point tended t o d r i f t slightly. 6 20 ml. of H20 added. C 10 ml. of H2O added. d 10 ml. of 1 3’ KC103 added.
SaBzOs Used
Na9S203 Theoretical
Error
t0.1 0.00 0.00 0.00 0.00 0.00 0.00
Experimental Aliquot portions of a standard 0.1 N potassium iodate stock solution were treated with various amounts of solid potassium Theoretical 25.53.
b Stood 5 minutes before titration. c
1 g. of KBrOs present.
biphthalate. Potassium iodide was added and the mixtures
were titrated with standard sodium thiosulfate. In each case the major portion of the thiosulfate was added from a pipet and the titration was finished with a microburet. This technique
A N A L Y T I C A L EDITION
March 15, 1943
175
Analytical Results TABLE111. TITRATIONS WITH 0.01 A’ SOLUTIOKS IS PRESENCE The data in Table I show that the conditions of the proOF 1 G R A M O F POTASSIUM BIPHTHALATE cedure permit a n accurate titration of iodate and that the 0.01 s 0.1 A0.009713 s ;h;a2S2+ KIOB KBrO? NazS?03 Theoretiral Error amount of biphthalate used is not critical. Tables I and I1 .MI. -Tf1 . Mi. ,1f1. 5% show that a fourfold excess of bromate or chlorate does not -0.12 25.71 25.74 25 0 interfere. 25,70 25.74 -0.16 25 0 25,74 +0.12 25 5 25.77 The approximate ratio of 2 grams of biphthalate t o 2.5 25.74 +0.12 25.77 25 J 25 1 25.75 25.74 +0.04 milliequivalents of iodate is necessary if results accurate 25 nu 25.71 25.74 -0.12 to 0.1 per cent or better are desired. The above ratio of a
25
0a
10 10
1
25.70 10.34 1 10.31 2 1111. of 1.0 .V KC103 present.
25.74 10.30 10.30
-0.16 +0.40
+0.10
permitted reproducibility to about 0.05 per cent in titrations requiring approximately 25 ml. of solution. Titrations were made also with varying amounts of potassium bromate or chlorate present. The following procedure was found to give excellent results. To 25 t o 50 ml. of solution (containing about 2 to 3 milliequivalents of iodate) 2 grams of potassium biphthalate are added and the mixture is swirled until solution is effected. Three grams of potassium iodide are added and the mixture is alloxed to stand for 3 minutes. The liberated iodine is then titrated with etandard 0.1 12’ sodium thiosulfate to a starch end point. T h e amount of biphthalate added supplies a threefold excess of hydrogen for the iodate-iodide reaction. The p H of a pure biphthalate solution is 4.0, but t h e reaction between iodate and iodide removes sufficient hydrogen ions t o raise the p H to 5.0 (with 2.5 milliequivalents of iodate). This is important, as t h e iodate reaction thus takes place within a few seconds a t the higher acidity and automatically reduces the hydrogen-ion concentration to a level at which the bromate reacts very slowly. If a much larger excess of biphthalate were to be added, a drifting end point and high results would be obtained.
biphthalate to iodate is not critical, but large excess of biphthalate gives results accurate to only 0.25 or 2 per cent if bromate is present in equal or greater amounts. If the order of magnitude of the iodate concentration is not known, a preliminary titration permits estimation of the proper amount of biphthalate to be added for the exact determination. The determination gives high results when very large concentrations of bromate are encountered. Thus, titration of 0.1 N iodate to which sufficient solid potassium bromate had been added to make its concentration 1.8 -V gave results about 1 per cent high. I n titrations with 0.01 A’ solutions the reaction b e h e e n iodate and iodide \vas found to be inconveniently slow unless the ratio of biphthalate to iodate was increased considerably. B y using 1 gram of biphthalate for 0.10 to 0.25 milliequivalent of iodate in 10 to 30 ml. of solution, fairly accurate results ryere obtained (Table 111).
Acknowledgment The authors wish to thank the Graduate School of the University of Minnesota for a grant in support of this study.
Literature Cited ( I ) Kolthoff, I. M., 2. anal. Chem., 60, 348 (1921). (2) Meulen, van der, J. H., Chem. Weekblad, 27, 578 (1930).
Vacuum Desiccator for the Synthetic Organic Laboratory F. P. PINGERT, Eastman Kodak Co., Rochester, N. Y.
T
HE conventional form of a vacuuni desiccator has
limitations and disadvantages which render its use impracticable. I n organic syntheses, whenever sharp drying of larger batches is required, the following simple adaptation of standard equipment has proved useful in this laboratory.
One of two similar round-bottomed flasks, B, is provided with a side arm for connection to the vacuum pump. (A glass stopcock in this place is desirable but not necessary. Its presence enables the flask to be used as a large separatory funnel.) A not too loosely fitting glass sleeve, C, serves as a guide for the union between flasks A and B. The sleeve carries a rubber gasket, D, conveniently cut from an old inner tube. The gasket seals the vacuuni, while the sleeve prevents the side-slipping of the contact surfaces. Without the guiding sleeve, the assembly is not safe. Special guiding clamps could be used, but they have no particular advantages in this case. When in use, A contains the product, and B, the drying agent; E is a steam bath, and F , any convenient support. The appara-
tus, assembled a t random from stock flasks of %liter capacity, will hold a vacuum of 2 mm. for 24 hours (with the aid of a high grade vacuum grease). The following features make the “dumb-bell desiccator” particularly desirable for synthetic work: (1) Frequently one operation may be saved, since a round-bottomed flask in which the reaction or process of concentration was carried out may be attached to the drying bulb without the need of a transfer. (2) Within limits, the desiccator may be made as large or as small as desired. With reasonable precaution, flasks up to 24 liters may presumably be used. (The author has found it useful to coat evacuated vessels on the outside with a thin film of a soluble plastic. The shattering hazards seemed t o be greatly reduced and experimentally induced implosions proceeded with not much more than a dull thud.) (3) While being dried the product may be readily heated on a steam bath and may be stirred b y rotating the assembly. This also exposes a new surface of drying agent a t each turn, thus hastening the process. A comparative test with a highly hygroscopic sirup has shown that the dumb-bell desiccator works about twice as fast as the conventional model under comparable circumstances (such as equal amounts of desiccant). K i t h gentle warming, the rate of drying mas increased fourfold or better. COYMUNICATION No. 904 from the Kodak Research Laboratories.
