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INDUSTRIAL h h D ENGINEERING CHEMISTRY
constant stirring until the cloud point \vas observed. Cloud point-composition data were consistent to 0.06" C. (0.1" F,), corresponding to 0.1 mole per cent of water in aniline solution. TABLE 11. CLOUD-POINT CALIBRATION (20 cc. of aniline-phase sample mixed with 5 cc. of rapeseed oil)
Wster M o l e yo
a
Cloud Temperature
F.
Water Mole %
Cloud Temperature F.
blade after conclusion of experimental work.
Two-phase samples were analyzed by the potentiometric titration when water predominated. When aniline was present in excess, the sample wa5 mixed with a definite quantity of pure aniline to obtain a single phase which was then tested by the cloud-point method.
Sampling Procedure It was usually necessary to obtain a sample from a twophase mixture. This was accomplished by shaking the mixture vigorously into a fine dispersion and immediately pipetting out the desired volume. The first pipetful was rejected as a rinse, since aniline rather than the dispersion wets the glass. Successive samples removed immediately after shaking showed no differences in composition greater than analytical error. apart showed no appreciable differences in the curve; however, the same stock of rapeseed oil was used throughout. The analytical procedure was to pipet 20 cc. of the sample and 5 cc. of rapeseed oil into a 2.5 X 20 cm. (1 X 8 inch) test tube, and insert a two-hole stopper containing an A. S. T. bl. paraffin melting point thermometer and a stirring rod looped at the bottom to encircle the thermometer. The end of the thermometer bulb was set 1.25 cm. (0.5 inch) from the bottom of the test tube. The tube was then warmed in a water bath until the solution was perfectly clear and transparent, removed, and cooled in air with
Acknowledgment The assistance of D. Andres, E. F. Arnett, and F. bl. Garland who obtained the experimental data is acknowledged.
Literature Cited (1) Callan, T., and Horrobin, S., J . Soc. Chem. Ind., 47, 334T (1928). (2) Griswold, John, Andres, D., Arnett, E. F., and Garland, F. M., IND.Eso. CHEM.(in press). (3) Happel, Thesis, Massachusetts Institute of Technology, 1930. (4) Jansen, J. D., and Schut, W., Chem. Weekblad, 20, 657 (1923).
Possible Source of Error in Gravimetric Determinations Involving Use of Hydrogen Peroxide Followed by Nitron RALPH C. YOUNG A ~ PETER D 31. BERNAYS Jlassachusetts Institute of Technology,:Cambridge, JIass.
I
r\' THE standard method for the determination of rhe-
nium, 30 per cent hydrogen peroxide is used to oxidize the precipitated rhenium sulfide to perrhenic acid, which is subsequently precipitated with nitron ( 3 ) . Since the nitron perrhenate obtained with the use of a standard rhenium solution was invariably found to be too high, the reagents xere investigated and the impurity was traced to the hydrogen peroxide. Although several acids form insoluble derivatives with nitron, the impurity causing the trouble was identified as nitrate (1, 2, 4 ) . Samples of 20 cc. of 30 per cent hydrogen peroxide, for laboratory use, from three companies were found by several determinations to contain, respectively, 12.5, 14.3, and 21.6 mg. of nitron nitrate, which was identified by its melting point and by analysis. It behaved identically with a known sample of nitron nitrate and
with a mixture of the two on being heated. Gradual decomposition took place below 260" C. and melting with decomposition at 263.5' (uncorrected). The nitron derivatives of other acids behaved differently. .4nalysis gave 19.0 and 19.1 per cent of nitrogen: calculated for C20HlaN,HN03,18.7 per cent. Literature Cited (1) Busch and Ilehrtens. Ber., 38, 860, 4056 (1905). (2) Cope and Barab. J. Am. Chem. SOC.,39, 504 (1917). (3) Hurd, L. C., "Scott's Standard Methods of Chemical Analysis", 5th ed., Vol. I, p. 771, New York, D. Van Nostrand Co., 1939. (4) International Committee on Ken- Analytical Reactions and Reagents, Union Internationale de Chimie, Tables of Reagents for Inorganic Analyses, 1935. COKTRIBVTION from the Research Laboratory of I n o r g a n i c Chemisrrv , Massachusetts Institute of Technology. No. 78.
