of I5y%, 1 1 . 5 % was obtained; and a t a level of joy%, ~ ' ~ 0 . 5 % was obtained. Assays of plasma hydrocortisone on aliquots of plasma taken a t weekly intervals from a single pool (137y0) over a 6nionth period (25 determinations) showed a deviation of &7.&.
Normal Values.
In 50 normal male and female subjects. the plasma hydrocortisone levels have ianged from 6 to 2 5 ~ 7 with ~ . a inem of 15 i 4.57% (standaid deviation).
( 8 ) Porter. C. C.. Silber. R. H.. J . Biol.
LITERATURE CITED
Allen. IT. >I., J . Clin.Endocrinol. 10, i 1 (1950).
Bayliss, R. I. S., Steinbeck, A. IT., Biochem. J . (London) 54, 523 (1953). (3) Bliss, E. L., Sandberg, A. il., Xelson, D. H., Eik-Xes, K., J . Clin. Invest. 32, 818 (1953). Bush, I. E., Biochem. J . ( L o n d o n ) 50, 370 (1952). Bush, I. E., Sandberg, A , , J . Biol. Chem. 205, i 8 3 (1953). Selson. D. H.. Samuels. L. T.. J .
Cherk. 185,'201 (1950). ' (9) Romanoff. E. B.. Hudson. P.. Pincus. G., J.' Clin'. Endocrinol. and Xetabolism 13. 1546 (1953). (10) Silber, R. H., Porter, C'. C., J . Biol. Chem. 210, 923 (1954). (11) Sweat, 11.L , -1s.4~.CHEJI.26, 773
(1954).
(12) Tomkins, G., Isselbacher, K. J., J . Am. Chem. SOC.76,3100 (1954).
(13) Weicheelbaum, T. E , Margraf, H. W., J . Clin. Endocrinol. and Metabolism 15, 970 (1955). RECEIVED for revieiv March 10, 1956. hccepted August 29, 1956.
J . Clin.Invest. 35, 552 (
Determination of Antimony in Indium Antimonide M. C. BACHELDER and PATRICIA M. SPARROW Institute for the Study of Metals, University of Chicago, Chicago, 111.
b Indium antimonide may b e brought into soluble form by fusion with equal parts of anhydrous sodium carbonate and sulfur. The fusion product i s dissolved in a minimum amount of concentrated hydrochloric acid, and the precipitated sulfur is oxidized with potassium chlorate. Chlorine is removed by boiling the solution and the antimony i s determined b y the iodometric method. The accuracy of the method for approximately 200 mg. of antimony i s 0.2%.
T
HE usual methods for dissolving antimony and its alloys are not applicable to indium antimonide. Seither hot concentrated sulfuric acid nor concentrated hydrochloric acid containing bromine or potassium chlorate dissolves the compound. Although the indiuni antimonide is dissolved by aqua regia, some antimony is lost by either volatilization of the chloride or precipitation of insoluble oxides of antimony prior to the analysis. Xitric acid containing tartaric acid also gives solution: but t n o valence states of antimony are formed, and the nitrate ion must be removed before the final determination of antimony. This proccldure lead3 to low results. The most expedient approach to sample solution and analysis mas found to be fusion with sodium carbonate and sulfur. This gives a hydrochloric acidsoluble melt that can be analyzed for antimony by a n iodonietric titration without separating the indium.
ground indium antimonide with six times its rreight of a mixture of equal parts of anhydrous sodium carbonate and pure sulfur ( 2 ) . Fuse the mixture in a covered porcelain crucible; initially heat with a low flame and gradually increase the height of the flame to a teniperature where the mass is in quiet fusion. Finally heat with a full flame until the excess sulfur is completely burned away. About 2 hours are needed to reach this point. Cool, place the crucible and cover in a 200-ml. Berzelius beaker, and add 20 ml. of 1 2 s hydrochloiic acid. K h e n the evolution of the hydrogen sulfide has subsided. remove the crucible and lid and wash with a minimum aniount of 1 2 s hydrochloric acid. -4dd 300 mg. of solid potassium chloride, and heat on the steam bath for 15 minutes to complete the reaction and expel the hydrogen sulfide. To the warm solution add solid potassium chlorate in small quantities until the solution is clear. Expel the chlorine by boiling. Transfer the hot solution to a 200-ml. Berzelius beaker using a minimum amount of 12.1- hydrochloric acid for rinse, and leave the small lump of agglomerated sulfur behind. 4 d d suffi-
Table 1.
EXPERIMENTAL DETAILS
During the fusion and while the crucible is m-arni, the cover should not be removed. Contact with air is sufficient to oxidize small amounts of the antimony to the quinquevalent form, which is difficult to dissolve. It is convenient to follox the fusion process by using a transparent quartz cover for the crucible. Dilute hydrochloiic acid or lvater must not be added to the products of the fusion, as antimony oxides formed by the hydjolysis Iyill precipitate. Solid potassium chloride is added to form the less volatile complex SbC4-, so that the hydrochloric acid solution may be heated on the steam bath without fear of losing antimony ( 8 ) . To remove the colloidal sulfur formed by the reaction of the sulfides with hydrochloiic acid and to ensure coniplete oxidation of the antimony to the quinquevalent state, solid potassium
Results of Antimony Determination"
Color End Point KO.of
cient 1 2 s hydrochloric acid to bring the total volume to 65 nil. Insert a thernionieter and bring this solution to constant boiling. Determine the antimony by the iodonietric method ( I ) .
Sb.
Potentiometric Titration s o . of
Sh.
mean % samples mein' % Sh 5 99.84i0.30 3 99.93 =k 0.03 Sb In20a 3 99.85 i 0 . 0 4 3 100.12 & 0.04 Sb InSb* 5 5 0 . 9 1 i 0.17 4 51.46 + 0 . 2 4 InSb 5 50.99 & 0 . 1 7 4 51.44 i 0.16 Approximately 200 mg. of antimony. i, % Sb in InSb = (total weight Sb found) - (weight Sb added) x 100. (weight of InSb) Sample
samples
++
5
PROCEDURE
Intimately mix 400 mg. of finely VOL. 29, NO. 1 , JANUARY 1957
149
chlorate is added to the warm solution after the expulsion of the hydrogen sulfide. A blank should be run using the same amounts of reagents and acid as for the sample. This procedure was used for the determination of antimony in samples containing pure antimony, antimony mixed with indium oxide, antimony mixed with indium antimonide, and pure indium antimonide. Spectrographically pure antimony was obtained from Johnson, Matthey and Co., Ltd.; indium oxide was prepared in the laboratory from high purity metal and examined spectrographically; indium antimonide (Midway Laboratory) was melted in vacuo, remelted in argon, and
then finely ground in a diamond mortar. The samples were prepared to give approximately 200-mg. quantities of antimony, and the latter was determined by the iodometric method, using a color end point and a potentiometric titration. RELIABILITY
OF
Titrating potentiometrically, the accuracy of the method is within 0.2%. The spread in the results for the determination of antimony in indium antimonide is believed to be due to inhomogeneity of the sample.
METHOD
Indium does not interfere. The theoretical percentage of antimony for the formula InSb is 51.48; a value of 51.44 was obtained by potentiometric titration and 50.99 by color end point (Table I). This difference of nearly 1% may be the result of personal sensitivity to the color change, for it was difficult to determine the end point by visual observation.
LITERATURE CITED
(1) Scott, W. W., “Standard Methods of Chemical Analysis,” 5th ed., vol. I, p. 75, Van Nostrand, New York,
1925.
(2) Treadwell, F. P., Hall, W. T., “Ana-
lytical Chemistry,” 9th ed., vol. 11, p. 94, Wiley, New York, 1951. (3) Zbid., p. 614. RECEIVED for review May 23, 1956. Bccepted October 10, 1956.
A ppI ic a ti o n of t he Iro n(II)-T it a nium(III) T it ra ti o n Procedure to the Determination of the Nitrogen Content of PropelIants JOSEPH GRODZINSKI Central laboratory of Israeli Military Industries, Ministry of Defence, le1 Aviv, Israel
,A volumetric method for determining nitrate nitrogen in commercial nitrocellulose has been modified to make it applicable to the analysis of both military-type nitrocellulose and smokeless powders. The modification consists in using an acetic acid-acetic anhydride solvent mixture to prevent premature precipitation of the sample during the reduction step with ferrous chloride solution and in adding the hydrobromic acid separately. The proposed procedure has a precision of *0.02% nitrogen and an accuracy comparable to that of the Devarda and nitrometric methods.
S
methods for the determination of nitrate nitrogen have recentlg been discussed by Becker and Shaefer ( 2 ) . Only few of them proved to be applicable for the determination of the total nitrogen content of nitrocellulose propellants, which consists of a simultaneous determination of nitrocellulose and nitroglycerin nitrogen in the presence of other propellant ingredients. The most widely applied is the Devarda method, adapted to the determination of the nitrogen contents of smokeless powders by Muraour (10). Its application has since been extensively investigated, and several mndXcations have been suggested (6, 8, 9 , I I ) . However, it remains relatively timeEVERAL
150
ANALYTICAL CHEMISTRY
consuming and requires reagents of a very strictly defined specification, if the results are to be exact ( 3 ) . The application of the nitrometric method (12) to the determination of the nitrogen content of propellants is also possible, as has been suggested by Grodzinski and Berkowicz (6). The interference of stabilizers with the nitrometric determination may be eliminated by applying a correction based upon a linear relationship existing between the amount of stabilizer and the lowering of results. Four nitric oxide molecules are fixed by each ethyl centralite molecule and nine nitric oxide molecules by two diphenylamine molecules. This method requires, of course, an exact determination of stabilizers simultaneously with the nitrometric determination. The results of the iron(I1)-titanium(II1) volumetric procedure of Knecht and Hibbert ( 7 ) , applied by Becker (1) for the determination of nitroglycerin, are unaffected by stabilizers present in propellants. However, this procedure is not suitable for the determination of the nitrogen content of propellants because of the incomplete reduction of nitrocellulose. Shaefer and Becker proposed a modification of this method ( I S ) for the determination of nitrocellulose which consists of the inclusion of hydrobromic acid in the ferrous chloride reagent. They
claim that very exact results may be obtained by this procedure. Tranchant (14) was unable to reproduce the experiments of Shaefer and Becker with the same precision and the results obtained by him were still too low as compared with those obtained by the Devarda method. He proposes to add an ammonium molybdate solution to catalyze the reduction of nitrocellulose by the ferrous ion. The introduction of ammonium molybdate, as proposed by Tranchant, presents, however, a serious disadvantage by affecting the sharpness of the end point of the titration, which is completely imperceptible in colored ’ or opaque solutions-e.g., in the case of graphite-glazed propellants. The differences between the results obtained by Shaefer and Becker and by Tranchant may be due to the use of different types of nitrocellulose. I n fact, in this laboratory the results of Shaefer and Becker were reproduced when samples of industrial nitrocellulose of high solubility were examined; with less soluble military grade nitrocellulose too low and irreproducible results were obtained. This may have been due to a partial reprecipitation of unreduced nitrocellulose from the acetic solution diluted viith water introduced with the ferrous chloride reagent. The author proposes to overcome this difficulty by applying as a solvent
