The limits of the method as outlined in the bcryllium procedure are from 0.2 to 10 y per 50-ml. volume; however, the procedure can be changed by reducing or increasing the volume and reagents to include lower or higher ranges. Table VI shows the data obtained from the fluoride analysis of several uranyl sulfate samples which had been produced commercially from the hexafluoride salt. The samples were first distilled from perchloric acid and the fluoride in the distillate was then determined by the beryllium-Chrome Azurol S method. T h e duplicates are in satisfactory agreement, and the fluoride content of the commercial uranyl sulfate was shown to be sufficiently low. Consideration should also be given to the impurities listed in Table 111. The beryllium-Chrome Azurol S
method for fluoride has the advantage of being more sensitive than other methods tried in this laboratory. It is easily reproducible to =kl y of fluoride per 50ml. volume. The sensitivity would be increased if smaller volumes were used. The interfering ions mentioned for beryllium and fluoride must be removed or accounted for in the standard curve preparation. LITERATURE CITED
(1) Babko, A. K., Khodulina, P. V., J . Anal. Chem. U.S.S.R. 7, 317 (1952). (2) Bumsted, H. E., Wells, J. C., AXAL. CHEM.24, 1595 (1952). (3) Fisher, S., Kunin, R., Zbid., 29, 400 (1957). (4) Horton, A. D., Thomason, P. F., Miller, F. J., Zbid., 24, 548 (1952). (5) hlacxulty, B. J., Roollard, L. D., Anal. Chim. Acta 14, 452 (1956).
(6) Price, M. J., Walker, 0. J., AXAL.
CHEM.24, 1593 (1952). (7) Revinson, D., Harley, J. H., Zbid., 25, 794 (1953). (8) Theis, M., 2. anal. Chem. 144, 192 (195.5). \ - - - - I
(9) Toribara, T. Y., Sherman, R. E., ANAL.CHEM.25, 1594 (1953). (10) Underwood, A. L., Keuman, W. F., Ibid., 21, 1348 (1949). (11) Vosburgh, W.C., Cooper, G. R., J. Am. Chem. Soc. 63, 437 (1941). (12) Warf, J. C., AKAL. CHEM.26, 342 (1954). (13) Willard, H. H., Horton, C. A., Zbid., 22, 1190 (1950). (14) U'ood, J. H., Mikrochim. Acta 1955, * < 11.
RECEIVEDfor review September 30, 1957. Accepted iZugust 26, 1958. Division of ilnalytical Chemistry, 132nd meeting, ACS, New York, N.Y., September 1957. Based on studies conducted for the U.S. Atomic Energy Commission under Contract AT-11-1-GEN-8.
Ce rimetric Tit rati o n of Iron Using a Mixed indicator SIR: Under the working conditions proposed b y Heumann and Belovic ( I ) for the cerimetric titration of iron, the calculated total indicator error amounts to approximately O.lS%, 0.15% being due to the warning indicator diphenylamine sulfonate. To reduce the error this indicator was replaced by the sodium salt of diphenylbenzidine decasulfonic acid, prepared according to Sarver and Fischer (3) and used in 0.001M solution (0.136 gram per 100 mi. of water). From 0.30 to 0.35 ml. of this solution per 100 ml. of titrated solution produced the same color change as 0.1 ml. of 0.01M solution of diphenylaminesulfonic acid sodium salt. Figure 1 shows the zones of color change of both warning indicators. The warning signal of the diphenylbenzidine decasulfonate extends over roughly 1% of titrant solution prior to the end point, which corresponds to 8 to 10 drops in a titration requiring about 40 ml. of standard cerate solution. T o compare the color and its intensity for both indicators, solutions in 1N sulfuric acid were prepared with the same concentrations of indicator as in the titrations. The indicators were oxidized b y adding O.Ol11i cerate solution in slight excess. By using a Beclrman DK-1 recording spectrophotometer, the absorption spectra of the colored solutions were taken within 1 minute after oxidation. Diphenylamine sulfonate showed its maximum absorption at 550mp; that of diphenylbenzidine decasulfonate appeared at 540 mp. T h e corresponding slight difference of color is difficult t o detect b y the eye. The
absorption produced by 0.1 nil. of 0.01M diphenylamine sulfonate in 100 ml. of 1 N sulfuric acid was equal to that obtained with 0.36 ml. of O.O001;1f diphenylbenzidine decasulfonate. This
I
98
I
I
99 100 Percentage of reoction
I 1
101
Figure 1. Zones of color change of warning indicators shown on cerium(lV)iron(II) titration curve (Potential readings with reference to
calomel electrode) % of Reaction at Start of PermaIndicator nent Color Change a. Diphenylaminesulfonic acid 99.1 b. Diphenylbenzidinesulfonic acid 99.5
compares f a i r k ne11 n-ith the 0.1 to 0.30 to 0.35 found visually in the titration of iron. Theoretically 0.5 ml. of 0.001M diphenylbenzidine decasulfonate should be equivalent to 0.1 nil. of 0.01M diphenylamine sulfonate, but the latter is probably oxidized to a lesser degree to diphenylbenzidine violet or the further oxidation of the violet to colorless products proceeds faster in the case of the diphenylamine sulfonate than v-ith t!ie other indicator. The titration errnrs for both indicators were determined hy adding to 300 ml. of I N sulfuric acid the same amount of indicator as in the titration of iron and titrating the solution with 0.01N standard cerate solution until the violet color was fully developed. Table I shows the indicator errors for the titration of iron, calculated on the basis of these determinations. The error due to the diphenplbenzidine dccasulfonate is only one fourth of that cnnscd by the diphenylamine sulfonate instead of one half, because a relatively larger amount of diphenylamine sulfonate is required for obtaining the same color intensity and a larger than the theoretical amount of oxidizing agent is required for its oxidation. The total indicator error, including that of the ferroin, is thus with diphenylbenzidine decasulfons te roughly one third of that with the other indicator. On the other hand, the latter provides a more extended warning zone. ACKNOWLEDGMENT
The authors wish t o thank G. Frederick Smith, TTniversity of Illinois, who suggested the use of the diphenylVOL. 31, NO. 1, JANUARY 1959
* 155
Table I.
benzidine decasulfonic acid or its sodium salt.
Indicator Errors
0.1.V Cerate Warning Indicator Added Solution Titration Error, 70 bl1./300 ml, for Oxidation, MI. Warning Xame titrated solution indicator Ferroin Total Sodium di henvlamine d'fonite
0 3, 0.01Jf
0 06
0 08
0.2
0.03
0.23
REFERENCES
(1) Heumann, W. R., Belovic. B., A N ~ L . CHE3I. 29, 1226 (1957) (2) Kolthoff, I. > f , , sarve;, L, A., J . - A ~ ~ . Chem. SOC.52, 4179 (1930). (3) Sarver, L. A . , Fischer, W. von, IND. ETG.CHE\f., A N A L . ED. 7, '271 (1935). WALTERR. HEEMANN C L A U D E ALLARD
Sodium diphenvlbenzidine decasulfonate
1.0,0.001~l4 0.02
0.02
0 05
0.03
0.08
Department of Chemistry Eniversitv of lfontreal Montreal; Canada
No. 177. Uranium Mononitride CHARLES
P.
KEMPTER, JOSEPH C. McGUIRE, and M. R. NADLER
Los Alamos Scientific Laboratory, University of California, Los Alamos, N. M.
T
crystal structure of uranium nitride has been investigated by Rundle, Baenziger, Wil.son, and hIcDonald (1) and found to be face-centered cubic with a lattice constant of 4 880 =k 0.001 A . They concluded that the structure was sodium chloride type, since the 420 reflection was of much greater intensity than the 331 reflection. The calculated density was 14.32 grams per cc. They did not tabulate the uranium nitride powder pattern. The authors gave no analysis of their HE
YJY." The ASTM x-ray diffraction file lists only one uranium nitride (card 3-1133). The formula is not stated. but a cubic lattice constant of 5.319 A. is given. This material is undoubtedly US2, be-
Table l.
Spectrographic Analysis of UN
hlajor
120 p.p.m.
