Determination of Cerium(III) Oxalate SIR: The oxalates are of importance in the analytical chemistry of the lanthanons. The latter are, as a rule, separated from other cations by precipitating the hydrated oxalates in acid media. The precipitates, using this procedure, contain the lanthanons in the trivalent state, and quadrivalent cerium, if present in the original solution, is simultaneously reduced to trivalent cerium. The analyst may then follow one or both of the following two methods: (1) titration with potassium permanganate; or (2) calcination to the sesquioxide. With the cerium and praseodymium oxalates, the products obtained on calcination are the higher oxides, CeOnand PnOll, respectively. In the course of a study of the thermal decomposition of the lanthanon oxalates, it waa necessary to determine the exsct composition of the oxalates. The permanganometric method was satisfactory with most of the lanthanons, but failed with the hydrated cerium(II1) oxalate, although this method is recommended by Deshmukh (1). Titration with permanganate gave consistently higher results than those obtained by calcination. It was also observed that near the end point the solution was colored yellow, indicating the presence of quadrivalent cerium. It was therefore proposed to separate the constituents of cerium oxalate prior to annlvsis, as indicatcd in the reaction ( 2 ): 6 OH -
+ [Ce,(CrO&.nH&]
solid -+ [Cez(OH)s.nH~O]solid 3 Cz04-2
+
The oxalate could then be titrated in
185.
the filtrate without interference, and the hydroxy hydrate calcined a t 900" C. in a muffle furnace, with a good access of air. PROCEDURE
Two different samples of cerium(II1) oxalate were employed: Lindsay Code No. 225 and hydrated oxalate prepared by precipitation from pure ,cerium(III) nitrate. All other reagents were of analytical grade. The precipitation of the oxalate was carried out by dissolving the cerium(II1) nitrate in 500 ml. of 0.15N nitric acid. The solution was warmed on the water bath and kept constant a t 60" f 2" C., while 1M oxalic acid was added dropwise with constant stirring, by a magnetic stirrer. When all the cerium precipitated, the solution was left on the water bath a t the above-mentioned temperature for 2 hours, and filtered next morning through a glass crucible. After being washed with distilled water until there was no reaction for oxalate, the precipitate was rinsed with 95% ethyl alcohol and ether, and stored in a stoppered weighing glass in the desiccator. The quantitative determinations were carried out as follows. The solid h drated cerous oxalate was weighed in(; a porcelain basin. A 15% solution of sodium hydroxide was added, and the mixture put aside on the water bath. The solid was occasionally ground with a glass rod to facilitate contpct between the solid oxalate and the hydroxide. One hour was sufficient for a quantitative extraction of the oxalate, The hydrated hydroxide was filtered, and the filtrate was acidified with sulfuric acid and titrated with potassium permanganate in the usual manner. The solid hydratrd hydroxide was calcined
a t 900' C., and weighed as the yellow CeO,. RESULTS
The titration of the filtrate (which reacted negatively to testa for the preeence of cerium), when expressed in equivalents of CeOt, was identical with those received from the calcination of the hydroxy hydrate, as well as the percentage of the cerium obtained from the calcination of the hydrated oxalate: Percentage of CeOz Determined by Various Methods No. of
Calcination of Cez(GO4)*.nH20 Calcination of Ch(0H)a.nHoO Titration All percentages refer drated oxalates.
yoCeOt
Detns.
49.2
4
49.3 49.2
3
3
to the original hy-
From these results the water content of the oxalate was calculated as nearly 8.5molecules of water. UTERATURE CITED
(1) Deshmukh, G. S., J . Sci. Research, Benutes Hindu Univ. 1, 121 (1951). (2) Wylie, A. W., J. Chem. SOC.1947,
1687. A. GLASNER M. STEINBERG
De artment of Inorganic and ifnalytical Chemistry The Hebrew University Jerusalem, Israel RECEIVEDfor review July 23, 1959. Accepted September 28, 1959.
Niobium
M. R. NADLER and CHARLES P. KEMF'TER Los Alamos Scientific Laboratory, University of California, Los Alomos, N. M.
N
has a body-centered cubic lattice with two atoms per unit cell; the space group is 0i-Zm3m. The first oorrect structure determination was carried out by Meisel (I). The X-Ray Powder Data File contains one niobium data card (1-1183) which liits approximate interplanar spacings with no Miller indices assigned. One spacing ( d = 0.826 A.) is missing and nearly all IOBIUM
1922
0
ANALYTICAL CHEMISTRY
of the relative intensities are grossly in error. The material used for this paper was Starck "grade I, high purity," -325 mesh niobium powder. The spectrographic analysis results (based on NbsOb) are shown in Table I. X-ray diffraction studies were carried out on a Norelco unit, using both a 114.59-mm. Debye-Scherrer camera and
a 120-mni. symmetrical back-reflection focusing camera. Only the inner emulsion of the back-reflection film was used and the shrinkage was measured by reference to six pairs of fiducial marks. The film was measured at constant temperature by three different readers. X-ray exposures were made a t 25" c. using nickel-filtered copper radiation. The Debye-Scherrer data are shown
