Table I. Determination of Azide Ion in Synthetic Primer Mixtures
Azide Ion Present, Mg. 0.50
Azide (Ns) Found, Mg. 0.46 1.04 1.01 2.01 3.40 3.49 3.88
1.00
1.00 2.00 3.50 3.60 4.00
Mean Standard deviation
Relative Error,
%
-8.0 +4.0
Nj,-+NOz-+2Hf-tH20
i-1.0 +o 5
The use of ferric sulfate in sulfuric acid to eliminate this difficulty was unsatisfactory, as color development with a sulfate reagent was poor. Azide ion gave, in equivalent concentration, a 57% T in a nitric acid reagent and 86% T in the sulfuric acid media. Samples of synthetic primer mixtures were prepared, using 10 mg. of antimony trisulfide (stibnite), 10 mg. of potassium chlorate (both approximate weights), and accurately measured amounts of sodium azide solution of known concentration. Table I indicates results for determinations on such mixtures. Table I1 shows azide ion values found from analyses of military grade lead azide, the purity of which was 92.05y0 by the Navy titration method ( 3 ) .
-2.9 -3.1 -3.0 -1.6 3.9
Table II. Determinations of N3in Lead Azide, Purity 92.05%
Azide Azide (NI) (No) Calcd., Found, Mg. 2.64 2.38 1.81 2.84 3.16 1.49 1.80 2.77 1.68 3.68
Mg. 2.66 2.42 1.74 2.67 3.20 1.50 1.85 2.64 1.79 3.55
Purity Found,
Relative
%
%
92.7 93.5 88.7 86.6 93.3 92.5 94.6 87.9 98.0 88.7 Mean 9 1 . 6 Standard deviation 3 . 6
to shift the standard curve slightly and it is advisable to prepare a ne\T standard curve when new ferric nitrate solution is prepared. The necessity for preparing a new curve with each batch of reagent is found in the reaction.
Error,
+0.8 +1.7 -3.9 -6.0 +1.3 $0.7 +2.8 -4.7 +6.5 -3.5 -0.4 3.9
‘undue exposure to air. Ricca (4) has shown that aeration causes appreciable fading of the color and suggests that this is due to the loss of hydrazoic acid. He has also presented evidence that the color is due not to undissociated ferric azide but to the complex ion Fe(NS)++. Interference from sulfites, thiosulfates, and sulfides is avoided by preliminary oxidation of the alkaline sample with hydrogen peroxide ( 2 ) . Cyanates and thiocyanates, however, interfere and render the method ineffective. Nitric acid batch variations may tend
+r\‘>+N20
While the relative errors shown are not considered excessive with small amounts of azide, they are too large to permit the use of the method for purity determinations. This is clearly illustrated by the purities calculated from the results and also shotvn in Table 11. LITERATURE CITED
( I ) Davis, T. L., “Chemistry of Powder and Explosives,” p. 430, Wiley, Xe-x York, 1943. (2) Feigl, F., “Spot Tests, Inorganic iipplications,” 4th ed., Vol. 1, p. 268, Elsevier, New York, 1954. (3) Military Specification, MIL-L-3055, Sept. 30, 1949. (4) Ricca, B., Gazz. chim. ilal. 75, 71 (1945).
( 5 ) U. S. Naval Ammunition Depot, Crane, Confidential Rept. QE/C 56-40.
RECEIVED for review August 27, 1956. Accepted December 13, 1956. The opinions and assertions contained in this article are the private ones of the authors and are not to be construed a8 reflecting the views of the Navy Department.
CORRESPONDENCE Determination of Potassium as the Metaperiodate SIR: After publication of “Determination of Potassium as the Metaperiodate” [ANAL. CHEM. 28, 2011-5 (1956)l our attention mas called to “Determination of Potassium in Soap and Mixed Caustic Lye” by W. T. Miller and J. T. R. Andrews [J. Am. Oil Chemists’ SOC.26, 309-12 (1949)]. These authors report increased accuracy and sensitivity of the Willard and Boyle periodate procedure for potas-
sium through (1) hand stirring during precipitation of the potassium periodate, (2) totally reducing the periodate to iodine, and (3) titrating the iodine ivith sodium thiosulfate solution. Because our own paper deals in part with these points, we wish to call this paper to the attention of those interested in this procedure. RALPHE. JENTOFT REX J. ROBINSON
154.
Yttrium Trifluoride, YF,,
155.
Samarium Trifluoride, SmF,, Orthorhombic Form
Orthorhombic Form
156. Ytterbium Trifluoride, Y bF,, Orthorhombic Form EUGENE STARITZKY and L.
B. ASPREY, The University of California, Los Alamos Scientific Laboratory, Los Alamos, N. M.
HE trifluorides of yttrium, samaT r i u m , and ytterbium were precipitated with hydrofluoric acid from aqueous solutions of corresponding chlorides.
The precipitates were oven-dried a t 110” C., dried under vacuum a t 1000” C.. and then heated under argon to about 100” C. above their melting point.
The yttrium oxide used as starting material for this preparation is believed to be about 99% pure. The samarium was purified by E. I. Onstott of this VOL. 2 9 , NO. 5 , M A Y 1957
855
laboratory by an electrolytic process (1). It contained 0.07% neodymium and 0.003y0 europium (determined spectrophotometrically). No other rare earth elements were detectable spectrographically in the ytterbium oxide used, which was pursed by ion exchange methods. The structure of these orthorhombic trifluorides, belonging to the space group Pnma - D:! with a unit cell containing four formula units, has been determined by Zalkin and Templeton (3). They reported the following unit cell dimensions: YFs
A. bo, A.
ao,
cn.A.
Volume per formulaunit,A.a Density (x-ray), gramspercc.
SmFa YbFs
Crossed polarized light
47.79 51.84 46.76 5.069 6.643 8.168
The powder x-ray diffraction pattern of yttrium fluoride is given on ASTM cards 50546, 5-0547, of samarium fluorideon card 5-0517, and of ytterbium fluoride on cards 5-0551, 5-0552. The density of the trifluorides crystallized from melts was determined with a Berman microbalance as 6.61 grams per cc. for the samarium salt; 8.17 grams per cc. for the ytterbium compound. CRYSTALMORPAOLOQY.The trifluorides crystallized from their melts as aggregates of coarse anhedrons cbaracteriaed by prominent (0101 cleavage and twinned polysynthetically on (101) (Figure 1).
157. 158.
Figure 1. Cleavage fragments of samarium trifluoride showing repea
6.353 6.669 6.216 6.850 7.059 6.786 4.393 4.405 4.434
OPTICALPROPERTIES. YF,
SmFa
1,536 1.553 1.569
1 , 577
YbF3
Refractive indices (5893 A.) n,
w nz
Geometric mean Molecuiar refraction,cc. Optic m i d sngle,2V
569 1.597 1.580 1.608 1.599
respect to the trace of the composition plane (1011. The angle between the Zdirections in adjacent twin hmellae ie 67" for samarium tduoride, 71" for ytterbium fluoride. Color. Samarium trifluoride is pink; yttrium and ytterbium fluoridesYare colorless. LITERATURE CITED
1.55% 1.594 1.58% 9.21
10.60 9.41
85'
72'
optic Orientation.
Z = a.
x = c;
(1) Onstott, E. I., J . Am. Chem. Sac. 77,
2129-32 (1955). (2) Zalkin, A,, Templeton, D. H., Ibid., 75, 2453-8 (1953).
78'
y
=
b;
Extinction Angles. Extinctions on (0101cleavage plates are symmetric with
WORK done under auspices of Atomic E~~~~ commission. Crystallographic data for pubhation in this section should be sent to W. C. McCrone, 500 East 33rd St., Chicago 16, Ill.
Lanthanum Trifluoride, LaF, Neodymium Trifluoride,
NdF,
EUGENE STARITZKY and L. 9. ASPREY, The University of California, Las Alamos Scientific Laboratory, Lor Alarnos, N. M.
anu nsouymiurn IIUIITKXS were precipitated with hydrofluoric acid from aqueous solutions of correspnnding chlorides. The precipitates were heated to 400' C. in an atmosphere of gaseous hydrogen fluoride, heated under vacuum to about 1000" C., and then melted under argon a t about 1400" C. The fluorides crystallized from their melts as coarse-grained anhedral aggregates. The lauthanum source material used was purified by ion exchange methods. Spectrographic analysis indicated the presence of O.O2y0 calcium aud 0.005y0 magnesium; no rare earth elements were LN'PHAN UM
L-
856
ANALYTICAL CHEMISTRY
aecemed. Spectrographic analysis of the neodymium salt indicated the presence of O.lyo magnesium, 0.01% calcium, 0.03rr/o iron, and 0.2y0 cerium. No other rare earth elements were detected. Oftedal (9) proposed a structure for hexagonal rare earth fluorides belonging B to the space group PG8/mcm - D ~ with a cell containing six formula units. Cell dimensions reported by Oftedal (1) for lanthanum fluoride are, after converting from ICX to Angstrom units, aa = 7.117 zt 0.007 A,, co = 7.344 0.007 A.; for neodymium fluoride corresponding figures are a. = 7.035 i. 0.007 A., co = 7.210 5 0.007 A.
*
X-RAY DIFFRACTION DATA. LaFr Cell dimensions ao, A. eo,
A.
da,
7.186 zt 7.030 f 0.001 0.001 7.352 zt 7.200 i 0.001 0.001 1.023 1.024
Volume per formula unit, A.8 54.80 Formula weight 195.92 Density, grams per CC.
NdFt
5.936
51.36 201.27 6.506
The above cell dimensions were determined hy linear extrapolation against the function (eos%/sin8 Cos28/8) to the zero value of that func-
+
