ml,
6.
3.54
Of
edtb
ml.
00025 M
3.13 ml.
“Synthetic” mixtures of thorium and the cerium group rare earths, analyzed by the method outlined showed good recovery of both thorium and the rare earths. This method is now being successfully used as routine analysis. Thorium o:tn he coprecipitated as the oxalate. tising a rare earth as a carrier (1I j foIloweti by photometric titration Procedure D. Sniall amounts of EDTA (0.1%) can be determined in the presence of large :imounts of the rare earths by the addition of a linoivn excess of thorium nitrate and .back-titration of the latter by EDTA ( 2 ) . Thorium and the r i m earths can be estract,ed with tributyl phosphate and then titrated piiotoiiietrically in :aqueous solutions.
3.05 m l .
~
1
Figure
4.
Effect of lead on the photometric titration of thorium A.
2.06 mg. ThOz
8. C.
2.06 mg. ThOz, 1 mg. Pb 2.06 mg. Tho*, 10 mg. Pb (see also Toble IV)
small amounts of the rare earths in thorium, the back-titration of thorium is preferred. It is difficult to exclude the possibility of some unknown, small contamination of the thorium nitrate stock solution. However, “blank titration” a t p H 3.7 could not be eliminated by additional purification of the thorium nitrate solution. No “blank correction” was applied in the determinations reported in Table 111. Analysis of Naturally Occurring Materials. Many cations and anions interfere in the complexometric titration of thorium (7) and the rare earths (3). All of them affect also the photometric titration curves. In some instances, however, by suitable extrapolation (Figure 4) of the straight parts of the curve, the photometric titration allows a reasonable determination to be made, even in the presence of an excess of the interfering ion. This is the case with lead (Figure 4), uranium, sulfate, etc. I n Table IV, results of thorium determinations (Procedure A) in the presence of some interfering ions are given. For the analysis of naturally occurring materials the interfering ions mufit be eliminated. Oxalate precipitation in the presence of hydrogen peroxide from slightly acid boiling solutions effectively separates thorium and the rare earths from many interfering ions (11, 18), and can be used in some cases as a purification step. (Samples rich in phosphate are first transformed into hydroxides by hot digestion with an excess of sodium hydroxide .) Calcinate the filtered and well washed oxalates in a porcelain crucihlc for 1 hour
Table IV. Photometric Titration of Thorium in Presence of Interfering Ions
ThOe, hlg.
IonAdded Pb++
UO,
++
so; (COO),-(PO,)- - F-
Mg.
Taken Found
2.04 2.06 2.04 2.10 2.04 2.36 1.02 1.02 1 . 0 2 1.01 1.02 0.99 1 1 . 0 2 0.98 4 1 . 0 2 0.97 8 1.02 0.95 4 10.20 10.11 0.06 1.02 1 . 0 0 0.3 1 . 0 2 0.97 0.02 2.04 2.02 0.1 2.04 1.84 0.2 2.04 1.61 0.02 1.02 0.90
1 5 10 30 240 2400
a t 900” to 1000° C. Dissolve the mixed oxides in the crucible, using for 100 to 200 mg. of oxides, 2 ml. of concentrated perchloric acid, and 0.1 ml. of a solution containing 5 grams per liter of sodium fluoride. Evaporate the excess perchloric acid on a sand bath. Use 0.5 ml. of perchloric acid in each evaporation and repeat twice t o eliminate any remaining hydrofluoric acid. Transfer the perchlorates of thorium and of the rare earths into a 250-mi. beaker. If the solution a t this point is not clear, filter it through a fine, fritted-glass filter funnel. Do not use filter paper, because both thorium and the rare earths may be partially lost by absorption on the cellulose. Wash the glass filter with 0.01Nhydrochloric acid. Complete the determination, according to Procedure ?3or E.
LITERATURE CITED
( I ) Bjerr urn, J.,Schw arzenbach, G . , Sillen,
L. G., “Stability Constants,” pp. 7 G 7 , Chemical Socsietv. London. 1957. (2) Bril, K., Aril,” S., Krumholz, P., J . Phys. Chem., in press. ( 3 ) Brunisholz, G., Cahen, R . . H c l r . Chinz. S r t a 39, 324 (1956). 0 ( 4 ) Ibzd., p. 2136. ( , 5 ) Flaxhka, H., Haw, Ti. ter, Bazen, J., Jltkrochim. d r t a 1953. 345. ( 6 ) Flaschka, H., Khalifalla, S., Z. anal. Chem. 156, 401 (1957). (7) Ford, J. J., Fritz, J. J., ANAL.CHEW 25, 1640 (1953): Atomic Energy . - Comm. Ilept. ISC 5 2 0 (1954). (81 Fritz, J . Y., Lane, W. J., Byetroff, A. S.,ANAI,.CHEM.29, 821 (1957). (9) Haar, K. ter, Bazen, J.: -4nal. C ~ ~ T J I . Acta 9, 235 (1953).
Jander, G., “Neuere ?vlassanalytische Methoden, p. 417, F. Enke Verlag, Stiittgart, 1956. (1 1j Kall, H. L., Cordon, I,.,ANAL.CHEX.
( 10)
25, 1‘256 (1953). (12) KrumhoL, P.?J . i4n1. Chem. SOC.71, 3654 (1949). (1.73 Menis, O., Maiming, D. L., Goldstein, s., ANAL.CHEW29, 1426 (1957). (14) %filkey,It. G., Ibid., 26, 1800 (1954). (15) Peppard, 1). I?., Mason, C:. W . , Maier, ,J. L., J . Znorg. and Nuclear Chena. 3, 215 (1956). f 16) Pribil, R., “Komplexometrie,” p. 37, Chemapol, Prague, Czechoslovakia, 1954. ( 1 7 1 Rinehalt. It. K.. . ~ N A I . . C(HE\I. 26. 1820 (19541: (181 Rodden, C. J., “Analytical Chemistrv of the Mnnhattan Project,“ pp. 49.%6,169-70, M&raw-Hill, Neu- York, 1950. (19) Sarma, 11. V. N., Rao, 73. S. V. R., .Inal. Chiin. .-lcta 13, 142 (1955).
Alternating Current Polarography-Correction In the article on “blternating Curlent Polarography” [Bauer, H. H.. Elving, P. J., ANAL. CHEM.30, 341 (195811 the caption t o Figure 1 should state: RI1.500,@%ohm potentiometer. VOL. 31, NO. 8, AUGUST 1959
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