electrolyte and recording the polarogram. For standardization of the method, a sample of tellurium free from iodine was prepared by first distilling the iodine and then following the procedure described by Scott (3). Recoveries of iodine were tested by adding standard amounts of iodine to pure tellurium samples so prepared and following the procedure described above. The results are tabulated in Table I. RESULTS AND DISCUSSION
Smith and Taylor (4) reported that it was not possible to concentrate iodine solution after oxidation owing to the escape of iodine in hydrochloric acid used in the process of evaporation. It was, however, found possible to concentrate iodine solution after oxidation, if, as described in the present procedure, sulfuric acid were used, qrovided of course that the concentration did not reach the fuming stage.
Table I. Recovery of Iodine Iodine, pg. Added Found
10.0
9.75
Recovery, %
97.5
A polarogram could not be taken directly on the alkaline solution used for absorbing iodine in the distillation procedure, since the mechanical carryover of traces of chromium was a serious interference (1). Therefore, it was necessary to extract the iodine in carbon tetrachloride and then backextract it into the aqueous phase. As the iodine contents in most of the samples analyzed were low, the results could not be compared with the usual colorimetric method. One sample of
tellurium could, however, be analyzed by both methods owing to its slightly higher iodine content. The values obtained were 56.8 p.p.m. by the polarographic and 58 p.p.m. by the colorimetric method. LITERATURE CITED
(1) Lingane, J. J., Kolthoff, I. hf., Chem. SOC.62,852 (1940).
J. Am.
(2) Miles, B. J., Fletcher, C. W.,Faires, R. A., Payne, B. R., Hudswell, F.,
Atomic Energy Research Establ. (Gt.
Brit.)I/R 1038 (1952). (3) Scott, W. W., 'Wmdard Method of Chemical Analysis, Vol. I, p. 787, Van Nostrand, Yew York, 1939. (4) Smith, S. W.,Taylor, J K., ANAL. CHEM.29, 301 11957). V. T.ATHAVALE R. G. DHANESHWAR S. V. GULAVANE M. S. VARDE Analytical Division Atomic Energy Establishment Trombay Bombay, India
Assay of Barium Compounds by Precipitation of Barium Chromate from Homogeneous Solution SIR: There is a pressing need for a method for the assay of barium compounds. Because available methods are unsatisfactory, barium compounds are usually not assayed a t all or the assay is made by analyzing for the anion ( I ) . Firsching (2) and Gordon and Firsching (3) determined barium by precipitating barium chromate from homogeneous solution; Firsching used EDTA, while Gordon and Firsching used urea. In the method of Gordon and Firsching the pH was adjusted to 1.7 to 1.8, ammonium acetate, potassium dichromate, and urea were added, and the solution was heated a t 95 O to 98 O C. until the pH changed to 5.7. This took 2.5 hours or more. The present author has found that if 7 ml. of hydrochloric acid, or 6 ml. of perchloric acid and 2 ml. of hydrochloric acid, are present in 225 ml., and the solution is boiled until a precipitate appears (about 15 minutes) and then for an additional hour, there is no necessity for adjusting the pH exactly. The pH after the boiling period is 5.5 and it does not change on continued boiling. The technique has been applied to the assay of commercially important barium salts, using a 0.5-gram sample. If less than 3% strontium compound is present, only one precipitation of the barium chromate is necessary; if more than 3% strontium compound is present, the barium chromate is reprecipitated after dissolving it in nitric and perchloric acids and evaporating to fumes of perchloric acid. All the barium compounds 312
ANALYTICAL CHEMISTRY
analyzed in this laboratory contained less than 3% strontium compound. Interference from carbonate, peroxide, and sulfide was eliminated by boiling with acid, and interference from fluoride, organic anions, and silicon was eliminated by fuming with perchloric acid. Barium sulfate was fused with sodium carbonate, and the barium carbonate filtered off and dissolved by fuming with perchloric acid. The amounts of iron and other elements found in barium compounds did not interfere with the method. PROCEDURES
1. Barium Nitrate, Acetate, Chlorate, Chloride, Hydroxide, and Perchlorate. Transfer a 0.5000-gram sample to a 400-ml. beaker, add 225 ml. of water and 7 ml. of hydrochloric acid, and stir to dissolve. Heat to about 80" C. and add with stirring 10 ml. of ammonium acetate solution (400/,), 25 ml. of potassium dichromate solution (lo%), and 10 grams of urea. Cover with a watch glass, heat to boiling, boil moderately until a precipitate settles on the bottom of the beaker, and then continue boiling for 60 minutes more. Midway during this 60minute boiling period, wash down the cover lid with water and bring the volume to 225 to 250 ml. by adding hot water. At the end of the heating period, filter through a tared sinteredglass crucible of medium porosity, transfer the precipitate to the crucible with potassium dichromate wash solution [made by diluting 50 ml. of potassium dichromate solution (10%) to 1
liter with water], and finally wash the precipitate four times with water. Dry a t 120" C. for 1 hour, cool, and weigh as barium chromate. 2. Barium Carbonate and Chromate. Add 100 ml. of water and 7 ml. of hydrochloric acid, and boil for 10 minutes to dissolve the sample and drive off carbon dioxide. Dilute t o 225 ml., heat to 80' C., add the ammonium acetate, and proceed as in 1. 3. Barium Fluoride. Weigh the sample in a platinum dish. Add 40 ml. of mater, 10 ml. of hydrochloric acid, and 6 ml. of perchloric acid. Evaporate to fumes of perchloric acid, dilute to 225 ml., and add 2 ml. of hydrochloric acid. Heat to 80" C., add the ammonium acetate, and proceed as in 1. 4. Barium Oxalate and Other Organic Barium Salts. Add 25 ml. of nitric acid and 6 ml. of perchloric acid, and evaporate to fumes of perchloric acid. Dilute t o 225 ml. and add 2 ml. of hydrochloric acid. Heat to 80" C., add the ammonium acetate, and proceed as in 1. 5. Barium Oxide, Peroxide, and Sulfide. Add 50 ml. of water and 7 ml. of hydrochloric acid and boil for 12 minutes. Filter off any residue and wash with hot mater. Retain the precipitate and filtrate. Ignite the precipitate and fuse with 4 grams of sodium carbonate. Leach with 200 ml. of water a t 95" C. for 45 minutes, filter, and wash with hot 0.2y0 sodium carbonate solution. Discard the filtrate. Dissolve the precipitate in 10 ml. of hot hydrochloric acid (1 to 2) and wash with water. Make the filtrate so obtained just alkaline to
litmus paper with ammonium hydroxide (1 to 1) and wash into the first filtrate. Heat to 80" C., add the ammonium acetate, and proceed as in 1. 6. Barium Sulfate. Mix the sample with 10 grams of sodium carbonate in a covered platinum crucible and heat over a Meker burner for 1 hour. Leach with 200 ml. of water a t 95" C. for 1 hour, filter, and wash well with hot 0.2y0 sodium carbonate solution. Transfer the filter paper and precipitate back to the beaker and add 20 ml. of water, 20 ml. of nitric acid, and 6 ml. of perchloric acid. Evaporate to fumes of perchloric acid and add 100 ml. of water. Filter off the silica that is usually present in this compound and wash with water. Dilute to 225 ml. and add 2 ml. of hydrochloric acid. Heat to 80" C., add the ammonium acetate, and proceed as in 1. 7. Barium Compounds Containing More Than 3yo Strontium Compound. Proceed as in 1 to 6 but filter the barium chromate through a mediumtexture filter paper and wash the precipitate into the filter paper with potassium dichromate wash solution. Transfer the filter paper and precipitate back to the 400-ml. beaker and add 15 ml. of nitric acid and 6 ml. of perchloric acid. Cover with a watch glass, evaporate to fumes of
Table 1. Compound Ba(NO& Ba(C2H30dz Ba(C108)2.H20 BaClz .2H20 Ba( OH)t. 8H90 Ba(C10d2 BaCOa BaCrOl BaF2 BaC204.HzO BaO Ba02 BaS BaS04 Ba picrate
Assay of Barium Compounds Grade Assay, %, Reagent 99.96, 100.04, 99.94, 100.00 Reagent 99.56, 99.64 Reagent 100,28, 100.26 Reagent 100.26, 100.32 Reagent 100.98, 100.90 Technical 99.20, 99.34 Reagent 98.90, 99.00 Technical 98.62, 98.74 Reagent 100.34, 100.40 Reagent 100.80, 100.70 Technical 91 .76, 91 . 8 2 Reagent 97.78, 97.84 Yellow 89.46, 89.54 U.S.P. 98.26, 98.38 Technical 86.58, 86.50
perchloric acid a t moderate heat, continue fuming a t moderate heat until the solution is red, and then fume for 1 or 2 minutes more. Dilute to 225 ml. and add 2 ml. of hydrochloric acid. Heat to add the ammonium and proceed as in but use ml* of potassium dichromate solution (loyo). RESULTS
The results obtained for the assay of barium compounds are shown in Table I. All the assays were made by analyzing for total barium and cal-
culating to the barium compound. Modifications for determining soluble barium are readily apparent. LITERATURE CITED
(1) American Chemical Society, Washington, D. C., "Reagent Chemicals," p. 66,
1951.
(2) Firsching, F. H., Talanta 2, 3%
(1959). (3) Gordon, L., Firsching, F. H., ANAL. CHEM.26,759 (1954). GEORGE KORWITZ Pitman-Dunn Laboratories Frankford ~~~~~~l Philadelphia 37, Pa.
Radiochemical Determination of Radium in Uranium Milling Process Samples SIR: A recent method (2) for the determination of total radium in uranium mill process samples has been modified to increase sensitivity, accuracy, and cut analyst time. Two basic changes have been made. First, to decrease the quantity of inert material accompanying the radium, 25% ammonium carbonate has been substituted for sodium carbonate as the reagent for metathesis of lead sulfate to lead carbonate. The change increased the yield from 77 to 95%. Sensitivity has also improved, because reduction of the solids content allows the entire purified radium sample to be mounted on a planchet. The second change involves the use of solvent extraction rather than ion exchange to effect the lead-radium separation. Aliquat 336, a quaternary amine, is used as the extractant, and lead is extracted as a chloride complex. This change has resulted in a significant reduction of analyst time. EXPERIMENTAL
Apparatus and Reagents. The counting equipment is a Nuclear Measurement Corp. PCC-1OA proportional converter used in conjunction with a Technical Measurement Corp. SG-24A scaler.
Lead carrier, 0.49M lead nitrate solution. lOOyo active Aliquat 336 (General Mills Co., Kankakee, Ill.), 30% by volume dissolved in benzene. This solvent is washed three times in equal volumes of 4M NaOH and then three times in equal volumes of 1.5M HC1. Solvent Extraction Modification. After adding 4 ml. of concentrated hydrochloric acid dropwise (stirring constantly) to precipitate lead chloride and cooling the solution in an ice bath, centrifuge, and pour the supernate into a 250-m1. separatory funnel containing 100 ml. of the washed Aliquat 336-benzene solvent. Shake for 2 minutes, allow the phases to disengage, and draw off the aqueous phase into a 250-ml. beaker. Add 15 ml. of 1.5M hydrochloric acid to the centrifuge tube containing the lead chloride precipitate. Stir well and cool in an ice bath. Centrifuge and pour supernate into the separatory funnel containing the Aliquat 336 solvent. Shake for 2 minutes, allow phases to disengage, and draw off the aqueous phase into the 250-ml. beaker containing the initial hydrochloric acid raffinate. Discard the lead chloride precipitate and the solvent. Evaporate the combined hydrochloric acid raffinates to dryness. Charring, resulting from dissolved organic material, may result a t this point. Place the beaker in a muffle furnace, adjusted
to 500" to 600" C., and bake for 10 minutes to destroy organic material. Remove beaker from the furnacf', allow to cool, and add 10 ml. of concentrated nitric acid. Evaporate the nitric acid to a volume of about 1 ml. on a low hot plate. Transfer the solution t o a IO-ml. volumetric flask with the aid of small volumes of 1M nitric acid. Before making the last transfer, carefully clean the bottom of the beaker with a rubber policeman. Evaporate an aliquot of the sample on a 2-inch cup-type stainless steel planchet and count immediately for alpha activity. For this procedure, the radium yield is %yowhen starting with either liquid or solid samples, if a 1-ml. aliquot is mounted for counting. If the entire sample is mounted, the yield is 81%.
Table 1. Analysis of Standard Sample (Sample 1. Pitchblende ore sample, theoretical radium content of 8750 d.p.m. of Ra/gram, including Ra228, Ra223, and daughters) Analysis D.P.M. , Error, No. Ra/G. % 1
2 3
4
8740
0.11
8800
0.57
8690 8530
0.46 2.52
VOL. 33, NO. 2, FEBRUARY 1961
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