Table I.
Typical Powders and Alloys Analyzed
RCL-256 channel analyzer Sample composition Representative powders, synthetic mixtures (1) CJz08 i i 50% hi0 22 50 (2) K O 84 76% Fe203 15 24
COO (4) CaO Cr203 FezOa ( 5 ) CaO
49.09 55.30 33.97 IO. 45 48.30 30.08 9.56 10.11
54.83% 34.91 10 26 49 9iyo T-205 30 10 COO 9 96 ZnO 9 97 Simulated cement #3 SiO, 29,99% CaO 65.00 FezOs 5.01 NBS portland cement 1014 Si02 19.49y0 CaO 63.36 Fe20a 2.50 Typical alloys 304 SS Cr 18-20% Ni 8-11 Fe 66-71 NBSD849 Cr 5 5y0 Xi 6 6 Fe - 4 4 NBS 1203 Cr 11 9% 75 5 Xi
Deviation
Peak height
+0.40 +2.09 -0.98 f5.16
Found 79 21 84 (On Rustrak 16 1 requires
Found 77.80 22.97 83.93 16.07 50.91
50.05
%
Peak height
(3) Fez% 49.95%
Miniaturized apparatus (Rustrak recorder)
i
Requires selective filtration
: 6.0
64 25
”
+0.86 -2.69 +l.85 -3.34 -0.10 -4 02 +1.40
56 36 10 52 29 11 9
-1.15 ., .
... 69 4.0
+3.06 -1.20
... 64 3.1
,
12.0 -6.7 +5
ACKNOWLEDGMENT
filtmt,inn . -..... I
92 52, )On-Rustrak 4,,,5( requires
+ ’
i
w/c
Deviation
iron, chromium, and nickel with good results. T h e d a t a are shown -graphitally in Figure 12. A tabulation of the analytical results for the various samples, is shown in Table 1. The samples were analyzed both with a RCL 256 channel analyzer and with the miniaturized single channel analyzer and Rustrak recorder.
filtration
+5 ,
..
+2 +3 -3 +4
+-9-310
The authors thank Dr. D. C. Stewart for his original suggestion on the possibility of a portable x-ray fluorescence apparatus using radioisotope sources. The authors thank C. Bloomquist, J. Hughes, and F. Schmitz for their participation in preliminary literature survey work. LITERATURE CITED
+6
(1) Abid Husain, S., 2nd U . AT. Intern. Conf. Peaceful Uses A t . Energy 19,
:
65 30 2.47 17.8 9.5 70 5 1 7 0 86 12 5 73 8
analyzed using both the peak height and peak area techniques. B. Synthetic and NBS Portland Cements. T h e NBS cements analyzed were portland cements 1011, 1014, and 1016. T h e synthetic mixtures made t o simulate the NI3S standards gave higher CaO results. It is possible to analyze the cements only for the CaO
... ...
-7 3 +6 1 +5 0
-2 3
... +1 ...
20 11
66 8
8
83 14 80
and Fe203 content. Figure 11 shows the results graphically. C. Alloys. The alloys analyzed were: 304SS, NBS D347, D’349, and D850 steels, and NBS 1190 and 1203 nickel-chromium alloys. The NBS and 1203 alloys were only analyzed for nickel and chromium with good results. T h e steels were analyzed for
213-4 (1958). (2) Cameron, J . F., Rhodes, J. R., Nucleonzcs 19, No. 6, 53-7 (1961). (2) Cook, G. B., Mellish, C. E., Payne, J. A., 2nd U . N . Intern. Conf. Peaceful Uses A t . Energy 19, 127-34 (1958). (4) Gatrousis, C., Heinrich, R., Crouthamel, C . E., “Progress in Xuclear Energy;” Series IX, Analytical Chemistry, J 01. 2, pp. 1-79, Pergamon Press, 1961. (5)-Goulding, F. S., Robinson, L. B., A t . Energy Can. I,td. AECL 767, CREL 778, (January 1959). (6) Kereiakes, J. G., Kraft, G. R., Weir, 0 . E.. Krebs. A. T.. Nucleonics 16. No. 1. 80-2 il9BFil. (7)’Narbutt, K. I., Barinskii, P. L., Smirnova, I. S., Dokl. Akad. N a u k SSSR 130, NO. 2, 291-4 (1960). (8) Reiffel, L., Nucleonics 13, No. 3, 22-4 (1955).
RECEIVED for review December 23, 1963. Accepted February 27, 1964. Based on work performed under the auspices of the U. S. Atomic Energy Commission.
Dissolution and Assay of Elemental Boron A. R. EBERLE, L. J. PINTO, and M. W . LERNER New Brunswick laboratory, U. S. Atomic Energy Commission, New Brunswick, N. 1.
b Two new methods for the assay of elemental boron are presented.
In one, the boron is dissolved by a potassium persulfate fusion carried out in quartz. The technique has certain advantages over the usual sodium carbonate-platinum crucible fusion. The boric acid obtained is determined by the conventional mannitol titration procedure. The other method involves a pyrohydrolytic separation of the boron. Substantially a pure boric acid is obtained which can be determined by titration in the presence of mannitol to a single end point. Both methods appear to be accurate and precise.
1282
ANALYTICAL .CHEMISTRY
A
( 1 ) from this laboratory briefly described various methods of dissolving elemental boron and proposed a new potassium persulfate fusion procedure. In the present work, a study of the mannitol titrimetric determination of the boric acid obtained with this persulfate fusion is reported, and the assay method is compared both to a conventional carbonate fusion method and to another newly developed method involving a pyrohydrolysis separation. In considering an alternative boron dissolution technique, it occurred to the authors that pyrohydrolysis, which has been utilized (3, 6, 6) for the separation RFCENT NOTE
of boron from various minerals, glasses, alloys, and boron compounds prior to total boron or isotopic ratio determination, might have one chief advantage in the assay of elemental boron. With this separation procedure, the possibility existed of titrating the boric acid in the distillate to a single end point, that of the mannitoboric acid. Thus, the titration might be relatively more precise and accurate than the classic titration involving both a mineral acid and a mannitoboric acid end point. Two conditions must be met to ensure the success of the pyrohydrolysis assay method: the total boron must be separated; the distillate must be free of
elements interfering in the mannitol titration. In regard to the latter condition, apparently few elements other than those occurring as anions accompany the boron. Small quantities of tungsten were found to distill. Williams, Campbell, and Magliocca (6) report that of the many glasses analyzed only high lead glasses may contaminate the distillate with quantities of lead, and that the distillate is alkaline when sodium silicate is used as a n auxiliary cataly5t .dong with uranouranic oxide. Kiederkehr and Goward ( 5 ) state that the distillate is “completely free of interfering elements” when the boron in bomn carbide, boronstainless steel alloy, Zircaloy-uraniumbase alloys, and mixiurea of boron or boron carbide n i t h uranium dioxide is separated and determined either titrimetrically or spectrophotometrically with quinalizarin. I t was felt, therefore, that essentially a pure boric acid product would be obtained from good commercial-grade boron, and that the chief concern would be the quantitative recovery. EXPERIMENTAL
Reagents and Apparatus. Standa r d boric acid was prepared by recrystallizing reagent grade material three times a n d dr) ing over sulfuric acid for at least 3 w e k s . Potassium persulfate fusions were made in a 250-ml. clear silica, round bottomed flask n i t h a 5-inch neck and a 24/40 3- joint to which was attached a 16-inch silica condwser and a borosilicate water jacket. Pyrohydrolyses were performed with a platinum reaction tube, fabricated from 20-mil sheet, 3 / 4 - i n ~ hi.d. and 15 inches long. The tube was fitted with a copper-jacketed, !rater-cooled ring condenser 1 inch wide and 2 inches in diameter to cool the flared entrance hole holding a rubber stopper through which the steam was led from the steam generator. So that the reaction tube could be inserted into a high-temperature resistance tube furnace (Uurrell No. d2-9), the ring condenser was made removable by means of a thread machined on a silver sleeve sweated on the flared end. T o the eyit end of the tube was welded a 22-inch piece of 3/,16-in~hi.d. platinum tubing which was bent to a right angle about 7 inches from the weld joint and was fitted with an 8-inch long copper-jacketed, watercooled condenser. A quartz tube liner wa5 placed within thi. reaction tube to protect the platinum in the event boron particles blew out of the reaction boat. The liner had to br replaced periodically. The boat wts con>tructed of 40-mil gold sheet and was made inch wide, ’ 1 1 6 inch deep and 2 l l 2 inches long. .A partial cover, ’116 inch wide and 13 inches long, alloii ed steam to enter the boat. .About ‘ / I 6 inch from each end of the c o ~ e r the , ”ridth was reduced to the inside width of the boat and these
ends were bent to a right angle: one end butted against the inside end of the boat, the other aligned the corer on the boat. Steam was generated in a three neck 2-liter balloon flask equipped with f joints. A silica tube carried the steam from the center neck to the reaction tube and was heated by a microcombustion tube furnace. A large stopcock fitted to one of the side necks controlled the steam flow to the reaction tube: when the water was boiling, steam entered the tube appreciably only when the cock was closed. The other side neck served for filling. The water reservoir flask was heated by a mantle connected to a Variac which served as a rough control on the steam flow rate. The water was kept alkaline by the periodic addition of a small quantity of lime. Titrations were carried out with a Photovolt model 110 p H meter. Sample Preparation. I n general, t h e finely divided samples are assayed “as is’’ and separate moisture determinations are carried out which can be used to convert the assays to a d r y basis. Chunk crystalline samples are best powdered by a striking and direct pressure action of a tungsten carbide pestle against the chunks held in a tungsten carbide mortar and then sieving out the fine particles produced. Conventional grinding action scratches the mortar badly. Procedures. PERSULFATE FUSION ASSAY. Transfer a 300-mg. sample of finer t h a n 80-mesh material t o t h e quartz fusion flask. Add 50 grams of potassium persulfate and rotate the mixture until t h e boron is Pather uniformly distributed. Add 0.25 ml. of water and swirl the flask until the salts are evenly moistened. Connect t h e flask t o the condenser. Clamp the condenser loosely to a ring stand and support the flask on an iron ring so that the neck of the flask can be held by tongs and the flask swirled during the fusion. Heat the flask with a blast burner, gently a t the start, a t full blast after the persulfate has melted. Swirl the flask and splash the molten salt around until a clear melt is obtained, generally after about 10 to 15 minutes. (Ignore for the present any trace of white boron nitride floating on the surface of the molten salt.) Allow the flask to cool to room temperature. Add about 100 ml. of water through the condenser. Dissolve the salts by heating gently with a burner. After dissolution, boil the solution for 2 to 3 minutes. R a s h down the condenser, transfer the solution to a 400-ml. silica beaker, and bring the volume up to about 250 ml. with wash water. Add 1 ml. of 0.1% phenolphthalein solution and neutralize the solution with 6JI sodium hydroxide to the first pink color, p H 7.8 to 8.0. Filter the solution through 15-cm. Whatman S o . 41 paper into a quartz beaker. K a s h the paper thoroughly with hot water previously made to p H 8.0 with dilute sodium hydroxide solution, and bring the total volume to about 500 ml. If nitride was seen to be present
during the fusion, use a Whatman No. 42 paper for the filtration of the impurity hydrosides. Ash the paper and fuse the residue with 3 grams of anhydrous sodium carbonate. Take the cooled melt up in water, digest the solution for a t least 1 hour on the steam bath. Filter the solution through Whatman S o . 41 paper and wash the paper thoroughly as described above. Add this solution to the main solution and bring the total volume t o about 500 ml. Add dilute sulfuric acid to the solution to p H 3.5 and 4.0. Cover the beaker with a watch glass and boil the solution gently for 3 minutes. Cool the solution rapidly to room temperature. Insert the p H meter electrodes, add a magnetic stirring bar, and titrate the stirred solution with 0.6N sodium hydroxide to 0.05 to 0.10 ml. in excess of the first inflection point occurring at pH 5.6 to 5.8. Add 50 -grams of mannitol and continue the titration to the next potentiometric break occurring a t p H 8.10 to 8.20. For both end points, titrate with a 10-ml. semimicro buret, adding 44 to 46 ml. of titrant to p H 7.0 to 7.6 from a calibrated 50-ml. buret after the first end point and then switching to the semimicro buret. Add the volume of titrant used in excess for the mineral acid inflection poirit to that used for the mannitoboric acid inflection point. Standardize the 0 . 6 s sodium hydroxide solution by adding the calculated amount of standard boric acid equivalent to the weight of sample together with 50 grams of mannitol to 500 ml. of freshly boiled and quickly cooled water and titrating to the potentiometric end point occurring- near p H 8.5. Determine a reanent blank correction by fusing 50 g r a i s of persulfate and carrying out a standardization of the titrant with the same weight of boric acid in the presence of the persulfate exactly as described for the sample titration. The difference between the volumes of titrant required for the identical amount of boric acid is equal to the reagent blank. This quantity amounts to less than 0.10 ml. of 0.6,V sodium hydroxide for the two different lots of potassium persulfate tested. PYROHYDROLYSIS ASSAY. Spread a 100- to 200-mg. sample of less than 80-mesh material over one end of the boat, covering about one half of the bottom area. Place the cover on the boat so that it covers the sample and butts against the sample end of the boat. Place the boat in the reaction tube so that the open end faces the steam inlet side. Dip the condenser tip into 100 ml. of water held in a 2-liter beaker. Connect the steam inlet tube and begin to heat the water reservoir keeping the large stopcock on the side neck open. When the water ia near boiling temperature, begin heating the reaction tube and the steam pre-heater. When the reaction tube temperature is near 700” C. and the water is boiling, close the relief stopcock and slowly increase the reaction tube temperature to a tested boat temperature of 1000” C. Msintain this temperature careVOL. 36, NO. 7, JUNE 1964
* 1283
Table I.
Sample So.=
Wt. basis
1 2 3
As is As is
4 6 6 7
Dry
Dry
As is As is As is
precision of the two methods is nearly identical.
Assay of Boron Samples
Persulfate fusion
Pyrohydrolysis
98.7, 98.8, 9 8 . 8 93.0, 9 3 . 1 94.2, 94.1, 9 4 . 2 94.0 93.8, 93.8 94.7, 9 4 . 7 96.9, 96.0 96.9, 97.1, 96.9 96.9, 96.9, 9 7 . 0 97.0
98.8, 98.8 93.1, 9 3 . 1 94.1, 9 4 . 3
Carbonate fusion . . ,
93.2, 9 3 . 2 94.2
93.8, 9 3 . 7 94.7, 94.8 96.1, 9 6 . 9 96.9, 96 8, 9 6 . 9 97.0, 96.8, 97.1 96.9, 96.9
... 94.8 96.0 97.2
a S o . 1 is chunk sample; KO.7 is coarse powder; remainder are fine powders of less than 200-mesh.
fully for 6 hours, collecting about 1500 ml. of distillate. Without any delay, remove the beaker and insert the p H meter electrodes and a magnetic stirring bar. Add 50 grams of mannitol and titrate the stirred solution with 0 . 4 5 sodium hydroxide to p H 8.30. Determine a sample blank by pyrohydrolyzing an empty boat for 6 hours and titrating the distillate, after the addition of 50 grams of mannitol, to a small inflection point occurring near pH 7.9. Standardize the titrant by titrating it quantity of boric acid equivalent to the boron in the sample in 1600 ml. of water in the same manner as described for the sample. Determine a standardization blank by titrating 1600 ml. of water after the addition of mannitol to a small inflection point occurring near pH 7.9. C A R B O N A T E F U S I O K .ASSAY. Conventional carbonate fusion procedure involving one of the more satisfactory fusion techniques ( 4 ) together with a titrimetric determination nearly identical to that described for t'he above persulfate fusion served as a comparison procedure. Tamp 5 grams of anhydrous sodium carbonate powder into a plat'inum crucible. Add to a depression in the sodium carbonate an intimate mixture of 200 mg. of sample and 1 gram of sodium carbonate. ,Jolt the two layer. together by gentle tapping and add 4 grams more of the sodium carbonate. Cover the crucible and place in a cold furnace. Heat the furnace to 1000" C. within 75 minutes and hold for 10 minutes a t this temperature. Dissolve the cooled melt in 200 ml. of water in quartz. Digest the solution on a steam bath for 30 minutes, filter through Xhatman S o . 42 paper, and wash the paper with 200 ml. of 0.1% sodium carbonate solution. Titrate the solution, after pH adjustment and carbon dioxide removal, with 0.4.Y sodium hydroxide to inflection points near p H 5.5 and 8.3. Standardize the titrant by titrating the same weight of boric acid in 400 ml. of water containing 10 grams of sodium carbonate. Use as the reagent blank the difference between this 1284
ANALYTICAL CHEMISTRY
volume of titrant and the volume needed for the same weight of boric acid in the absence of sodium carbonate. RESULTS
The assays of several samples of boron by the two proposed procedures and by a typical carbonate procedure are shown in Table I. The agreement between the results of the new procedures is excellent. The results by both procedures also agree well with those obtained with the conventional carbonate procedure. I n the persulfate (and carbonate fusion) assay procedure, standardization of the titrant against standard boric acid agrees with t,he standardization against the primary standard potassium acid phthalate within 1 part per thousand under the given conditions of titration. I n the absence of suitable boron standards, this agreement must suffice for the estimate of accuracy of the titration step. Considering the fusion tests with boric acid, given below, it can be reasonably assumed that any loss associat'ed with the fusion step must' be very small. The error from occlusion of boron in the hydroxide precipitation must also be insignificant because of the small quantity of hydroxides precipitated. The standardizations of the titrant in the pyrohydrolysis procedure against standard boric acid and pot'assium acid phthalate are identical by the nature of the fixed pH end point described below. Other effects decreasing the overall accuracy such as mechanical loss of boron during pyrohydrolysis and distillation of interfering impurities can be expected to be minor in the light of remarks made previously and below. Reproducibilit,y of the two proposed procedures was studied by carrying out replicate analyses of sample S o . T. The standard deviation for the fusion procedure is 0.08; for the pyrohydrolysis procedure, 0.10. Thus, the
DISCUSSION
Persulfate Fusion Assay. The efficiency of t'he reflux condenser in preventing losses of boric acid was tested by fusing 1.2-gram samples of boric acid with 50 grams of potassium persulfate for 10 minutes aft,er a melt was obtained. The recovery was 100.070. Fusing 0.6-gram samples for 20 minutes gave a n apparent recovery of 99.9%. The addition of 1 to 2 nil. of water to either mixture before fusion gave significantly low recoveries. When very finely divided elemental boron samples are fused, 1017 results are obtained if 0.25 ml. of water is not used to moisten the persulfate. This loss is due to the blowing out of a quantity of the powder during the fusion and it was traced by observing the particle; caught by a glass wool plug placed in the condenser outlet t'ip. The 0.25-ml. volume of water recommended is less than the quant'ity of water in 1.2 grams of boric acid as used in the recovery tests described above. Pyrohydrolysis Assay. When the quantity of boric acid equivalent to 100 to 200 mg. of boron is titrated in the large volume of about' 1600 ml. after the addition of mannitol, the potentiometric inflection point is small and poorly defined. Attempts to sharpen this break by evaporation of the solution to about 500 ml. in the presence of the 50 grams of mannitol ( 2 ) resulted in small losses, about 0.4yo, of boric acid. The use of 150 grams of mannitol in the 1600-ml. volume gave a measurable break but this quantity of mannitol was considered to be prohibitive for rout,ine work. The poorly defined break in the presence of 50 grams of mannitol occurs very near pH 8.30. When the same quantity of standard boric acid under the same conditions is titrated with sodium hydroxide solution standardized against potassium acid phthalate, the required quantity of titrant has been added when t.he pH is exactly 8.30. The fixed pH of 8.30 was, therefore, used as the end point. The sample blank generally is betweer., 0.20 and 0.25 ml. and needs to be determined only occasionally. This blank value can be reduced to less than 0.10 ml. if the condensate is protected from the atmosphere during collection. The range of the standardization blank is 0.10 to 0.15 ml. The value for this blank correction can also be obtained by titrating 1600 ml. of water containing 50 grams of mannitol t,o an inflection point near pH 7.8 to 7.9 before adding the weighed amount of boric acid for the standardization. This step results in a
saving of 50 grams of mannitol. -1 similar technique applied to the sample dist,illate yields a potential break too poor to be used; the blank is best obtained as described above. These blanks, when subtracted from the appropriate volumes of standard sodium hydroxide, correct 110th for reagent impurities and also (:arbon dioxide in the solutions. The initial pyrohydrolysis experiments were conducted a t 1350' C. with a platinum boat. Although sodium silicate, used previously as a supplementary catalyst in the pyrohydrolysis of siliceous boron ma:erials ( 6 ) was unnecessary and indeed to be avoided, a bedding material was needed to protect' the platinum b o a t , therefore, t'he customary urano-uranic oxide (6) was used. However, the technique of spreading 200 mg. of Iloron powder over 3 grams of urano-uranic oxide as the charge material frequently resulted in black particles being found in the distillate, and the p.latinum boat was occasionally damaged. This blow-over proved to be very troublesome: no variation in rate of steam flow or temperature rise, or t .ming of the initial flow of steam eliminated it consistently. Some success w3,s obtained by pelleting samples of fine powder in a hand press and placing the pellet on a bed of thorium ox.de. Only white powder, the thorium oxide, now appeared in the distillate. With this arrangement the boat was only infrequently damaged. Spectrographic a n a l p i s of the thorium oxide aft.er pyrohydrolyzing several different samples a t 1350' C. for 3.5 to 4 hours obtaining from 1400 to 1500 ml. of distillate indicated that from 120 to 160 p g . of boron invariably remained in the bedding material. Increasing the time to 5 hours and t,he temperature to 1375' C. did not lower this quantity significantly. With 2 200-mg;. sample, this loss correspond;+ to O.O70j,. Attempts made to eliminate the bedding material completely by using boats of stainless steel, monel, nickel, iridium, and quartz failed. A11 the boats were severely damaged and result,s were low.
Although the pellet-thorium oxide technique (with added correction) gave satisfactory results for finely powdered boron samples, chunk samples presented another problem because of the difficulty in grinding boron without contamination to a powder fine enough to be pelleted. Small pieces, from 1 to 2 mm. in cross section, obtained by crushing large chunks, were individually embedded in the thorium dioxide in a few runs but the boat was often damaged and the results low. Boron does not attack gold below its melting point of 1063' C. Accordingly, the recovery was tested with a gold boat without a bedding material and a t a pyrohydrolysis temperature of 1000' C. Measurements of the temperature inside the reaction tube indicated that 1000' C. would be maintained a t a furnace pyrometer reading of 1075' C. Blow-over was prevented by placing a gold cover over the rear portion of the boat, the area over which the sample was spread. The forward open portion allowed entrance of the steam. The pyrohydrolysis was found to be complete in 6 hours with a slightly slower flow rate of steam than was used previously, resulting in the same volume, about 1500 ml., of distillate being collected. Both very fine samples and those of less than 80 mesh obtained by crushing chunk samples and sieving were satisfactory. The film of impurities left in the boat was found to contain less than 50 pg. of boron. Thus, the loss is less than O.O25QJ, and can be neglected in the light of the possible sample weighing error. .L\pparently some other element present in the samples or in the water reservoir accompanies the pyrohydrolyzed boron since it was found that the initial pH, before the addition of the mannitol, may vary by one to two tenths of a pH unit. This variation, however, is equivalent to less than 0.02 ml. of 0.4N sodium hydroxide and contributes an insignificant error. General Comparison. T h e persulfate fuyion assay takes about 2.5 hours to complete; t h e pyrohydrolysis assay about 6.5 hours. The carbonate
fusion assay requires about 4 to 5 hours. Thus, the pyrohydrolysis assay is t h e slowest; however, t h e beautifully clean separation is applicable t o a variety of samples: the assay should be a good referee method. It may also prove to be most uieful in those cases in which a pure boric acid solution must be obtained. Such a requirement will exist here in the near future in connection with another method of boron determination being developed. A disadvantage of the carbonate fusions is that they are not always successful. Fusions over the blast burner may fail because of splattering, creeping, flaring, etc. Damage to the platinum crucibles is common. The furnace fusions are smoother, but relatively large particles easily dissolved by the persulfate fusion technique are sometimes incompletely dissolved. In addition, certain impurities such as chromium are not removed by the carbonate fusion and subsequent precipitation. These impurities may interfere with the titration by their buffering action. I n the persulfate fusion with its reducing conditions as a result of the sulfur dioxide liberation ( I ) , chromate for example is reduced to chromium(II1) and is precipitated along with the other hydroxides such as aluminum and iron.
LITERATURE CITED
(1) Eberle, A. R., Lerner, M. W., AKAL. CHEM.36, 674 (1964). (2) Feldman, C., Zbid., 33, 1916 (1961). (3) Finley, H. O., Eberle, A. R., Rodden, C. J., Geochim. Cosmoschim. Acta 26, 911 (1962). (4) Hermann C. Starck, Berlin (Germany), procedure, private communication, J. J. Collins, Shieldalloy Corp., Sewfield, S . J., to S. J. Broderick, U. 8. Atomic Energy Commission, Kew Brunswick Laboratory, 1963. ( 5 ) Wiederkehr, V. R., Gon-ard, G. W., ANAL.CHEM.31, 2102 (1050). ( 6 ) Williams, J. P., Campbell, E . E., Magliocra, T. S., Ibid., 31, 1560 (1959).
RECEIVED for review January 17, 1964. Accepted March 17, 1964.
VOL. 36, NO. 7 , JUNE 1964
1285
