1283
V O L U M E 2 2 , NO. 10, O C T O B E R 1 9 5 0
siderably higlicr concentrations thaii \yere 1,cquired in the study of interferences in the present in\-estigation. Kelrher ( J ) , apparently referring to the work of Kolbling and Steiger, states, “It is important to know that osmium, which in its other analytical reactions resembles ruthenium, does not react’ with rubeanic acid; for this reason rubeanic acid can be used for the detection of ruthenium in the presence of osmium.” The original article by Wolbling and Steiger states, “Osmium salt solutions give, with rubeanic. acid, no essential color change; with large amounts, the ethyl acetate estract is brown.” In the present work, no estraction procedures with organic solvents \Yere used. Rather large amounts of ethj*l alcohol and strong acid, and elevated teniperatures, were required to give rapid development of the blue ruthenium-dithio-oxamide color; under these conditions osmium gave a color; when the reagents were mixed the solution assumed a greenish color, which on heating changed rapidly to a brownish red, then more slowly to a n olive green color. By the proposed method, therefore, reasonably sharp prior separation of osmium from ruthenium, by an appropriate distillation procedure ( 2 ) , would be required. Compared with the thiourea method, the dithio-oxamide method has a slightly lower optimum concentration range, although the difference in ranges is hardly large enough to be of importance in application to analyses. The choice between the two methods probably would be based upon the kind and amount of interfering substances present in the sample.
CONCENTRATIOI+, P P Y . R u
Figure 3. Calibration Curve for Ruthenium w i t h Dithio-oxamide, 650 mw
after several hours. Between 450 and 800 mp, stable readings were obtained from the start. After about 2 hours the transmittancies in the lower w a v e - h g t h region had undergone a reversal, so that the transmittancy of the 5 p.p.m. solution was considerably lower than that of the 10 p.p.m. solution; the spectral curves for the two concentrations crossed at about 410 mp. Above 450 mp the two curves were still parallel in their proper relation to concentration and at the same transmittancies as when first measured. This behavior was checked throughout; no explanation has been found as yet, and the effect should be studied further. T h e osmium curve shown in Figure 2 was plotted from data taken about 2 hours after color development. Kolbling and Steiger ( 6 ) found t h a t palladium and platinum salts yield red precipitates with dithio-oxamide. These precipitates form only when palladium and platinum are present in con-
ACKNOW LEDGM E S T
T h e authors hereby acknowledge their thanks to the American Platinum Works for providing samples of ruthenium metal and ruthenium trichloride used in part of this investigation. LITERATURE CITED (1) Ayres, G. H.. Axar.. CHEM.,21, 652 (1949).
(2) Ayres, G . H., and Young, Frederick, Ibid., 22, 1277 (1950). (3) Hiskey, C. F., Ibid., 21, 1440 (1949). (4) Welcher, F. J., “Organic Analytical Reagents,” Vol. IV, p, 154, iXew York, D. Van Nostrand Co., 1948.
(5) Wolbling, H.. Ber., 67B,773 (1934). (6) Wolbling, H., and Steiger, B., Mikrochemie, 15, 295 (1934).
RECEIVED January 24, 1950. Condensed from a thesis submitted b y Frederick Young t o the faculty of t h e Graduate School of t h e University of Texas i n partial fulfillment of the requirements of the degree of master of arts, 1950.
Determination of Sodium Monoxide in Sodium LEONARD P. PEPKOWITZ AND WILLIAM C. JUDD Knolls Atomic Power Laboratory, General Electric Company, Schenectady, ,V. Y .
T
HE initial attempt by the authors to devise a method for the determination of sodium monoxide in sodium n-as to use the water formed by the reaction of sodium monoxide with dry hydrogen chloride a t high temperatures. The water formed immediately reacts with the excess sodium to form sodium hydroxide, which is reduced by the sodium a t the elevated temperatures t o reform sodium monoxide ( 4 ) . 2YaOH
+ 2Ka --+ 2 S a 2 0 + HS
sodium-vapor phase reactions at elevated temperature and in dry benzene ivvith iodine, bromine, and hydrogen chloride. Dry glacial acetic acid has some promise as a reagent, if a method could be developed for detecting the small quantity of water formed and if the glacial acetic could be dried reproducibly. 2Sa NazO
(1)
I n all such reactions the total sodium sample must react completely before the water equivalent to the oxygen present will be released. The determination of the small amounts of water produced in the presence of the very large quantity of sodium chloride is as difficult a task as the primary determination. Such exploratory attempts made without success included reactions with dry hydrogen chloride or carbon tetrachloride in liquid
+ 2H.4~+2SaAc + H, + 2HAc +2SaAc + H20
(2)
(3) The measurement of the water conductometrically appeared to be very sensitive but nonreproducible because of the original variable water content of t’he glacial acetic acid. The simple method reported in this paper depends on the physical separation of sodium from the sodium oxide by repeated extractions with mercury. The sodium oxide is insoluble in the resulting sodium amalgam and floats on the surface of the amalgam, Folloiving the extraction, the sodium monoxide is dis-
ANALYTICAL CHEMISTRY
1284
A method is presented for the determination of sodium monoxide in sodium. The basis of the procedure is the extraction of the metallic sodium with mer.cury in a special apparatus, effecting a quantitative separation from the sodium monoxide. The mean deviation obtained is *0.00570 oxygen. A novel sampling procedure is described which is an integral part of the method.
solved in water and titrated to a phenolphthalein end point, or alternatively the sodium equivalent to the oxygen is determined ivith a flame photometer. The sample size is determined by titration of the separated sodium amalgam. From t8hesetwo determinations the percentage of oxygen in the sample can be calcuInt et1. The wa.sh water must be corrected for the carbon dioxide content. In practice the wash water is carefully neutralized to a phenolphthalein end point before use. This has given more reproduc.ible results than titrating t o a methyl orange end point. . i t ruoni temperature, oxygen can exist in sodium as sodium hydroxide, sodium monoxide, sodium peroxide, or sodium carbonate. However, a t higher temperatures sodium hydroxide ( 4 ) and sodium peroxide are reduced to sodium monoxide by sodium. Ileppnteti attempts to detect carbonate in sodium which had been 1ie:ited to approximately 400" C. by dissolving the sodium in acid untl nie:twring the carbon dioxide liberated indicated that no c~ni.l,oiiate\vas present in the sample investigated. Accordingly i t tlii, wtlium to be analyzed is heated to 400" C. before sampling, .socliuni monoxide is the only compound that need be considered. Thi. simple titration procedure will not measure the osygen pre..cnt i n the sodium as zinc oxide, magnesium oxide, or any t~ompouiidwhich is insoluble in sodium amalgam or mercury and \\-hitah i.: not titratahlc to a phenolphthalein end point. If any otlirr titr:tt:ilile oxitlcb ir involved in the titration, it n-ill be inclutlecl i n t l i t , c:ilcul:iti~on
hT
3
2 MM C A P I L L A R Y
PREPARATION OF SAMPLE
One of the most difficult,problems in any procedure for the determination of oxygen in sodiuni is an adequate and reliable sampling technique. The described estraction procedure allows for a simple solut,ion to t h r sampling difficulties. The samples are taken 1)y dra\ving u p the molten sodium (125' C.) from a container into standard 0.25-inch (0.6-cm.) borosilicate glass tubing, 12 inrhcs (30 em.) long. The sodium is allowed to solidify and the tube containing the sample is brought out into the air. The sodium-filled tubes are cut into 3-inch lengths (ca. 2 grams of sodium), thus affording three aliquots of the sample. The ends of the 3-inch lengths are sealed with de Khotinskycement to prevent the oxide particles, formed during exposure to the air, from contaminating the equipment during the subsequent handling. The %inch length is deeply scored about 0.75 inch from each end, taking care not to break through the walls of the tubing, and the sample is thoroughly wiped and dried. There has been no evidence of further diffusion of oxygen down the sodium column even after many weeks of exposure. This observation has also recently been reported by Dostrovsky and Llewellvn ( 2 ) . Samples 6f sodium distilled in vacuum into small glass capsules which were sealed under vacuum gave identical results (0.017, oxveen) as samoles of the s a m ~sodium distilled into 0.25-inch " tubing and treited as in the ahove sampling procedure. For much of the preliminary irivestigition thFse small sealed bulbs (1 to 2 grams) of triple-distilled sodium were used as described below. I
APPARATUS
The extraction apparatus is shown in Figure 1. A is a length of Gooch rubber tubing, which is closed a t one end and cemented and wired t o a male 28/15 senliball joint at the other. The sodium sample contained in thwglass tube previously described is placed in A . The stirring roJ, B, which is connected to the extraction chamber through t,he gas-tight flexible rubber sleeve, C, is used t o break the glass sample tubes, stir the amalgam, and scrub down the walls of the estraction chamber. The dry, inert gas (nitrogen or argon) enters the extraction chamber through the side arm, D. The vacuum flask, E, is the receiver for the sodium amalgam and is replaced by a similar flask during the solution of the sodium oxide. The mercury is introduced into the extractor through.funne1 F , which is mounted on the gas inlet tube. The gas purifying system is visible in Figure 2, which is an over-all photograph of a unitized assembly for two extraction chambers. The tank gas, argon or nitrogen, is passed through a reducing valve and a safety valve into a drying tube filled with Anhydrone. From the drying tube the gas passes over freshly reduced copper contained in two furnaces, as shown in Figure 2, a t a temperature of 400" C. to remove the oxygen and then over Anhydrone to remove any residual moisture. The gas is led to the two extractors through a manifold visible in Figure 2. PROCEDURE
Figure 1.
Extraction Apparatus
Although a number of the results reported in this paper were obtained by the titration procedure, the above difficulty can be eliminated by determining the sodium equivalent to the oxygen by means of a flame photometer ( I ) , using lithium as an internal standard (see Table \').
Preparation of Extractor. The extractor, after thorough cleaning and drying, is attached to the gas manifold by means of D (Figure 1) and an asbestos-paper wrapped clamp (Figure 2) All joints and stopcocks are lubricated with silicone stopcock lubricant. The 3-inch length of tubing containing the sodium, after being wiped with a moist cloth and then with a dry cloth, is flamed carefully to remove the last traces of moisture and placed in sampling tube A (Figure 1). After the cap and stirring rod B have been flamed, the apparatus is assembled and dried by heating with a torch during the subsequent flushing and evacuation. The air in the extractor is removed by alternate flushings with nitro en and evacuation. Approximately 50 such cycles, which take Yess than 5 minutes, will remove the air from the extractor and provide a sufficiently satisfactory inert atmosphere. During this interval the extractor is thoroughly flamed with a torch t 1 remove any moisture which may have condensed within tile
1285
V O L U M E 22, N O . 10, O C T O B E R 1 9 5 0 apparatus. When the extractor is dry and free of oxygen, tripledistilled mercury is poured into F and about 20 ml. are run into the extractor. The front and back ends of the sample tube are broken off inside A a t the scratches and the pieces contain@g the contaminated sodium are retained in A . The middle portion of the sample tube containing the uncontaminated sodium is dropped into the extraction chamber. T a b l e I. Recoveries of Oxygen Added as Sodium M o n oxide to I-Gram Samples of Triple-Distilled Sodium Oxygen Added
Oxygen Found
Deviation
%
%
% Oa(av. of3 determination$
0.07 0.07 0.0s; 0.19 0.22d 0.24 0.29 0.64 1.14
0.02 0.08 0.07 0.07 0.19 0.23 0.28 0.34 0.63 1.09
I n order to test the method, weighed amounts of sodium monoxide were added to a bulb of triple-distilled sodium in the extraction chamber, the bulb was broken under the mercury, and the amalgam was stirred vigorously to disperse the added sodium monoxide. The sodium monoxide wzs standardized by dissolving in water and titrating withstandard hydrochloric acid to a phenolphthalein end point. Because the recovered sodium monoxide was meesnred in an identicel manner, the original titer value can be used to calculate the recovery, despite the fact that t.he sodium monoxide used was not. pure but. contained some sodium hydroxide. The recovery data given in Tahle I indicate the effectiveness of themethod.
+0.01 0
-0.01
0 +0.01 +0.04
os -0.01 -0.05
L" ,
.
-
^^
Extraction. A positive gas pressure, distending the rubber tubine. is maintained throughout the subsequent extraction steps.
~.. ,- ~ ~ ~
~
~
~
~~
~
1. The mercury amalgamates vigorously with the aodiumdnd ..
..----a
~~~~~~~
tion. When cool, the amalgam is &awn in& the suction fl&k by applying a very slight suction. The amalgam is withdrawn until 1 to 2 ml. remain in the extractor to retain the oxide. If the am& gam is completely removed, a lass of sodium monoxide will occur. The extractions are repeated until the extractor, stirring rod, and glass fragments are free from any metallic luster. About eight to ten cycle8 are usually required to remove all the sodium. When the extraction is thought to be complete, the lower s t o p cook is elo8ed and t,he flask containing the amalgam is replaced with a fresh flask containing 5 ml. of water and a few drops of phenolphthalein. Another extraction is performed and the mercury is drawn into the suction flask. If no sodium is present in the mercury, the indicator will remain colorless and the extraction is complete. If there is same residual sodium, the ext,raations are reomted: the amalgam is added to the original . flask ";til all the sodium is'removed. Following the complete removal of the sodium, the extractor cap is removed and the'stirring rod is washed with distilled water, i s used to dissolve the sodium oxide in the extractor. The whiah~~~.~~~~~ resultine sodium hydroxide is drawn into a clean suction flask. ~
~
~
~~
monoxide in the sample Mg. of oxygen = ml. of HCI
Over-all View of A p p a r a t u s
It was determined experimentally that, a t least in times of the order of 45 seconds, there was no loss of oxide by solution or entrainment in the amalgam. The amalgam W&Bremoved within 45 seconds after formation, followed by a second addition of mercury which was also removed within 45 seconds. The remaining sodium was extracted as usual. The experiment was repeated with intervals of 15 minutes and 4 hours. The data obtained are included in Table I.
T able 11. Recoveries of Known A m o u n t s of Oxygen
...-~ . ~ - . ~~
Figure 2.
-
(Supplied 8 s HgO or HQO after reduction with sodium amalgkm)
x
0.005 X 8.00
(4)
If the flame photometer is used, 1W p.p.m. pf lithium are added as an internal standard ( I ) , and the solution IS filtered through a
2NdHg) Oxygen Taken %
+ HgO
Nan0
+ Hg
Oxygen Found
Deviation
%
%
coarse sintered-glass filter with a layer of Supercel as the actual filter medium and made to 100 ml. The instrument is used as directed by the manufacturers (5). In order to determine the sample size, an excess of standard hvdrorhlaric acid is added to the semrated sodium amalgam with -~, vigorous stirring and is back-titraced with standard sodium hydroxide to a phenolphthalein end point. There is rapid evolution of hydrogen in this step, nith attendant fire hazard. ~~~
~
~
EXPERIMENTAL RESULTS AND DISCUSSION
For convenience of comparison and interpretation of experiment, theanalytical results are caloulated FLS per cent oxygen and are reported as such in the tables instead of per cent sodium monoxide (% Na.0 = % oxygen X 3.88).
I n order to determine whether the simple phenolphthalein test indicated the complete removal of sodium, the following experiments were performed. Became the residual oxides are dissolved in water, a n y sodium that may be present will evolve an equivalent amount of hydrogen. The hydrogen, if present, was swept over hot copper oxide and the resulting water wes absorbed and
ANALYTICAL CHEMISTRY
1286
weighed. Known amounts of hydrogen were generated within the extractor by dissolving weighed amounts of magnesium ribbon in hydrochloric acid added through the side arm. Quantitative recoveries of the hydimgen released in this manner were obtained. However, no hydrogen due to residual sodium was ever detected following the extraction; this indicated the complete removal of sodium from the oxides and the validity of the simple phenolphthalein test for the completeness of extraction.
T a b l e 111. Recoveries of K n o w n A m o u n t s of Oxygen (Supplied as HgO after reduction with sodium in sealed capsules) Oxygen Taken Oxygen Found Deviation
k
%
%
0 .OS'
0.04 0.07 0.14 0.20 0.24
-0.01 0
0.07a
0.12 0.23 0.23'
+0.02 -0.03 +0.01
Av. i O . 0 1 a Saiiiplea heated to ca. 200' C. for 0.5 hour with constant agitation to ensure good dispersion.
In order to determine whether there was any mechanical loss of finely dispersed sodium monoxide in the amalgam during the extraction process, known amounts of sodium monoxide were formed by the reduction of mercurous or mercuric oxide by sodium amalgam within the extraction chamber. To effect the complete reduction, the amalgam was heated by flaming the outside of the chamber during constant stirring. After the reduction, the extractor was cooled with an air blast and the sodium was removed as described. The recoveries are given in Table 11. It is apparent from these results that there is no loss of oxide by entrainment within the amalgam nor is there any detectable solubility of sodium monoxide in the amalgam or in the mercury. This point was further checked by vigorously shaking sodium monoxide with mercury. No sodium could be detected in the mercury. This experiment was also performed at 200' C. with the same result. Standard samples were prepared by distilling sodium into glass bulbs containing weighed amounts of mercuric oxide. The bulbs were sealed off and the sodium was melted by heating to ca. 125' C. to complete the reduction of the mercuric oxide. This procedure resulted in standard samples of sodium containing known amounts of oxygen with the resulting sodium oxide dispersed in the sodium. However, the extent of uniform dispersion is not known. The recoveries are given in Table 111. The data in Table IV indicate the precision that can be obtained with the method, using triple-distilled sodium as replicate samples. In order to compare the results obtained by the flame photometer and titration methods and to substantiate the validity of the statement that only sodium monoxide need be considered under the described sampling conditions, the following experiments were performed. Following the titration, the lithium internal standard was added directly to the resulting neutralized solution. The solution was filtered, made to volume, and run in the flame photometer, The results are given in Table V. The pickup of oxygen from glass by sodium is negligible a t temperatures up to 200' C. for periods of an hour. In fact, the glass can have a very slight golden discoloration without a significant increase in the oxygen content. However, over extended periods of heating a t 200' C. or a t higher temperatures, there is a decided attack on the glass, which is indicated by a blackening of the glass with a n accompanying increase in the oxygen content of the sodium. The normal oxygen content of triple-distilled sodium is approximately O.Ol%, but after the sealed glass capsule had been heated to 400" C. for an hour, the oxygen content was 0.5%.
The solubility of sodium in mercury at room temperatures is 0.7% by weight ( 3 ) . ,\ppt'oximately 20 ml. (272 grams) of mercury are used for each extraction; therefore (2i2)(0.00i) = 1.9 grams of sodium could theoretically be removed in one pass. In actual practice eight to ten passes are made to wash down the sodium and amalgam thrown up on the walls of the extraction chamber during the amalgamation. The mechanism of the separation involved is entirely analogous to any eutraction procedure where one component (sodium) IS extracted by a solvent (mercury), and the second component (sodium monoxide) is not evtracted by the solvent. The great difference in density (Hg = 13.6, S a c 0 = 2.27) of the two substances adds to the efficiency of the process, as does the negligible solubility of the oxide in the amalgam and the anomalous low viscosity of mercury (HlO at 20' C. = 0.0101 poise, mercury at 200" C. = 0.0102poisr). Within the limitations in obtaining representative and reproducible samples of sodium, the mean deviation of the method is *0,005% oxvgen. The theoretical precision of the method is determined only by the precision of the final sodium determination. However, in actual practice because the method is essentially a physical separation, the precision and accuracy are strongly dependent on technique and euperience. The lower limit is set, a t present, by the mean deviation. An experienced operator can easily obtain a mean deviation of *0.0057~ oxygen on triplicate aliquots from the same sample. By the same token, there is no maximum limit except that set by volumetric considerations.
T a b l e IV.
Oxygen C o n t e n t of Triple-Distilled Oxygen
7%
%
0.004 0.005 0.005 0,006 0.008 0.008
-0,004
-0.003 -0,003 -0,002 0 0 f0.002
0.010
0.016 hlean 0.008
T a b l e V.
Sodium
Deviation from Mean
4-0.008
t0.003
Comparison of Titration and Flame P h o t o m e t e r Methods
Titration 0.004 0,005 0.006 0.007 0.008 0.012
(Per cent oxygen in sodium) Flame Photometer 0,004 0.004 0.008
0.011 0,009 0.011
Deviations
n -0.001
+0.002
f0.004 +0.001 -0.001 AY. t 0 . 0 0 2
The application of this technique to other systems in which t h e oxide is not soluble in the resulting amalgam is obvious. Such a system is zinc-zinc oxide. .4n investigation of the determination of zinc oxide in zinc by the present method is planned for the future. LITERATURE CITED
(1) Berry, J. W., Chappell, D. G., and Barnes, R. B.. IND. ENG. CHEM..ANAL.ED.,18, 19 (1946). (2) Dostrovsky, I., and Llewellyn, D. R., J . SOC.Chem Ind.. 68, 20s (1949). (3) Hansen, M., "Der Aufban der Zweistofflegierungen," Berlin,
Julius Springer, 1936. Pepkowitz, L. P., and Proud, E. R., ANAL. CHEM.,21, 1000, (1 949). (5) Perkins-Elmer Corp., "Instruction Manual, Model 52A," 1948. (4)
RECEIVEDMarch 8 ; 1950. T h e Knolls Atomic Power Laboratory is operated by the General Electric Research Laboratory for the Atomic Energy Commission. T h e work reported here was carried out under Contract No. W-31-109 Eng.-52.
