splattering. which may have been overlooked since the reaction occurred in a small platinum crucible. 9 n average 99.59i., rwovery was always obtained with pure germanium (semiconductor grade) hy the proposed procedure. For further improvement of the accuracy, there might be no objection to an empirical correction -Le., using an empirical gravimetric
factor of 0.6976 instead of the theoretical one, 0.6941. LITERATURE CITED (1) Bertin, E, p,, ~ ~carp.d of ~i ~ ~ Harrison, S . J., unpublished work,
Feb. 1963.
o., H e h . PhyS. A C t U 33,437 (1960). (3) Gardels, Marvin C., Lincoln Laboratory, Massachusetts Institute of Tech-
( 2 ) Busch, G.,
nology, Lexington, Mass., private communication, 1962. (4) Gardels, Marvin C., Whitaker, Hubert H., ANAL. CHEW 30, 1496 (1958). (5) Johnson, ~ ~E. R.1 i Chistian, ~ s. 1 ~T . j Phys. Rev. 9 5 , 560 (1954). RECEIVEDfor review March 21, 1963. hccepted >lay 1, 1963. The research reported was supported by the Department of Savy, Bureau of Ships under contract Sobs-84660.
The Determination of Oxygen in Lithium R. J. JAWOROWSKI, J. R. POTTS, and E. W. HOBART Pratt & Whitney Aircra1:t-CANEl,
Middletown, Conn.
b A method i s propo!,ed for the determination of oxygen in lithium and in other alkali metals involving solution of the metal in liquid ammonia followed b y filtration and titration of insoluble oxides. Quantitative iretention of the oxides b y fritted glass filters i s demonstrated b y the agreement of results obtained using coarse-, medium-, and fine-porosity filters. Nitrogen dissolved in lithium samples i s not retained b y the filter as indicated b y analysis of the residues. Titration curves almost always reveal the presence of carbonate in the solution of the residues in an amount approximately equivalent to the total carbon content of the lithium, as determined b y the combustion method reported previously. This observation, coupled with the previously observed fact that carbon in lithium ordinarily forms carbonate when samples are dissolved in water, leads to further speculztion regarding the form of carbor dissolved in lithium. Various methcds for handling lithium samples prior ‘0 analysis are discussed, as i s validation of the method b y recovery of known additions of oxygen as lithium oxide to lithium and b y cornparkon of results with the amalgamation method when applied io sodium, ipotassium, and cesium.
T
high heat capacity, and broad range of liquid temperatures of lithiuri qualify i t for use as a high-temperati re heat-transfer fluid. For the successful use of this substance in any such application. its interactions with container materials must be evaluated. It is well known t h a t traces of the e1em:nts carbon, nitrogen, and oxygen exert disproportionate effects on the corro+e behavior of hot alkali metals. T o study such effects, methods for the determination of traces of these element3 have been required. The development of such methods has been a tremendous chalHE LOW DESSITY,
lenge to the analytical chemists involved. Perhaps the most difficult of these problems has been the development of a method for the determination of oxygen in lithium, principally because of the fact that the chemical behavior of lithium is not typical of that of the alkali metals in many respects. This report deals with the development of a new approach to the solution of this problem-the use of liquid ammonia to separate oxides of lithium from lithium. Slthough i t has not been possible to validate fully the proposed method because of the lack of standard samples and because of the absence of sufficient comparison analyses, we feel that the results obtained to date are sufficiently promising to warrant announcement of the technique at this time. A number of methods have been proposed for the determination of oxygen in alkali metals. The first and by far the most frequently applied of these methods is the amalgamation technique proposed by Pepkowitz and Judd (6) This method involves solution of the alkali metal in mercury followed by separation and titration of the insoluble oxides. Williams attempted to adapt this method to lithium but found i t to be impractical because of the low solubility and the slow rate of solution of lithium in mercury (12). TVhite. Ross, and Rowan ( 2 1 ) devised an ingenious method for the determination of oxygen in sodium and in sodiumpotasyium alloy. This technique involves the reaction of the alkali metal sample with a n alkyl halide in a 11-urtz synthesis to produce an alkane and the halide of the alkali metal. The unreacted oxides could then be extracted and titrated. Kirtrhik (4) has modified the method and applicd it to the analysis of potassium. Unfortunately, attempts to adapt the method to the analysis of lithium failed both in our laboratory and a t Oak Ridge (10) because of various ill-definrd side reactions. The first method rrported for the chemical determination of oxygen in
lithium was that of Sax and Steinmetz (8). This method, a n adaptation of Eberle, Lerner, and Petretic’s technique for oxygen in calcium ( d ) , involves the solution of lithium in anhydrous methanol, neutralization of the solution with salicylic acid to form the salicylate of lithium and an amount of water equivalent to the oxide in the lithium, and titration of the resulting water with Karl Fischer reagent. The method as proposed suffered from intolerably-high blanks due to residual water in the methanol and was quite complex. Attempts to improve the method in our laboratory succeeded in reducing the blank to an acceptable value by substituting distilled and molecular sieve-dried butyl cellosolve for the anhydrous methanol originally proposed. The method was further . coulometric generation of cher reagent using a refinement of lleyer and Boyd’s technique (6). Unfortunately, the resulting method x w i o tedious and complex as to make it of little value Turovtseva and Lit! inor a (9) have done some work in Rusqia which indicates that oxygen might be determined in lithium by a vacuum fusion technique. It involves a predistillation of the alkali metal from a graphite crucible at a lower temperature than is required for the reduction of the oxides by carbon, followed b> a vacuum fusion analysis of the residue. Since vacuum fusion equipment is fairly common in this country, further investigation of this approach would seem to be in order. Quite recently, Goldberg (5) reported that oxygen can be determined in lithium using a high temperature fluorination technique. =it the time this work began, the only useful method available for the determination of oxygen in lithium was the neutron activation method proposed by Bate and Leddicotte ( 1 ) . Unfortunately, the required equipment is not generally available so that there still exists a need for simple methods for the determination of oxygen in lithium using VOL. 35,
NO. 9, AUGUST 1963
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Figure 1. Schematic view of apparotus for liquid ammonia separotion of alkali metols from their oxides T: V: C: E:
Twin NHJ purifiers Vents to Hg bubblers NHa condenrer Expondon vessel H: ti iampie holder F: Fritted glass tllter R: Li-NH8 receiver SrSa: Gloss stopcocks R: Teflon %topcock
conventional laboratory apparatus. The method to be presented in this rcport involves solution of lithium in liquid ammonia followed by filtration of the resulting solution and titration
liquid ammonia reaction. Other alkali metals may be sampled in larger amounts. The apparatus is assemhled as indicated in Figure 1. The mercury bubblers are attached to the system with glass tubing of sufficient length t o allow a vacuum of 30 inches of mercury t o bc drawn on the system without the danger of drawing mercury into the system. With stopcocks SI,Sj, and Soclosed and stopcocks S?, SI, and ST opened, the apparatus is evacuated and checked for leaks by observing that the level of mercury in the vent tubes does not change. The system is alternately filled with argon, which has heen passed through Drierite and Ascarite, and evacuated to remove any moisture from the inside of the system. While the system is filled with argon, stopcock SSis momentarily opened and then closed before the next evacuation. When the system is evacnated for the third time, stopcocks S3 and S; are closed. Liquid ammonia is then admitted through stopcock 8, to the distillat.ion flasks, each containing about 1.5 grams of sodium. The flasks are filled to about half their volume hefore any ammonia is condensed in the
1
cnis invesrigauon 1s mown In Y1gui-e I. Essentially, the equipment consists of a pair of 500-ml. flasks containing sodium from which anhydrous ammonia is distilled, a cold finger condenser t o recondense the ammonia, a reaction vessel in which the lithium sample is dissolved in the liquid ammonia, and a fritted glass disk through which the lithium-ammonia solution is filtered. Ot,her parts of the apparatus include a sample carrier fashioned from a 15-mm. bore stopcock, a flask used as a lithium-ammonia solution receiver, and mercury bubblers used to relieve pressure in the system without opening it to the atmosphere. The filter assembly is shown in Figure 2. I t consists of a medium-porosity filter crucible attached to a 50150 standard taper joint. The entire system is assembled in a laboratory fume hood to dispose of ammonia vapors. Titrations of the residues are performed by coulometric generation of hydronium ions in a 0.01M sodium sulfate medium at a pla,tinum anode using a Sargent coulometri~-currrnt source. The rcsalting titrat.ion curve is recorded using a Leeds and Northrup 7664 pH meter as a preamplifier for the potentiomet.ric recorder. A typical titration curve is reproduced in Figure 3. The double brcak, rharacteristic of a hydroxidecarbonate mixture, is ohserved in pract,ieally all cases and n-ill he discussed further. Procedure. Lithium samples are prepared in a n inert gas filled dry bos and loaded into sample carriers. The sample size is limited t o about 1.5 grams because of the vigorous lithinm1276
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ANALYTICAL CHEMISTRY
rise into the expansion vessel of the system, 9, is opcned and the solution drained. This is repeatcd until the entire sample is dissolved. To remove any spattered material, the fritted section is filled with ammonia to the standard taper joint betr
