and 20.04 ml. For this series, the mean value is 20.07 ml. with a standard deviation of 1k0.02 m1.-Le., a relative standard deviation of 0.1%. Reproducibility of titration values and stoichiometry of reaction were studied over a range of phosphate concentrations from about 0.3M t o O . O 3 V , and the results are shown in Table I. These figures show that there is a linear relationship between true molarity of the phosphate and apparent molarity as calculated from the potentiometric titration. When true molarities are plotted against apparent molarities, the straight calibration line passes through the zero point. INFLUENCE
OF
OTHER I O N S
Experimental figures have shown that many of the commonly occurring anions do not interfere with the potentiometric determination of phosphate. Nitrate had no effect when solutions with nitrate t o phosphate ratios u p to 40 t o 1
were investigated. Sulfate, a t concentrations up t o 20 times that of the phosphate, and acetate up t o five times, did not interfere with the method. Fluoride had no significant effect when present a t five times the phosphate concentration. The other halides form precipitates n i t h the silver nitrate titrant. However, this proves advantageous in t h a t the halides are precipitated before the silver phosphate. It was shown experimentally that chloride, bromide, or iodide could be determined with phosphate in a single titration. Figure 2 is a first derivative tracing for titration of a mixture of bromide and phosphate against silver nitrate. At the p H values a t which the potentiometric titration is performed, many cations-e.g., Ca+2,hIg+*, will precipitate as phosphates and so cause gross interference with this method. Cations which would interfere in this way can be removed relatively simply by the ion-exchange
separation recommended by Rieman and Beukenkamp ( 5 ) . After the separation, potentiometric titration is preferable to acid-base titration of the eluate because the former method is specific for phosphate whereas in the acid-base titration any weak acids or bases present cause spuriously high titration values of phosphate. LITERATURE CITED
(1) Firsching, F. H., ANAL. CHEY. 33, 873 (1961). (2) Gerber, A. B., Miles, F. T., IND. ENG.CHEM.,ANAL.ED. 13, 406 (1941). (3) Ivanova, Z. I., Kovalenko, P. N., Zhur. Anal. Khim. 14, 87 (1959); Anal. Abs. 6, No. 4353 (1959). (41, Rieman, W., Reukenkamp, J.,
Treatise on Analytical Chemistrv,” Kolthoff, I. M., Elving, P. J., Eds., Part 11. Vol. 5 , pp. 317-402, Interscience, S e w York, 1961. (5) Zbid., p. 375. (6) Van Wazer, J. R., Griffith, E. ,J., McCullough, J. F., ANAL. CHEM.26, 1755 (1954).
RECEIVEDfor review June 24, 1963. Accepted October 30, 1968.
Separation of Uranium, Thorium, and the Rare Earth Elements by Anion Exchange JOHANN KORKISCH Analytical Institute, University of Vienna, IX, Wahringerstrasse 38, Austria GUSTAF ARRHENIUS Scripps Institution of Oceanography, University of California, l a Jolla, Calif.
,A method is described for the simultaneous quantitative separation o f uranium, thorium, the rare earth elements, yttrium, cadmium, lead, and bismuth by means of anion exchange in a nitric acid-acetic acid medium. The anion exchanger employed is the strongly basic resin Dowex 1, X8 (nitrate form). The elements concerned are strongly adsorbed on the resin from a medium consisting of 90% glacial acetic acid and 10% 5N nitric acid. All other elements investigated including iron, aluminum, magnesium, and calcium pass into the effluent and are thus quantitatively separated. For the development of this method measurements of the distribution coefficients were carried out for numerous elements as a function of varying concentrations of nitric acid, acetic acid, and of the elements in question. Analogous experiments were performed in propionic acid media for the sake of comparison. The method was developed particularly for the analysis of marine sediments. A standard sample of homogenized deep sea clay was used as test material. 850 *
ANALYTICAL CHEMISTRY
I
NVESTIGATIONS of
the anion exchange behavior of uranium, thorium, and the rare earth elements have shown ( 1 , 2, & l S , 15, 18-24, 26-51) that the adsorption of these elements on strongly basic anion eschange resine of the quaternary amine type is much stronger from mixed and nonaqueous solvents than from solutions containingwater and mineral acids only. Previous research has shown that high adsorption coefficients are obtained particularly in mixtures of nitric acid and organic solvents (5-7, 10, 15, 22). Among the organic solvents methanol was found to yield the best results for the separation of thorium (22)and the rare earth elements (6); however, uranium is not quantitatively adsorbed under these conditions. Since the inclusion of this element in the subsequent analysis is essential, the suitability of other aliphatic alcohols was investigated by Korkisch, Hazan, and Arrhenius ( 1 5 ) . For achieving the simultaneous separation of thorium, uranium, and the rare earths from the more abundant elements, isopropanol was found to be the most efficient solvent. Some of the elements abundant in silicate rocks are,
however, partially coadsorbed and consequently interfere with the separation procedure. T o eliminate this difficulty the adsorption conditions were investigated in media consisting of acetic and propionic acid in misture with nitric acid. Successful separation of uranium, thorium, and the rare earth elements from all elements interfering with the subsequent analysis was achieved with acetic acid as the solvent component. EXPERIMENTAL
Reagents. The resin used for t h e separation experiments and equilibrium studies was Dowex 1, X8 (100-200-meshJ nitrate form). T h e nitrate form of the resin was prepared from the chloride form as earlier described (22). The resin was soaked in a solution of 90 volume % glacial acetic acid (chemically pure) and 10 volume % ’ 5 N nitric acid. For the determination of the distribution coefficients the air-dried form of the resin was used. Standard solutions of uranium, thorium, the rare earths, and other elements were prepared by dissolving reagent grade nitrates in 5’11 nitric acid. The acetic acid-nitric acid solution men-
tioned above was also employed for washing the columns (washing solution). Also used was chemically pure propionic acid. Apparatus. T h e columns were of t h e same type a n d dimensions earlier described (Id), t h a t is the resin bed had a length of 10 cm. and a diameter of 0.6 cm. For the spectrophotometric measurements a Beckman Model 13 spectrophotometer was used. The polarographic and fluorometric determinations of uranium were carried out with a Polarocord 216, Methrom AG polarograph, and a Ga1van.k Morrison, Mark V fluorometer. Procedure. Separation of Uranium, Thorium, anc the Rare Earths from Iron, Aluminum, Magnesium, Calcium, Manganese, a n d Other Major Elements: PRETREATMENT OF RESINBED. The resin (nitrate form) was transferred to the ion exchange (column taking care that no air bubbles a e r e introduced into the resin bed, and mas treated with 50 ml. of the washing solution. SORPTIONSTEP. The sorption solution consisted of 45 ml. of glacial acetic acid and 5 ml. of 5 N nitric acid with known amounts of uranium, thorium,
Table 1.
Separation of Uranium, Thorium, and Rare Earths in H N O r A c e t i c Acid Medium Uranium, pg. Added Found Foreign ion used (mg.) 10 1 0 . 2 ~Th:5), La(5), Gd(5),
and/or rare earth elements and with comparatively large quantities of the elements to be removed. This solution was passed through the column at a flow rate of 0.2 to 0.3 ml. per minute. During this operation uranium, thorium, and the rare earth elements were adsorbed on the resin, whereas most of the other elements passed into the effluent. WASHINGAND ELUTION.After complete sorption the resin was washed portionwise with a total of 50 ml. of the washing solution. This volume was in all cases sufficient to remove quantitatively all elements which have small distribution coefficients in the medium. The elements adsorbed were eluted by passing 100 ml. of 1N nitric acid through the column. DETERMINATION OF URANIUM,THORIUM AND RAREEARTHS IN ELUATE. The determinations were carried out after evaporation of the eluate and further treatment as earlier described for eluate residues containing uranium (R7), thorium (62), and the rare earths (16). Titrimetric, spectrophotometric, fluorometric, and polarographic methods were employed. For the titrimetric determination of the rare earths and thorium (in the milligram and submilligram range) E D T A with xylenol orange as indicator was used. Microgram amounts of the rare earths (5 to 50 pg.), thorium (2 to 200 pg.), and uranium (5 to 300 pg.) were determined spectrophotometrically by employing Solochromate Fast Red as colorimetric reagent (15-17). Very small amounts of uranium were either determined polarographically (0.1 to 20 pg.) (14) or fluorometrically (below 0.1 pg.) (25). RESULTS AND DISCUSSION
Thorium, pg. Added Found Foreign ion used (mg.) 10 10.3" As above except that 100 103 2a uranium was used 1000 1010.25 iii place of thorium. Lanthanum, pg. Added Found Foreign ion used (mg.) 10 9.8" As rtbove except that 100 103.2" thorium was used 1000 1014" in place of lanthanum. Gadolinium, pg. Added Found Foreign ion used (mg.) 10 10. l5 As above except that 100 98.5" lanthanum was used 1000 1010. l5 in place of gadolinium. Lutetium, pg. Added Found Foreign ion used (mg.) 10 9 .7" As ,%hove except that 100 97.4" gadolinium was used 1000 996.3" in place of lutetium. a Mean value of separations of 11 different8 pairs of eleinents with similar distribution coefficients (for instance, from Mg-Ca or Ti-Zr)
Of t h e elements investigated, uranium, thorium, yttrium, the rare earths, lead, bismuth, and cadmium are strongly retained b y the resin from a mixture of 90% acetic acid and 10% 5N nitric acid. Titanium and zirconium are also adsorbed b u t to a less extent. Small amounts of titanium (below 1 mg.) are effectively removed by treating the resin with the washing solution (50 ml. of this solution are usually sufficient to remove a few hundred micrograms of titanium quantitatively). Milligram amounts of titanium can be quantitatively desorbed by washing the resin with 50 ml. of a mixture of a n acetic acid-nitric acid solution containing hydrogen peroxide; the titanium is in this way eluted as t h e yellow peroxide complex. The solution in question was prepared b y adding 10 ml. of concentrated nitric acid t o 10 ml. of water and 10 ml. of 30% hydrogen peroxide. Five milliliters of this solution were diluted with acetic acid to 50 ml. The elution process for titanium which does not affect a n y of the other adsorbed elements has to be carried out at relatively low temperatures (below 10 to 15' C.) to avoid t h e formation of oxygen bubbles interfering with the elution process.
The zirconium, however, cannot be removed quantitatively from the column b y washing t h e resin with 50 ml. of the washing solution and usually accompanies the strongly adsorbed elements more or less, depending on its original amount present in the sorption solution. The results of a number of separation experiments are given in Table I. As representatives for the rare earths the elements lanthanum, gadolinium, and lutetium were used. From thece results i t is seen t h a t practically all separations were quantitative. By selecting suitable spectrophotometric (15-17) , titrimetric, and other methods (14, 25) for the determination of uranium, thorium, lanthanum, gadolinium, and lutetium, the interference of the coadsorbed elements cadmium, lead, and bismuth was eliminated. The results on the three rare earth elements investigated, when present together, refer to the sum of their concentrations. K i t h regard to the effect of various anions on the separation procedure, it was found that even large amounts (50 to 100 mg.) of phosphate, sulfate, or chloride showed no effect. Considerable interference was, however, apparent in the presence of milligram amounts of fluoride ion. I n connection with the development of the separation procedure outlined above, the distribution coefficients were determined for all of the elements concerned. For this purpose always 2 ml. of 5N nitric acid containing 5 mg. of the element in question mere mixed with 18 ml. of acetic acid. To this solution 1 gram of resin (nitrate form) was added and agitated on a shaking machine for 24 hours. The re& was filtered off and the elements were determined in the filtrate using a suitable analytical procedure. Table I1 gives the results, and for the sake of comparison, also those obtained in propionic acid-nitric acid mixtures. From these data i t is evident t h a t thorium has by far the highest distribution coefficient followed by bismuth and lanthanum. All of the common cations in silicate rocks such as magnesium, calcium, iron, and aluminum have in the acetic acid medium distribution coefficients far below those of the elements for which complete recovery is attempted (distribution coefficients around 70 and higher). Under these circumstances a quantitative separation of the two elemental groups from each other is relatively easy. The Kdvalues obtained in propionic acid medium are generally still higher than those found in acetic acid media. For separation purposes, however, the propionic acid-nitric acid medium is less suitable because the distribution coefficients of the common elements are also much higher so t h a t a separation of the strongly adsorbed ions from those which are weakly adsorbed is considerably more difficult to achieve on a VOL. 36,
NO. 4, APRIL 1964
851
i I
i
00
Figure 2,
-
____~
--.-1
- -L-
0.5 1 .o CONCN. OF HNOa I N T O T A L SAMPLE SOLN. O V E R - A L L AClDllY (NORMALITY OF “ 0 2 )
c
1.5
Influence of nitric acid concentration in presence
of 90% acetic acid 0
PO
100
80
40 60 ACETIC ACID 40 60 WATER
80
100%
PO
0%
Figure 1 . Influence of acetic acid concentra tion
quantitative basis. Analogous experiments performed in formic acid-nitric acid media showed t h a t in these mixtures thorium, uranium, and the rare earths are only weakly adsorbed. To investigate the effect of acetic acid concentration, the distribution coefficients of a number of elements (representatives of the adsorbed di-, tri-, and tetravalent ions) were determined at different concentrations of acetic acid a t a conatant overall nitric acid concentration of 0.5N (in 20 ml. of solution containing 2 ml. of 51v nitric acid and 18 ml. of acetic acid-water mixtures of varying composition). The results (Figure 1) show t h a t the increase of adsorption with increasing concentration of acetic acid is more pronounced in the case of the tri- and tetravalent ions than of those in the divalent ionic states. Furthermore, i t is evident t h a t distribution coefficients high enough to ensure quantitative adsorption of microgram and milligram quantities of the elements can only be obtained in t h e region from SO to 90% acetic acid. The effect of nitric acid concentration on the adsorption of some elements is
852
ANALYTICAL CHEMISTRY
shown in Figure 2 from which i t is seen that a slight increase of adsorption with increasing acidity takes place only in the case of the tri- and tetravalent ions, whereas the divalent ions show a slight trend. These investigations were carried out in mixtures containing 18 ml. of acetic acid and 2 ml. of nitric acid of varying normality. T o study the influence of the nitrate ion concentration varying amounts of ammonium nitrate ranging from 0.1 to 1.0 gram were employed. These experiments showed t h a t the nitrate concentration had no effect whatsoever on the distribution coefficients of the elements. These esperimente were also performed in media with 90% acetic acid and 10% 5N nitric acid. T o determine the working capacities of the resin for the ions concerned, their distribution coefficients were measured in mixtures of 90% acetic acid and 10% 5N nitric acid containing variable amounts of the elements (1 to 175 mg. dissolved in 20 ml. of the mixtures). The results in Figure 3 show t h a t the regions in which the Kd-values remain constant are diminished with decreasing K d so t h a t for instance in the case of uranium only 10 mg. can be adsorbed without a noticeable change in Kd. T h e highest capacity of all the elements is that found for thorium; the K d in this case remains constant through the
whole range of element concentration investigated. The results of the separation experiments and the relative values found for the distribution coefficientsindicate that the method should be suitable for the assay of silicate rock samples. I n order to test this application of the method a standard marine sediment sample (3) WAS analyzed after adding known amounts of the elements uranium, thorium, lanthanum, gadolinium, and lutetium to the sample solution (5N with regard to nitric acid) and after carrying out the ion eschange procedure described above. The results of these separation experiments are shown in Table I11 from which i t is seen t h a t a quantitative recovery of the added element could be obtained in practically all cases. The standard sediment sample contains the order of a hundred micrograms of the rare earth per gram; however, the content of uranium and thorium is of the order of 3 and 12 pg. per gram, respectively. I n order to see the analytical effect of adding small amounts of rare earths it was necessary to remove by a preceding column operation the naturally occurring rare earths from the sample solutions used in the analysis of lanthanum, gadolinium, and lutetium before adding the analytical spikes of these elements. The removal of the
~~
~
Table II. Distribution Coefficients in HN03-Organic Acid Medium on Dowex
5 -
Ion IJO,( 11) Th(1V) Sc(II1) Y(II1) La(II1) Ce(II1) Pr( 111) Nd(II1) Sm(II1) Eu( 111) Gd(II1) Tb(II1)
4 -
E m
Er( 111) Tm(II1) Yb(II1) LU( 111) Cu( 11) R.Ig(II)
*TL
o
~~
I 0
Figure 3.
I
' 90
I
" 40
'
!
"
'
'
'
'
'
'
60 EO 100 190 MILLIGRAMS ELEMENTDO ML. MIXTURE
Influence of concentration in 90% acetic acid-1
~
~
140
L 160
180
0% 5N H N 0 3 mixtures
Influence of total amount of elements
naturally occurring rare earths was effected by a separate column operation; the spike was added to the effluent which was then subjected t o a separation test ab outlined in the woi-king procedure. Dissolution of the> sediment sample was achieved b y leaching first with hydrochloric acid and then nitric acid; the residue was dissolved in a mixture of nitric acid a n d hidrofluoric acid to remove the silica. After removal of the chloride and fluocide ions b y means of concentrated nitric acid, the sample was dissolved in 5 N nitric acid and this solution was used for the column operations (see working prclcedure), I n general, t h e method described above is well suited for the quantitative separation of uranium, thorium, the rare earth elements, yttrium, cadmium, bismuth, and lead as :t group from other elements. I n particular, the method was designed to provide a concentrate of these elements from marine sediments in order to permit subsequent x-ray spectrometric assay of the individual trace elements. Removal of t h e main constituents of the sediment is essential in
this case to obtain the desired accuracy. Electron microprobe analysis provides a particularly useful form of x-ray spectrometry in view of the small amounts of trace elements that can be separated from reasonable quantities of sediment sample. X detailed description of this technique is given elsewhere (3). Precision. T h e following values for precision were obtained: standard deviations in t h e acetic acid-nitric acid system; ~ k 1 . 5 2 (U), h 1 . 6 2 (Th), 1t1.70 (La), =t1.67 (Gd), and A1.74 (Lu). T h e 100-pg. quantities of these elenients added and subsequently found (see Tables I and 11) after application of the working procedure were taken as the basis for the calculation of the standard deviations.
Ca(I1) Sr(I1) Zn(I1) Cd(I1) Al(II1) Ga(II1) In(II1) Pb(I1) Ti(IV) Zr( IV) Bi(II1) V(V) Cr(II1) Mn(I1) Fe(II1) Co(I1) Ni(I1)
10
0 4 7 1
10 8 2
83 0 1 5 4 21 261 45
$2
10.5 25 36 37 173 3 13.6 28 u
(I
50 3550 14 0 1 6
0 1
3 2 2 0
64 7100 25
2 3 22 4.4 25.2 18.4
a In this medium, partly or completely insoluble.
Table 111. Application of Method to Analysis of Sediment Standard Element, fig. added to Element,
sorption solution containing rg. found in eluate 0.5 g. of sediment sample 0 1.5 Uranium 10
100 Thorium
1000 0
10 100
1000
Lanthanum
11.6
101.3 1002 0 6 .O 16.1 106.3 1005.4
n IO
100 Gadolinium
1000 0
Lutetium
1000 0
LITERATURE CITED
(1) Antal, P., Korkisch, J., Hecht, F. J . Inorg. & Nuclear Chem. 14, 251 (1960). (2) Antal, P., Korkisch, J., Hecht, F., Austrian Pat. KO. 219,013, June 15, 1961. (3) Arrhenius, G., Korkisch, J., Unpublished data, Scripps Institution of Oceanography, University of California, La Jolla, 1963.
1 -X8 Distribution coefficients 90% 9OC,r, Acetic Promonic acid, 10% acid; 10% 5N HKOa 5N HNOa 100 158 160,000 160,000 21 100 73 200 1400 1400 1300 1300 1100 1200 1000 744 605 364 283 456 180 354 341 146 105 230 242 100 100 250 200 100 90 264 250 100
10 100
10 100
1000
9.8 98.7
1000
10 102 1003 9.7 97.5 989 4
a Individual rare earths present in sediment sample were not determined individually. Sum of their masses amounted to 150 pg./gram sample.
VOL. 36,
NO. 4, APRIL 1964
853
( 4 ) Edge, R. A., J . Chromatog. 5, 526 (1961). ( 5 j Zbid:, p. 539. ( 6 ) Faris, J. P., Warton, J. W., ANAL. CHEM.34,1077 (1962). ( 7 ) Fritz, J. S., Pietrzyk, D. J., Talanta 8 , 143 (1961). (8) Janauer, G. E., Korkisch, J., J . Chromatog. 8, 516 (1962). ( 9 ) Katzin, L. I., Sullivan, J. C., U . 8. Pat. KO.2,840,451, June 24, 1958. (10) Korkisch, J., Repts. to International Atomic Energy Agency and U S . A t . Energy Comm., Contract AT(30-1)-2623 (February and August 1961, and April 1963). (11) Korkisch, J., Antal, P., Z . A n a l . Chem. 171, 22 (1959). (12) Korkisch, J., Antal, P., Hecht, F., J . Inorg. & Nuclear Chem. 14, 247 (1960). (13) Korkisch, J., Antal, P., Hecht, F., Z . A n a l . Chem. 172,401 (1960).
(14) Korkisch, J., Farag, A., Hecht, F., Mikrochim. Acta 1958, 415.
(15) Korkisch, J., Hazan, I., Arrhenius, G., Talanta 10,865 (1963). (16) Korkisch, J., Janauer, G. E., ANAL. CHEM.33,1930 (1961). (17) Korkisch, J., Janauer, G. E., Anal. Chim. Acta 25,436 (1961). (18) Korkisch, J., Janauer, G. E., Talanta 9.957 (1962). (19) Korkisch,' J., Tera, F., J . Znorg. & Nuclear Chem. 15,177 (1960). (20) Korkisrh, J., Tera, F., J . Chromatog. 6,530 (1961). (21) Korkisch, J., Tera, F., Zbzd., 7, 564 (1961). (22) Korkisch, J., Tera, F., ANAL.CHEM. 33, 126.5 (1961). (23) Korkisch, J., Tera, F., Z. Anal. Chem. 186, 290 (1962). (24) Korkisch, J., Urubav, " . S.. . Talanta. in press, 1964. (25) Schonfeld, T., El Garhy, hl., Friedmann, C., Veselsky, J., Mikrochim. Acta, 1960, p. 883. '
(26) Tera, F., Korkisch, J., J . Inorg. & Nuclear Chem. 20. 335 f1961). (27) Tera, F., Korkisch,' J., -Anal. Chint. Acta 25,222 (1961). (28) Tera, F., Korkisch, J., Hecht, F., J . Znorg. & Xuclear Chem. 16. 345 (1961). (29) Urubay, S., Janauer, G. E., Korkisch, J., Z. A n a l . Chem. 193,165 (1963). (30) Crubay, S.,Korkisch, J., Janauer, G. E., Talanta 10, 673 (1963). (31) Wilkins, D. H., Smith, G. E., Zbid., 8 , 138 (1961).
RECEIVEDfor review October 23, 1963. Accepted January 6, 1964. This research was carried out under a grant from the U.S. Atcmic Energy Commission [AT( 1 1-1 )34-83)]. Additional support was provided by an award from the American Chemical Society Petroleum Research Fund (Aaard 875-66). The generous support from these agencies is gratefully acknowledged.
Determination of Butyllithium in Hydrocarbons by Thermometric Titration with Butanol w.
L. EVERSON
Shell Development Co., Emeryville 8, Calif.
b Butyllithium in hydrocarbon solution can b e determined b y thermometric titration with a standard hydrocarbon solution of butanol. The reaction is stoichiometric; lithium butoxide, normally the major impurity, is the titration product and does not interfere. The simplicity of the method makes it more rapid and convenient than alternative methods; precision and accuracy are comparable. The method is believed to b e generally applicable to compounds containing lithium-carbon bonds.
F
the double-titration method of Gilman and Haubein ( 4 ) has been the accepted procedure for determining alkyllithium in hydrocarbon solutions. I n this method, one sample portion is hydrolyzed and titrated with acid to give total alkalinity; a second portion is reacted with dry benzyl chloride to convert RLi to LiCl and the alkalinity after hydrolysis (representing LiOR, LLO, etc.) is subtracted from the total alkalinity. Recently, two improved methods have been proposed. Clifford and Olsen ( I ) reacted the sample with excess iodine in ether solution and back-titrated the excess; they found accuracy to be superior to that of the double-titration method. Collins et al. (2) oxidized butyllithium with excess vanadium pentoxide and titrated the reduced vanadium potentiometrically with sulfatoceric acid. Their method gave OR SOME YEARS,
854
ANALYTICAL CHEMISTRY
accurate results and was believed to be generally applicable to alkyllithium . compounds. Thermometric titration is proposed as an additional approach which gives results of comparable accuracy with maximum speed and simplicity. Butyllithium, in hydrocarbon solution, is titrated directly with a standard hydrocarbon solution of butanol: RLi BuOH LiOBu RH
+
-
+
EXPERIMENTAL
D r y C.P. grade toluene over calcium hydride. D r y n-butanol over activated Molecular Sieve 4A. The purity, including isomeric butanols, should be better t h a n 99.5y0 and is best evaluated b y making a gas chromatographic scan for impurities. Eastman Kodak Co. White Label grade was found satisfactory for use without further purification. A standard 1 M solution of n-butanol is made by dissolving 37.06 grams of the reagent in dry toluene and diluting to 500 ml. Apparatus. From the titration vessel it is essentiallthat air and moisture be excludable and t h a t t h e vessel have A roundlow heat conductivity. bottomed, vacuum-jacketed, cylindrical flask of 100-ml. capacity was used in these studies and has been generally useful for analysis of airsensitive materials. The rounded top of the flask has a central -$19/22 opening and three peripheral f7/15 openings. The latter are located 90' apart; the middle one (for the thermistor) is vertical and the other two Reagents.
(for purging and for sample and titrant addition) are inclined outward a t an angle of 15' from the vertical. thermistor, sealed into 5-mm. glass tubing with a 8 7 / 1 5 joint a t the upper end, is used. Eposy resin can be used for sealing; glass-encased thermistorse g . , Veco (Victory Engineering Corp., Union, K. J.)-can be sealed into soft glass by a glassblower. When seated in the titration vessel, the tip of the thermistor should be near the bottom of the vessel. Wheatstone bridge circuitry is not critical, but should provide means for balancing over a temperature range of 10' C. or more and for reducing t h e sensitivity. A suitable circuit has been described by Jordan and Alleman (5). The fised arms should equal the nominal resistance of the thermistor used; the variable (balancing) arm should be adjustable from about 40 t o 120% of this value. Sensitivity can be controlled by connecting a tapped voltage divider across the output. Total resistance of the voltage divider should be not less than the nominal thermistor resistance; suitable tap values are of the total voltage 1/1,,, and divider resistance. A 10-ml. hypodermic syringe with Teflon plunger (Hamilton Co., Ontario, Calif.) is used for the buret t o minimize leakage and evaporation problems, Titrant is delivered through a 2-foot Teflon capillary which is slipped over an 18-gauge hypodermic needIe at the buret end, and over a &inch length of stainless steel capillary tubing at the other end. The delivery end of this tubing is ground t o a n angle of about 45'. Glass syringes, lubricated A\
