The polarization resistance is a more sensitive function than the polarization capacity for the detection of small amounts of reversibly reducible substances. I n alkaline solutions of HPbOz- oxygen is reversibly reduced, and this offers a n interesting and sensitive detector of dissolved oxygen. In neutral or acid solution the effect of dissolved oxygen is also readily observed. A dropping gallium electrode has been developed and found to work sufficiently well to permit making impedance measurements a t its surface. It operates over a smaller range of potentials than mercury, but has some special advantages, the most important of which is that it provides data on a liquid metal markedly different from mercury. Impedance measurements can be made in a wide variety of nonaqueous media, and these give new information about the nature of electrode reactions in these media. Impedance measurements also give rise to new information about the kinetics of adsorption. ACKNOWLEDGMENT
(3) Borisova, T., Ershler, B., Frumkin, A,, J . Phys. Chem. U.S.S.R. 22, 925 (1948); 24, 337 (1950). (4) P_ P ~Chem. . ~, Brever. B.. Rev. Pure and A . 6, 24G (1956). (5) Breyer, B., Bauer, H. H., Hacobian, S., Australian J . Chem. 3, 500 (1952); 6, 211 (1953); 7, 225, 305 (1954); 8, 312, 322, 467, 472, 480 (1955); 9, 1, 7, 425, 437 (1956). (6),,Breyer, B. Gutman, F., Bauer, H. H., Osterreich. &hem.-Ztg. 57, 67 (1956). (7) Breyer, B., Gutman, F., Hacobian, S., Australian J . Sci. Research A3, 558 (1950); A4, 595, 604, 610 (1951). (8) Ibid., A3, 567 (1950). (9) Breyer, B., Hacobian, S., Anal. Chim. Acta 16,497 (1957). (10) Delahav, P., “Kew Instrumental hlethods “in Electrochemistry,” pp. 146-78, Interscience, New York, 1954. (11) Ershler, B., Discussions Faraday SOC. 1, 269 (1947); J . Phys. Chem. U.S.S.R. 22 , 683 (1948). (12) Frumkin, A. N., Proceedings of Symposium on Electrochemical Surface ComDounds and Their Role in the Adsorpt’ion Phenomenon, p. 53, Moscow Univ. Press [Available in translation (T-43) from D. C. Grahame]. (13) Frumkin, A. N., 2. Elektrochem. 59, 807 (1955). (14) Frumkin, A. N., Florianovich, G. hI., Doklady Akad. Nauk S.S.S.R. 80, 907 (1951). (15) Frumkin, A., Gorodetzkaya, A., 2. physik. Chem. 136, 215 (1928). (16) Frumkin, A. N., Melik-Gaikazyan, V. I.. Dokladu Akad. Nauk S.S.S.R.
T h e author is indebted to the Office of Naval Research for financial support of this project. LITERATURE CITED
(1) Bagotski, V. S., Doklady Akad. Nauk. S.S.S.R. 85, 599 (1952). (2) Bockris, J. O’M., Conway, B. E., J . Chem. Phys. 28, 716 (1958).
77, 865 (1951): (17) Gerischer, H., 2. Elektrochem. 5 9 , 604 (1955). (18) Gerischer, H., 2. physik. Chem. 198, 286 (1951). (19) Grahame, D. C., J . Am. Chem. SOC. 63, 1207 (1941); 68, 301 (1946); 71, 2975 (1949). (20) Grahame. D. C.. J . Electrochem. SOC. ’ 99, 370C (1952) ’ (21) Grahame, D. C., 2. Elebtrochem. 59, 740 (1955).
(22) Grahame, D. C., Ireland, R. E., Petersen, R. C., U. S. Office of Naval Research, Tech. Re& 22 (March 23, 1956); Contract N8-onr-66903. (23) Grahame, D. C., Poth, M. A., Cummings, J. I., J . Am. Chem. SOC.74, 4422 (1952). (24) Ha‘ckerman, S . , Popat, P. V., U. S. Office of Kava1 Research, Tech. Rept. (March 15, 1958); Contract Nonr-375( 02). (25) Hansen, R. S., Minturn, R. E., Hickson. D. 4.. J . Phvs. Chem. 60. 1185 (1956). ’ (26) Iota, Z.’ A., Shimshelevich, Y. B., Andreeva, E. P., J . Phys. Chem. U.S.S.R. 23, 828 (1949). (27) Kolotyrkin, Ya. M., Bune, N. Ya., Ibid. 29, 435 (1955). (28) dol~hoff, I. hI., Lingane, J. J , “Polarography,” 2nd ed., p. 216, Interscience, New York, 1952. (29) Laitinen, H. A., Osteryoung, R. .4., J . Electrochem. Soc. 102, 598 (1955). (30) Lyons, E. H., Jr., Ibid., 101, 363, 376 (1954). (31) Melik-Gaikazvan, T’. I., J . Phys. Chem. U.S.S.R. 26, 560, 1184 (1952). (32) Miller, I., Grahame, D. C., J . Am. Chem. SOC.78, 3577 (1956); 79, 3006 irnc?\ (lYdl).
(33) Muratzejen-, A, Gorodetzkaya, A., Acta Physicochini. U.R.S.S. 4 , 75 (1936). (34) Nikolaeva, X. V., Shapiro, N. S., Frumkin, A. S., Doklady Akad. Nauk S.S.S.R. 86, 581 (1952). (35) Proskurnin, hf. A,, Frumkin, A. N., Trans. Faraday SOC.31, 110 (1935). (36) Randles. J. E. B.. Discussions Far’ aday SOC.1 , 11 (1947). (37) Randles, J. E . B., White, W., 2. Elektrochem. 59, 666 (1955). (38) Rice, 0. K., Phys. Rev. 31, 1051 (1928). (39) Robertson, W. D., J . Electrochem. SOC.100, 194 (1953).
RECEIVEDfor review May 15, 1958. Accepted August 29, 1958.
Glass-Silver Electrodes in Nonaqueous Titrimetry M. G. YAKUBIK, L.
W. SAFRANSKI, and JOHN MITCHELL, Jr.
Polychemicals Departmenf,
E. 1. du
Ponf de Nernours &
b Potentiometric titration curves with sharp voltage peaks are obtained in nonaqueous systems using glass-silver electrodes with an electronic potentiometer, and the proper combination of solvent and titrant. The shape of the titration curves is similar to the first derivative curves from ordinary potentiometric titrations. The voltage peak coincides with the equivalence point, and is suitable for the quantitative determination of many acids. The same electrodes give S-shaped curves for very weak acids, such as phenol. It is possible to distinguish certain acidic functional groups. This behavior can b e explained by a cornbination of chemical and polarization effects. The voltage peak method is rapid and the potentials are steady.
Co.,Inc.,
Wilrningfon, Del.
The end point of the titration is easily anticipated. In the range of 0.4 to 1.5 meq., the precision and accuracy are to about 0.270. Less than 0.02 meq. can b e detected.
A
of electrode combinations and solvents have been used for the determination of acids and bases which cannot be titrated satisfactorily in water or water-alcohol mixtures. Some investigators modified the glasscalomel electrode pair for use in nonaqueous media (4, 7). Others employed metal electrodes in titrations for meak acids-e.g., antimony-hydrogen and antimony-isolated antimony in ethylenediamine ( I I ) , antimony-calomel in dimethylformamide (5) and ethylenediamine (8), antimony-glass in butylVARIETY
amine (6), anodically polarized platinum wire in ethylenediamine (8),and platinum-rhodium alloy us. graphite or antimony-graphite in benzene-methanol (10).
I n this research a new system was devised which exhibits unusual behavior in acidimetric titrations. K i t h most acids the glass-silver electrode pair, in combination with certain neutral or basic organic solvents and alkali metal titrants, gives potentiometric curves with voltage peaks. These are similar to the calculated first derivative curves from conventional potentiometric titrations. The voltage peak coincides with the equivalence point. With very weak acids, such as phenol, normal S-shaped curves are obtained on direct titration. The new technique serves as the basis VOL. 30, NO. 1 1 , NOVEMBER 1958
1741
Table
I. Analytical Results for NBS Benzoic Acid
Weight, Mg. Recovery, iiddeda Found % 100.2 4T.9 48.0 99 8 50.4 50.3 102 5 102 7 100 2 100 0 148 9 148 9 200 4 100 2 200 0 Av. 100.1 j= 0.14 a Weight added covers range from 0.4 to 1.5 meq. for a broadly applicable method of analysis for acids. EXPERIMENTAL
Several combinations of solvent and titrant were found suitable for use w t h glass-calomel electrodes. I n general, sodium methylate is recommended as the standard reagent, and pyridine as the solvent. Reagents. Standardized 0 . 1 s sodium methylate in benzene-methanol 1). Pyridine, reagent grade. (4 Apparatus. Line or battery-operated pH meter, such as Beckman Model H or G S. General-purpose glass electrode, Beckman S o . 119080. Silver electrode, Beckniaii S o . 4919-V6B, or silver nire. The electrode is prepared easily by polishing periodically with a suitable cleanser or by immersing t h e electrode in concentrated ammoiiiuni hydroxide. The electrodes are stored in distilled water when not in use. The buret is protected from carbon dioxide by an riscarite tube. Procedure. The sample, preferably containing 0.4 t o 1.5 meq. of acid, is transferred to a 15O-ml. beaker containing about 50 nil. of preneutralized pyridine. (The pyridine can be titrated conveniently t o t h e thymol blue end point.) T h e contents of t h e beaker must be protected from carbon dioxide a t all times by keeping the system under nitrogen. The solution is titrated potentiometrically with the standardized sodium methylate. With most acids the end point is marked by a sudden reversal in potential. Very weak acids will give conventional S-shaped curves. Mixtures containing acids of n%lely varying strengths niay give tn-o inflections, equivalent to the strong and weak acids, respectively. The sodium methylate may be standardized against benzoic acid, following this procedure.
+
as illustrated in curve C of Figure 1. Typical results are shown in Table I. The difference between the values in the first two columns does not exceed two parts per thousand. I n other experiments, as little as 0.02 meq. of the acid was determined using 0.05N sodium methylate. Thymol blue gave a sharp color change simultaneous u-ith the voltage peaks. Some of the acids which gave voltage peak titration curves in the same system are listed in Table 11. The titrations appear to be stoichiometric, because the recoveries are in the purity range expected for the acids. The results do not necessarily represent the limit of accuracy. The primary purpose of this investigation was t o determine n hich acids gave titration curves with voltage peaks. In general, aliphatic and aromatic carboxylic acids gave voltage peak titration curves. Single peaks were observed for the dicarboxylic acids equivalent to the neutralization of both carboxyl groups. ilminobenzoic acid gave a single peak equivalent to titration of the carboxyl group. Usually the electrodes responded rapidly up to the end point of the titration. Immediately beyond the peak, electrode equilibration was relatively slowv. Hon-ever, after addition of a few drops of titrant, the electrodes responded rapidly to potentid changes. K i t h the di- and trihydroxybenzenes, resorcinol and pyrogallol, the potentials were unsteady, and the electrode response nas slow throughout the titration. The voltage peaks were not sharp and, consequently, the branches of the titration curves were extrapolated to obtain the end point. The equiralence points corresponded to titration of all the hydroxyl groups. Hydrochloric, sulfuric, and phosphoric acids gave voltage peak titration curves. -4 .ingle peak was observed with sul-
furic acid corresponding to titration of both hydrogens. The titration curve of phosphoric acid had a single gradual inflection, equivalent to one hydrogen. Precipitate formation w s noted and the potentials were erratic, precluding titration of the remaining hydrogens. -4s a general rule, sharp voltage peak curves n-ere obtained with this electrode syst,em for acids having ionization constants in water of or greaker. Keaker acids, such as resorcinol and pyrogallol, gave less ]Tell defined peaks. Some very weak acids, on the other hand, with ionization const,antsof about 10-lo, ga,ve normal S-.shapetl curves. These included phenol, plienolplitha~lein, and methyl salicylate. BINARYMIXTURES. Two inflections were obtained for binary mixtures of acids having widely different ionization constants (Figure 2). I n the curve of benzoic acid and phenol, the first inflection n-a,s of the vo1ta.ge peak type and corresponded to the titration of benzoic acid. The next inflection n-as S-shaped and was due to the reaction of phenol with the titrant. For the hydrochloric-benzoic acid mixture, the S-shaped curve appeared first, and was due to the neutralization of the inorganic acid follon-ed by the voltage peak curve of benzoic acid. (Hydrochloric acid alone ga,ve t'he voltage pea,k end point.) The over-all acid strength of the solution appears to determine nhether p m k of S-sha,ped curves will be obtained. Figure 3 shows the potentioniet,ric titration curves for sa,licylic acid, a,cetyl salicylic acid, and methyl salicylate. Salic;\-lie acid, curve A , gave tn-o inflections. The first break represent,ed the neutralization of the carboxyl group. Froin an examination of this curw, it n-as difficult' to det,ermine whether the first inflect,ion wa,s of the 8-shaped or voltage peak type. Results h s e d on the peak end point most closely
- 50 a F -150 z W
-200
- 250
50
100
150
% NEUTRALIZED
Figure 1 . Potentiometric titration of benzoic acid in pyridine A.
B.
RESULTS
C.
Potentiometric titration curves with sharp voltage peaks were first observed with benzoic acid using glass-silver electrodes. Pyridine was used as solvent. and 0.1N sodium methylate in benzene-methanol, as titrant. -4nalyses of samples in the range of 0.4 to 1.5 meq. demonstrated that the voltage peak corresponds to the equivalence point.
D.
1742
ANALYTICAL CHEMISTRY
I5O
50 100 150 % NEUTRALIZED
Glass VI. calomel electrodes Silver VI. calomel electrodes Actual titration curve, silver vs. glass electrodes Calculated composite curve
agreed with the expected value. K h e n 0.318 meq. of salicylic acid was titrated, 0.316 meq. was found, using the voltage peak end point. From an Sshaped curve only 0.288 meq. was found. Further evidence in favor of the voltage peak end point was obtained from calculation of the phenolic hydroxyl. The difference between the roltage peak end point and the second inflection n a s 0.314 meq. B is the curve for acetyl salicylic acid 11-here the hydroxyl group is blocked by an acetyl function. The curve I\ hich represents the titration of the carboxyl group is characterized by the voltage peak end point. Curve C wa,; obtained from titration of niethyl salicylate and corresponds to the titration of the hydroxyl group. Thus, the t n o acid functions present in a single compound may gi\ e rise to separate distinct inflections of a different type. EFFECT OF TTATER.Usually only small amounts of water can be tolerated in nonaqueous titrimetry. To determine the effect of n-ater in the new system, various amounts were added to pyridine solutions of benzoic acid; 10% or less had little effect either on the sharpness of the peak or on the accuracy of the titration. With greater than lo%, voltage peaks became less distinct and shifted from the equivalence point. I n these cases, recoveries of the acid nere greater than 100%. E F F E C TO F SOLVEUTS. -4number of solvents n ere investigated for titration of benzoic acid n i t h the glass-silver electrode pair. Voltage peak-type curves were observed in inert solvents such as acetone, acetonitrile, and the benzene-methanol mixture; aniphiprotic solvents such as iiopropyl alcohol; and a fen hasic solvmts including pyridine, dimethylformamide, and aniline. -4cetonitrile n a i unusual in that the potential response n as opposite to that observed in the other solvent systems, giving a voltage peak with a maxiniuni potential rather than the minimum obsei\ ed n ith other solvents investigated. K i t h isopropyl alcohol the voltage peaks were not sharp and extrapolation of branches of the titration curve was necessary to find the end point. K h e n water v, as the solvent, normal S-shaped curves were obtained with this electrode pair. S o inflections nere observed in benzylaniine, ethylenediamine, or piperidine. An S-shaped curve n-as obtained in n-butylamine. EFFECTOF TITRAXTS. voltage peak curveb were obtained n hen reagents such as sodium methylate, sodium hptlrouide, and potassium methylate were used with the glass-silver electrodes. Benzene-methanol was a satisfactory solrent for the titrant. However, only rnougli methanol n-as used to obtain a lioniogeneous solution, because relatively large amounts of the alcohol
I
I
I
I
I
Table
II.
Analytical Results for Acids
ReWeight, Mg. covery, Compound Added Found yo Titration of Carboxylic Acids Formic 31.9 32.0 100.3 28.6 28.3 98.9 -4cetic Monochloroacetic 41.8 41.4 99 .O Benzoic 47.9 48.0 100.2 hcetylsalicylic 3 7 . 3 36.9 98.9 ~~
Maleic ~
I I IS0 MI. NoOCHI IN BENZENE-METHANOL ( 4 + I )
Figure 2. Voltage peak titration curves for acid mixtures in pyridine
I MI I I 100 MI. NaOCHS IN BENZENE-METHANOL (4 +I)
Figure 3. Voltage peak titration curves for salicylic acid and some derivatives in pyridine A. 6. C.
Salicylic acid Acetyl salicylic acid Methyl salicylate
caused sinal1 inflections. -4 normal Sshaped titration curve instead of the voltage peak n-as obtained when tetramethyl aiiimonium hydroxide was used as titrant. DISCUSSION
The nature of the potentiometric curves in nonaqueous media appears t o depend on the elrctrode pair, solvent, and titrant. T h a t an interrelationship exists has been demonstrated. For example, n i t h glass-silver electrodes, titration curves having voltage peaks n-ith minimum or maximum potentials or S-shaped curves are obtained, depending on the particular combination of solvent and titrant. The abrupt change in potential a t the voltage peak end point appears due to the fact that the role of each electrode may change during the titration. This is illustrated in Figure 1 JXhich includes titration curves obtained n hen both
Fumaric -2dipic Sebacic o-Phthalic nL-Phthalic o-Aminobenzoic
4 1 . 9 41.9 100.0 3 4 . 2 3 4 . i 99.7 51.8 5 1 . 3 99.0 60.3 59.7 99.0 51.2 50.8 99.2 5 2 . 5 51.9 98.9 102.9 103,O 100.1
Titration of Hydroxybenzene Derivatives i 2 . 4 i 2 . 6 100.3 Vanillin Resorcinol 9 . 8 10.0 102.0 Pyrogallol 4.4 4 . 2 95.5 Picric acid 103.1 102.6 9 9 . 5
electrodes n ere used independently n i t h the saturated calomel as a reference. Curve A shows the titration of benzoic acid in pyridine a i t h sodium methylate using the electrode conibination, glass 2's. calomel. Curve B was obtained using silver 2's. calomel elrctrodeq under identical conditions. I n the former. the potential is changing in a negative direction, while in the latter, the potential changes in a positive direction. The oblique marks on the titration curves indicate the equivalence points, both of R hich coincide with the color change of thymol blue indicator. The gradual reversal of potential beyond the end point in curve A is probably the result of the inability of the glass electrode to function properly at the high alkalinity level. Figure 1, C, shows the voltage peak titration curve obtained experimentally n-hen using the combination glass vs. silver to follow the potential changes during the titration. Also shown for coniparison is the composite curve, D, derived from measurement of the net potential changes of the titration curves 11ith the reference calomel electrode shown in curves A and B. The similarity is apparent in the shape of the calculated curve to that actually obcerved for the titration n i t h a glasssilver electrode pair. It appears that both electrodes in this system function as the indicator Fleetrode a t some interval during the titration. Potential changes occur a t both electrodes. Up to the end point, the glaqs probably is the indicator clectrode, silver acting as a variable reference electrode. -4t the end point, because the electrode potentials are changing in the opposite direction. a reversal of the direction of the electromotive force occurs. Interestingly enough, the addition of a small increment VOL. 30, NO. 11, NOVEMBER 1958
1743
of water to the titration cell, prior to the end point, causes a lowering of the observed potential. Beyond the voltage peak, however, addition of small amounts of water causes a potential rise, indicating a different electrode response before and after the end point. In this method, the glass-silver electrodes are not polarized by an external source. To the authors’ knowledge only one previous method, a nonacidimetric procedure, was reported, where voltage peaks were observed with unpolarized electrodes. Bishop (2) obtained these on titration of halides with thiocyanate in absolute ethyl alcohol using silver-antimony electrodes. He obtained S-shaped curves in argentometric titrations rvith glass-silver electrodes. Voltage peak curves in redox titrations were obtained by Bishop using his technique of differential electrolytic potentiometry (3). I n this method, a minute stabilized current was passed between two platinum electrodes. The behavior of the electrodes was reported to depend on the nature of the ions in solution, magnitude of the current, size, and separation of the electrodes. A simple circuit consisted of the electrodes immersed in the solution connected through a series (ballast) resistor to a battery. Potentials were measured with a p H meter. For ultramicroanalysis, Bishop recommended use of a current of 1 to 5 X 10-9 ampere with 0.07-mm. diameter platinum electrodes which were 1 mm. long and 0.5 mm. apart, a 1- to 2-volt battery and a 400- to 1000-megohm resistor. For macrotitrations he suggested use of a 2- to 120-volt battery with a 200-megohm resistor. Recently, Kirsten, Berggren, and Nilsson (9) used a glass-silver electrode pair with an applied potential of 500 mv. in titrations of certain organic and inorganic bases. Sodium tetraphenylborate served as the titrating agent. With one exception, S-shaped curves were reported. An abnormal curve showing a maximum voltage peak was obtained from the titration of o-phenanthroline hydrochloride. The behavior of the glass-silver electrode system in this investigation can be explained by a combination of polarization and chemical effects. Contrary to popular belief, minute currents with an electronic potentiometer are sufficient to produce polarization in an
1744
ANALYTICAL CHEMISTRY
unpoised system. This was demonstrated by Rogers and coworkers (1.2) in their study of the bromine-bromide potentiometric end point where as little as lo-’* ampere mas sufficient to produce polarization. That polarization is a factor in this system was shown by observing the influence of electrode area and rate of stirring. Three electrodes were studied: an 80-mesh silver gauze electrode, 7.3 cm. X 2.5 cm.; a Beckman silver billet electrode with an area of 3.51 sq. cm.; and a silver wire electrode, area 0.112 sq. cm. The potentials observed were proportional to the area of the electrode. The voltage peak of the titration, however, was not displaced. Small changes also were observed in the potential with marked changes in the rate of stirring. Evidence was obtained which suggests that chemical effects influence the behavior of this electrode system. Silver oxide or silver salt formation on the silver electrode surface may contribute free silver ions for the electrode response. I n this respect a silver-silver chloride electrode with the glass electrode produced voltage peak titration curves, as did the clean silver electrode which probably had an oxide film. [Anson and Lingane (1) have shown that oxide films exist even on such a noble metal as platinum.] Depletion of the free silver ions a t the electrode surface would be expected to result in the usual electrode behavior. Through the use of a large excess of halide, therefore, the silver should behave as a normal reference electrode. This was shon-n experimentally by titrating benzoic acid in pyridine saturated with sodium iodide. (Sodium iodide is soluble in pyridine.) This titration gave a normal S-shaped curve for benzoic acid. A mixture of hydriodic and benzoic acids gave two Sshaped curves and the recovery of the benzoic acid was quantitative. Potentially, the voltage peak method offers advantages over the usual potentiometric procedures for titrations of acids in nonaqueous solvents. With the glass-silver electrode pair in the pyridine system, the method is rapid and simple. For most of the acids studied, the electrodes respond quickly
S o . 3jl S o . 42, S o . 43,
118.93 138.35 139.10
3-Methylheptan e p-Xylene m-Xylene
to changes in cell potential and the potentials are stable. The approach to the end point is easily anticipated and the necessity for plotting the titration curves is eliminated. Apparatus requirements are simple and no special equipment is needed to perform the titrations. The voltage peak method appears suitable for use in automatic titrations. ACKNOWLEDGMENT
The authors wish t o acknowledge the helpful suggestions by L. B. Rogers, Massachusetts Institute of Technology. Thanks are due to R. N. Peterson, who helped obtain some of the data. LITERATURE CITED
(1) Anson, F. C., Lingane, J. J., J. Am. Chem. SOC.79, 4901 (1957). (2) Bishop, E., Analyst 77, 672 (1952). (3) Bishop, E., Mikrochim. Acta 1-6, 619 (1956); Analyst 83, 212 (1958). (4) CundifT, R. H., Markunas, P. C., ANAL.CHEM.28,729 (1956). (5) Fritz, J. S., “Acid-Base Titrations in
Nonaqueous Solvents,” G. Frederick Smith Chemical Co., Columbus, Ohio,
1952. (6) Fritz, J. S., Lisicki, N. M., ANAL. CHEM.23,589 (1951). (7) Fritz, J. S., Yamamura, S. S., Zbid., 29, 1079 (1957). (8) Harlow, G. A,, Noble, C. M., Wyld, G. E. A., Zbid., 28,784 (1956). (9) Kirsten, W. J., Berggren, A., Nilsson, K., Zbid., 30, 237 (1958). (10) Malmstadt, H. V., Fett, E. R., Zbid., 27, 1757 (1955). (11) Moss, M. L., Elliott, J. H., Hall, R. T., Zbid., 20, 784 (1948). (12) Purdy, W. C., Burns, E. A., Rogers, L. B., Ibid., 27, 1988 (1955).
RECEIVED for review February 25, 1958. Accepted June 9, 1958.
Application of Gas-Liquid Chromatography to Analysis of Liquid Petroleum Fracti ons-Co rrect ion I n the article on “Application of GasLiquid Chromatography to Analysis of Liquid Petroleum Fractions” [ (D. H. Desty and B. H . F. Whyman, ANAL. CHEM.29,320-9 (1957)], in Table I the correct data are as follorrs: 10.58 25.72 26.02
1.025 1.410 1.116
9.35 55.63 57.78
0.971 1.745 1.762
