112
ANALYTICAL EDITION
oxidized a t a temperature of 300" C., the catalyst being completely reactivated. Mixtures of hydrogen and carbon monoxide can thus be oxidized a t 300" C. 3. Hydrogen in a hydrogen-hydrocarbon mixture may be determined by fractional combustion with oxygen by passing the gases from four to six times at a rate of 30 to 50 cc. per minute over the catalyst a t a temperature of 100" C. 4. Further studies are being made on the extent of oxidation of methane and higher hydrocarbons under the conditions required for carbon monoxide oxidation.
Vol. 5 , No. 2
LITERATURE CITED (1) Burrell and Oberfell, J. IND: ENG.CHEM.,8, 228 (1916). (2) Hempel, 2. angew. Chem., 25, 1841 (1912). (3) Henry, Ann. Philosophy, 25, 428 (1825). (4) Kobe, IND.ENQ.CHEM.,Anal. Ed., 3, 159 (1931). (5) Ibid., 3,262 (1931). (6) Nesmjelow, Z. anal. Chem., 48, 232 (1909). (7) U.S. Steel Corp., "Methods for Sampling and Analysis of Gasses'' Carnegie Steel Co., Pittsburgh, 1927. (8) Ibid., p. 29. RECEIVED October 18, 1932.
Volumetric Methods of Estimating Nitrites RAYMOND D. COOLAND JOHN H. YOE, Cobb Chemical Laboratory, University of Virginia, University, Va.
A
LARGE number of procedures for the volumetric estimation of nitrites, or nitrous acid, are to be found
in the literature. Because of the considerable difference of opinion as to the accuracy of these various methods, and the lack of a critical systematic study of them, a careful comparison has been made of a number of the procedures, in order to determine their relative values and see which might be expected to give accurate results when used by the average analyst under ordinary conditions. Recalibrated precision volumetric ware and the best grade of c. P. chemicals were employed throughout the investigation. Conductivity water was used for all solutions, which were protected from light, blanks were run on all the reagents, and the usual end-point and temperature corrections were made. Standard solutions were made either from analyzed reagents of known purity, or the solutions were standardized against certified analytical standards, as, for example, Bureau of Standards sodium .oxalate for permanganate. Standardizations, comparisons, and blanks were made under the same conditions as the determinations. Samples of 50 to 100 mg. of sodium nitrite (10 to 20 cc. of a solution containing 5.0000 grams of recrystallized c. P. sodium nitrite per liter) were used for individual determinations.
PERMANGANATE METHODS Direct titration of nitrite in strongly acid solution with potassium permanganate proved unsatisfactory. When the neutral nitrite solution was acidified a distinct odor was noticeable, indicating a loss of nitrous acid, and the results were invariably low. The process was also very slow because of gradual fading of the pink coloration near the end point. Decolorization was hastened by heating the solution to 50" C. near the end of the titration, but the loss of nitrous acid on acidifying the nitrite solution still introduced an error and the results were always low. In an attempt to overcome the loss of nitrous acid when the solution was strongly acidified, permanganate was added to a neutral sodium nitrite solution until it became pink; it was then made slightly acidic and the titration was completed without further addition of acid. While the results obtained were nearer the theoretical than those with the preceding procedure, they were still low, giving a constant error of - 1.4 per cent when 50 mg. of sodium nitrite were present, and a practically constant error of -2.2 per cent with 100 mg. of sodium nitrite. When the slightly acidic solution was strongly acidified just before reaching the end point (6), a nearly constant error of - 1.3 per cent resulted with 50 mg. of sodium nitrite, and -1.4 per cent with 100 mg.
A procedure suggested by Adie and Wood (1) gave results with an average error of +0.1 per cent (procedure A, Table I). The amount of permanganate required to react with a measured quantity of the sample was determined approximately by adding standard potassium permanganate to a strongly acidified solution of nitrite. For the exact determination, standard permanganate solution was added to the neutral nitrite, diluted to 100 cc., to within 1 cc. of the amount found in the preliminary approximate analysis. Then 10 cc. of 6 N sulfuric acid were added and the titration was completed. Lunge (17) claimed that if the titration process is reversed, so that the nitrite is added to acid permanganate, the nitrogen trioxide set free from every drop of the nitrite is immediately oxidized before it can decompose into nitric oxide and nitrogen pentoxide. On adding the nitrite solution to permanganate, 0.6 N with sulfuric acid, an average error of -0.4 per cent resulted (procedure B, Table I). However, decolorization of the permanganate takes place very slowly near the end point, and the large errors obtained in some of the determinations were probably due to the titrations being carried out too fast, with a consequent over-stepping of the end point. In order to hasten the decolorization near the end point and thereby shorten the time of titration, determinations were made with the permanganate heated to 30" to 40" C. as recommended by Lunge (17) a t different rates of titration. The results obtained indicate the necessity of carrying out the titration slowly, especially near the end point, which still appears slowly in spite of the heating, although it is faster than a t room temperature. When the titrations were carried out as fast as possible, the average error amounted to -0.5 per cent. At a moderate rate of titration the error decreased to -0.1 per cent, and when the titration was conducted very slowly near the end an average error of +0.1 per cent was obtained (procedure C, Table I). TABLEI. SUMMARY OF RESULTS OF SATISFACTORY METHODS
PROC~DURE A B C, fast c moderrtte c:slow D, 3-36% excess KMn04 D, 127-132% excess
EG
H
I J
Maximum
Minimum
Arithmetical mean
%
%
%
$0.2 -0.7 -0.7 f0.6 +0.3
fO.0 -0.1 -0.3
+0.1
4-0.4
+o.s
+0.4 i-0.4
4-0.3 +0.8 -0.4 +0.5
-0.4 -0.5
2to.o *0.2
-0.1 $0.1
10.0 +0.4
+0.3 +0.6 +0.3
+0.2 AO.0
*o.o *o.o *o.o
+0.1
+0.2 +0.2
t",:", +0.1
Average deviation from arithmetical mean
% 10.1 f0.2 f0.2
fO. 4 f0.2
AO.1 2c0.2 *0.1 *0.2
*0.1 10.2 f0.2 10.2
March 15,1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
The reaction may be hastened by adding the nitrite to an excess of acid permanganate which may then be determined with sodium oxalate, oxalic acid (IS, 25), or ferrous sulfate (19, 9). This procedure also eliminates the necessity of a clean buret (required in Lunge's method) for each sample of nitrite. When sodium oxalate was used to determine the excess permanganate, the average error amounted to +0.3 per cent with from 3 to 36 per cent excess permanganate, and +0.6 per cent with about 130 per cent excess permanganate (procedure D, Table I). I n these determinations the solutions containing the excess permanganate were heated to 90" C. before adding the sodium oxalate, and the temperature was not allowed to fall below 60" C. until the titration had been completed. When a large excess (130 per cent) of permanganate was present, a heavy precipitate was formed at about 60" to 65" C., on heating the solution. This was dissolved by the addition of a,small excess of sodium oxalate. The titration was then completed by adding a slight excess of permanganate and titrating with sodium oxalate to the disappearance of the pink coloration. When only a small excess of permanganate was present, no precipitate formed while the solutions were being heated. However, in the determinations of the 100-mg. samples precipitates formed while the solutions were standing at 90" C., waiting for the initial buret readings to be made. An average error of +0.3 per cent resulted when ferrous ammonium sulfate was used to determine the excess permanganate a t room temperature (procedure E, Table I). When the sulfate was added slowly a slight precipitate settled out, but when added rapidly no precipitate was formed. The dissolving of the precipitates by excess reducing agents suggested the possibility of using first excess acid permanganate, then excess reducing agent, and finishing the titration with permanganate. Experiments demonstrated that such a method would work successfully, and a search through the literature showed that such a procedure had been reported by Kubel (16), Fresenius (8),and Laird and Simpson (16). Sodium oxalate (procedure F, Table I), ferrous ammonium sulfate (procedure G), and hydrogen peroxide (procedure H), were used as reducing agents. Each gave an average error of +0.2 per cent. Experiments were made to determine the stability of the standard nitrite, hydrogen peroxide, ferrous ammonium sulfate, and sodium oxalate solutions, and the standard potassium permanganate was restandardized several times during its use. The sodium nitrite solutions seemed to be, quite stable. No change could be detected in solutions which had been made up for from 4 to 5 weeks. In a month the normality of the ferrous ammonium sulfate (containing 5 cc. of concentrated sulfuric acid per liter) had decreased from 0.1014 N to 0.0914 N , while that of the sodium oxalate had decreased from 0.0995 N to 0.0990 N . No change could be detected in a solution of hydrogen peroxide (made up in 1.0 N sulfuric acid) which had stood for 3 weeks. A solution of standard potassium permanganate which had been prepared by dissolving the salt in redistilled water, boiling the solution gently in a covered beaker for about 20 hours, filtering through washed ignited asbestos, and diluting with sufficient redistilled water to make the solution tenth normal showed no change in normality during the 8 months it was used, and there was no trace of a precipitate in the bottle when it was emptied.
IODOMETRIC METHODS Two of the iodometric methods tried proved satisfactory. Both, however, involved oxidation of nitrite with excess acid permanganate and determination of the excess permanganate iodometrically. The method given by Griffin (IO),in which
113
the nitrite is heated to boiling with standard permanganate, acidified, let stand 10 minutes, and then cooled before adding potassium iodide, gave an average error of -0.1 per cent (procedure I). A similar, but simpler, procedure proposed by Raschig ( $ I ) , in which the nitrite was added to permanganate, acidified, and let stand 2 minutes a t room temperature before adding potassium iodide, yielded a n average error of +O.l per cent (procedure J). This procedure differs from that quoted by Laird and Simpson (16) as "Raschig's method" in that they have the nitrite and neutral permanganate stand together 2 minutes before acidifying, and not after, whereas Raschig (21) recommends acidifying and after 2 minutes adding potassium iodide. Kolthoff (14) used a similar procedure. The procedure was also carried out as given by Laird and Simpson (16) with unsatisfactory results. Nitrite is not oxidized in neutral solution in the cold by potassium permanganate ($), and unless there is a short wait after acidifying, the oxidation of the nitrous acid may not be complete. Some of the solutions became blue again on standing after completion of the titration. Raschig (21) claims that in such a case the nitrous acid and the permanganate have not stood together long enough and all the nitrous acid has not been oxidized. It might be pointed out, however, that oxidation of hydriodic arid by the air will also cause the reappearance of the blue color. Attempts to estimate nitrite by determining the amount of iodine liberated by it from potassium iodide, both in the air and in an atmosphere of carbon dioxide, according to the different procedures proposed by Davisson (6), Robin (22), Winkler (26), Raschig (iodide-nitrite reaction, Z l ) , and Clarke (4) proved unsatisfactory. Some of these require a technic which must be perfected by practice, and none is considered satisfactory from the standpoint of this investigation. The methods proposed by Phelps ($0) and Rupp and Lehmann (23) also failed to give satisfactory results.
MISCELLANEOUS METHODS A method proposed by Sanin (24, using hydroxylamine hydrochloride which is titrated with standard sodium hydroxide before and after the reaction NaN02
+ NH,O.HCI
= NaCl
+ N20 + 2H20
gave an average error of +0.4 per cent when using 50 mg. of sodium nitrite, but the average error with 100 mg. was - 1.2 per cent. The methods suggested by the publication of Grossman ( l l ) Fischer , and Steinbach (Y),Moir ( I @ , Grutzner ( I d ) , and Green and Evershed (9) gave results with large and variable errors.
SUMMARY Thirty-one procedures were tried for the volumetrio determination of nitrites. Ten proved satisfactory. Eight are listed as permanganate methods, and the other two, listed as iodometric methods, involve the oxidation of nitrite by acid permanganate. Sanin's method with hydroxylamine hydrochloride proved satisfactory when not over 50 mg. of sodium nitrite were present. When made with special precautions, potassium permanganate and sodium nitrite solutions were shown to be stable for some time. It was shown that neither sodium oxalate nor ferrous ammonium sulfate solutions are stable for a period as long as one month. However, sodium oxalate is much more stable than ferrous ammonium sulfate.
ANALYTICAL EDITION
I14
Hydrogen peroxide, made u p in 1.0 N sulfuric acid solution, was found to be stable for as long as 3 weeks.
LITERATURE CITED (1) Adie and Wood, J . C h m . Soc., 77, 1076 (1900). (2) Atkinson, Pham. J., 16, 809 (1886). (3) Beckurts, “Massanalyse,” p. 515, Friedr. Vieweg und Sohn, Braunschweig, 1913. (4) Clarke, Analyst, 36, 393 (1911). (6) Davisson, J . Am. Chem. SOC.,38, 1683 (1916). (6) Feldhaus, 2.anal. Chem., 1,426 (1862). (7) Fisoher and Steinbaoh, Z. anorg. Chem., 78, 134 (1912). (8) Fresenius-Cohn, “Quantitative Chemical Analysis,” Vol. 2, p. 196, Wiley, 1911. (9) Green and Evershed, J. SOC.Chem. Ind., 5, 633 (1886); Z . anal. Chem., 26, 638 (1887); Chem. News, 65, 109 (1892). (10) Griffin, “Technlcal Methods of Analysis,” p. 28, McGraw-Hill, 1921. (11) Grossman, Chm.-Zto.., 16, 818 (1892).
Vol. 5 , No. 2
(12) Griitzner, Arch. Pharm., 235, 241 (1897). (13) Kinnicut and Nef, Am. Chem. J., 5, 388 (1883!; (14) Kolthoff and Furman, “Volumetric Analysis, Vol. 2, p. 302, Wiley, 1929. (15) Kubel, J. prakt. Chem., 102, 229 (1867). (16) Laird and Simpson, J.Am. Chem. Soc., 41,524 (1919). (17) Lunge, Ber., 10, 1074 (1877); Chem.-Ztg.,28, 501 (1904). (18) Moir, J. S. African Assoc. Anal. Chem., 4, 3 (1921). (19) Pean de St. Gilles, Ann. chim. phys., 55, 383 (1859). (20) Phelps, Am. J . Sci., 167, 198 (1904). (21) Raschig,Ber., 38, 3911 (1905). (22) Robin, J.pharm. chim.,(vi), 7, 575 (1898). (23) Rupp and Lehmann, Arch. Pharm., 249, 214 (1911). (24) Sanin, J . Russ. Phys.-Chem. SOC.,41, 791 (1909). (25) Scott, “Standard Methods of Chemical Analysis,” p. 521, Van Nostrand, 1917. (26) Winkler, Chem.-Ztg., 23, 454 (1899). RFJCEIVED November 29, 1932. Contribution 109 from the Cobb Chemical Laboratory, University of Virginia.
Determination of Carbon Dioxide in Continuous Gas Streams WILLIAMMcK. MARTINAND JESSE R. GREEN Department of Chemistry, Montana Agricultural Experiment Station, Bozeman, Mont. The problem of quantitative removal qf carbon dioxide f r o m continuous gas streams by absorption in barium hydroxide and its subsequent determination by direct titration has been investigated. An eficient absorber for carbon dioxide or other soluble gases, in which the absorbing solution m a y be directly titrated, is described. The eficiency of absorption of soluble gases f r o m a continuous gas stream is determined by the design of the absorption vessel, the concentration of the absorbing solution, and the rate of flow of the gas mixture. The eficiency of a n absorption vessel is
I
N AN attempt to study the effect of petroleum spray oils on the respiratory activity of growing plants, it was discovered t h a t the carbon dioxide in the air drawn continuously from the respiration chambers could not be completely absorbed by the apparatus and methods generally used. As a foundation for subsequent work o n respiration it was decided t o investigate the methods for absorbing and quantitatively determining carbon dioxide in continuous gas streams. For the benefit of those who are confronted with the problem of choosing, or devising, a method or determining carbon dioxide in other than routine studies, the results of a literature review are herein presented. T h e methods described in the literature have been developed largely in connection with the determination of carbon dioxide derived from t h e oxidation of organic substances in combustion analysis, from the oxidation of carbon in steel, from carbonates, and from the respiratory activities of living organisms. Upon the basis of differences in principle the methods may be briefly classified as follows : 1. Gravimetric Methods. a. Carbon dioxide absorbed in strong alkaline solutions, or solid absorbents, such as soda lime and ascarite (sodium
determined more by the length of the path of the gas bubbles through the absorbing liquid than by the extent of surface exposed to the gas stream. The addition of barium chloride to barium hydroxide solution appreciably increases its eficiency in absorbing carbon dioxide f r o m continuous gas streams. However, the small amounts generally used have but little practical effect. W h e n solutions containing suspended barium carbonate are stirred with a ciarreni of carbon dioxide-free air they cannot be litrated with acid stronger than approximately 0.07 N . hydroxide dispersed on asbestos fibers), and the increase in weight of absorbent determined. b. Absorbed in dilute solution of sodium or potassium hydroxide and weighed as barium carbonate. c. Absorbed in a strong solution of barium hydroxide and the resulting carbonate either weighed directly or converted to the corresponding sulfate. 2. Titrimetric Methods. a. Carbon dioxide absorbed in a dilute standard solution of sodium or potassium hydroxide and the carbonate determined by double titration, using phenolphthalein and methyl orange or other suitable indicators. b. Absorbed in a standard solution of barium hydroxide and the carbonate determined by a single titration. c. Absorbed in a dilute standard solution of sodium or potassium hydroxide, an excess of neutral barium chloride added, and the excess of alkali titrated. d. Absorbed in a strong solution of barium hydroxide and the resulting carbonate filtered, washed, dissolved in a standard acid solution, and titrated. 3. Gasometric Methods. a. By volumetric gas apparatus. Carbon dioxide absorbed directly in strong alkali in gasometric apparatus and the decrease in the volume of the gas mixture measured a t atmospheric pressure; or absorbed in strong alkali, carbon dioxide liberated in an acid solution in a gas apparatus, and its voIume measured a t atmospheric pressure. b, By manometric gas apparatus. Carbon dioxide absorbed in strong alkaIi and Iiberated in the manometric gas
