readily and undergoes autoxidation on exposure to air (16). ACETANILIDE-BORON TRIFLUORIDE. A solution of acetanilide in chloroform was added to an excess of boron trifluoride dissolved in diethyl ether. The crystalline product was filtered, washed, while wet, with ether, and stored in vacuo over anhydrous calcium chloride for 48 hours before analysis. The product melted, with decomposition, a t 143" to 149" C. [133" C. with decomposition ( I S ) ] . PROCEDURE
The combustion tube was conditioned in a stream of oxygen for 24 hours, after which a few unweighed samples of benzoic acid were burned to restore moisture equilibrium and activate the platinum gauze. The furnace temperature was maintained a t 725" f 25" C. and the heating mortar a t the boiling point of p-cymene. The sample contained in a platinum boat was placed 6 to 7 cm. in front of the platinum gauze (Figure 1) and the sample burner was placed 2 to 3 cm. in front of the boat. For the analysis of relatively stable compounds such as phenylboric oxide, the sample burner temperature was adjusted immediately to 1000" C. The burner was left in its original position for 5 minutes and then slowly moved to the platinum gauze over a period of 15 minutes. Without further movement of the burner, heating was continued for 10 minutes (or until all black residue was gone) ; then the remaining gases were flushed out for 20 minutes more. The oxygen flow rate was maintained at 5 ml. per minute throughout the combustion, a total volume of 250 ml. being used. The absorption tubes were flushed with 50 ml. of dry carbon dioxide-free air, wiped in the usual manner ( l l ) and , weighed. For highly combustible compounds such as n-butylboric acid, the sample burner temperature was lowered to 300"
to 400" C. and the first burning completed, as described above, in 15 minutes. The burner was nioved back to its starting position and a second pass, requiring a period of 15 minutes with the burner a t 1000" C., oxidized any residue. The remainder of the operation was as described before, I n determining carbon and hydrogen in amine-boron triff uoride complexes, such as the acetanilide-boron trifluoride reported in Table I, the burning procedure was the same as that for phenylboric oxide; the combustion tube packing, however, was as illustrated in Figure 1,B. After 50 to i o runs on the complexes, the silver wire in the section after the platinum gauze was colored yellow and the quartz tube a t this point had become thin and fragile. It was necessary, therefore, to cut this portion out, fuse the good sections together, and repack the tube. When nitrogen was determined by the usual micro-Dumas method (8) but with 10- to 15-mg. samples, the results were high by about 1 part in 10. Therefore, the procedure was modified using a longer combustion tube with two permanent packings in sequence or when the conventional packing was employed, using 5- to 7-mg. samples and somewhat lower than usual burning rates. I n either case a little more free space (10 cm.) was provided ahead of the temporary packing, for such compounds have a tendency to volatilize back toward the mouth of the tube. The permanent packing of the Dumas apparatus is slowly rendered ineffective by amine-boron trifluoride compounds; consequently, if large samp1es-e.g. , 10 mg.-are used, the packing usually needs to be replaced after 6 to 8 runs. Such deIeterious effects of halogen compounds on Dumas packings have been noted ( I S ) . RESULTS AND CONCLUSIONS
A study of the results given in Table I
shows that with all compounds used in this investigation, the accuracy and precision obtained for both carbon and hydrogen are highly acceptable, the results being comparable with those expected from ordinary organic compounds. ACKNOWLEDGMENT
The authors gratefully acknowledge the assistance of the Oklahoma A. and M. Research Foundation in obtaining the financial assistance needed to carry on the research described in this paper. LITERATURE CITED
Ainley, A. D., Challenger, F., J . Chem. SOC.1930, p. 2177. Brown, H., Sefeshi, S., J . Am. Chem. SOC. 70,2793 (1948). Clark, H. S., Rees, 0. W., Illinois State Geol. Survey, Rept. Invest. No. 169, (1954). Gel'man, N. E., Korsun, M. O., Doklady Akad. Nauk, S.S.S.R. 89, 685-7 (1953). Khotinsky, E., hfelamed, M., Ber. deut. chem. Ges. 42,3090 (1909). Krause, E., Xobbe, P., Zbid., 63, 934 (1930). Michalis, A., Becker, P., Zbid., 15, 180 (1882). Niederl, J. B., Niederl, V., ''MicrOmethods of Quantitative Organic Analysis," 2nd ed., pp. 79-95, Wilev. New York. 1942. Ibid., 101-16. ' Zbid., pp. 107-12. Zbid., pp. 123-4. Seaman, W., Johnson, J. R.,J . Am. Chem. SOC.53,715 (1931). Shelberg, E. F., ANAL. CHEM.23, 1492 (1951). Snyder, H. R., Iiuck, J. A., Johnson, J. R., J . Am. Chem. SOC.60, 105 (1938). Zbid., p. 108. Sugden, S., Waloff, M., J . Chem. SOC.1932, p. 1496.
pi.
RECEIVEDfor review July 19, 1957. Accepted August 7, 1957.
Determination of Carbon Dioxide in Gas Streams PAUL
E. TOREN
Phillips Pefroleum
and B. J. HEINRICH
Co., Bartlesville, Okla.
b A
method has been developed for determination of carbon dioxide concentrations ranging from 1 p.p.m. to 100% in a gas stream. The sample to be analyzed is passed through a saturated solution of an alkaline earth carbonate containing excess solid carbonate. At equilibrium, the pH of the solution is measured and the carbon dioxide content of the gas is determined from a previously prepared calibration chart. The method is precise to within =k5% of the carbon di-
1854
ANALYTICAL CHEMISTRY
oxide content measured. The procedure can be easily adapted to provide automatic recording and control of the carbon dioxide content of a gas stream.
T
effect of carbon dioxide on the solubility of calcium carbonate in water has been known since the time of Cavendish and has been studied by a number of workers (2), but this phenomenon has not been applied to continHE
uous determination of the carbon dioxide content of a gas. Measurement of the acidity of a carbonate-bicarbonate buffer in equilibrium with a gas has been used to determine the carbon dioxide content of the gas ( I ) , but this particular procedure was applied to only a limited range of carbon dioxide concentrations. Consideration of the equilibrium relationships which must be satisfied in a saturated solution of calcium carbona!e shows that, if a solid carbonate phase :is
if no solid phase other than the carbonate is formed. Therefore, it should be possible to determine the carbon dioxide content of a gas stream by measuring the pH of a saturated carbonate solution in equilibrium with it. As long as the saturated solution and equilibrium conditions are present, the p H measurement should be specific for carbon dioxide. This paper describes the development of a method for the determination of carbon dioxide based on such a carbonate equilibrium system.
present, the pH of the solution is determined by the carbon dioxide content of the gas phase in equilibrium with the solution. This should also be true with saturated solutions of other carbonates,
TO pH M E T E R
RPrn
_-
APPARATUS
IN
The apparatus found best for this determination is illustrated in Figure l. Although the size of the carbonate cell is not critical, the cell should be constructed to contain a minimum amount of liquid. The conical shape of the cell and the pierced glass disk promote efficient and thorough mixing of the carbonate slurry and the gas stream passing through the cell. A fritted-glass disk was used before the pierced glass disk was adopted but with use it became filled with solid carbonate and required
:0 I SK
I
40MM-
Figure 1.
Apparatus
LEGEND : -.SrC03 -SrC03 +CsCO3 -CaCq)
I N H 2 0 AT 0°C. IN H 2 0 AT 25'C. IN H 2 0 AT 25'C. IN 0.1MCaC12AT 25'C.
REAGENTS
Carbonate Cell Solution. Distilled water or a solution of a soluble salt of the same metal as the carbonate used-i.e., with a calcium carbonate solid phase, the cell solution might be either distilled water or a solution of calcium chloride. Carbonate Slurry. Place 50 grams or more of calcium carbonate or strontium carbonate in a widemouthed screw-cap jar. Add about 100 ml. of the carbonate cell solution. Mix well, allow t o settle, and decant the liquid phase. Wash the solid five times in this way. After the last wash, leave enough liquid to cover the solid in the jar. Store the washed slurry, and use as needed in charging the carbonate equilibrium cell. pH 7 Buffer, for standardizing the p H meter. CALIBRATION
Calibrations are prepared by measuring the pH of the desired carbonate and cell solution in equilibrium with gases of known carbon dioxide content. These calibrations should be linear (plotting p H us. log CO,) from 1 p.p.m. to 100% carbon dioxide. Several typical calibrations are shown in Figure 2. These calibrations are reproducible and can be used directly for measurements with the appropriate reagents prepared according to directions.
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