Gas-Volumetric Semimicrodetermination of Carbon A Wet Method for Aliphatic and Cyclic Compounds E. BERL
4VD
W. KOERBER
Carnegie Institute of Technology, Pittsburgh, Penna.
T
for about 8 to 10 minutes. Care must be taken that a vacuum remains in the apparatus during the whole operation. This depends on the amount of gas formed, the vacuum used, and the tightness of the stopcocks. Before heating, the apparatus is connected at C with a leveling flask by means of a rubber connection. This leveling flask is filled with an acidified hydrochloric acidsaturated sodium chloride solution colored with methyl orange. Stopcock C is opened slightly, so that under the influence of vacuum very minute amounts of this salt solution enter the buret. If an overpressure is formed, the sodium chloride solution recedes. In such a case it is best t o atop the procedurt: and discard the whole experiment.
0 LEAR?; the nature of the oxidation products of arti-
ficial carbohydrate coals and for other purposes i t was necessary to determine quickly the carbon content of those organic compounds (acids, organic salts, and neutral substances). A quick and reliable method by wet Combustion with the use of chromic acid and phosphoric acid was described by Berl and Innes (I), and was used with success for the analysis of aliphatic compounds, especially of carbohydrates with rather high oxygen content. These previous experiments gave poor results for the analysis of cyclic compounds. This method has now been changed somewhat to determine the carbon content of cyclic compounds with rather low oxygen content. Such compounds are formed by the wet oxidation of artificial cellulose coals ( 2 ) and natural bituminous coals (3). I n these older experiments the wet combustion of aromatic compounds gave too low figures for carbon because, besides carbon dioxide, carbon monoxide and hydrocarbons were formed which are not absorbed by alkali hydroxide. Another inconvenience was observed if volatile acids, like benzoic acid, had to be analyzed. Because the combustion must be carried out in a vacuum, the volatility naturally causes low figures for carbon. Both difficulties can be overcome by dissolving acids in carbon dioxide-free sodium hydroxide and precipitating them with an excess of chromic acid and phosphoric acid. The organic acids result as finely dispersed material which is oxidized very quickly, so that the volatility does not cause too low figures for carbon. Mercury, as before ( I ) , was used as a catalyst. Experiments were carried out with mercury oxide and sodium vanadate but these substances gave unsatisfactory results except in the case of mellitic acid, which mith its high oxygen content can be burned easily in a n acid medium to carbon dioxide. Mercury also gives very good results in the oxidation of oxygen-free symmetric compounds (experiments 8 and 9) and nitrogen-containing compounds (experiment 10). This wet method can be used with success for the quick determination of carbon in salts of acids containing oxygen, as well as the carboxyl group (experiment l),which with dry combustion in some cases give rather unsatisfactory results.
\IllI
:I: Yn C
II
Method of Procedure The sample (8 t o 25 mg., depending upon the carbon content), one drop of mercury, and, in the case of acids, one pellet of carbon dioxide-free sodium hydroxide and a few drops of water are placed in the oxidizing flask (Figure 1). (The outside of a pellet which contains sodium carbonate is removed with a knife.) All joints and stopcocks of the apparatus are greased with viscous 100 per cent phosphoric acid. With stopcock A closed and stopcocks B and C open, the apparatus is evacuated a t C. After reaching good vacuum with a water-vacuum pump, C is closed and the connection with the water pump is disconnected. Five milliliters of concentrated chromic acid solution are poured into the funnel at A . Carefully opening A , practically all the liquid is introduced into the flask, but no air should enter. A fern drops of water are added, and stopcock A is carefully opened so that no air enters. The chromic acid in the capillary is replaced. Five milliliters of concentrated phosphoric acid are introduced into the flask; again no air should enter the evacuated apparatus. The flask is gently heated so that its contents boil in the vacuum
FIGURE 1. DIAGRAM OF A P P A R A T U S After the sample has been burned completely B is closed, concentrated hot sodium sulfate solution is added to funnel A , A is opened, and the flask is filled with this solution. S o air should enter through A. When no further sodium sulfate solution enters the flask, B is opened. The sodium sulfate solution fills the capillary between the combustion flask and the buret and reaches the lower part of the bore of stopcock B . B is closed and the buret is disconnected from the combustion flask. A period of about 25 minutes is required for the warm gas in the buret to reach room temperature. A thermometer must be fixed with its mercury bulb in the middle of the gas column in the buret. Then C is opened and saturated acidified colored sodium chloride solution is introduced until the levels in the buret and in the leveling flask are the same. The volume of gas (carbon di245
INDUSTRI.4L -4KD ENGIKEERIKG CIIEMISTRY
246
YOL. 12, NO. 4
TABLEI. DETERMINATION OF CARBOK Expt. NO.
-
.
Substance
Conversion to Sodium Salt Catalyst
Gram
1
Sodium oxalate. CrOlPia~
2a
Benzoic acid. C;HsOr
2b
0.0273 0,0254 0.0159 0.0129 0,0141 0.0126 0.0109 0.0120
20 2d
2e 2f 3 4
5, 5b 50 5d 6 7 8
Phthalic acid, CrHeO,
0.0193 0.0169 0.01405 0 0214 0.0172 0.0196 0.0216
Salicylic acid, CiH6O3 hIellitic acid, C ~ H ~ O L ?
Benzene pentacarbonic arid, CnHsOm
0.0191 0.0190 0.0141
Diphenic acid, CL~HIOO; a-Xaphthoic acid, C I I H ~ O ~
0.0139 0.0127 0.0092 0.0120
Phenanthrene, ClrHlo
9 10
Diphenyl, CnHm
11
0.0086 0.0084
Diphenylamine. (C6Ha)lNH
0.0004 0.0100
-
+-
+ +++ ++ +
+
t
f
++ + ++ -
-
-
oxide plus foreign gas, mostly air) in the buret is now read. A slight vacuum is created in the buret by lowering the leveling flask, closing C, and introducing a 50 per cent potassium hydroxide solution through the funnel above B. B is closed, and the buret shaken in a horizontal position. iifter the carbon dioxide absorption is finished, some concentrated sodium chloride solution is added through the funnel above B. Then the volume of nonabsorbed gas is read n-ith the help of the leveling flask. BAROMETRIC PRESSURE
MANTISSAS OF LOGARITHM (0, -1)
050g6350 TEMPERATURE VAPOR PRESSURE MEASURE0
720
1 FOR CARBON DETERMINATIOS FIGURE 2. NOMOGRAM
Thie nomogram is from a-series published in 1930 by Julius Springer, Berlin, under t h e title "Nomographic Charts for the Chemical Industry". I n the original preparation E. Berl had the assistance of W. Herbert and W,VVahliz,
Hg Hg Sone Hg Hg HgO TdrOa
COz .Wl. 10.00 9.80 10.20 12.30 20.90 18.50 14.20 16.20 23.70 21.00 18.36 19 00 15 60 17.05 19.19
Hg Hg Hg
17.80 18.00 20.60
24 25
Hg
22.10
25 21 25.2 28.2 23 25 25.8 24.4
Xone Sone
Hg
Hg Hg Hg Hg Hg Hg
19.90 18.55 24.6 17.05 16.70
17.10 18.20
t
C. 20 22
23
24 25
24 20 18 24.5 25 23 24 25.8 20.5 22.8
23.5
P Mrn. Hg
746
727
Carbon Found Calculated
%
%
17.73 18.00
17.91
745 74 1 735 738 736 740
735 735 740.6 i42 736 744.5 739 744 738 746 746 742 741 740 737 741 741 736
68.85
57.31 57.83 61.86 41.93 41.91 41.90 42.03
57.81
44.13 44.27 69.55 75.13 75.02 94.52 94.52 93.37 94.32 85.07 85.06
44.29
61.31 42.10
69.42
76.74 94 34 93.50 85.16
The combustion can be carried out in a few minutes. The reading of the of gas, the absorption of carbon dioxide, and the reading of the residual gas also need a few minutes. Therefore, this method, where it can be used, gives very quick and satisfactory results. The nomogram ( ~ 2) helps i to ~calculate ~ the ~carbon~ content very quickly in a graphical way. EXAJIPLE.At p = 740mm. of mercury pressure and t = 30" C., a certain volume of carbon dioxide in contact with saturated sodium chloride solution has been found. The weight of the carbon in this volume of carbon dioxide is t o be determined. Point 740 on line at left is connected with point 30 on the temperature line. The extension of this line cuts the third line at 0.9278 - 1, which is the logarithm of the correction factor and on the right at 0.6595 - 1, which is the logarithm of the milligrams of carbon in 1 ml. of the gas volume read (at p mm. of mercury and t o (2.). The experimenter therefore reads the absorbed carbon dioxide in milliliters, takes its logarithm, adds the logarithm figure obtained by connecting with a straight line the points for observed temperature and pressure, subtracts the logarithms of the weight of the substance investigated, and gets at once the per cent of carbon in the substance.
Table I shon-s the results obtained. Experiment 2 sho~vs that unsatisfactory results are obtained by burning benzoic acid, because of the 1-olatility of this acid in a vacuum. By conl-erting the acid into it's sodium salt and using mercury as a catalyst, excellent results are obtained in a very short time. Experiments 2e and 2f, using mercuric oxide and vanadium pentoxide as catalysts, did not give satisfactory results. In the analysis of mellitic acid mercury oxide and vanadium oxide (experiment 5, a, b, c, and GI) gave good results. Experiments 9, 10, and 11 show that aromatic hydrocarbons and aromatic amines can be analyzed with good results. This vet, semimicrochemical method can be carried o u t Ivith cheap laboratory apparatus found in all laboratories. Recai.ce of its simplicity it has perhaps some advantages over the excellent Tan Slyke method (4).
Literature Cited (1) Berl, E., and Innes, d.G., Ber., 42, 13C5 (1909:. (2) Berl and Koerber, ISD. EXG.CHEM.,32, in press (1940,. (3) Bone and Himus, "Coal, Its Constitution and Uses", S e w Tork, Longmans, Green and Co., 1936. (4)Van Slyke. D. D., J . B-'c2. Chem., 102,636 (1933).
