V O L U M E 20, N O , 1 1 , N O V E M B E R 1 9 4 8 Table 11. Determination of Oxygen Concentration of Nitrogen by Continuous -4nalysis Percentage Oxygen Present X lo3 0.0 3.2 5.4 10.7 16.1 21.5 26.8
Percentage Oxygen Found X 103 0.0, 0.0, 0 . 6 3.2, 3.2, 2 . 9 5.9, 5.9, 5 . 6 11.0, 10.5, 1 1 . 0 17.1, 16.5, 16.5 21.5,21.0,21.5 27.5, 26.3, 26.8
Av. 0.2 3.1 5.8 10.8 16.7 21.3 26.9
CONTINUOUS ANALYSES OF GASES
Turn stopcock 4 so that gas from the sample line passes through the apparatus. Adjust the gas flow to 0.75 cubic foot per hour. Turn stopcock 1 so that the reagent must flow continuously from the gas separator to the absorption cell, through the reducing column and orifice, and through stopcock 1 into the scrubber. Adjust the liquid level carefully. As there is an inherent response Iag in the instrument, about 10 minutes must be allowed for the equipment to indicate correctly the oxygen content of the gas. Because of the lag in response this apparatus cannot be used to follow the composition of gases whose oxygen content fluctuates rapidly. Refer to the calibration curve to find the oxygen concentration of the sample.
In Table I1 are portrayed analytical results using this procedure to determine the oxygen concentration of nitrogen. These results were obtained under ideal conditions, but experience in a plant control laboratory shows this procedure is accurate to a t least *0.0005% when the oxygen concentration of the gas analyzed is near 0.005%. DISCUSSION
This method has been used for over a year to determine the oxygen content of widely varying gases including nitrogen, acetylene, and mixtures of nitrogen] carbon dioxide, and carbon monoxide. The equipment is simple in design and lends itself well to plant control. In order to obtain consistently good results the following precautions must be observed: Because the scrubbing solution, analytical reagent, is photo-
1037 sensitive, it should be protected from direct sunlight. The reagent should be drained from the apparatus and replaced every 24 to 48 hours, or as experience dictates] with fresh solution that has been stored in a brown bottle. The amalgamated zinc should be reactivated whenever it becomes dark gray, or as often as experience indicates it is necessary. Usually once every month is sufficient. I t can be reactivated several times before it is necessary to replace it, by removing the reducing column from the apparatus and covering the amalgamated zinc with 1 to 4 hydrochloric acid until it assumes a bright metallic look. After reactivation, the acid is drained off and the amalgam washed thoroughly with distilled water until the washings show no zinc present. This is important, as zinc salts will be precipitated by the alkaline anthraquinone reagent and may plug the orifice. If the orifice is ever plugged, it should be carefully removed from the system and cleaned with cleaning solution; all the cleaning solution should be removed before the orifice is reinstalled. ACKNOWLaDGMEh-T
The author is grateful to T. H. Kilmer, who carried out most of the tests. He also wishes to acknowledge with thanks the many helpful suggestions of F. R. Balcar. LITERATURE CITED
Binder, K., and Weinland, R. F., Ber., 46, 255 (1913). Binder, K., and Weinland, R. F., Gas W o r l d , 59, 125 (1913). Cohn, G., IND.ENQ.CHEM.,ANAL.ED.,19, 832 (1947). du Pont de Nemours & Co., E. I., private communication. Fieser, L. F., J . Am. Chem. Soc., 46, 2639 (1924). Hand, P. G. T., J . Chem. Soc., 40, 1402 (1918). Mohr, F., Z. anal. Chem., 12, 138 (1873). Rideal, S., and Burgess, W. T., Analvst, 34, 193 (1909). Shaw, J. A . , IND.ENG.CHEM.,ANAL.ED.,14, 891 (1942). White, H. A., J . Chem. Met. Mining SOC.S. Africa, 18, 292 (1918).
Winkler, L. W., Ber., 21, 2843 (1888). Window, E. H., and Liebhafsky, H. .4.,IND. ENQ.CHEM.. -&SAL. ED., 18, 565 (1946). RECEIVED March 8, 1948.
Quantitative Determination of Elemental Sulfur in Aromatic Hydrocarbons H. E. MORRIS, R. E. LACOMBE,
AND
W. H. LANE, iMonsanto Chemical Company, Texas City, Texas
+
A volumetric method based upon the reaction S Na2S03 --+ Na?S?Oihas been developed for elemental sulfur in the range 0.1 to 209’0 in aromatic hydrocarbons. The sodium sulfite and butyl mercaptan methods have been investigated and found to be unsatisfactory for quantitative determination of elemental sulfur in aromatic hydrocarbons in the range 0 to 100 p.p.m. No reliable method for elemental or total sulfur in this concentration range appears to exist.
A
RECENT paper by Mapstone (’7) gives an excellent de-
scription of the Sommer test, the inverse doctor test, and the mercury test for the detection of elemental sulfur. However, Mapstone devotes his attention chiefly to the problem of detection rather than quantitative determination. One A.S.T.M. method (5) makes use of the mercury corrosion test for detecting the presence of free sulfur, while other A.S.T.M. methods (1, 8, 4) describe the copper strip corrosion test for the qualitative detection of free sulfur. In a recent publication Bolt (6) sur-
veyed the different types of copper strip corrosion tests currently in use and made recommendations for their standardization. The butyl mercaptan (butanethiol) or inverse doctor test for the quantitative determination of free sulfur has been described by Wirth and Strong (IO) and is incorporated in a Universal Oil Products method (9). Ball (6) states, “The use of mercury t o remove free sulfur gives good results; however, it should not be employed as B qualitative t e s t , as peroxides also give the black precipitate.
ANALYTICAL CHEMISTRY
1038 The use of copper is less reliable, as several observers state that the presence of peroxides inhibits the reaction with free sulfur." Of the many methods which he considered, Ball found that the butyl mercaptan method of Wirth and Strong (10) is the best. Nevertheless, the results which he obtained on three solutions containing known amounts of free sulfur gave values of sulfur found in excess of the amount present by 15, 36, and 387,. Ball concluded that there is no generally recognized quantitative method for determining elemental sulfur in hydrocarbons.
Table 11. Determination of Small Amounts of Elemental Sulfur in Aromatic Hydrocarbons by Sodiiim Sulfite Method Slllllli.
Sninple
Gwmu
C'oncentraticiri
Ilu.
100 100 1
10
no
0 0 20.0 20.0 2.0 2.0
ELE3JIENTAL SULFUR I? RANGE 0.1 TO 20.0Yc
I t was essential that an adequate method for the determination of substantial quantities of free sulfur in the presence of other sulfur compounds be developed. -4rapid, quantitative, volunietric method for the determination of free sulfur in rubber, described by Oldham, Baker, and Craytor (a), has been modified slightly and applied to the determination of free sulfur in aromatic hydrocarbon solutions. Method. Sample size may be varied, depending on the content of free sulfur. Transfer the sample of the aromatic hydrocarbon to a 250-ml. wide-mouthed Erlenmeyer flask which contains 100 ml. of a 15Y0 solution of sodium sulfite. Add 10 ml. of 0.1% aqueous sodium stearate to facilitate contact between the aqueouj and organic layers. Boil vigorously for 2 hours, adding hot water as needed to keep the level constant. Cool to room temperature. Add 15 ml. of 37% formaldehvde Mith swirling and then add 10 ml. of 6 S hydrochloric acid. Finally, add 10 ml. of 10% potassium iodide solution. Titrate withO.1 potassium iodate until about 1 1111. in excess has been added. Backtitrate with 0.1 S sodium thiosulfate, using starch to indicate the end point if desired. The method dependq upon thp reaction: a\
S
+ SalSOT +Na?S203
25.0 25.0 IZ.,? 12,.5
Determination of Elemental Sulfur in St! Solutions 133- Sodium Sulfite Ilrthod
S o . of experiment
1 00 1.01
101 .i
ELEMEYT4L SL'LFt R I \
24
2
2.00 1.96
.i00 4 X!4
98.0
4 8
!Ci X
22
10.00
10 04
rene
7
20.00 19.99
100.4
100.0
1.8
2.2
R A l G E 0 TO 100 P.P.M.
I t was desired to develop a quantitative method which aoulti be sensitive to + 5 p.p.ni. of elemental sulfur in the concentration range 0 to 100 p.p.m. in styrene. An attempt was made to adapt the previously described sodium sulfite method to this range. Experiments were carried out on known solutions of elemental sulfur in toluene and styrene (Table 11). Sample size varied from 100 to 500 grams and sulfur concentration varied from 0 to 100 p.p.m. The normality of the potassium iodate and sodium thiosulfate reagents was reduced to 0.01 in order to secure an appreciable titration volume. The end points in the standardizat i i i t i of the sodium thiosulfate solution against the potas5iuni
.Mu.
9 7 10 1 8.0 0 0 3.8 2.9 2.0
10 10
0 10 in 1
0 0 0 1
1
2 , .? 2.5 2 , r, 2 .J
Sulflir Herowry r'i
9i 101
80 :3 8 24 200 0 0
0 0 0 6
0
A4 A4
1 6
Table 111. Determination of Small Amounts of Elemental Sulfiir in Hy-drocarhons by BUt>-l Mercaptan Method Sulfur ('onrentration i'.P. rn.
Jaiiiplt.
Ommn
200 toiuenf.
10.0 10 0
200
10.0 I0 0
qtyrt'rii'
The thiod f a t e is determined from the potassium iodate consumption.
Table I .
Sulfur Found
iodate solution were always sharp and reproducible in spite of the high dilution. However, in the experiments of Table I1 the t ~ points d in the potassium iodate titration and subsequent fIICAL &XIIT\-, nallan,
Measurement of Rates of Spread of Solutions of Surface Active Agents JOK11A H Y Y P I i , Research Lnhorntory. Ocikite l ’ m r l i r c t s , l n c . , V e i ~I-ork. \ .
i n apparatus is described for measuring the rate of spreading of liquids on various surfaces. .4 measured volume of liquid or solution is placed upon the siirface and automatically- photographed at definite time intervals. Any plane surface, w-hether transparent or opaque, may be used. Measurements of the resulting series of photographic images are plotted against elapsed times to obtain curves which indicate the relative rates of spread of the solutions
A
V.4RILTL’ of methods has been used to evaluate the relative wetting powers of surface active agents, yet most o f thvse methods arc confined to the measurement, of a single factor in wetting, or are limited to action on one type of surface. The rorrrlation of surface tension and interfacial tension wit,h the spreading charactrristics of one liquid upon another is well known, but such methods cannot as yet be applied to the spreading of liquids on solids because no method has been devised for measuring the surface tension of solids. Thta assumption has frequently been made that surface tension :rlone is a measure of wetting ability, but that such is not the case has been adequatell- demonstrated by Vermorel and Dantony (.3) arid by (’ooper and Suttall ( 2 ) . The Draves test has been of i-onsiclemble use in the textile industry, but because it measiirw peirrt ration as well as surface wetting. results obtaintd by this method should not be regarded as applicable to other types of wetting problems. The ability of a solution to produce foam is no longer - accepted as a reliable indication of wetting pom er. Other ingenious methods, such a i the Ihrtell cell technique and the measurement 01 rontact angles, have given much valuable infoi mation, but do not yield the type of information niost useful to industrial research. The instrument herein described is used to riiea\ure the rate of spreading of solutions of Netting agent5 on any plane surface. With it the relative spreading powers of different wetting agents may be compared by observing their action on a standard wrface. On the other hand, it is adapted to detailed qtudies to drtermine the effect of a variety of surfaceq on the performxti(*cof any single wetting agent. The tests are not limited to d i d iurfaws, but may be applied to liquid surfaces and (w1n to f e , \ t i l c - htrcltrhed on suitable flames. The effrrtq ot tempera-
)..
under comparison. The rate of spreading is shown to be a function of the nature of the surface on which spreading takes place. This is demonstrated by a comparison of the spreading behavior of typical anionic, cationic, and nonionic wetting agents on two types of surfaces. Surface active agents of similar ionic type have been found to exhibit characteristic spreading when they are compared on the same type of surface.
ture, pH, and concentration are easily studied. In the industrial laboratory the method should be of particular value in observing 1 he action of wetting agents on both natural and artificial soils.,
n
Figure 1.
Pipet
Essentially, this method consists of ejecting a measured volumc of solution a t a definite velocity onto a suitable surface, and making a series of photographs of the spreading liquid at short
