ANALYTICAL EDITION
90
Molybdenum can be precipitated as the sulfide and weighed as lead molybdate so that the percentages thus obtained are (0.02 x the percentage)], or in other accurate to * [0.02 words, if molybdenum is determined in this manner, the results obtained should not deviate from the theoretical result for any definite molybdenum content by more than the value obtained by means of this equation. This value is designated as the allowable error in the following discussion, and if the results obtained deviate from the theoretical by more than this calculated error, it must be assumed that either the analyst or the method is a t fault (1). If the proposed method is to be considered as accurate as the method to which the above equation is applicable, the maximum deviations of the percentages of molybdenum determined from the theoretical percentages in Table I must be equal to or less than the allowable errors as calculated by this equation. It is evident, however, if the results are ex-
+
Vol. 4, No. I
amined in this manner, that the maximum deviations for the higher percentages in this table are greater than the calculated allowable errors. Because of this fact, it must obviously be concluded that the proposed method cannot be used for a molybdenum content of more than 0.8 per cent, if it is considered necessary to determine this element as accurately as it can be determined by precipitating as the sulfide and weighing as lead molybdate. LITERATURE CITED (1) (2) (3) (4)
Am. SOC. Testing Materials, "Standards," Part 1, p. 377 (1930). King, IND.ENG.CHEM.,15, 350 (1923). Maag and MoCollam, Ibid., 17, 524 (1925).
U. S. Steel Corp., "Methods of Chemists of the lJ; S. Steel Corp. for Sampling and Analysis of Alloy Steels, 2nd ed., p. 72 (1921).
RECEIVEDJuly 16, 1931.
Determination of Total Sulfur in Gases E. LIEBERAND R. ROSEN,Standard Oil Detelopment Company, Linden, N. J . A N IMPROVED method for the determinaa boiling point of 92" to 93" C., HE use of gases containof gases is and thiophene (synthetic), Easting a minimum amount tion of the total sulfur Of organic is presented. A study of its reliability based upon Analysis man Kodak in this Co.,laboratory 83" to 85"ofC. a tial for the successful operation anab'sis of a series O f of a number of industrial procmixfures con- sample of sodiu'm c a r b o n a t e esses. In the development of taz'ning a number of types of sulfur compounds from Eimer and Amend labeled in concentrations found in refinery gases, and "special purified, sulfur free," methods for the removal of oralso covering a wide range of B. t. u. values, showed zero sulfur. ganic sulfur from gases it is preThe gases ethane, propane, requisite that a method be showed a mean error of 0.03 per cent, correspondand butane were available in able for the determination of pering t~ a mean centages of organic sulfur of the Of 2-4 per cent On a basis 3-pound cylinders. Samples of of the actual sulfur content of the gas. Anmagnitude of one grain per 100 these gases when burned by the alysis by two operators on similar equipment8 combustion apparatus described cubic f e e t , 0.008 per cent by volume. analyzing samples of the same gas agree within in this Paper showed zero Sulfur. Oxygen, n i t r o g e n , and The methods wed 1 per cent of the actual sulfur content. hydrogen were obtained from for official gas testing are those in which the gas is burned with An analysisy by the procedure described rethe Air R e d u c t i o n Company. quired from 1 to 100 liters of gas. Combustion oxygen or air, the resulting sulfur Samples of these gases burned may be completed in 1 to 4 hours, and the sulfur with hydrogen in the combusdioxide being converted to sulin the absorbent medium is determined granition apparatus also showed zero furic acid and the final product metrically as barium sulfate, sulfur. determined by gravimetric Or The various sulfur compounds volumetric means. Dennis (2) were diluted by means of a gives a bibliography including many of these and describes the three methods recommended specially purified benzene which showed 0.015 per cent sulfur by the Bureau of Standards (1)-i. e., the Referees, the Hin- by the lamp method (correction was applied for this sulfur man-Jenkins, and their modification of the Drehschmidt (5). in all determinations in which it was used). The Bureau of Standards (1) states that each has its parAPPARATUS ticular advantage and that it is not possible to combine all of these in any composite apparatus, nor is any of the The complete set-up for the proposed modified Drehthree superior to the other two for all purposes. Further, Schmidt apparatus is shown in Figure 1. It consists of the it is noteworthy that none of the authors has demonstrated flowmeters, etc., which are used for measuring the volumes the reliability of his method on the basis of the analysis of of the gases used in the combustion process; the combusgases of known sulfur content. tion apparatus, E , shown in detail in Figure 2, in which the The purpose of this paper is to present a method which, gases are burned; and the Milligan absorption bottles, L, in addition to its demonstrated accuracy, possesses a number which contain the absorption solution through which the of advantages over the standard methods in use in the in- products of combustion are bubbled. A is a 5 0 0 - ~ round~. dustry. bottom flask with stopper as shown, and B is an ordinary wash bottle whose inlet tube has been severed midway; MATERIALS USED these are expansion bulbs provided to even out fluctuations Carbon bisulfide, high grade c. P., showed no residue in pressure. The combustion apparatus (Figure 2) consists of the upon distillation and boiled within a narrow range (b. p. 46.0' to 46.2" C.). Ethyl sulfide, Eastman Kodak Co., had chamber in which the combustion takes place and the con-
T
January 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
denser, C, to condense the water vapor formed in the combustion and to cool the gases so as to render the absorption of the oxides of sulfur more efficient. The gas jet, T, is sealed into tube D with the relative positions of the tip of the jet and the primary oxygen inlet as shown in the diagram. The capillary tube and stopcock Sz permit fine control of the primary oxygen and thus give a steady flame which is essential to the successful operation of the apparatus. The ground-glass joints are interchangeable and require no stopcock grease. The gas mixture is ignited by means of a spark produced at the terminals of platinum leads, F , by means of an induction coil of the ordinary Ford type. The spark is turned off and on by means of a switch not shown in the diagram. The ground-glass joints on the Milligan bottles do not require stopcock grease; a film of water, obtained by wetting both members of the joint before closing the bottles for use, serves to maintain a tight joint. The mercury manometer (T, Figure 1) measures the pressure a t which the gas sample is introduced into the apparatus. The gases oxygen and nitrogen are supplied from the original pressure containers fitted with Hoke valves. The gas to be burned is run either directly from its source (if under pressure) and its pressure controlled by a needle valve, or from its container-e. g., a 20-liter bottle-by water displacement a t constant pressure. If hydrogen sulfide or other sulfur compounds soluble in water are present, it is necessary to determine these in another sample. The entire apparatus including the combustion tube (D, Figure 2 ) is constructed of Pyrex glass.
91
primary oxygen and adjustment of the supply of nitrogen. If the flame should be extinguished for any reason whatever when the spark is turned off, the flow of the combustible gas must be stopped immediately. The apparatus is flushed out with the oxygen-nitrogen mixture for about 2 minutes, the spark turned on, and the ignition started again in the manner described above. Xerious explosion may occur if this
simple precaution of JEushing out the apparatus is not followed.
When the flame is steady, it is only necessary to keep the gas flow constant and observe that the gas always burns with a Bunsen-like flame. When sufficient gas has been burned (from 1 to 100 liters), the combustion is stopped by first closing stopcock Sz and then shutting off the gas flow at the Hoke valve, Figure 1. The apparatus is flushed out with the oxygen-nitrogen mixture for about 2 minutes before shutting off this mixture.
OPERATIONOF APPARATUS The combustion apparatus is washed with distilled water by removing ground-glass stopper K and draining through outlet SB. Stopcock SIis kept closed during this washing and stopper K is replaced after drying. The absorption bottles are washed with distilled water and filled with 5 per cent sodium carbonate solution containing 2 per cent bromine. Stock solutions should be well stoppered to p r e g n t contamination with sulfur compounds from the atmosphere. The absorption train is connected in the manner shown in Figure 1, making sure that all glass connections are made butt to butt and that pure sulfur-free gum-rubber tubing is used for all connections. Water is circulated through condenser C. Stopcocks 8%and Xs are closed and SIis opened. Oxygen, 50 to 100 per cent in excess of the theoretical amount required for the combustion of the gas concerned, is allowed to flow through the apparatus at the rate of approximately 0.05 cubic foot per minute. Nitrogen is then admitted at the rate of about 0.02 cubic foot per minute. When the apparatus is flushed out with the oxygen-nitrogen mixture, the spark is turned on, and the gas to be burned is introduced into the apparatus at the rate of 0.005 to 0.01 cubic foot per minute by proper control of the Hoke valve. Ignition takes place in a few seconds without explosion or backfire, and the mixture is allowed to burn steadily for 15 seconds before the spark is turned off. At this point, the flame normally appears pale blue, topped and streaked with yellow. If the flame is entirely yellow and smoky, insufficient oxygen is being used and the volume should be increased with a proportionate increase in the volume of nitrogen. Primary oxygen is introduced by opening stopcock Xz gradually until the yellow portion of the flame disappears and the flame burns with a clearly defined inner and outer cone. Too much primary oxygen should not be used since it produces an unstable flame. This is recognized by its tendency to be sucked down into the tube (D, Figure 2), whereupon backfire may result. A steady purplish to blue Bunsen-like flame may always be obtained by proper regulation of the
FIGURE 1. APPARATUS ASSENBLED FOR DETERMINATION
The solutions in the Milligan bottles are transferred to a common container, and each piece is rinsed three times with 50-cc. portions of distilled water. The stopper K is removed from the combustion apparatus which has cooled down in the meantime and, with expansion bulb B (Figure 1) still attached, the combustion chamber is washed with 50-cc. portions of distilled water, allowing some of the water to run through the exit line into bulb B. This is repeated and finally the contents of B are run into the common container and then B is rinsed twice. The apparatus is now ready for another combustion. The collected washings, which average about 800 cc., are now analyzed for sulfur gravimetrically as barium sulfate. The weight of barium sulfate obtained is corrected by a blank which must be run on all reagents and distilled water. The sulfur in the gas is calculated by means of the following equation:
215 ___ fr 4-37.1
= grains
S per 100 cu. ft.
where
weight of barium sulfate in grams atmospheric temperature during analysis = volume of gas per minute from flowmeter rending = time in minutes required to burn gas P = barometric pressure S = pressure on gas as indicated by manometer T (Figure 1) IU
T p F
= =
DETERMINATION OF SULFUR AS BARIUM SULFATE To the collected washings, which consist of a solution of sodium carbonate and soluble sulfur compounds, 1 or 2 cc. of liquid bromine are added, and the liquid is concentrated upon a hot plate to about one-half of its original volume.
92
ANALYTICA L EDITION
1701.
4, No. 1
ORGANICSULFURGASEOUS COMBUSTIONS TABLEI. SYNTHETIC 29 30 Run 0.0411 Sulfur sought. crams 0.0988 0.0418 0,0966 Sulfur fouid, ' c a m s 152.0 63.3 Sulfur sought, grains 100 cu. it. 148.8 6f.i Sulfur found, grainsk00 cu. f t . 2.2 Deviation from sulfur sought, % 3.08 $:b8 Sulfur sought, % 3.01 3.12 Sulfur found, 0.04 0.07 Error % Type'of sulfur compound csz csz P M Diluent gas" 0 M, methane: E, ethane; P, propane; H, hydrogen: B, butane.
The alkaline hypobromite solution containing the completely oxidized sulfur compounds is now rendered acid with concentrated hydrochloric acid and evaporated to dryness, whereupon all bromine is liberated. Any silicon dioxide resulting from the action of alkali upon the glass beaker is thereby completely dehydrated. The residue, which is now free from excess hydrochloric acid, is cooled, taken up with 200 cc. of water, and filtered through a quantitative filter
42 0.0306 0.0310 47.1 47.7 1.3 1.05 1.06 0.01 (CzH6)zS M
44 0 0132 0.0139 20.3 21.4 5.4 1.05 1.11 0.06 (CzH5)zS P
46 0.0264 0.0255 40.6 39.2 3.4 0.93 0.90 0.03 C~HIS H
50 0.01.1 0.011 1.7 1.7 0.0 0.027 0.027 0.0 C~HIS E
52 0.0004 0.0004 0.6 0.6 0.0 0.027 0.027 0.0 CIHB €3
prcducts of combustion were determined gravimetrically as barium sulfate. The procedure consisted of making up stock benzene solutions of the organic sulfur compounds, carbon bisulfide, ethyl sulfide, and thiophene, in concentrations of 0.03 to 3 per cent of sulfur. Frcm 1 to 3 grams of the stock solutions were introduced in the breviously weighed empty bubbler container shown in Figure 3. The stopcocks were closed, and the exit tubes were blown dry by means of air and again weighed to ascertain the weight of sample in the container. The container was then connected a t points marked X X (Figure 1). A pure hydrocarbon gas or hydrogen was run from its reservoir, a 5-gallon bottle, by water displacement a t constant pressure and bubbled through the benzene-organic sulfur solution a t the rate of 0.015 cubic foot per minute until all of the liquid was evaporated and burned in the combustion apparatus with the necessary oxygen and nitrogen. Additional hydrocarbon gas or hydrogen was passed through for 5 minutes to clear the lines of the synthetic sulfur mixture. The results on a number of runs using the several sulfur compounds combusted are given in Table I.
DISCUSSION The method described in this paper permits the determination of total sulfur in the gas when the sample may be taken directly from its source under pressure. When it is necessary to displace the sample from its container by water displacement, any sulfur compounds present in the gas which are soluble in water-e. g., hydrogen sulfide-must be de-
FIGURE 2. DETAILS OF COMBUSTION APPARATUS
s?/
I
J
1
paper to remove the silicon.dioxide. The filtrate is diluted with water to about 250 cc., just acidified with hydrochloric acid, using methyl orange to indicate the acidity, and brought to boiling. At this time 25 cc. of a filtered 10 per cent barium chloride solution are added drop by drop and the whole volume stirred vigorously. The liquid containing the barium sulfate is again returned to the hot plate and brought to the boiling point. Finally, it is allowed to remain on the hot plate at gentle heat for 12 hours. If the amount of barium sulfate present is less than 4 mg., it is advisable to use a micro Gooch crucible and a microbalance in determining the amount present. The barium sulfate is filtered through the prepared Gooch crucible, washed, dried in the oven, ignited, and weighed.
EXPERIMENTAL PROCEDURE AND RESULTS I n determining the reliability of the proposed apparatus using the procedure described below, a number of synthetic gaseous mixtures containing known percentages of organic sulfur were burned in the apparatus, and the sulfur in the
HYDROCARBON
COMBU5TION TRAIN
SOLLlTlON OF SUVlJR COMPWND IN BENZENE
USEDIN PREPARATION OF FIGURE3. BUBBLER SYNTHETIC MIXTURES
termined first by methods which are quite well standardized. Since, however, where small quantities of total sulfur are concerned, hydrogen sulfide is either absent or has been removed from the original gas, this is seldom necessary. I n the investigation of the applicability of this method, the compounds thiophene, ethyl sulfide, and carbon bisulfide were chosen as representative of those sulfur compounds which may occur in refinery gases and also as compounds representing various degrees of stability. From a summary of the data in Table 11, it is apparent that the mean error by the proposed method is only 0.03 per cent and the mean deviation from the sulfur sought is 2.4 per cent.
January 15, 1932
.INDUSTRIAL AND ENGINEERING CHEMISTRY
The reproducibility of results by the proposed method is illustrated by the following tabulation, obtained by two different operators burning the same type of gas a t approximately the same rate on two similar equipments: hPARATUB
A B
SULFURFOUND 9 . 7 graina/100 cu. it. 9.6 grains/100 cu. ft.
In the case of most of the synthetic mixtures, a hydrocarbon was used as the diluent for the sulfur compound. To demonstrate that the method is applicable to gases of low B. t. u. value, several synthetic samples were burned using hydrogen as the diluent. It is apparent from Table I that equal reliability was obtained for the range of B. t. u. value of the gases investigated. TABLE11. SUMMARY OF ACCURACY DATA CARBON ETHYL THIO-
Substanoe burned D I s U L P I D E SULFIDE PHENE MEAN’ 2 2 3 7 Number of runs 0 03 0.05 0.06 Maximum error, % 0.07 0.00 0.01 0.04 0.01 Minimum error, % 5.4 3.4 3 9 Maximum deviation, % 2.2 1.7 1 3 00 09 Minimum deviation, % 0 04 0 02 0.03 Mean error % 0.06 Mean deviitition, % 2.0 3 4 17 2 4 0 Baaed upon t h e aeighted average of the three previous columna.
Analysis of sulfur by the method described requires from 1 to 100 liters of gas. Combustion may be completed in 1 to 4 hours, and the sulfur in the absorbent medium is de-
termined gravimetrically as barium sulfate. The improvements which the proposed method offers over the previously suggested modifications of the original Drehschmidt method ( 3 ) , in particular that of the Bureau of Standards, may be enumerated as follows: 1. Demonstrated accuracy and reliability on the basis of the analysis of gases of known organic sulfur content.
93
2. Elimination of rubber and cork stoppers, wax, and de Khotinsky cement by the use of all Pyrex-glass construction with ground-glass joints, stoppers, and stopcocks. 3. Addition of a condenser to cool the products of combustion, thereby increasing the efficiency of their absorption by the absorption solution. 4. Use of platinum-to-glass sealed leads for the spark gap, instead of copper- or nickel-platinum leads, eliminating the reaction of the sulfur dioxide with the copper or nickel. 5. Use of a spherical combustion chamber to prevent impingement of the flame and subsequent collapse of the glass walls. 6. Entering of gases into the apparatus at pressures above atmospheric and thus eliminating suction required in other methods. 7. Use of pure oxygen and nitrogen instead of air for the combustion, thus eliminating possible contamination of gas burned with sulfur that may be present in the air. 8. Elimination of dangers due t o explosions. 9. Adaptability of the method to gases over a considerable range of B. t. u. value. 10. Use of burner constructed of Pyrex sealed directly to and being a part of the combustion chamber, thereby eliminating quartz or porcelain. Since the latter required rubber seals, this source of contamination is obviated. The Pyrex burning tube has shown no tendency to melt and close up after being in use for several months. In fact, a crystalline ring of silicon dioxide forms at the tip and is heat-resistant.
In the procedure described, the sulfur is determined gravimetrically as barium sulfate. When the sulfur content of gas is high, the sulfur may be determined with sufficient accuracy by iodine titration of the collected washings or by means of a turbidimeter. These methods, however, have not been found satisfactory when the sulfur content of the gas is less than 2 and 3 grains per 100 cubic feet.
LITERATURE CITED Standards, Circ. 48, 129 (1910). (2) Dennis and Nichols, “Gas Analysis,” p. 351. Maomillan, 1929. (3) Drehschmidt, Chem-Ztg., 11, 1382 (1887), (1) Bur.
RECEIVED August 26, 1931.
A Bicycle-Chain Stirrer S. B. LIPPIKCOTT, Purdue University, Lafayette Ind.‘ STIRRER has been devised which will lie close to the wall of a flask and when turned will scrape the wall clean. It is made from a short piece of ordinary bicycle chain. A hole is drilled through the middle link and an iron rod is chosen which just fits into the link. A hole similar to the one in the link is drilled through the rod near one end. The chain is fastened to the rod with a small pin in such a way that it can be inserted into the flask so that the smooth side of the chain lies against the glass. The rod may be passed through a mercury seal if so desired. The advantages of such a stirrer are: (1) that it can be inserted and removed from the flask very easily; (2) that it fits perfectly the wall of the flask whether with round or flat bottom; (3) that it can be used (within limits) in different sized flasks without varying the length of the chain, since in small flasks the extra links simply double back; and (4) that it functions smoothly even though the rod is out of line with respect t o the axis of the flask. It is recommended for use in any case where it is desired to keep a solid worked free from the wall of a flask and an
L
ordinary stirrer fails to do so. Of course, it cannot be used in cases where iron will interf e r e w i t h the d e s i r e d reaction. The author has used it successfully in a vaporphase reaction between magn e s i u m and chlorobenzene in the absence of a solvent. RECEIVED October
1 Present
address. University of New Mexioo, .4lbuquerque, N. M.
23, 1931.
A BICYCLE-CHAIN STIRRER
