ANALYTICAL CHEMISTRY
154
ACCURACY 4ND PRECIS103
Table \-, Analysis of Used Lubricating Oils Sample S o . 1 2 3
Element Fe
5
Pb Fe cu
Fe Pb
Sn
.4nalysis, P.P.M. Chemical Spectrographic 145 140 175 155 3.9 4.2 3.9 3.9
Precision of & l o % is generally obtained by this method. Typical results are shown in Table IV. Table V shows results obtained by both chemical and spectrographic analysis of six samples of used lubricating oils. It is expected that the same general procedure will be applicable to the analysis of oils, crude or processed, for trace quantities of other metals. ACKNOWLEDGMENT
27
12 0.5
34 13 0.6
6
The authors wish to express their appreciation to Harry Levin, L. L. Gent, and C. P. Miller for their assistance and suggestions during the development of this method and the preparation of the paper, and to Norma Bovino who prepared the manuscript. LITERA’TURE CITED
and may be used for photometry. Background density ie low and requires no correction. Obtain the per cent transmittance values of the spectral lines shown in Table 111 by means of a microphotometer. Calculate intensity ratios of the element lines, using the intensity of the Xi 2821.29 A. line as the internal standard. From the analytical curves, discussed under “Reagents and Calibration Standards,’, obtain the concentration of the trace elements directly in parts per million. Exposure of three spectrograms per sample and averaging intensity ratios are recommended where better precision is desired. However, reproducibility is generally good, and one G r two exposures per sample will provide adequate precision where time and sample load are factors.
(1) Calkins, L. E., and White, M. If,,A’atl. Petroleum S e u s , 38, R519 (1946). (2) Cassidy, W.A , , Mech. Eng., 72, S o . 10, 854 (1950). (3) Gambrill, C. M., Gassmann, A. G., and O’Nedl, W. R., A R ~ L . CKEM.,23,1365 (1951). (4) Gassmann, A. G., and O’Keill, W. R., Ibid., 21, 417 (1949). (5) Harvey, C. E., “Method of Semiquantitative Spectrographic Analysis,” Glendale, Calif., Applied Research Laboratories, 1947. (6) &Brian. R.. J . Pacific Ru.Club. 32. S o . 2. 6-12 (1948). (7) McBrian, R., and -itchison, L. C.,’S.A.E. Journal, 58, S o . 7, 19-21 (1950). (8) Pagliassotti, J. P., and Porsche, F. W,, ANAL.CHEM.,23, 1820 (1951). (9) Sennstrom, H. R., Ry. Mech. Elec. Eng., 126, Issue 4, 65 (1952). RECEIYED for review May 21, 1952. .4ccepted October 2, 1952.
Analysis of Sulfuric Acid Contact Plant Exit Gas Critical Review of Analytical Methods f o r Acid Mist and Sulfur Dioxide JOSEPH B. LOMBARD0 American Cyanamid Co., Calco Chemical Division, Bound Brook, S.J .
A
PRilCTIC.4L analytical method for the determination of SUI: furic acidmist and sulfur dioxide in sulfuric acidcontactplant exit gas M-asdeveloped after a comprehensive search of the literature disclosed the absence of such a method, which is essential for the proper control of the process and evaluation of air pollution. Its application has contributed materially to the intelligent control of a modern sulfuric acid contact plant.
REVIEW OF ANALYTICAL METHODS SULFURIC ACID MIST
The entire list of analytical methods for mist can be divided into two classes. Those of the first class separate and retain the mist, which is subsequently estimated by any of several methods. The other class depends upon various modifications of the Tyndall effect for a measure of mist concentration. Separation. FILTRATION. Cotton was employed by Alekseeva and Andronov (%),Gille (34), and Rabovskii and Shaposhnikova (69) both as a cotton fiber plugandimpregnatedinvarioussolutions. However, the use of cotton was criticized by Schmidt (86). Alekeeeva and Andronov ( 2 ) also combined cotton with either filter paper or alignin. Asbestos as an absorbent has found very extensive use. Weber studied its possibilities (110) and its use has been popularized, particularly by inclusion in two widely distributed industrial publications (12, 79). The inconvenience with asbestos absorption lies in the preparation of the asbestos
plug and the eventual washing of the acid from the asbestos. Goodeve (40) discusses in a general way the use of glass filters, while Flint (%8) directly uscs sintered glass as a filter for sulfuric acid mist in a power house flue gas installation. .41undum as a filtering agent is discussed by Weber (110) and was studied by Taylor and Johnstone (98). Although filter paper for filtration was tried by Weber ( I I O ) , its use has not been popular until very recently and then only for the determination of mist in air by Mader and others (56, 5 7 ) . Glass wool, rock wool, and other synthetic fibers have been found to be very efficient filters (9). ABSORPTION.The absorption of sulfuric acid mist in water or aqueous solutions has attracted considerable attention. Johnstone (47)proposed breaking up the large bubbles by means of sintered-glass porous membranes and thereby bringing about rapid absorption of the acid mist in water. Friedrich (31) investigated the effect of various types of laboratory gas washing bottles to determine the most efficient type for absorption. He found the screw type gave best results, especially when ground glass of the size of coarse sand was added to the bottles. Adadurov and Gernet ( I ) found that if the “fog” is allowed to re main in contact with steam for 3 to 6 seconds, reaction takes place and 99% of the sulfur trioxide is recovered. Remy and Vick ( 7 8 ) also investigated different types of gas washing bottles and, a t the same time, the use of alcohol and gelatin in the water to effect better absorption. They found that, whereas the type
V O L U M E 25, NO. 1, J A N U A R Y 1 9 5 3
A critical review of the literature of the analysis of sulfuric acid contact plant exit gas for the two important constituents-sulfuric acid mist and sulfur dioxide-disclosed the lack of a practical analytical method. Such a method is essential for the proper control of the process and for evaluation of air pollution. Sulfuric acid mist in the range of 0.1 to 10 mg. of sulfuric acid per cubic foot is determined by filtering the particles on a specially designed sinteredglass unit; sulfur dioxide in the range of 1 to 100 mg.
of wash bottle slightly affects the efficiency of absorption, the use of fritted glass to introduce the gas into the absorbing solution is the predominating factor, while the presence of ingredients in the water, such as alcohol and gelatin, had practically no effect on absorption. Kraus ( 5 2 ) effected absorption of sulfur dioxide and “SOS” in a gas stream by saturating with boiling water (steam) and then directing through a cooling zone. Complete precipitation of the mist was obtained, while the remaining gas oontained all of the sulfur dioxide. Coste and Courtier ( 1 6 ) combined sulfuric acid mist and a a t e r in the vapor phase and condensed it by passing through a cooled chamber. Gillham (35) found that he could get quantitative absorption in water by means of a sinteredglass disperser and used that principle in developing an elaborate automatic device for determination of “sulfur trioxide” in flue gas ( 3 6 ) . Greenwood ( 4 2 ) depended on a time factor to effect absorption of mist in water containing hydrogen peroxide He made no attempt to break donn the bubble size of the mist, but merely introduced the sample through a glass tube underneath the surface of the liquid. Although they make no mention of sulfuric acid mist, Fox and Groves (29) use a method for determination of total sulfur acids in which the sample is absorbed in dilute hydrogen peroxide without any particular precautions about absorption. The effect of bubble size and rate of flow of mist on absorption is covered by Remy and Seemann ( 7 7 ) . The iinthony Venturi scrubber has been adapted to an analytical procedure in studies of the smog problem (59,94). Quantitative absorption of mist in aqueous alkali has been used with varying success by Axford and Sugden ( I O ) , Dieckmann (21), Johnstone (43,and Sander (83). Theoretical absorption studies were made by Remy and Behre ( 7 4 ) and Remy and Holthusen (76). Remy ( 7 3 ) cited the difficulties in absorbing acid mist in aqueous solution. Alekseeva and Andronov ( 2 ) devised a bubbling column resembling a Meyer absorber which, under controlled flow conditions, gave complete absorption of the mist in 0.02 N alkali. ELECTROSTATIC PRECIPITATION. Tolman andothers (104)in 1919 described an apparatus based on the Cottrell precipitator principle intended for analyzing “any smoke independent of its chemical nature.” No results are given, and hence no appraisal of the apparatus can be made. Drinker and others (25) used electrostatic precipitation for the determination of mist in air. This seems adaptable to routine analyses. Weber (110) and Artamonov ( 6 ) give details for construction of a miniature Cottrell-type precipitator with which they obtained very successful results. Patrick ( 6 6 ) and Schmidt ( 8 7 ) developed electrostatic precipitators intended for dust collection, but give some very valuable details on fabrication and theory of electrostatic precipitation apparatus. Gitzen (38) combined microscopic techniques with electrostatic deposition in connection with dust and fumes. Schadt and others ( 8 4 ) used an electrostatic precipitator for determining sulfuric acid mist in the atmosphere. The effect of sulfur dioxide was studied, and continuous washing with a stream of water was used to extract the precipitated acid. Recently, plastics have been suggested as electrostatic attractors
155
of sulfur dioxide per cubic foot is found by oxidation by, and absorption in, hydrogen peroxide and subsequent titration with sodium hydroxide. The application of the proposed method has contributed materially to the intelligent control of a modern sulfuric acid contact plant. The literature survey, the most comprehensive to be found anywhere pertaining to this subject, is of particular benefit to research and development workers in the sulfiiric acid industry or in the field of industrial hygiene.
of charged particles ( I S ) . This seems to be an ingenious way of separating acid mist in an apparatus similar to the conventional precipitator without the necessity of using an external electric source. I n the commercial field a device is on the market ( 6 2 ) which, although not particularly developed for sulfuric. acid mist, has been used for that purpose, apparently very successfully. SONIC AGQLOMERATIOK. I n recent years, the use of sound TTaves has been suggested as the source of energy to agglomerate and precipitate mist particles. The application of sonic principles to sulfuric acid plant installations is covered by Danser ( 1 9 ) , and theoretical considerations are given by St. Clair (82). Gucker (4.3) applies sonic waves t o analytical methods in his determination of concentration and size of particles. ~ ~ D S O R F T I O N . With such filter media as paper, cotton, asbestos, and Alundum, no doubt a large portion of the particles is retained by means of adsorption. As mentioned by Mader (&?), for example, filter paper \Tith a pore size of 2 to 5 microns can be used to trap 1-micron mist partirles. However, certain materials have been found to be highly adsorptive for sulfuric acid mist to the extent that adsorption is the largest factor in the retention. Such a study was conducted by Remy and Finnern (15) and Remy (73) using calcium Phloride, pumice stone, and activatrd charcoal as adsorbents. IMPIXGEMEST. Impingrnicnt techniques depend upon the projection of particulates on a surface, usually of such materials as wax, jelly, or plastic. The embedded particles can then be examined microscopically for final evaluation. These methods are discussed by Goodeve (40),Crozier and Seeley ( 1 8 ) , and Ranz and Wong (70). Such techniques have only limited application for control of stack gases in sulfuric acid plants. Their main virtue lies in the occasional particular invrstigation, for which specially trainrd personnel are available. A detailed discussion of the Sonkin impactor can be found in a report by the Stanford Research Institute ( 9 3 ) . Johnstone ( 4 8 ) described the theory and design of an impactor in detail, based on work by May (60). A portable motor-driven midget impinger apparatus is described by JaTvorski and Lavetter ( 4 6 ) . Convenient, hand-operated midget impingers are available commercially (69). Estimation. PRODUCT O F SEPARATION. The most common method of estimation is the acidimetric titration of the product of separation. Tvpical of these methods are those recommended by Gillham (35) and RabovskiI and Shaposhnikova (69). Industrially, the Chemical Construction Corp ( l a ) and Researrh Corp. (79) use the acidimetric titration for thP estimation of arid which has been collected on asbestos fiber. I n home methods, such as those described by Dieckmann ( 2 1 ) and Sander (831,the acidimetric titration for sulfuric acid mist is combined, with the necessary modifications, with the determination of sulfur dioxide. In the exceptional case, to prevent interferences the collectrd sample is sometimes estimated by means of a more specific test. Such a modification is preferred by Johnstone ( 4 7 ) , Tho precipitates the sulfates as benzidine sulfate, and Gillham ( S i ) and Flint (28), who precipitdtr the collected acid as barium sulfatr. The determination of sulfuiic. arid mist by means of a turhidity
ANALYTICAL CHEMISTRY
156 reading upon precipitation with barium chloride is recommended by Coste and Courtier (16). This method is very applicable when interfering acids are present in the gas stream and is rapid and fairly precise. Corbett (15)describes a very practical device for a photoelectric procedure. Osherovich and Rabovskii ( 6 4 ) report a similar method for determining sulfur dioxide, which could be easily modified for use in the determination of mist. Conductometric analysis is particularly useful for continuous measurement and recording if necessary. Such an apparatus is described by Greenwood (42) and by Gillham (36). Coste and Courtier ( 1 6 ) use p H as a means of evaluating sulfuric acid mist in their condensation studies. Axford and Sugden (10) titrated the sulfate resulting from sulfuric acid mist amperometrically by means of lead nitrate. This is rather specific, rapid, and presumably, with certain modifications and elaborations, could be converted to an automatic determination. The use of the microscope in identifying and estimating sulfuric acid mist is related to the method of separation by impingement, Such combination of techniques is described by Drinker (85) in connection with testing atmospheric contamination, Gitzen ( 3 8 ) who worked particularly with dust and fumes, and Crozier and Seeley ( 1 8 ) who also worked with air contaminants. Illicrosropy was suggested in connection with the Sonkin impactor (93). TYSDALLOMETRIC DETERMINATION. I n industrial installations, the most common form of equipment for visual estimation of mist is a simple steel tubular cell capped a t each end with glass disks. It is not surprising to find difficulty with a crude device of this sort. Scott ( 8 8 ) found that the angle which the light makes with the longitudinal axis of the cell has an important bearing in accentuating the Tyndall effect. He devised apparatus which not only took care of the angle of light but was able to give the method some degree of quantitative objectivity. Fairlie ( 6 6 ) gives directions for the construction of a practical type of Tyndall apparatus. Although this is somewhat crude, it seems suitable for industrial installations. According to some investigators, the Tyndall beam effect is so sensitive that Weber (110), Drinker and others (85), Goodeve (40),and blader and others ( 5 6 ) used it as a measure of efficiency in methods which they aere developing. Work done by Fuks and Oshman ( 3 6 ) indicated that the Tyndall beam effect disappears when maximum concentration of mist of 109 drops per cubic centimeter is reached. On the other hand, Goodeve (40) is of the opinion that filtration n-ill separate particles even when mist concentration is so low that no Tyndall beam is present. He bases this opinion on the fact that not only does the filtration depend on retention of particles which are larger than the porosity of the filter, but also because of Brownian movement much smaller particles than the porosity of the filter are retained. Gucker (43) and LaMer ( 5 3 ) discussed some new theories and apparatus for estimating dispersed systems, such as sulfuric acid mist. LaMer particularly recommends an instrument type of installation with which automatic and continuous determinations can be made. Amelin and Mickhal'chuk ( 4 ) described a method for the determination of moisture n-hereby they introduced sulfur trioxide to form sulfuric acid mist and then determined that mist photoelectrometrically. Presumably such a device can be used for determination of mist itself. Similar commercially available photometers are easily adaptable to the determination of mist in a flowing gas stream. Gucker (43) described a highly complicated electronic device for particle counting. Bn interesting but hardly applicable apparatus is reported by the Stanford Research Institute (93, page 33). 4 transmissometer is described whereby by means of reflecting mirrors light can be passed through a 40-foot column of air one or more times. An adaptable photoelectric turbidimeter is described by Atherton ( 7 ) . The calibration of a mist meter is covered by Meissner and Mickley (61). A device (14) is commercially available particularly intended for smoke measurements of power house flues. However, with slight modifications
there is no reason why it should not be made to function for the detection of mist and for installation within sulfuric acid stacks, The device is not only an indicator but can be simply and quickly converted to a means of automatic recording. Stone and others ( 9 5 ) describe a photoelectric device for determining low concentrations of dust, which seems to be easily converted to a mist meter. Practical laboratory-type tyndallometers with some theoretical considerations are covered by Tolman and others (105,106). SULFUR DIOXIDE
The most commonly used procedure for sulfur dioxide determination is the iodine oxidation method, n i t h the reagent serving simultaneously as an absorption medium. I n accomplishing this, workers have used various means, all based on work originally done by Reich (7Z). MeKay and Ackerman (55) used starch iodide-iodine solution whose color is evaluated by comparison with a blank. The Chemical Construction Corp. (18) and Research Corp. ( 7 9 ) recommend iodine absorption and oxidation. Dragt and Greenan ( 2 4 ) investigated the Reich test as applied to sulfuric arid burner gas. Some pertinent notes are contributed by Plotnikov and PeEar (67, 6 8 ) on the stability of iodine solutions. Schmidt ( 8 5 ) reviewed the earlier methods and favored iodine absorption. Thomas and Cross (108) made a study of iodine absorption, from the standpoint of both iodine stability and absorption efficiency. They found that even 0.0011 N iodine solution was much too strong and hence too unstable when large volumes of sample nere to be used. T o achieve excellent efficiency it was necessary to reduce the iodine concentration to less than 0.0001 N. More recently, Thomas (100) found that the stability of iodine solutions depends not only upon the potassium iodide content, but also upon the presence and amount of starch indicator. By increasing the starch content of an absorber, the concentration of iodine can be increased tenfold with no greater loss of stability. Khere cost of reagent is not important, Thomas also suggests the use of very strong potassium iodide solution, in the order of 40%, as excellent stabilizer for iodine, even without the presence of starch. Sweeney and others ( 9 7 ) preferred to absorb and oxidize sulfur dioxide in dilute permanganate solution. From the standpoint of vapor pressure effect no doubt permanganate has an advantage over iodine solution. In so far as over-all stability is concerned, its superiority may be questionable in spite of the indicated preference by the vorkers just cited. When nitrogen oxide gases were present in the gas stream, Raschig ( 7 1 ) introduced a modification to prevent their interference. Absorption of sulfur dioxide in aqueous solutions, either water or alkali, has involved considerable controversy centering particularly on the stability of the resulting solutions. Haller (44) investigated and Axford and Sugden (10) recommended glycerol as an antioxidant, while Ries and Clark ( 8 0 ) found glycerol gave erratic results and recommended stannous chloride instead. Dieckmann (20) and Ferguson ( 2 7 ) insisted that inhibitors were not essential; in contradiction, Berl (11 ) found stannous chloride an ides1 inhibitor and Johnstone ( 4 7 ) favored the use of benzyl alcohol, while Flint ( 2 8 ) discusses the advantages of isopropyl alcohol based on work by -4lyea and Backstrom ( 3 ) . I n the treatment following absorption in alkali, conductivity was studied by Saillard and Bregmann ( 8 1 ) . Scidimetric titrations were investigated by Dieckmann (81), Haller (44),and Sander ( 8 3 ) . I n addition, Sander introduced a modification involving the use of mercuric chloride with the formation of hydrochloric acid: NaHSOa
+ HgClt
-c
HgC1.NaSOa
+ HCI
followed by a titration of the liberated hydrochloric acid. Rabovskir and Shaposhnikova ( 6 9 ) absorbed mist and sulfur dioxide
157
V O L U M E 25, N O . 1, J A N U A R Y 1 9 5 3 in neutral p-aminophenol and titrated the absorbed acid with sodium hydroxide. At the end point, hydrogen peroxide was added to convert sodium bisulfite to sodium bisulfate, and the titration m s continued to an end point. The use of hydrogen peroxide for simultaneous oxidation and absorption of sulfur dioxide is highly favored by Coste and Courtier ( 1 6 ) , Francis and others (SO), Thomas and Abersold ( f O f ) , Greenaood (@), and Gillham (36). hleasurements of the resulting solutions ai e amenable to diverse and simple treatments, particularly instrumental evaluation. Fox and Groves (29) used the oxidized absorbed solution to determine its p H with a continuous automatic and recording apparatus. Inasmuch as they madr no attempt to separate mist previous to this treatment, thr final results are in terms of total acidity. Osherovich and Rahovskii ( 6 4 ) evaluated the resulting sulfuric acid turbidimetricallv. Conductivity n-as used by Francis and others (SO), Greenv ood ( 4 2 ) , and Thomas and Abersold (1Of ). 4tkin (8),Grant ( d f ) , and Kozlyaeva (61) described colorimetric methods for sulfur dioxide based on the fuchsine reduction. Gandolfo (33) reported a colorimetric method using zinc nitroprusside as reagent. Vrone and Boggs (108) have applied spectrophotometry to this type of determination. The particular value of these methods lies in their availability as independent, chemicallx- unrelated, check procedures.
TO
UPPER
PEROXIDE
ABSORBER
CHAMBER
Mechanical problems of sampling stack gases have been grossly neglected. For example, Tygon tubing has been found to be a boon in all work with these acid gases. The choice of a pump has not been very perplexing, since the pump usually follows the absorption train and the gas sample has been freed of the acid constituent. On certain occasions, however, it may become necessary to have gas samples pumped into the absorption train. Under such conditions, a pump as described by Glenn and Hackerman (39) will be found very appropriate. I n the course of sampling, problems of location are the most serious ones encountered. Taking a wet-test gas meter to a precarious location is not feasible. -4lthough Smith and Friis (91) describe a portable battery-operated pump unit, that also is impractical to perch atop an exit stack. Portable hand crank-type air samplers are commercially available (63). Presumably, the pump described by Glenn and Hackerman (39) can be converted to a manually operated type by replacing the pulley x i t h a hand crank. The Fletcher bellows are commonly used, particularly in England, as a mrans of stack gas sampling. Windmill-operated pumps have been used very successfully ( 5 )and seem to have a practical application either for large area studies or localized installation adjacent to an exit stack. Gisclard ( 3 7 ) has employed a glass syringe as an aspirator. This sampling technique was particularly developed in conjunction with a microchemical method for acid mist and sulfur dioxide. When large-particle interfering bodies are present, a prefilter, such as suggested by Flint ( 2 8 ) or Stratton and others (96‘)) may be in order. GENERAL AND THEORETICAL CONSIDERATIONS
I
I
M I S T ABSORBER
In a series of papers, Remy and others (73-78) discussed different aspectsof sulfuric acid mist absorption. Fuks and Oshman (32) cover theoretical considerations of mist behavior. Dooley and Goodeve ( 2 3 )give a review of the various theories relative to mist formation and reaction. Parkes ( 6 5 ) discusses the nature of exit gases. Cralley ( 1 7 ) gives a general treatment of the subject and reviews a system of arbitrary definitions. Some excellent reviem and symposia have been published (45,673,58, 107).
SCALE-FULL SIZE FROM S A M P L I N G
TUBE
FIG I -
PRACTICAL PLANT CONTROL METHOD FOR ACID MIST AND SULFUR DIOXIDE
GAS SAMPLING AKD SAMPLING EQUIPMENT
The use of a sintered-glass disk for retention of acid mist and the oxidation of sulfur dioxide by, and absorption in, hydrogen peroxide is the basis of the following practical and simple method for the determination of those two constituents in contact plant exit gas. Procedure. SAMPLIXG.The salient points of samplingnamely, that the gas stream linear flow within the flue must be the same as that within the analytical apparatus and that the analytical apparatus be as close to the main stream as possiblemust be given due consideration. The gas stream from which samples were taken for this work had been scrubbed by an aqueous terminal tower after leaving the conventional absorption towers of a Chemic0 sulfuric acid contact plant. The sample is, therefore, saturated with water vapor a t a temperature of about 35’ C.
Details specific for sampling stack gasesare given by the Research Corp. (?9)and the Chemical Construction Corp. (12). I n addition, Silverman (90)discusses general problems of atmosphere sampling; Smith and Friis (91) describe a portable pump unit. Thomas and Abersold (101), Thomas (99), and Greenwood ( 4 2 ) also mention briefly apparatus or techniques for sampling. Problems of atmosphere sampling are covered in “The Smog Problem in Los Angeles County” (92). Donoso ( 2 2 ) and Velten (109) describe devices which automatically divide the gas stream into two predetermined constant proportions. Theoretical sampling problems are treated by LaMer (53)in some detail.
~ P P A R A T U ~ .The sampling tube consists of a piece of straight heavy-walled glass tubing, long enough to reach from the center of the main flue to as close as possible to the inlet side of the apparatus (mist absorber). Its diameter is calculated so that linear flow in the tube is equal to the linear flow within the main stack. The mist absorber shown in Figure 1 is fabricated from a 30mm. borosilicate sintered-glass tube. A medium porosity (such as Corning M) filter tube is selected so that when air is passed through it a t room temperature and under 740-mm. pressure, a flow of 3.3 0.2 cubic feet per hour is obtained. The peroxide absorber for sulfur dioxide (Figure 2) is a conventional gas washing bottle of 250-ml. capacity fitted with a coarse sintered-glass disperser whose porosity is not critical.
Coste and Courtier ( 1 6 ) investigated the oxidation of sulfur dioxide in the gaseous state to form acid mist. This suggests the possibility that this principle could be developed further into a tyndallometric method for sulfur dioxide evaluations. Industrial installations of automatic sulfur dioxide analyzers are commercially available (54). Laboratory-type installations are described by Fox and Groves (29), Thomas (99), Thomas and others ( f O S ) , Francis (SO), Greenwood (42), Katz (49), and Shaffer and others (89).
*
158
ANALYTICAL CHEMISTRY
The inlet to the b l o leg ~ is fitted with a standard-tapered 24/40 joint. The meter is a standard wet-test gas meter. The suction pump is a Vernon rotary-type pum Scientific Glass Apparatus Co., Catalog No. 17540, p:wered a l/ghp. motor. The inlet side of the pump while being connected t o the meter is fitted with a glass T air bleed and stopcock for the adjustment of flow. Tygon tubing connects all glassware except connections made through ground lass joints. REAGENTS. zydrogen peroxide solution is prepared directly in the peroxide absorber. T o 150 ml. of distilled water, 5 ml. of Superoxol (30% hydrogen peroxide) is added followed by 4 drops of methyl red indicator. If necessary, 0.1 A' sodium hydroxide is used to adjust the color of the solution to a golden amber. Xeutral distilled water is prepared by adding 10 drops of methyl red indicator solution t o about 300 ml. of water and adjusting its color to a golden amber. The titrant for both the mist absorber contents and the peroxide absorber acidity is 0.1 S sodium hydroxide.
C A P I L L A R Y TU0E I N T O STACK
n
,TIGON
TUBING
w
Table 11.
Efficiencj of 3list Absorber 0.1 S Sodium Hydroxide Consunled, 311. B y mist
Detn.
absorber plus sampling tube
NO.
1
7.3 9.1 .5. 1 1.85 0.73 1.45 0.25 4.7 2.4 2. I 0.1 0.3
2 3 4 5 6 7 8 9 10 11 12
By asbestos "after" filter 0.00 0.00 0.10
