Small Amounts of Sulfur Dioxide in the Atmosphere I. Improved Method for Determination of Sulfur Dioxide When Present in Low Concentration in Air S. W. GRIFFINAND W. W. SKINNER Bureau of Chemistry and Soils, Department of Agriculture, Washington, D. C. Attention is directed to the significance in the air under field conditions such as are usually enof small amounts of sulfur dioxide, having its countered in rural areas. source in combustion or in smelting operations. Old A compact field testing outfit is described which is methods for the determination of sulfur dioxide light and portable, and it is possible with this apin air are reviewed. paratus to make a great many individual sulfur The authors have developed a n improved iodine dioxide tests in the course of a single field trip. method for the determination of very small amounts The improved iodine method, for the determinaof sulfur dioxide in the atmosphere. Under usual tion of small amounts of sulfur dioxide in air, was j e l d conditions the method is chemically delicate employed as a method of control in sulfur dioxide to 0.02 part of sulfur dioxide per 1,000,000 parts fumigaling tests on plants. This is the first of three papers dealing with the of air. The employment of a tower or tube of soda lime in connection with the tests makes it possible industrial aspect of sulfur dioxide fumes from smeltto obtain accurate blanks or control tests as often as ing and other operations in relation to agriculture, desired. The specificity of the test is satisfactory forestry, cattle raising, etc.
ULFUR dioxideladen smoke has been a subject of
S
discussion and controversy for many years and, in urban and industrial communities, certain of its injurious effects were recognized long before it was identified and isolated chemically. It is well known that most field, forest, and garden crops do not thrive in an atmosphere contaminated with sulfur dioxide gas, and it would be trite to enter into a description of the corrosive action of this gas in moist air on metals, calcareous building stone, mortar, cements, paint films, textiles, and leather. That the sulfur dioxide question has hygienic and physiological aspects is indicated by the poison fog disaster which occurred in the Meuse Valley in Belgium in January, 1931. Notwithstanding the more or less general appreciation of the importance of sulfur dioxide in respect to the question of atmospheric pollution, it is only in recent years that a growing realization of the significance of the presence of minute quantities of this gas in the air has given impetus to a study of improved methods in its determination. It was inevitable that this impetus should also extend to a study of the effects of these very low concentrations of sulfur dioxide, particularly on vegetation.
PREVIOUS HISTORY AND LITERATURE England’s history records that the smoke and fume question has been one of concern to its citizens for centuries, and continental Europe has, for nearly a hundred years, been engaged in a determined effort to free itself from the pall of * smoke and fume which has hung over and about its industrial centers. The Saxon Government, in the year 1848, initiated an investigation looking to a study of the harmful gases and fumes containing sulfur dioxide and trioxide emitted by foundries and smelting works. This was one of the earliest of the German investigations which since have become
famous, and it was a t this time that there was laid the foundation of a new science of industrial smokes and gases. Although the German investigators of the nineteenth century succeeded in isolating and determining the causal qualitative damage factors, the literature shows that the scientists of that period were handicapped by the inadequate development a t that time of the fine analytical, chemical, and physical tools for precise quantitative determinations, the availability of which we have come to take for granted in our modern laboratories. This manifested itself most importantly in the lack of precise methods for the determination of small amounts of sulfur dioxide in the air. Because of these considerations many of the older German references are of doubtful value when it is now attempted to express or interpret them in t e r n of field conditions. SULFURDIOXIDEAS COMBUSTION PRODUCT AND AS GASEOUS EFFLUENT FROM METALLURQICAL OPERATIONS I n the United States a number of important smoke survey8 have been conducted in the past and others are now in progress. Urban dwellers have demanded abatement of the smoke nuisance, and as a result many cities in our country today have antismoke ordinances. Moreover, the city dweller has come to understand that the term “smoke” is most frequently employed in its broader significance, including not only such constituents as the fixed carbon and tarry matter, but also invisible acid-forming constituents which may function in roles of vast importance as property destroyers, Rural and suburban communities have suffered to moderate degrees from the drift from nearby cities of the dense coal smoke and from the sulfur dioxide and sulfur trioxide released into the air in the cornbustion of sulfurcontaining fuel. However, far greater damage is done to agricultural enterprises by the smoke, fumes, and gss evolved
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August, 1932
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and released into the air i n mmection with larg~~soale to be doubted if the Selby method is susceptible to still furmetallurgical ore-reducing and refining operat.ions, such as ther improvement over that described by McKay and the roasting and smelting cif sulfur-containing ores arid con- Ackerman. centrates of coppr, lead, zinc, and iron. IMPROVUD METHOD*'on ~ E T E I ~ X I N A T I OF ~ X SMALL When it is considered that some of these great plants emit AMOUNTB OF SULFUR DIOXIDE I N AIR hundreds of t.ons of sulfur dioxide into the air daily and that this gas mny be diluted millions of times and still be present In tlie course of a recent study of atmospheric pollution by in measurable quantities, it is not surprising that examination sulfur dioxide released from t,he stacks of a large smelter, the of the atmosphere often reveals the presence of the gas many need became apparent for a method particularly adapted to miles from the source of polthe accurate determination of Intion. extremely s m a l l concentrations of this gas in the air. Moreover, it was desirable HOLMES, FBANKLIN, AND that the apparatus employed COULDSTUDY be of an easily portable or W i t h i n the last twentymobile type, and that it be five years a number of imapplical~lefor use under unportant smelter-smoke and favorable weather conditions fume surveys have been conas well as in difficult topoducted in the United States. graphical situations. Of t h e s e t h e H o l m e s Tile Selby methodislaboriFranklin-Gould i n v e s t i g a ous and the apparatus did not tinn is probably t h e m o s t seem well adapted, in respect widely k n o w n . The Selby R~~~~~ SCI~NI: h~ TI>,Eon D ~ vtsrrnTroW ~ ~ toeasymobilityandincertain ~ ~ ) ~ smelting and Lead Company "ameiter i t ~ m e 'lrane ' give" indiatitinat outline to row of tiees in backsround. aspects of manipulation, to conducted roasting and smeltthe carrying on of the thouing of sulfurous ores near the city of Benecia, Calif. Alleged sands of tests which were contemplated. Becauseof this and damage to plant and animal life, bo the soil, and to rrietallic I)ccause of previous experience and Connection with problems objecte in the vicinity led to a11 injunctim decree and of a somewhat similar nature in the determination of traces finally to the creation of a commission rmder whose super- of varioiis gases by a preliminary absorption in bubblers or vision an extensive investigation was eonducted. The scrubbers, a procedure quite different from tliat of the Selby various solid, liquid, and gaseous eflurnta of the smelt,er method was developed for these tests. This procedure conwere studied, but it soon became apparent that sulfur dioxide sists in passing metered volumes of air through scrubbers or gas was the principal offender, particnlarly in respect to absorbers which contain very dilute solutions of iodine (about damage to vegetation. The findingd of the experts engaged 0.00003 N ) in aqueous solution of potassium iodide. A small in the investigation are embodied in the well-known Selby amount of starch is also present in the absorbing solution. Smelter Commission Report (e). After the period of absorption, or bubbling, the solution in SELBY METHOD FOR DETERMINATION ox' SULFUR ~)rOXrnE the scrubber is drawn nut and the excess iodine is determined I N ATMOSPHERE. Tbe chemists participating in the Selby immediately by titration with 0.0010 to 0.0015 N sodium investigation developed a method by which "less than 0.1 tliiosulfate solution. part of sulfur dioxide in 1,000,000 Darts of air" mizht be determined. Just how much le& than 0.1 part is normade clear. However, it is doubted if these authors contemplated a claim in sensitivity of much less than 0.1 p. p. m. This is made apparent in subseqrient individual priblications of these experts (3, 8). The Selby method was a notable advance over methods previously known and described in the literature. I t permitted tlie making of numerous determinations of sulfur dioxide a t fairly low concentrations in the air. It is true that there w1~9a necessity for favorable conditions in which to conduct t,lie tesk; nevertheless, when compared with other available methods, the Selby procedure was unrivaled as to rapidity, sensitivity, and accuracy. Certain difficulties and deficiencies in the method have since brought forth comment HUHAL SCENE AFTER PASSrNO OF SuLFun I)roxrDr: VIslTATloN from various experimenters, but these tronhles do not seem Row of trees in baokgiound is well defined. to be fundamental or impossible of solution. Wierbach (70) demonstrated that the use of rubber stoppers introduced For a time two bobblers were used in series to accomplish appreciable errors in analysis, and Thomas and Cross (8) the sulfur dioxide absorption. However, the scrubbing reported a 5 per cent error as possible of introdnation by efficiency is so high that one bnbbler is sufficient, a this will failure to appreciate the adiatiatic cooling of the bottle on remove more than 90 per cent of the gas from air containing exhausting and the adiabatic heating on admitting the air sulfur dioxide in such concentrations as is ordinarily ensample. countered in the field. I f the scrubbing efficiency of a parThe Selby method has been much improved by McKay ticular absorber is known for the conditions under which it is and Ackerman (3) who have since introduced a number of being used, proper factors may be applied to the end that refinements in procedure. These investigators were able, by reported results are correct. means of these refinements, to reach a sensitivity in the ordrr There is, of course, nothing new or novel in the idea of of rnagnidude of about 0.05 p. p. m. This represents great absorbing sulfur dioxide in excess iodine solution and then improvement over the method as originally developed. It is back-titrating with sodium thiosulfate. The reactions in-
I 1 1) I : S T 1% I A I.
8b.l
A N D I5 N G I N E E R I N G
volved iii t,lie gt:nerd prowdum are f a m i l i a r io most analytical cliernists and are iii ~ o n m ~ ouse n in voliniiet-
application nf these roact,ions ie cxt,r(mely dilute solutiori has not, until recently, h e w takeii very seriously in the field of analytical chemistry. Particularly has it been held that the back-titer with sodium thiosulfate in such d liite solutions leads t o erratic r e i u l t s (3, 4.). I l o w c v e r , opiniun in this direction has not been unanimous ( I O ) . It has been the authors' experience that, by nieaus of improvement in appa.ratus aod modifieations in p r o eed iire a.nd technic, there is inlierent in the mebliod, a t low concentration of reagents, a degree of delicacy a n d precision hitherto nut deemed possible of achievement. l'al,csuuirE I S I?IPHOVEU l o ~ r s iMETHOD ~ OF SULFUK DIQXIDEDETEHMINATION
In the method, as finally developed and employed in the field, air is metered through 100 cc. of the tlihite niarchpotassium iodide-iodine absorbing solution at a rate of 7.5 liters per minute for a period of 4 minute,?. This j,'' I Y i ! S a 30-liter air sample, or approximately that, after rnaking the necessary volume correction for temperat,iire and pressure. Immediately following the absorbing period, the solution is drawn out of the scrubber into a 250-cc. Rask, a pinch of sodium bicarbonate is added, and back-titration of the exccss iodine is accomplished with standard sodium thiosulfate solution (The thiosulfate employed averaged about 0.0013 N . ) Titration t.o an entirely colorless solution is not attempted. R,at,her, the t,hiosulfatc is run in until a predetermined light shade of blue is reached. This light blue end point may he set arbitrarily at various color depths. The light blue color standard is prepared by dissolving commercial dyes, such as Diamond dyes, in water. This color standard contains both blue and pink of the commercial colors as well as a trace of India ink to impart a \.cry slight turbidity in simulation of that caused by colloidal starch particles. Such a standard is quite fast in color and may be tined fur weeks in the field. A color standard prepared hy bleaching the absorbing solution to the desired faint !)lrie color is not sufficiently stable even in diffused sunlight. Such a standard may fade appreciably in the course of a half-hour. When continuous sampling of the smoke stream was desired, two scrubbers or absorbers were employed alternately, one running for 4 minutes, followed by the other one functioning for a like period, and so on indefinitely. SUDA-hlE
TOWER
FOR
EST.4BLlSIlhlENT
OF COHKECT
R L A N R ~ .An important feat,ure of the method, and one which gives it appreciable advantage over other procedures of a similar nature, is the employment of a tower containing soda lime in the freqnent establishment uf correct blank trsts in situ. In theory it shoirld !jp pmsilh nintl~ci,intir::lll\.~~~,:~~,ii!:~il~ to wmpute
C 1-1E >I1 S 'I' II Y
V o l . 24, No. ti
the valrie uf t h e s t a n d a r d iodine used irr the 100 cc. of ahsorbing sohit,hrr at the iniLiation of each test. This iodirre value, in terms of aliility to oxidizc s u l f u r dioxide, conld then be niathematically compared with that which remained after the sulfiir &oxide absorption and oxidatinn. The diffcrence betwecn these t w o iodine valiies woidd then rcprescnt that nrhich had l>een rcrlueed Ily tho sulfur dioxide gas. I I o w e v e r , those who have liad ocoasiun t.o experiment with a test of this kind know to what ail important degree a c t u a l comparisons rleviat,e from theoretical relationships. Tliehloeiodinriudidestarcli absorbing soliition is somewhat unstahle as to the effect of light. E v t ~ i more important, is its unstelile nature in respect t,o aeration with pure air. When pure air is bubbled through this b l u e a b s o r b i n g solution, a certain proportior1 of the i)loxll,a free iodine is v o l a t i l i z e d . T h e a m o u n t of iodine carriad off from the solution by volatilization depends upon a number of variable factors, socli as the concentrat,im of free iodine and that uf the potassium iodide. rate of bribbling or aeration of the solution, barnmetric pressure, and, most important of all, the temperature of this iodine-iodidestarch absorbing solution and that of the air whicli is passed through it. A nrathematical correction, taking into account all t i m e variables, would be tedious indeed, if not impossible. It has been demonstrated by Thomas and CTOSS(8) t.liat, with very dilute solutions of iodine in aqueous potassium iodide, there is only a slight tendency toward volatilization of iodine by aeration with pore air. Nevertheless, with 12or 13-inch (30.5 or 33-em.) bubblers, unpacked with lieads, such as are employed in the improved iodine method, there may he measurable volatilization even in cold weather. At, sinmiier temperatiires iodine volat.ilization from absorbing or scrubbing solutions sometimes mounts to a position of importance even with very dilute iodine concentrations in the allsorbing liquid. This tendency toward iodine volatilization may he partly overcome by incorporating greater amounts of potassium iodide in the aqueous aisorbent. However, a limit is so011reached heynnd which this means of st.abilization may not he taken, as a large amount of potassium iodide in the solution decreases tlic sensibilit), of the iodine-starch-sodiurn thiosulfate titer. I3ecaiise of t.liese several varying factors it is desirahle for precise determinations to have a practical blank test in which correction for t l m e particulars is accomp~ished. In effect:, tile chcriiist~ with his testing equipment niust niomentarily be transported to some locality, perhaps quite distant, where the ntmosphere is not cont,anrinated with sulfur dioxide. As the blank tests should be interspersed with more or less frequenclamong the actual sulfur dioxide tests, i t is ol~vionslyirnpossible actually to accomplish this move to some distant point sufficiently often to make siicli a procedure a practicable one. Some experimenters have det.crminrd t.hrir iilanks in the laboratory hcfore going intn hlie field or nftrr retiirning
866
INDUSTRIAL AND ENGINEERING CHEMISTRY
up in boiled distilled water and is standardized Kith 0.001 N iodine solution. The strength employed varies from 0.0015 to
N . In wsrm thios,,,fate solution strength at the rate of about 10 per cent per week. It should he
checked frequently against the standard iodine solution.' Starch Solution. This solution is prepared by dissolving 2 grams of soluble starch in 1 liter of hot distilled water. Tile liquid is filtered while hot in order to remove undissolved starch particles. The use of preservatives is avoided. This solution is employed in a volume of 25 cc. per liter in niiiking up the blue absorbing solution. Color Standard. This solution is prepared fnxn eommercid organic dves and India ink, as previo&ly stated
Vol. 24, No.
a
The results give11 in tlie last coluIrrn are averages of a p proximately ten tests lllade t,lle impro5-d iodine method, each test lasting 4 Ini~Utes. Series 1 consisled of eleven individubi 4-minute tests, the results varying from 0.28 to 31 p. p. m.; the average was 0.80
p. p.
m.
Series 2 consisted of ten individual 4iminute tests, the results varying from 0.29to 0.3p. p. m.; the average was 0.31 p. p. m. Series 3 consisted of ten individual Pminute tests, the results varyinp from 0.56tu 0.61 p. m.; the average wag 0.57 p. p. m. &rim 4 consisted of ten individual 4minute tests, the results varying from 0.96 to 1.09 p. p. m.; the average was 1.04p. p. m
b'RoVED IODINE METHOD NOT,=. owing to small temperature nuetusr Lions obtaining within the oabinet duiing the The long, narrow IO-cc. buret may progre~eof such tests, slight variationa in auleasily be read to onehalf scalc divifur dioxide eoncentrations _e bound t o ooour sion or to 0.025 cc. of standard sodium regardless of onrefvl Bosmster and nnemomc thiosiilfate solution. With t,he soteroontroi. A lurthsi aheek in aoour~oywith respect to the improved iodine method WBB. dium thiosulfate at 0.0013 N , unehuwemr. obtained by oondiiotins B aeries of half scale division is equivalent to parailai sulfur dioxide wnoentration teats. 0.0010 mg. of sulfur dioxide; or, on mnde by memi of nil eiectriosi aonduetivity a basis of the usual 30-liter sample, method. I t ia planned to present thia campmative data in a paper which will be pmthe sulfur dioxide concentration repsented subsewently. resented is 0.000033 mg. per liter. At ordinary conditiona of temperaSI~ECI~IWI~Y OB' IMPROVED IODINE ture and pressure this is about 0.013 LVETHOD part of sulfur dioxide per 1,000,000 parts of air. Under the usiial field The method, as described, is sa& conditions (not necessarily the most factorily specific in so far as it relates favorable conditions for the test) this to the determination of sulfur dioximproved met.hod is chemically deliide in smelter fumes. It is true that Powraau? FiELn Awanrrus, Snowrno HAND-OPERATED SUCTION DEVXCE cate to 0 . 0 2 ~p.. m. Thesignificance hydrogen sulfide is oxidized by iodine of thia degree of chemical precision is solution as is s u l f u r dioxide. but apparent ;*hen it is considered that the mass of sulfur dioxide hydrogen sulfide is not normally to be found &s i~ constituent represented is only 0.0010 mg., a much smaller mass than is of gaseous smelter efffuents. It is therefore not necttss2try to gravimetrically measurable wit,h a fine analytioal balance. make a n independent estimation of-r correction for--this Mechanically the method is no more precise thau is the impurity. Sulfur trioxide may be present in traces. It has measurement of the air volume. The flowmeter readings no effect on the iodine solution. as taken in the field are accurate to *2.5 per cent. The possible reducing effect of pollen and dust suspended The improved iodine method (as herewith described) has in the air has been given some thought and attention, albeen carefully checked and compared against synthetically though in rural communities it is usually possible to select prepared admixtures of sulfur dioxide and air. That a very testing sites where interfcrence from such suspended matter satisfactory degree of concordance between actual and is uot appreciable. %'hen dust or pollen seem to be present theoretical concentrations bas been obtained is shown in in the air in appreciable amounts, the air inlet of the flowTable I, but lack of space prevents more than an incomplete meter should be protected by a thin filter. A thin mat of presentation of the data in this paper. asbestos or of cotton linters, "sucked on" to a fritted glass base or funnel, makes an excellent filter for protection against 1 ABLE I. COMPARISON ow S ~ L P U RDIOXIDEADMIXTUFCE~~ WITH AIR AND MIXTURES SYNTHETICALLY ESTABLISHED dust or pollen. Eowever, the a t e r must be of low resistance to the air flow, otherwise it is necessary to make correction for the disturbing effect of this resistance on the flowmeter. I'. 0. m. P . 11 m Moreover, when the air is passed through a filter, the first 1 0.29 Or30 few sulfur dioxide readings should be discarded. Any filter, 2 0.83 0.31 8 0.58 0.57 regardless of thinness, may show an initial adsorptive tend4 1.04 1.04 ency in respect to sulfur dioxide gas. The sulfur dioxide-air admixtures employed in tlie course IMPROVED IODINE TFST AS METHOD08 CONTROL IN of these comparisons were established in cabinets about 4 FUMIGATING TESTS feet (1.2 meters) square. The atmospheres were in rapid movement through the cabinet at all times and were in An extensive series of sulfur dioxide fumigating tests I r a constant measurement and control by a system of flow- been conducted during the last three years. The tests were meters and anemometers. It is not possible to accomplish made in order to determine the effects of very low concendesired comparisons of this nature with static admixtures of trations of sulfur dioxide in air upon crop plants, certain sulfur dioxide gas and air. weeds, and small seedling trees. PiLrticular attention was Each of the four series of tests presented herewith repre- directed to sulfur dioxide concentrations lower in order of sents a period of ahout 1.5 hours during which the concentra- magnitude than those formerly considered as significant ( 1 , 6 ) . tion of the sulfur dioxide was maintained at the strength This work was done in cooperation with expert plant patholoindicated in the theoretical column. gists and physiologists of the United States Bureau of Plant Industry. During the conrse of these experiments the im8 With b 30-liter air Bsmpie. I cc. 01 0.0013 N thioauiiate ia equivalent to about 0.5 p. p. m. sulfur dioxide. proved iodine procedure was employed as a method of dePKEClSloN OP
,.
August, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
termination and control of sulfur dioxide. At; times these tests were supplemented and compared with other determinations obtained by means of an electrical conductivity recorder (7). However, the iodine method was employed as the fundamental standard of accuracy. ACKNOWLEDGMENT Through the courtesy of the United States Chemical Warfare Service the flowmeters employed were originally calibrated in the War Department laboratories a t Edgewood Arsenal, Md. After some months of use, these flowmeters were checked for accuracy in the proving laboratory of the Spokane Gas and Fuel Company, Spokane, Wash.
867
LITERATURE CITED (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Haywood, U. S. Dept. Agr., Bull. 113 (rev.) (1910). Holmes, Franklin, and Gould, Bur. Mines, Bull. 98 (1915). McKay and Ackerman, IKD.ENQ.CHEM.,20, 538 (1928). Seidel and Meserve, U.S.Hygienic Lab., Bull. 92, 14 (1914). Shimpf, “Essentials of Volumetric Analysis,” 4th ed., p. 191. 1926. Swain, IND.ENG.CHEX, 15, 296 (1923). Thomas and Abersold, Ibid., Anal. Ed., 1, 14 (1929). Thomas and Cross, IXD.EKQ.CHEM.,20, 645 (1928). Wells, Ibid., 9, 640 (1917). Wierbach, Am. J. Botany, 13,81 (1926).
RECEIVED March 3, 1932. Presented before the meeting of the Bmerican Association for the Advancement of Science, New Orleans, La., December 28, 1931, to January 2, 1932.
Flame Radiation and Temperature Measurements on an Internal-Combustion Engine A. E. HERSHEY, Engineering :Experiment Station, University of Illinois, Urbana, Ill,
A
NY investigation or discussion of flame radiation and temperature is beset with many difficulties. The source of excitation causing radiation has not been definitely determined, nor is the mechanism of emission clearly understood. As to the meaning of flame temperature, an exact definition is difficult to formulate because of the absence of thermal equilibrium in regions of intense chemical activity. These considerations apply t o flame as it occurs in continuous combustion in a stationary flame and in the cyclic combustion in an internal-combustion engine. I n the case of the latter, however, the situation is further complicated by the flame movement, the lack of homogeneity in the combustible, and the short duration of the cycle. One method of dealing with the difficulty of defining flame temperature is to employ an operational concept of temperature and define it by describing the operation of temperature measurement. Since the operation of measuring flame temperature may be performed in several different ways, all of which may be regarded as defining the temperature, all should be applied and those selected as being satisfactory which give equivalent results. Three distinct methods of temperature measurement may be considered. These are: (1) Thermometric measurement with a solid in thermal equilibrium with the flame, corrections being made for the effect of the solid on the flame. ( 2 ) .Radiometric measurement from the flame radiation, corrections being made for the imperfections of the radiator. (3) Thermal and chemical measurement (calculated temperatures) from the AH for the combustion reaction and the specific heat of the products of combustion, correction being made for dissociation and losses.
All of these methods of measurement have been used in determining the temperature of continuous flame (11). It is here proposed to compare the last two methods as applied to a determination of flame temperature in an internal-combustion engine. The radiometric temperatures are the results of the present investigation and were obtained from measurements of the intensity of radiation from the flame during combustion in an engine. The calculated temperatures used for comparison are those found by Goodenough and Baker (6). The temperature of an imperfect radiator, determined by means of a radiation pyrometer, is not the true temperature of the radiator but is the radiation temperature, T,, or the
temperature a t which a perfect radiator would emit the same total radiant energy as the imperfect radiator. The true temperature of the imperfect radiator is found from the relation : T
=
--T ,
‘dei
(1)
where ei = total emissivity of imperfect radiator From Kirchhoff’s law the relation between the total radiation for an imperfect and a perfect radiator at the same temperature is: Ei
z = ai where E; = total radiation from imperfect radiator Ep = total radiation from perfect radiator a, = total absorption of imperfect radiator
But this ratio of total radiant energies is, by definition, the total emissivity of the imperfect radiator, hence, ei = ai
(3)
To find the emissivity of a flame, a method developed by Schmidt (12) may be employed. This method consists of a determination of the absorption by means of radiation measurements on the flame alone, on some continuous radiating source alone, and on the two superimposed. Thus, if the subscriptsf and 1 refer to the flame and to a tungsten filament lamp, respectively, the absorption of the flame may be found from (4)
where Ef.i = total radiation of flame and lamp together Having found at and hence q,we may now calculate the true flame temperature from the observed radiation temperature by means of Equation 1. This radiometric method of temperature measurement assumes that any source, the temperature of which is to be found, is emitting radiation owing to thermal excitation alone. It is scarcely necessary to discuss here the validity of this assumption as applied to flames in general or to the flame in an engine in particular, since many articles on flame radiation appear in the literature (1,6,8). The purpose of this investigation is to compare the results found from radiation measure-
