INDUSTRIAL AND ENGINEERING CHEMISTRY
1016
A A , CC) is the luminous portion of the flame. If a picture is taken of such a flame over a period of time T'IT1, the result is of the type No. 1, Figure 1, where the letters indicate the position of the several boundaries. At a slightly later time (T'zT2) another picture will appear as a t 2. Here the luminous portion has increased in area owing to the rise of the boundary line A . At a still later time (T'3T3)a different type of picture (double picture) is obtained as shown in No. 3. The next picture will be of about the same kind as No. 1 and the series then repeats itself. These are just the type obtained with the moving-picture camera. of Draft on Rate of Flicker of Natural Gas F l a m e (Constant gas rate, 77.91 liters per hour) PIC- MAX- RATEOF FLAME SPEED AMPLISERIES TURES IMA FLICKER DRAFT tower Upper TUDE Vibrations Liters/ per min. hour Cm./sec. Cm./sec. Cm. Bza a 33 10 582 1275.0 47.8 64.7 4.98 b 66 17 583 C 66 20 582 Bzs a 29 9 596 1062.0 45.1 68.0 4.98 b 55 17 593 C 65 20 591 Bn a 42 13 594 850.0 49.7 60.3 4.74 b 68 21 593 Bza a 39 12 591 637.0 47.4 64.7 5.73 b 52 16 691 ~. . Bzs a 47 14 573 425.0 45.5 58.7 4.98 b 67 20 673 Bsoa 47 14 573 212.0 61.3 4.23 38.0 b 67 20 573
Table 11-Effect
~
.
The process of combustion can be analyzed by following the gas molecules from the tip through the flame. On the diagram such molecules and their products of combustion will follow the general path of the line PIP'l. At about where PIP', crosses line D sufficient oxygen has diffused into the issuing gas, so that it is within its maximum limit of inflammability and combustion starts. The combustion continues with the formation of incandescent carbon a t b, giving the lower visible flame front. When the particle reaches the p i n t a, the luminous stage ends, and the molecules continue on into the upper zone and into the atmosphere. Consider now gas molecules Pp leaving the tip somewhat
VOl. 20, No. 10.
after PI. The first stages are exactly the same as before, but the luminous stage continues for a longer period of time, until the molecules reach the height k. Apparently the oxidation has taken place a t a slower rate and allowed combustion to continue for a longer period. I n the case of a particle P3 the combustion stage continues still longer, but in the case of Pd the active stage ends a t m. Thus the distinction between the flame fronts A A and CC is purely arbitrary, as they represent the same kind of a change from luminous to non-luminous. I n the case of a particle P6 the luminous stage not only ends a t a lower point, but also ends before the corresponding change from P,. This point n is a critical one, for it is here that the flame divides into two portions, one giving the flame ending a t g and the other being the main continuous flame. We have the peculiar phenomenon, then, of the main flame periodically giving off another minor flame. Whether the end of the luminous stage is considered to be due to the lack of oxygen or of combustible gas, the periodic nature of the phenomenon is due to alternate decreases and increases in the rate of diffusion of oxygen into the flame. A slow rate of diffusion would be associated with the minima of flame heights, the high rate of diffusion with the maxima. I n that there is a flame-speed phenomenon in the envelope around, the true flame, the passage of this flame upward and outward leaves the flame envelope covered with the products of the combustion. The flame is then seen in its original state, as there is a time interval before the slower moving air can diffuse through this envelope and again form an envelope of gas-air mixture that willinflame when it reaches its maximum limit of inflammability if it has attained its ignition point. As air diffusion is greater in the same time in the upper portion of the flame structure, the flame speed will be greater. Acknowledgment
The authors are indebted to H. H. Romig, a senior student in chemical engineering in Lehigh University, for his help and study in obtaining and correlating these data.
Flame Speed of Hydrogen Sulfide D. S. Chamberlin and D. R. Clarke LEHICHU N I V E R S I T Y , BETHLEHEM. PA.
An apparatus and method for determining the flame speed of hydrogen sulfide in air by horizontal flame propagation are described. The flame records were made by photographic method, the gas being inflamed in a 2.5-cm. glass tube, open at one end and 1 meter long. The maximum flame speed was found to be 49.5 cm. per second on burning 10.8 per cent hydrogen sulfide.
HE various methods for the measurement of flame speeds are well understood as there has been a decided development in the experimental method starting with Bunsen in 1867. Mallard and LeChatelier' first applied the photographic method which was later developed by Dixon,2 Bone,3 WheelerJ4 and other investigators. Little difficulty was met in the manipulation of the various combustible gases of which we have flame-speed data, as their
T 1 3
8 4
Ann. mines, 8, 274 (1883). Phil. Trans., SOOA, 346 (1903). Proc. Roy. Soc. (London),1148,402 (1927) J . Chem. SOC.(London),lOST, 2606 (1914).
solubilities and chemical activities were so low they could be easily measured and manipulated over water, aqueous solutions, or mercury. Hydrogen sulfide, on the other hand, is readily soluble in aqueous solution, oils, mercury, and liquid organic compounds, and in many cases chemically combines with them. Nevertheless, Jones, Yant, and Bergers determined the limits of inflammability of hydrogen sulfide and made quantitative measurements over saturated hydrogen sulfide water. Applebey and Lanyon6explained a system for the generation, storage, and delivery of pure hydrogen sulfide over a saturated hydrogen sulfide solution. It was found that all the existing methods for the storage, manipulation, and quantitative determination of air-HzS mixtures were so inaccurate that even approximate analyses could not be made. It was therefore necessary to develop a method for handling hydrogen sulfide in which it did not come in contact with liquids. ENG.C H E M . , 16, 363 (1924). J . Chrm. SOC.(London),2983 (1926).
IND. 6
I-VD USTRIAL A.VD E-VGIA'EERILVG CHEMISTRY
October, 1928
Apparatus and Materials
The apparatus used for the handling and analysis of the H2S-air mixtures, shown in Figure 1, consists essentially of gas-measuring pipets s and (7, absorption tube p , and balloons i and o for containing the H&air mixtures. Figure 2 shows the flame speed set-up similar to others in use.' A constant speed motor, a. drives a cone drive, d.
I
Figure 1-Apparatus
for Collecting a n d Analyzing Mixtures of H2S a n d Air
This is ronnected to a drum carrying film f in the camera box. The lens is at g and the flame tube in the proper focus a t 1. The flame tube is 1 meter long and 2.5 cm. internal diameter. A vacuum-tight removable end holds a three-way stopcock for evacuating and filling the tube with the proper mixtures. Hydrogen sulfide containing a trace of air was used from pressure cylinders as obtained from the Mathieson Alkali Company. The air was contained in a reservoir over water at 2.5" C. and slightly above atmospheric pressure.
from reservoir c through e to the bag i, and the air displaced by the added inflation of the bag was measured a t g. I n this way a rough mixture of hydrogen sulfide and air was made. By alternately raising and lowering the leveling bottles f and t with communicating cocks open, the gases were %-ellmixed. A N A L Y S I S - ~order ~ to obtain an exact analysis of the mixture, a sample of the gas from i was run into the small gas bag o and the volume accurately measured by air-water displacement in pipet s. By turning the cock n to communicate with the gas-absorption pipet p , the contents of o can be forced into a 10 per cent solution of ammoniacal cadmium chloride. After analysis the completely evacuated flame tube was attached to m and the gas mixture in i expanded into the tube. The residual gas in i was again sampled into o and a check analysis run. ~IEASUREMEXT OF FLAME PROPAGBTION-The photographic method by which the uniform propagation of the hydrogen sulfate flame was measured was carried out by a method similar to those previously mentioned. The flame tube of a capacity of 464 cc. was ignited from the open end by a taper. Immediately after the inflammation the tube was closed so that the products of the combustion could be investigated. The film used to obtain the flame speed record was 45/~6inches (11 cm.) wide and 20 inches (50.8 cm.) long. The constant factors were the focal length of the lens and the distance of the lens from the flame tube. The variables n-ere the speed of the film as measured by the r. p. m. of the drum and the angle formed by the image of the moving flame on the film. From these data the speed of the flame in centimeters per second was easily obtained.
HzS Per cent 7.5 1
1017
8.0
8.9
9.0
Table I-Flame Speed-HrS-Air Mixtures FLAME FLAXE SPEED HzS SPEED HzS Cm. per sec. Per cent Cm. p e r sec. Per cent 16.0 9.5 48.0 12.5 40.1 10.0 49.5 16.2 45.8 12.2 48.0 20.0 46.5
FLAMR SPEED
Cm. per SCC. 40.1 26.4 24.0
Results and Discussion
The values for the flame speed of HnS-air mixtures are shown in Table I and plotted in Figure 3. The curve conforms very closely to the flame-speed curves for other combustible gases but differs in some detail. The fact that the Figure 2-Apparatus
for Determining Speed of Flames
Experimental Method
The limits of inflammability of H2S-air mixtures by horixontal propagation with one end of the tube open are as follows: Tube Diameter
LltnltS
Cm.
Per cent 5 3 t o 35 0 5 9 to 27 2
7 ; 6 0
From the data one can assume that the limits of inflammability in a 2.5-cm. diameter tube would be within the above limits. h~AXIPrSL4TIOh--~k small hydrogen sulfide cylinder of compressed gas was connected to cock m (Figure 1). The circuit e , e', k , I , m, 42, 0,was evacuated with cocks h and r open to the atmosphere. Cock h was then turned to communicate with the 1-liter pipet g , and hydrogen sulfide allowed to flow through k into the dry rubber bag i. Air was then run in Bone and Townend, "Flame and Combustion ~n Gases,'' p 122, Longmans, Green & Company.
J H ~ B h 91." Figure 3-Flame-Speed Curves for HIS-Air Mirtures by Horizontal F l a m e Propagation
ILVDLTSTRIALA,ITD ESGINEERIATGCHEMISTRY
1018
sulfur in hydrogen sulfide can be oxidized, as follows, from S-- + S o + SI: + S :, indicates that the following reactions can express the conditions that give rise to flame speeds with proportions of hydrogen sulfide in air within its limits of inflammation:
+ 502 + 5 X 3.76N2 = 2H20 + 2SOz f 202 + + 402 + 4 X 3.76N2 = 2H20 + 2SO2 + 02 + -+ 302 + 3 X 3.76Nz = 2H20 + 2S02 + 3 X + 202 + 2 X 3.76N2 = 2H20 + SO2 + S + 2 + 02 + 1 X 3.76N2 = 2H20 + 2s + 1 X 3.76N2
2H2S (7.75%) 5 X 3.76N2 2HzS (9.51%) 4 X 3.76No 2H2S (12.29%) 3.76N2 2H’S (17.35%) X 3.76ih’z 2HzS(29.60%)
From actual analyses of the gases in the flame tube resulting from the combustion, the plots of the amounts of SS,SO*,and SO3, corresponding with the same abscissas as in Figure 3, show that the hydrogen is to a great extent selectively oxidized. This fact was also noted in that gas mixtures that contained percentages of hydrogen sulfide above 12.3 per cent, showed poorer images on the film due to the increasing amount of hydrogen burned and the formation of greater amounts of sulfur. I t is well known that the flame speed of
VOl. 20, s o . 10
hydrogen cannot be determined in the time allowable by photographic method due to the fact that the light rays that are given off are in the ultra-violet and do not affect the photographic film rapidly. Between the points A and B, if no sulfur had been deposited and only sulfur dioxide formed, the curve would no doubt have conformed to its proper shape as shown by the dotted line and the flame speed not abruptly retarded by the formation of suspended sulfur. I t is interesting to note that the slowest maximum flame bpeed heretofore measured was that of carbon monoxide in air in a 2.5-cm. tube and found to be 60.0 cm. per second. I t is now evident that hydrogen sulfide a t its maximum flame speed of about 50.0 em. per second moves much slower than carbon monoxide and thus will affect the burning of combustible gases containing hydrogen sulfide. I n these experiments the sulfur trioxide content of the gases of combustion was a t a maximum on igniting a 7.0 per cent mixture of hydrogen sulfide in air. A continuous method for the production of sulfur trioxide by burning hydrogen sulfide in an internal-combustion engine warrants further study.
The Gaseous Explosive Reaction at Constant Pressure’ F. W. Stevens BUREAUOF STANDARDS, WASHIBCTON. D. C.
The course of the gaseous explosive reaction at constant pressure is described and then followed experimentally by means of photographic time-volume records obtained by a simple device that is found to function as a transparent bomb of constant pressure. It is found that at constant pressure the uniform rate of propagation, s, of the zone of explosive reaction, when measured relative to the active gases, is proportional to the product of their concentrations (partial pressures) : s =
k, [AIn1 [B]”2[CIn3... . . .
In the light of this relationship studies have been made of the effect of inert gases and of composite fuels on the rate of the gaseous explosive transformation.
’EARLY all the investigations that have been made of the gaseous explosive reaction have been carried out under conditions of constant volume. This has seemed necessary from the very nature of gases. Of all these investigations, those that show some connection with the line of substantial development taken by our knowledge of gaseous transformations, and that have sought the direction for further advance indicated by well-established general principles and laws, have been devoted to thermodynamic studies of the reaction and have concerned themselves principally with gaseous equilibria. The significant advance that has resulted from such studies must be attributed in large measure to the fact that they took advantage of the leadership and direction provided by the theoretical consequences involved in the principles and laws of thermodynamics as applied to chemical equilibria. These deductions were early (1876) set forth in the far-reaching theoretical investigations of Gibbs. As a result of his -cork “chemical science has been able to use these results of theoretical physics with immense benefit t o itself and to deal quantitatively with the most complex equilibria without any knowledge of the intimate ‘mechanisms’ underlying physical and chemical phenomena.”*
N
1 Published
b y permission of t h e Director, S a t i o n a l Bureau of Stand-
ards.
On the other hand, kinetic studies of the gaseous explosive reaction made under conditions similar to those imposed for thermodynamic investigations have not shown a corresponding advance. As compared with thermodynamic studies, the number devoted to the kinetics of the reaction and based in any way upon or directed by the probable consequences of a kinetic theory of gases are few; yet for the kinetic phase of the reaction the opportunity has long been a t hand to adapt experimental devices and methods to the principles of statistical mechanics. Even with a primitive kinetic theory, early attempts in this direction met with significant success: “The first attempt a t a quantitative kinetic expression is met 15ith in the equation pv = RT.”3 Very early also (1864) “the assumed correspondence between the order and mechanism (of a reaction) which finds its rational explanation on the basis of a kinetic theory of molecular motions, was, of course, the original hypothesis of Guldberg and Waage in the formulation of the law of mass action. * * * The rational procedure seems to be to regard the order of any simple reaction as prima facie evidence of its m e ~ h a n s i m . ” ~ The advance in physics of late years has been somewhat diverted from the physics of large aggregates to the physics of individuals, thus depending for a prediction of the behavior of the mass on the behavior of an isolated individual. The direction taken by this more recent development is said “to hold out the hope that the time will come, perhaps in no very distant future, when the structure and activity of the material world will be understood in terms of a theory based on the potentialities and activities of electrons, protons and radiation, or possibly of radiation alone. Although such a theory already exists, it is not sufficiently developed to suffice for the needs of the chemist,”2 whose problems are for the most part concerned with systems, often of great complexity. “Among the immediate developments to be wished for statistical mechanics will be its increasing applicatioris to Ehrenfest, P a n d T., Encyklop. math. Wissen , 4, 4, 11 (1924). Tolman, “Statistical Mechanics with Applications to Physics and Chemistry,” p 239, T h e Chemical Catalog Co , I n c , 1927. 3
4
Donnan, Chem Weekblad, 23, 422 11926)
