444 ANDREW : THE WATER-GASXLVIII.-TheBYIT has been foundWuter-Gas Equilibrium in Hydro-cmebon Flames.GEORGE WILLIAM ANDREW.that when such hydrocarbons as methane,ethylene, acetylene, etc., are fired with certain proportions ofoxygen, the cooled products from the reaction may consist largelyof water, hydrogen, carbon monoxide, and carbon dioxide.The experiments described herein were made at ManchesterUniversity during 1905-6 at the suggestion of Professor Bone, asan extension o l his researches on hydrocarbon combustion, toascertain how the relative proportions of such constituents, con-sidered more especially from the equilibrium point of view, variedwith variation in the composition and pressure of the gaseoasmixture fired, it being considered possible that thereby some addi-tional light might be obtained on the subject of hydrocarboncombustion.The reversible water--gas reaction :CO + H,O S CO, + Hz,giving a t any temperature to the relation between the concentra-tions of the constituents :has been investigated by many workers, and the results obtainedfrom the interaction of these constituents, either alone or associatedwith inert gases, cover a wide range of temperature.The early experiments of Bunsen (Annaleri, 1853, 85, 137) onthe partition of oxygen between carbon monoxide and hydrogen,when mixtures containing an excess of the combustible gas areexploded, were vitiated by several inaccuracies, particularly thosedue t o the use of a wet eudiometer in the experiments.The sourca of error in Bunsen's experimenh were pointed outby H.B. Dixon (Phil. Trans., 1884, 175, 617), who systematicallyre-investigated the question, and established two essential condi-tions necessary f o r a correct determination of the final equilibriumcondition, either in presence or absence of an inert gas, namely, theuse of a heated eudiometer in order to prevent condensation ofsteam during the initial cooling of the exploded gases, and theattainment of a certain minimum flame temperature. When theseconditions are complied with, Dixon demonstrated that the finalequilibrium is defined by the expression EQUILIBRIUM I N HYDROCARBON FLAMES. 44 5The experimental results of Horstmann (Annulen, 1877, 190,228; Bey., 1877, 10, 1626; 1879, 12, 64) subjected to thermo-chemical analysis by Hoitsema (Zeitsch.physikal. Chem., 1898, 25,695) are untrustworthy, since the above-mentioned conditions werenot complied with.I n 1892 Smithells and Ingle (T., 1892, 61, 214) mentioned thatin their experiments on the composition of the interconal gasesof hydrocarbon flames, the ratio ”’ H90 calculated from theirmost trustworthy analyses, did not differ greatly from 4.0.Later investigations on the water-gas equilibrium have been madeby Hahn (Zeitsch. physikal. Chtem., 1903, 44, 510; 1904, 48, 735),who passed mixtures of steam with carbon monoxide, and hydrogenwith carbon dioxide respectively, over platinum as contactsubstance, a t temperatures below 1400°, whilst Haber, Richardt,and Allner (Haber, Thermodynamics of Technical Gas Reactions,”pp.142, 299, e t Sep.) have obtained figures for the equilibriumconstant Rt in open flames a t temperatures as high as 1500O.Hahn also subjected the reaction to thermodynamic treatment,and has deduced the equation:where F= t + 273.t 0 x H,O’log Kt= - 2232/ T - 0.08463 . log T - 0.0002203T + 2.5084,From such an equation the following values of Kt are derived :to ............... 1006 1205 1405 1600Kt ............. 1.65 2.54 3.43 4-24which are in general agreement with the experimental resultsobtained by Haber, Richardt, and Allner.All attempts experimentally to determine the value of the equili-brium constant at high temperatures are liable t o inaccuracy owingto further interaction in the gaseous system during the coolingperiod.This is accentuated when the gases are in contact withheated surface, but it has also been found that such re-adjustmentmay take place even in free gas space, with considerable rapidityat temperatures above 1600O.EXPERIMENTAL.Mixtures of the individual hydrocarbons, methane, ethane, andethylene with oxygen, were prepared in proportions such as wereknown to give on ignition practically only the constituents of thewater-gas reaction, the actual mixtures employed correspondingapproximately with Clr, + O,, 2CH, + 30,, 2C2HR, + 30,, 2C2H, +Every care was exercised in the preparation of the hydrocarbons,502, CaH, + 202446 ANDREW : THE WATER-GASwhich were finally subjected to rigid purification by low tempera-ture fractionation prior to use, the purity of the hydrocarbon beingproved by explosion analysis.The oxygen was prepared from recrystallised potassium perman-ganate, and the desired gaseous mixture of ascertained composi-tion was dried by passage over calcium chloride, and filled into dry,cylindrical, boro-silicate glass bulbs of 60 C.C.capacity, fitted withplatinum firing wires, similar t o those used by Bone and Drugmanin their experiments on the explosive combustion of hydrocarbons(T., 1906, 89, 662). The pressure and temperature of the gaseousmixture in the bulbs was noted, and the capillary connexionssealed. The bulbs were then heated to 130° in an air-bath, main-tained a t this temperature for thirty minutes, and the contentsthen fired by a spark.The dimensions of the bulbs were such asto permit of ordinary inflammation only; detonation was, of course,impossible. Pinally, the bulbs were cooled, opened in connexionwith a vacuous, capillary manometer, and the pressure and tem-perature of the gaseous constituents ascertained (suitable correc-tions being applied for the dead space of the manometer and thetension of aqueous vapour), and a sample of the gaseous productswithdrawn for analysis.From such data it was possible, by preparing a balance sheetof carbon, hydrogen, and oxygen in the original mixture andproducts respectively, to deduce the amount of water present inthe products within the limits of an experimental error subsequentlynoted, and the reaction constant X t was obtained therefrom.I n general, with a given gaseous mixture, experiments werecarried out a t more than one pressure in order that the effectof a variation in flame temperature might be investigated.I n no way was any deposition of carbon noticed, a point whichis confirmed by the carbon balance sheet.I n some bulbs a faint aldehydic reaction was detected, but thequantity of aldehyde present was not sufficient to materially affectthe results of the investigation.The quantity of water finally present is deduced by the fore-going method and checked by the H2 : 0, ratio in the condensedproducts was probably, in most cases, accurate to within 3 per cent.from the mean value accepted.Tubulat ed Results.The tabulated results refer t o experiments with the six hydro-I n the tables are carbon-oxygen mixtures previously mentioned.noted EQUILIBRIUM I N HYDROCARBON FLAMES.447(1) The percentage composition of the dry nitrogen-free mixtureand products respectively.(2) The absolute pressures reduced to Oo in mm. of mercuryof the dry, nitrogen-free mixture and products noted as P, andP2 respectively.(3) The ratio P, : Pz.(4) The balance sheet of carbon, hydrogen, and oxygen in drymixture and dry products respectively, from which the waterfinally present is deduced.(5) The absolute pressures in mm. of mercury reduced to Oo ofthe carbon monoxide, carbon dioxide, steam, and hydrogen in thefinal products.CHzo deduced from the above data. (6) The constant Kt= ccocvcoz x Gl,TABLE I.Experiments with Mixture CH, -I- 0,.Analysis ofEx-- original mixture Analysis of productspen- (percentage). (percentage).No.CH,. 0,. CO,. CO. &. CH,. mm. mm. P,/P,.ment - PI. P,. /1. 49-5 50.5 8-70 39-65 51-10 0.55 396 400 0.9902. 49.5 50.5 8.60 39.60 51.25 0.55 396 400 0.9903. 49.5 50.5 8.80 39.70 50.85 0.65 532 535 0.994TABLE Ia.Experiments with Mixture CH, -I- 02.Absolute pressure water-vapour in mm. reduced to 0'EX.-peri- Calcu-ment lated UnitoNo: from carbon.Originalmixture... 1961. Producta . 196Deficit . . . .Originalmixture ... 1962. Products . 1951i Deficit . . . .0 riginalmixture.. . 263Deficit . . . .Calcu- Calcu-Units lated latedhydro- Units from fromgen.oxygen. hydrogen. oxygen. Mean.784 400418 228 183 172 277.8366 172784 400419 227 183 173 178.0365 1731051 538558 307 246 231 238.0493 23448 ANDREW : THE WATER-GASTABLE I b .Experiments with &fixture CH, + 0,.Absolute pressures of constituent gases in mm. reduced to Oo.1. 159 177-5 34-8 204 3.982. 158 178.0 34.4 205 4.003. 212 238.0 47.1 272 3.95Mean... . . . . .. K = 3.98.TABLE 11.Ezperiments with Mixture 2CH4 + 30,.Analysis ofEx- original mixtureperi- (percentage). (percentage).ment <-J-, I A \Analysis of productsNo. CH,. 0,. CO,. CO. H,. CH,. P, PY PI lPB'4. 39.70 60.30 35-46 35.45 28.60 0.50 310.0 mm. 172 mm. 1-805. 39.45 60-55 33.90 35-90 29-70 0.50 437.0 mm. 243 mm. 1-806. 39.45 60.55 34.50 35.30 29.70 0.50 437-Omm.243 mm. 1.807. 39-45 60-55 33.90 35.90 29.65 0.55 264.5 mm. 146 mm. 1.818. 39.45 60.55 33.90 35.86 29.70 0.55 264-5 mm. 146 mm. 1-81TABLE IIa.Experiments with Mixture 2CH4 + 30,.EX.-peri- Calcu-ment lated UnitsNo. from Carbon.Originalmixture.. . 1234. Products . 123Deficit . . . .Originalmixture ... 172-55. Products . 271-0i I Deficit . . . .Originalmixture ... 172.5Products . 171.0Deficit .Absolute pressure water-vapour in mm. reduced to 0".h/ \ Calcu-lated Calcu-Units from latedHydro- Units Hydro- fromgen. Oxygen. gen. Oxygen. Mean.492 374102 183 195 191 193390 191690 529149 252 270 277 274541 277690 529149 253 2 70 276 273541 27EQUILIBRIUM IN HYDROCARBON FLAMES.449TABLE IIa (continued).Experiments with Nixture 2CH4 + 30,.Absolute pressure water-vapour in mm. reduced to 0".EX-peri- Calcu-ment lated UnitsNo. from Carbon.Originalmixture... 1047. Products . 103Deficit .Originalmixture.. . 1041Deficit . . . .<Calcu-lated Calcu-Units from latedHydro- Units Hydro- fromgen. Oxygen. gen. Oxygen. Mean.418 32090 151 164 169 166328 169418 32090 151 164 169 166328 169TABLE 116.Experiments with Mixture 2CH4 + 30,.Absolute pressures of constituent gases in mm. reduced to 0".ment K=Experi- cco x CH20,No. c o . s o . co,. H,. CC02 X cH24. 60.9 193.0 60.9 49.2 3.925. 87-2 274.0 82.4 72-2 4.026. 85.8 273.0 83.8 72-2 3.877. 52-4 166.0 49.5 43.3 4-068. 52.3 166-5 49-5 43-4 4.05Mean .........K=3.98.TABLE 111.EX:pen-mentNo.9.10.11.12.Experiments with Mixture 2C2H6 + 30,.Analysis oforiginal mixture Andy& of products(percentage). (percentage).C&& 0,. COP CO. C,H,. H,. CH,. mm. mm. P,/P239.0 61-0 5.35 44.60 nil. 49.00 1.05 272 417 0.65138.9 61.1 5.40 44-50 nil. 49.35 0.75 339 518 0.65538.9 61.1 5.70 44-40 nil. 49.30 0.60 339 519 0.654* & / \ P,. P*.39.0 61.0 5.50 44-15 0.30 49.35 0.70 272 413 0.65450 ANDREW THE WATER-GASTABLE IIIa.Experiments with Mixture 2C2H6+ 30,.Absolute pressure watervapour in mm. reduced to 0'.EX.-peri- Calcu- Unitsment lated Units Hydro- UnitsNo. from Carbon.Originalmixture. , , 2 129. Products . 213Deficit . . . .Originalmixture ...21210. Products . 210Deficit . . . .OriginalI1 mixture ... 264Deficit . . . .Originalmixture.. . 264Deficit . . . .gen. Oxygen.636 331425 230Calcu-lated Cdcu-from latedHydro- fromgen. Oxygen. Mean.105 101 103.0211 101636 331424 227 106 104 105.0212 104792 414527 286 132 128 130.0265 128792 415524 290 134 125 129.5268 125TABLE IIIb.Experiments with Mixture 2CzH6 + 30,.Experi-ment cco x cJ&oNo. co. H,O. co, . =2. K = - cco2 -~ x CR,9. 186.0 103.0 22- 3 205 4.2010. 182-0 105.0 22.7 204 4-1411. 230-5 130.0 28.0 256 4.1912. 230.0 129.5 29.6 256 3.94Mean ......... K=4-12.TABLE IV.Experiments with Mixture ,2C2H6 + 50,.Analysis ofEx: original mixtureperi- (percentage).ment /-A--No. C2q,.0,.13. 27-20 72.8014. 27.15 72.8515. 27.15 72.8516. 27.15 72.85Analysis of products(percentage).A/ ~ P,. P,.CO,. CO. C,H,. H,. CH,. mm. mm. P,/P,.40.35 36.40 0.30 22-65 0.30 454 320 1.42041.85 35.25 0.75 21.85 0.30 293 201 1.46042.25 35.50 0-35 21.75 0.15 293 200 1.46542-05 35.55 0-40 21.70 0.30 346 239 1.45EQUILTRRIUM IN HYDROCARBON FLAMES. 451TABLE IVa.Experiments with Mixture 2C;H, + 50,.EX.-pen- Calcu-ment lated UnitsNo: from Carbon.Originalmixture.. . 247Deficit . ...Originalmixture.. . 15914. Products . 158Deficit . ...Originalmixture.. . 15915. Products . 157Deficit . . . .Original{i mixture.. . 188Deficit . . . .Absolute pressure tvater-vapour in mm. reduced to 0".*/ \ Calcu-lated Calcu-Units from latedHydro- Units Hydro- fromgen.Oxygen. gen. Oxygen. Mean.742 661153 375 294 286 290589 286477 42796 239 190 188381 188477 42791 240 193 187386 187564 505110 286 227 219454 219189190223TABLE IVb.Experiments with Mixture 2CT,H,+ 50,.Absolute pressures of confitituent gases in mm. reduced to Oo.Experi- CCO XQHgOCCOzXCH, 'ment K=NO. co. H,O. GO,. =213. 116.5 290 129.0 72.50 3-6114. 70.8 190 84.1 43.90 3.6215. 71.0 190 84.4 43.50 3-6616. 85.0 223 100.5 51.85 3-64Mean ......... K=3*63.EX-peri-mentNO.17.18.18.20.TABLE V.Experiments with Mixture 2C,H4 -I- 50,.Analysis oforiginal mixture Analysis of products(peroen tap). (percentage).- A PI. pz.c,H,. 0,. CO,. CO. H ~ . CH~.' mm. mm. PJP,30.05 69.95 47-80 36-90 15-00 0-30 738 520 1.42030.05 69.95 47.60 37.30 14.80 0.30 738 518 1.42030.05 69-95 47.55 36.95 15-25 0.25 375 265 1-41530.05 69.95 47.75 36.75 15.20 0-30 375 267 1.40452 ANDREW : THE WATER-GASTABLE Va.Experiments with Mixture 2C,H4 +- 50,.Absolute pressure water-vapoir in mm. reduced to 0'EX-peri- Calcu-ment lated UnitsNo. from Carbon.Originalmixture ... 44417. Products . 442Deficit . . . .Originalmixture.. . 444 ii Deficit . , . .Originalmixture.. . 22519. Products . 225Deficit . . . .Original i Deficit . . . .mixture.. . 22520. Products . 226r Calcu-lated Calcu-Units from latedHydro- Units Hydro- fromgen. Oxygen. gen.Oxygen. Mean.887 1032162 689 362 343 353725 343887 1032159 686 364 345 354728 345451 52484 350 184 174367 174451 52485 353 183 171366 171179177TABLE Vb.Experiments with Mixture 2C2H4 + 50,.Absolute pressures of constituent gases in mm. reduced to (lo.Experi- cco x Ctf.20 K =CCO? X CH2 'mentNO. co. H'2.0. cop H2.17. 192.0 353 249.0 78.0 3.4918. 193.0 354 247.0 76.7 3.6219. 97.9 179 126.0 40-4 3-4420. 98.1 177 127-5 40.6 3.35Mean ......... K=3*47.General Conclwsions.(1) The ratio Kt="O CHzo is almost constant for the mixturesused within limits of experimental error, the value, as thus deter-mined, being to a considerable extent independent of the natureof the hydrocarbon-oxygen mixture fired or the pressure of thegas before ignition.Hence this ratio is apparently independent ofthe maximum flame temperature; the average value is practicallyG o 2 x GIEQUILIBRIUM IN HYDROCARBON FLAMES. 4534, a figure previously found by Dixon (Zoc. cit.) in the inflamma-tion of mixtures containing carbon monoxide, hydrogen, andoxygen.(2) Since under the stated conditions the maximum flame tem-perature would vary with the composition and pressure of themixture ignited, the experimentally-determined constant mostprobably does not correspond with the maximum flame temperature,but is characteristic of some hypothetical temperature, the equili-brium condition a t which corresponds with the integration of thechemical changes which occur in a rapidly cooling mixture fromhigher to atmospheric temperatures.This purely hypotheticaltemperature, which may be referred to as “ t h e temperature offinal reaction” (since it may be supposed that the gases are inequilibrium, and cease to further react at this temperature), isidentified both on thermodynamic and experimental groundsbetween the limits 1500O and 1600O.(3) No calculation is attempted of the flame temperature, sincethere is no accurate information available relative to the increasedspecific heat of the gases, the radiation from the flame, or thenature of any reversible reactions having thermal effects character-istic of high temperatures. In all cases, however, the flame tem-perature would, no doubt, be higher than 1600°, and, assumingequilibrium to be attained in the flame, subsequent readjustmentduring cooling is thus found to take place.(4) The results, thus interpreted, prove the rapidity with whichthe secondary reaction, GO + H,O Z CO, + H,, proceeds during thecooling period of such hydrocarbon flames, and the ready adjustiment of equilibrium in such systems down to a comparatively lowtemperature.(5) Since in the author’s experiments there was no carbondeposited, and the amount of methane in the final gases neverexceeded 1.05 per cent.(being usually 0-3 to 0.6 per cent. only), noconclusion can be drawn therefrom as to the possible influence ofsuch factors on the water-gm equilibrium. Fortunately, however,the previous experiments of Bone, Drugman, and Andrew (T.,1906, 89, 1614) on the explosive combustion of mixtures C,H6+0,and 3C2H4 + 20, under varying conditions, in all cases carbon beingdeposited and larger quantities of methane formed, provide amplematerial for deciding this point.Although in these experiments the temperature of the enclosingvessel was below the saturation temperature of the ultimateproducts, the results, according to the author’s calculations (whichare summarised in the following paragraphs), approximately con-form, so far its the proportions of carbon dioxide, carbon monoxide454 ANDREW : THE WATER-GAShydrogen and water in the final gases are concerned, to the requirements of the water-gas equilibrium at about 1600O.This fact points to the conclusion that in hydrocarbon explosionsthe adjustment of the ‘‘ water-gas” equilibrium during the coolingperiod is not greatly influenced even when relatively large quanti-ties of methane and carbon are found in the final products.(a) Experiments with Ethane.The results obtained with the mixture C,H,+ 0, are reproducedin tabular form, showing the products obtained when this mixturewas fired in a tube, in a spherical vessel, and detonated in a coilrespectively, the yields of deposited carbon and aldehyde producedshowing wide variation, according to the type of vessel.From thecomposition of the gases, the volume of steam as a percentage onthe dry gas, calculated for a thermodynamic constant .ZKt=4, isderived, and the figures are also quoted showing the actual steamequivalent of the condensed hydrogen and condensed oxygenrespectively.It is seen that the proportion of steam thus calcu-lated is in general agreement with that required to account f o r thecondensed products, when it is recalled that in the case of the tubeexperiment these products contained considerable quantities ofaldehydes.MixtureCylindrical vessel.Percentage com- ‘0-position of dry C~HJgaseous products.Calculated steam per-centage on dry pro-ducts from &=a.Steam deducedcondensed hydrogzm}Steam deducedcondensed oxygen.from}Percentage original car- \bon deposited. 1C2HG + 0 2 .Sphericalvessel.3.4036.10 34.800.157.2544.50 53-05E}8.8521.5 20.029.8 17.826.3 15.37.6 18.0Detonation incoil.1.8039.10{ :::: 7.7050.009.213.211-73.0( b ) Experiments with Mixture 3C,H4 + 20,.Three experiments were made with the same mixture, correspond-ing with 3C2H, + ZO,, fired in three vessels of different shape anddimensions.The .following summarised calculations point, ae inthe case of the mixture C,H, + O,, to the general agreement, withinthe limits of experimental error, between the quantity of wateEQUILIBRIUM IN HYDROCARBON FLAMES. 455actually formed and the calculated amount required for a thermo-dynamic constant Ht = 4.Descriptionof vessel.cop co.Percentage com- C2Hpposition of dry C,H,.gaseous products. CH,.Steam per cent. on dryproducts calculated fromSteam deducedcondensed hydrogeFm}Steam deducedcondensed oxygen.from}Percentage original car-bon deposited.I Ha.Kt = 4.Shortnarrowcylinder.2.6537-3510.002.904-1542-200.7512.016.614-716.0Longerand widercylinder.2.5040-101.255.2047.20nil11.718.012.329.03-75 \Sphericalveseel.0.5041.450.402.9054.75nil2.64.83.931.0( c ) Experiments with Mixture 2C2H2 + 0,.A similar deduction might perhaps also be made from the resultsobtained on ignition of a mixture 2C,H2+0,, which has beenshown by Bone and Andrew (T., 1905, 87, 1241) to give rise to aseparation of carbon without any visible condensation of moisture.From the results obtained from the final products i t is found thatthe value Kt = 4 would only require the presence in a bulb originallyfilled at 727 mm.of an amount of water-vapour having a partialpressure of 12 mm. Such an amount might readily escape con-densation a t room temperature.(6) It is thus apparent that the explosive combustion of numer-ous hydrocsrbon-oxygen mixtures, under widely differing condi-tions of incomplete combustion, gives rise to products which atleast approximately conform to the requirements of the water-gasequilibrium with a value of 4 for the thermodynamic constant, andthat this value is not greatly altered even when large quantitiesof carbon are separated or a considerable percentage of methanefound in the ultimate products; it is possible that other secondaryreactions also play an important r61e,' and the author believes thata fuller knowledge of t h s e possibilities, together with moreaccurate data relative to the thermal decomposition of hydro-carbons a t the very high temperature of flames and their possibleinteraction during cooling with primary decomposition and combus-tion products, would throw additional light on the subject ofhydrocarbon combustion. Professor Bone has, in his publishedlectures, emphasised the important r61e which secondary reaction456 FRANKLAND AND TURNBULL: THE ACTION OF PHOSPHORUSmust play in explosive combustion; thus in comparing the condi-tion of slow and explosive combustion of hydrocarbons, he expressedthe opinion (lecture at the Royal Institution, February 28th, 1908,p. 6 ) that whereas the mechanism of combustion is essentially thesame above as below the ignition-point in so far as the result of theinitial molecular encounter between the hydrocarbon and oxygenis concerned, yet “ a t the higher temperatures of flames secondarythermal decompositioiis undoubtedly come into operation at anearlier stage, and play a more important r61e than in slow combus-tion, but they do not precede the onslaught of the oxygen on thehydrocarbon, but arise in consequence of it.”The author desires to express his thanks to Professor Bone forsuggesting the research, and for advice during its progress.RUTIiwuL R.S. O.,DUMFRIESSH IRE