INDUSTRIAL AND ENGINEERING CHEMISTRY
1008
Vol. 20, No. 10
band lamp directly, with the lens removed. This absorption amounted to 29" C., and is a negative correction to the flame temperature, just about canceling the color correction described above. The cooling effect of the water in the salt-solution spray was found experimentally by inserting a platinum strip in the non-luminous flame and reading its temperature on the pyrometer, with and without pure water being sprayed at the same rate as used in the measurements with the flames. The amount of cooling was 15" C. for all the flames except the carbon monoxide flame, where it was 5" C. because less air was used. The measurements of Henning and Tingwaldtlg showed that the salt in the spray had no cooling effect.
a function of heating current when using a bright platinum strip gave 1770" C. when corrected for emissivity. The agreement to within 20" C. between the two methods is regarded as satisfactory when it is remembered that they are so different in character, the one depending upon a comparison of brightness temperatures of a tungsten radiator and of sodium vapor radiating due to the temperature that it assumes from the gases of the flame, the other depending upon the heat gained by a solid radiator, corrected for radiation loss, from the flame gases. The method of line reversal is much more convenient and rapid, however, and from an experimental standpoint would be chosen in preference to all others.
Gases
Comparison with Calculated Temperatures
The methane was obtained from a natural-gas well and analyzed 97 per cent CHI; the propane was of commercial grade. Both gases were stored in cylinders under pressure. The Pittsburgh natural gas (85 per cent methane, 14 per cent ethane, 1 per cent nitrogen) was taken from the city mains. The carbon monoxide was prepared from formic acid, dehydrated by phosphoric acid, and purified with potassium hydroxide solution together with an absorbing tube of Cardoxide and charcoal; its purity was better than 99 per cent by analysis.
It is interesting to compare the measured values of temperature with the calculated temperatures. The calculations were based upon the A H of the reaction and the specific heats of the gases, both from the data of Lewis and Randall, and taking into account the degrees of dissociation of water and carbon dioxide. Calculated maximum temperatures are as follows: Pittsburgh natural gas, 2000" C.; methane, 2000" C.; propane, 2050" C.; and carbon monoxide, 2230" C.; the measured values, 1875" C., 1875" C., 1930" C., and 1960" C., respectively. The difference is due to the radiation from the particular flame under investigation, and to possible inaccuracy of the specific heat data. It is to be noted that the maximum temperatures as measured correspond to gas-air mixtures somewhat higher than the theoretical mixtures for complete combustion. This is perhaps due to the fact that some air is drawn into the flame from the surrounding atmosphere. Further measurements are under way for many other combustible gases, mixed with air and with oxygen. It is planned to measure the temperatures of these flames with various designs of burners, and supplement these measurements of temperatures with measurements of total radiation.
Results
The results of the measurements by the line-reversal method are shown in Figures 2, 3, 4, and 5. The corrected temperature is plotted as a function of per cent gas in the gas-air mixture, except in the case of Pittsburgh natural gas where per cent total hydrocarbons is plotted. Comparison with Solid Radiator in Flame
It was thought advisable to compare the results by the line-reversal method with measurements by another method that should differ from it as much as possible. The method as proposed by the National Physical Laboratory as outlined in the introduction, was chosen, using a natural gas-air mixture of 10.83 per cent total hydrocarbons, which gives a temperature of 1750" C. according to the method of line reversal. The intersection of the curves of temperature as
Acknowledgment
The writers' thanks are due to J. E. Crawshaw, explosives engineer, for his assistance in making temperature calculations, and to J. S. Brown, junior explosives chemist, who assisted in the experimental measurements.
Radiant Energy from Flames W. E. Garner DEPARTMENT OB PHYSICAL CHEMISTRY, BRISTOL UIIVERSITY. ENGLAND
The thermal and the chemiluminescence theories of the radiant energy from flame are discussed and the conclusion is reached that the emission is very largely chemiluminescence. New experimental evidence on the radiation from the carbon monoxide flame is in agreement with this conclusion. The study of the radiant energy from flames offers a line of approach to the problems of catalysis of the processes of combustion, and this is illustrated by reference to experimental work on the catalysis of the carbon monoxide flame by hydrogen. I t is concluded that the action of hydrogen is twofold in character. It acts as a catalyst in the chemical sense when the hydrogen percentage exceeds 0.02, and as a conserver of chemical energy within the flame throughout the whole range of concentrations up to 2 per cent. The latter type of catalysis is termed "energo-thermic," and in the above example it is con-
cluded that either the proton or the electron is the effective agent. The chemical energy is conserved within the flame by collisions between protons or electrons and the newly formed products of the combustion process.
HE study of the radiation from flames is in the embryonic stage of development. Ittshows promise, however, of becoming a highly specialized branch of knowledge, which will play an important part in the elucidation of the mechanism of the processes of combustion occurring in flame. The advance of modern physics has made us aware of the almost infinite variety of "unit mechanisms" which can occur during the interaction between molecules and between molecules and radiation. These mechanisms have been classified and certain laws concerning them have been made known. There exists, therefore, a much broader, and a t the same
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October, 1928
IaVDCSTRI-41; A S D ELVGINEERING CHELVISTRY
time a more detailed, basis for the investigation of the phenomena of flame than was possible before the advent of the new ideas on the relationship between matter and radiation. A development of experimental technic for the measurement and analysis of radiant energy has accompanied the growth of theoretical knowledge, and has placed in the hands of the experimenter a variety of new weapons of attack. The application of this technic to the study of the flame offers a line of approach to its problems which will enable us to understand more clearly the mechanism of the processes of combustion which intrigued the minds of van Helmont and Hooke several centuries ago. Chemiluminescence from Flame
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drogen flames. This he held to be conclusive proof of the thermal origin of the radiation. Paschen also drew attention to the fact that the band maxima occurred a t very nearly the sam? positions as the absorption maxima previously observed by Angstrijmj for carbon dioxide. These observations admit of only one interpretation; they prove that the oscillators emitting the radiation from hydrocarbon flames are molecules of carbon dioxide and water. They leave undecided, however, whether or not the emitters are in a state of thermal equilibrium, as was maintained by Paschen. All that has been demonstrated is that thermally excited molecules give the same spectrum as that of the same molecules when excited in the flame. It is still possible, however, to maintain the theory that the products of reaction lose a portion of the internal energy which they acquire as a result of chemical change, directly as radiation, and it is equally allowable to hold Paschen's view that thermal equilibrium is so rapidly attained in the flame that the bulk of the radiation is emitted by carbon dioxide molecules activated by collision. R. von Helmholtz devised an experiment which he considered would give an unequivocal decision on the merits of the two hypotheseq. He attempted to raise the flame temperature by preheating the gases, and found that the radiation was not augmented as would be expected according to the thermal theory, but that there was a decrease in intensity, which is an effect predictable from the theory of chemiluminescence. Haslam, Lovell, and Hunneman4 have repeated the experiment with a similar result, but they point out that it is inconchisive on account of the preliminary reaction, which may occur during the preheating, which would lower the chemical energy available in the flame itself, and thus lower its temperature.
The source of the radiant energy from flames 1s the chemical energy set free during the oxidation of combustible substances. This energy is transformed by a chitin of molecular processes into the energy of chaotic motion; a t some stage in the chain of reactions and collisions radiant energy is emitted. R. von Helmholtz,' Paschen,2 Pringsheim3 and others have tried to determine a t what stage in this series of processes the emission of energy occurs, but have been unable to come to an unequivocal decision, even with regard to the main points a t issue. Helmholtz and Pringsheim have favored the view that the radiant energy is emitted during or directly after the chemical change-i. e., that it is chemiluminescencebut Paschen has regarded it as a purely thermal phenomenon which was solely a consequence of the high temperature of the gaseous products. On the second view the emission of radiation does not occur until the energy of chemical combination has been completely converted into thermal energy. The experimental evidence was not decisively in favor of either hypothesis, but as a result of the controversy that Table I-Total Radiation f r o m F l a m e ensued a number of important facts have been established COXPOSITIOU~ PRESSURE TOTAL RADIATIONb concerning the nature of the oscillators emitting the radia.42mos. tion from flame. 2co + 0 2 1.00 21.7 1.33 23.6 " 0 + 202 A comprehensive study of flame spectra, undertaken by 25.1 1,33 2CO + 0 2 f h-? Julius' in 1889, brought out the main difference between the 0.75 19 2 2co + 0 2 1.2
