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Active Nitrogen

Lord Rayleigh // William Strutt

In the 1930s and 40s, Lord Rayleigh reported to the Royal Society of London about his experiments with active (electrically excited) nitrogen and other gases. In 1940, he gave an account of his discovery of the anomalous energy released by active nitrogen at reduced pressure. He explained the anomaly in the abstract of his second paper published on the subject in 1940, thus:

"The amount of energy collected from the gas was surprisingly large, and is difficult to reconcile with existing theories of the nature of active nitrogen. In some cases the energy was as high as 10 eV for every molecule of nitrogen that passed through the discharge. [Later research raised the energy level up to 223 eV/mol.] This quantity of energy can with difficulty be accounted for by dissociation, even if it occurred to the extent of 100%."

In addition, he showed that "pieces of sheet gold, copper, silver or platinum may be made red hot or even melted by exposing them to active nitrogen produced in a low-pressure discharge. The nitrogen gives up its energy to the metal, which remains unacted on... Gold was selected as the most active metal...."

"The energy radiated as after-glow under favourable conditions is only of the order of 10­­-3 of the energy collected by the metal." This extra energy was about 1000 times the amount radiated by active nitrogen alone under the most favorable experimental conditions he devised.

"The after-glow consists chiefly of three heads of the first positive nitrogen bands. The maximum luminosity of the visual spectrum is at 5550, and the wavelengths of the bands in question and their luminosities in terms of this maximum are as follows:

Colour         Wave-length     Luminosity
Green 0.930
Yellow 5802 0.870
Red 6251 0.321

"The question may be raised whether the 'a' system of bands have great energy in the infra-red... We may fairly infer [based on the work of Kichlu and Acharya (1929)] that the infra-red contribution is not important."

Rayleigh calculated the "theoretical maximum for integrated nitrogen after-glow" to be 4.82 x 102 candle-sec., and used this number as a standard datum for his studies. He noted:

"Although the luminosity in the bulb remains visible for hours, its equivalent duration at the initial intensity is only about 3 seconds. The prolonged faint luminosity contributes very little to the total."

Lord Rayleigh also studied the effects of increasing and reducing the concentration of nitrogen, injecting active nitrogen into inert nitrogen, temperature change, other gases and metals, and the "wall-effect".

In 1946, Rayleigh published a sequel study on "The surprising amount of energy which can be collected from gases after the electric discharge has passed." In the abstract of the article, he stated:

"A new form of experiment is now described... in which... a platinum strip is kept hot by periodic discharges... [B]y making the experiment (1) with the Pt exposed to the gas and (2) with the Pt protected by a thin glass sheath it is possible to determine what part of the total energy is to be attributed to catalytic action of the discharge products. This amount of energy was found to be very great. Reckoning in electron volts per molecule of gas present it increased rapidly as the gas pressure was lowered and at the lowest pressure used it rose as high as 223 eV/mol. Results of the same order were obtained with other gases, so it is not clear that the glow of active nitrogen is the essential condition. This great liberation of energy much exceeds what can be explained by dissociation of the molecules and single ionization of every atom which results, which would only afford 36 eV." (Figure 1)

"To produce the electrodeless discharges, the same oil condensor was used as in my previous work. It was charged with an induction coil with a slow mercury break... An ebonite wheel with a conducting segment is mounted on an axle which is inclined at 45o to the horizontal. This wheel is immersed in Hg and makes and breaks contact once a revolution. The Hg is covered with a layer of alcohol...

"Along the axis [of the discharge vessel] there is stretched a Pt strip, over which a glass sheath can be slipped. The Pt can be heated by a current from a battery, and the tube is wound with a wire coil, which is used to excite the electrodeless discharge. When the discharge passes, the Pt strip gets heated, and its resistance increases. This is attributed partly to the direct-heating action of the discharge, and partly to the action of the Pt strip in catalyzing the discharge products (ions and dissociated atoms?).

"During an experiment, the Pt strip is kept at an arbitrary but constant resistance of R ohms. For this purpose it is made one arm of a Wheatstone's bridge, and the current is adjusted to heat the strip until the given resistance is attained. The current (C1 amp.) is measured. Then the glass sheath is slipped into position, so as to screen the wire from dissociation products. A larger current (C2 amp.) must now be passed to restore the resistance to its standard value of R ohms. The energy given up to the Pt wire by the dissociation products is   (C22-C12) Rt W-sec., when t is the time interval in seconds from one discharge to the next.

"This energy is derived from, and therefore is contained in, the gas volume v at pressure p cm. of Hg.

"Thus the energy per unit volume reckoned as at atmospheric pressure is

(C22-C12) Rt x 76 / W-sec./cc. vp

"In a typical experiment, when the conditions were adjusted to get the best effect at the chosen pressure, C = 0.78 amp., C2 = 1.73 amp., R = 0.470 ohm, t = 0.25 sec., v = 19 cc., p = 2.6 x 10-3 cm. Hg. In this case the energy is 432 W-sec./cc. as at N.T.P., or 98.5 eV/mol. of N present."

Rayleigh calculated that the probable length of travel of the molecules of nitrogen, from the point where they received energy to central strip where they gave it up, to be about 1 cm. (the radius of the discharge vessel).

"The duration of the discharge (several oscillations) was estimated... and found to be 3.76 x 10-6 sec.. This requires the molecule considered to have a velocity of... 5 x 105 cm./sec.. Now the molecular velocity of nitrogen is 5 x 104 cm./sec. at 273 K. To raise it 10 times, the absolute temperature must be increased 100 times, i.e. to the temperature of the hottest stars. It seems clear, therefore, that a molecule could not travel fast enough to give up energy to the Pt strip more than once during the short duration of a discharge. If not, it must carry 98.5 eV at one time and it is not easy to see how according to current ideas how it could do this. The energy of dissociation of nitrogen is 7.4 (?) V, and this, together with the ionization of both the atoms, would only afford 7.4 + 2 x 14.5 V or 36 V. Considering that the discharge gives a band spectrum and not a line spectrum, the idea of complete dissociation and ionization is somewhat fantastic; but even if we make this assumption the difficulty remains.

"There appears to be no advantage in increasing the number of turns to the maximum, and close winding was inconvenient, because the coil showed a tendency to spark over. A coil having 26.5 turns was used in further experiments, as being about the useful maximum.

"The pressure was then varied, leaving the other conditions unaltered:

[Table not shown in the online version]

"It appears, therefore, that the energy per molecule increases very greatly as the pressure is diminished.

"It was of interest to see whether these very large values of the energy per molecule are peculiar to nitrogen, or whether they would be found in other gases also. A few results only are available at present:

Gas P, pressure (cm.)          W-sec./cc.       eV/mol.
Oxygen             2.6 x 10-3              432              98.5
Hydrogen          4.3 x 10-3              470             107
Nitrogen           2.6 x 10-3               309                70.6

"These are of the same order of magnitude as the results for nitrogen, one of which is repeated for convenience of reference."

The high energy output of this relatively simple experiment suggests that a convenient source of "free energy" might be available therein. Aside from that notion, despite repeated reading of Rayleigh's articles on active nitrogen, this writer remains baffled as to how active N, O or H could possibly form Mass 5 as claimed by Ron Kovac (Infinite Energy #15/16, July-Nov. 1997 and elsewhere). Kovac does not explain the reaction pathway(s) involved.

Rayleigh: Proc. Roy Soc. A. 176: 1, 16 (28 August 1940); ibid., 182: 296-299 (1946); ibid., 151:567-584 (1935)

Lord Rayleigh's Active Nitrogen Experiment


Chemical Abstracts (1942)

Proc. Roy. Soc. (London) A-180: 123-139 (1942)

"Further Studies on Active Nitrogen: Experiments to show that traces of oxygen or other impurity affect primarily the walls of the vessel, and not the phenomena in the gas space."

When a minute O2 tributary is added to the N2 gas stream it takes longer to assert its action than the time needed to change the gas composition, which indicates that the effect on the O2 tributary is on the walls of the tube. The fact that when the O2 tributary is checked the action persists confirms this view. The O2 modifies the glass wall favorably for the accumulation of active N. The restoration of the afterglow by a tributary O2 stream is very marked with electrodeless discharges at 0.3 mm. An increase of intensity by a factor of 32 is achieved by the introduction of the O2. The observed phenomena are complex and not easy to explain. The effect of treating the vessel is examined. Strong preliminary heating in vacuo makes a vessel destroy the afterglow, Heating in N2 at atmospheric pressure has the same effect. Heating in O2 at even 1 mm pressure restores the glow. The effects can be explained in terms of gas-layer formation or removal. The behavior of the gas away from the surface is different; in this case purity of N2 favors the promotion of active N phenomena.

Ibid., pp. 140-150 ~ "The ionization associated with active nitrogen"

The ionization associated with afterglowing N is investigated thoroughly. The ionization is completely cut off if the test vessel is separated from the afterglow by a silica wall. The ionization is thus not produced by light (at least of wavelength greater than 1850 A). No increased current is observed when the surface action is such as to make a testing cathode red hot. This seems to exclude electron emission as the cause of the ionization. The ionization is nearly the same when the cathode is one of the common metals or a surface coated with meta-phosphoric acid, but a copper cathode, when clean, gives a much larger effect. It is concluded that the surface electron emission is small compared with the volume ionization of the gas space. The number of ion pairs generated and the number of photons emitted per cc at various stages of a decaying glow are measured. The number of photons is at first greater but at very low intensities the number of ions probably exceeds the number of photons. It is considered that different mechanisms are involved in the two processes. The admission of inert N2 increases the instantaneous photon emission and also the instantaneous ionization. Evidence is produced which points to the fact that the ionization process and afterglow process are in some measure independent. The ionization potential of the N2 molecule (15.51 v) is such that the energy attributed to active N2 on spectroscopic grounds, as calculated from the emitted band spectrum, is open to suspicion. It is considered that previous attempts to explain active N2 have laid too much stress on the spectroscopic aspect and have ignored the question of ionization. This was previously considered a subordinate phenomenon, but the work here shows that under some conditions ionization may involve as many atoms as the light emission.

Further Studies on Active Nitrogen. IV. The Ionisation Associated with Active Nitrogen, by Lord Rayleigh  © 1942 The Royal Society.

In this paper the ionization associated with afterglowing nitrogen is examined more thoroughly than has yet been done. It is found that this ionization is completely cut off if the testing vessel is separated from the afterglow by a silica wall. The ionization cannot therefore be directly produced by light, at any rate within the range from ? 1850 to the visible. No increased current is observed when the surface action of the active gas is so vigorous as to make the testing cathode (of gold) red hot. The ionization is in general nearly the same when the cathode of the testing vessel is one of the common metals or a surface coated with metaphosphoric acid. Copper, however, is an exception. While the copper is clean it gives an effect several times larger, though this soon goes off, as it becomes dull by the action of the gas. It appears therefore that though there is some surface emission of electrons, it is in most cases small compared with the volume ionization in the gas space. Comparisons are made of the number of ion pairs generated, and the number of photons emitted, per cubic centimetre at various stages as the glow dies down. At first the number of photons is many times greater, but as the glow gets down the numbers become equal, and at intensities too low for convenient observation it is likely that the number of ion pairs may become greater than the number of photons. It is certain that the light emission and the ionization do not go down at the same rate. The latter goes down much more slowly, and gains relatively. The interpretation of this is discussed. It is found that the admission of inert nitrogen which is known to increase the (instantaneous) emission of photons, also increases the (instantaneous) ionization. It is pointed out that the ionization of nitrogen requires 15· 51 V, and the presence of this ionization seems to throw much doubt on the attempts to calculate the energy of active nitrogen from the band spectrum emitted, which suggests an energy of 9· 6 V.


Nature 154, 576-577 (04 November 1944) | doi:10.1038/154576a0

Variations in the After-Glow Brightness of Active Nitrogen under Varied Experimental Conditions


LORD RAYLEIGH, in a remarkable series of experiments, has studied photometrically the variations in the after-glow brightness of active nitrogen under varied experimental conditions. The results are of extreme importance in testing the various theories of active nitrogen. In the present note, some of these results will be considered in the light of the hypothesis recently proposed by me1,2, namely, that active nitrogen is simply the ionized nitrogen molecule in the N2+(X?) state produced by the discharge. If the walls of the vessel are suitably ‘conditioned’ to prevent the surface from acting as catalyst, the recombination of the positive ions with electrons proceeds mainly in the volume of the gas by a three-body collision process in which neutral nitrogen molecules act as the third body.

   1. Mitra, S. K., Science and Culture (Calcutta), 9, 49 (1943); 10, 133 (1944).
   2. Mitra, S. K., Nature, 154, 212 (1944).
   3. Rayleigh, Lord, Proc. Roy. Soc., A, 151, 567 (1935).
   4. Rayleigh, Lord, Proc. Roy. Soc., A, 176, 1 (1940); see data in p. 5; see also ref. 3, p. 576.
   5. See ref. 4, p. 10.
   6. See ref. 3, p. 13.
   7. Thomson, J. J., Phil. Mag., 47, 337 (1924). | ChemPort |

Charged Particles as Active Species

At one time RIIitra (44) suggested that the activity of active nitrogen was due to the presence of Nz+ ions. This theory was based on analogous processes
that were thought to occur in the emissioil of the spectrum of the night slry, and on the very large energies transferred to metal foils in some experiments
made by Lord Rayleigh (54). It has since been found that the interpretation of the atmospheric spectrum in terms of Nz+ was wrong (7) and that Rayleigh's
results were due to bombardment by electrons from the exciting discharge (2). Mitra has therefore suggested recently (45) that the activity of active nitrogen
is due to nitrogen atoms...

 Energy Imparted by Active Nitrogen

Authors:  Mitra, S. K.
Affiliation:  c/o Royal Society, London. Nov. 10.
Publication:  Nature, Volume 154, Issue 3922, pp. 831 (1944). (Nature Homepage)
Publication Date:  12/1944
DOI:  10.1038/154831a0
Bibliographic Code:  1944Natur.154..831M
SPECTROSCOPIC evidence1 shows that the maximum energy of excitation which a molecule of active nitrogen can impart to another molecule (or atom) is 9.45 eV. Lord Rayleigh, however, from a study of the incandescence of metals immersed in active nitrogen, finds2 that each molecule of active nitrogen delivers to the metal energy of, at the least, 10 eV. These apparently conflicting results can be reconciled and satisfactorily explained on the hypothesis recently proposed by me, namely, that active nitrogen is simply the ionized molecule of nitrogen N2 + (X') produced by the discharge.