Green Mercury Line Research Articles

THE SEPARATION OF THE TWO TYPES OF IODINE MOLECULE AND THE PHOTOCHEMICAL REACTION OF GASEOUS IODINE WITH HEXENE

Soon after Dennison had deduced from the specific-heat curve that ordinary hydrogen gas consists of a mixture of two types of molecule, the so called and para hydrogen, a similar state of affairs in the case of iodine gas was demonstrated by direct experiment by R. W. Wood and F. W. Loomis (1). In brief, these experimenters found that the iodine bands observed in fluorescence stimulated by white light differ from those in the fluorescence excited by the green mercury line λ 5461, which happens to coincide with one of the iodine absorption lines. Half of the lines are missing in the latter case, only those being present which are due to transitions in which the rotational quantum number of the upper state is an even integer. In other words, in the fluorescence spectrum excited by λ 5461 only those lines appear which are due to what we may provisionally call the ortho type of iodine molecule. It is evident than that by irradiating iodine gas with the green mercury line it is possible to selectively activate molecules of the ortho type. Furthermore, as shown by these experiments, a molecule of the ortho type has an average life time in this form longer than the time it remains in the activated condition before emitting radiation. It occurred to one of us that these facts might be made use of in effecting a separation of the two molecular types. If some substance is added to the iodine gas with which only the activated molecules will react, one should be able to get rid of them, leaving only the other type of molecule which does not absorb the mercury line.

XXIV.Densitometer curves of the green mercury line

XXIV.<i>Densitometer curves of the green mercury line</i>

Optically Excited Iodine Bands with Alternate Missing Lines

WE have recently been studying, under improved conditions, the fluorescent bands which develop around the ‘fundamental’ doublets when iodine is excited, in the presence of helium, by the green mercury line. The use of a battery of four mercury arc lamps surrounding the iodine tube excites such a brilliant fluorescence that it is possible to photograph it in 24 hours in the second order of a 9-foot grating. On the plates so obtained it is apparent that only alternate lines of the corresponding absorption bands occur, namely, those for which m' is even. Now the fluorescent bands are known to be developed by collisions of the second kind between excited iodine molecules and helium atoms, wherein m' is changed from 34, the value originally excited, to various neighbouring values. The new data, then, show that the rotational quantum number of the excited iodine molecules can change only by even numbers during these collisions of the second kind.

Correlation of the Fluorescent and Absorption Spectra of Iodine

The lines near Hg5460 in Wood's fluorescent spectrum of iodine excited by the quartz mercury arc are identified with definite lines in the absorption spectrum. This identification furnishes the key to the analysis of the absorption spectrum. Values of the constants of the iodine spectrum, based on new measurements, are as follows: for the unexcited state ${{B}_{0}}^{\ensuremath{'}\ensuremath{'}}=0.037300\ifmmode\pm\else\textpm\fi{}0.000003$, ${{I}_{0}}^{\ensuremath{'}\ensuremath{'}}=7.42\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}38}$ g.${\mathrm{cm}}^{2}$, ${{r}_{0}}^{\ensuremath{'}\ensuremath{'}}=2.66\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ cm; for the excited state ${B}^{\ensuremath{'}}(26)=0.023368\ifmmode\pm\else\textpm\fi{}0.000005$, ${I}^{\ensuremath{'}}(29)=11.83\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}38}$ g.${\mathrm{cm}}^{2}$, ${r}^{\ensuremath{'}}(29)=3.37\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ cm; $C(29, 0)=\ensuremath{-}0.013932$, ${{m}_{H}}^{\ensuremath{'}\ensuremath{'}}(29, 0)=1.677$. The identification, in the absorption bands, of both components of the fluorescent doublets makes possible the calculation of absolute rotation quantum numbers; and these furnish direct evidence for the hypothesis of half quantum numbers. Lines in Wood's magnetic rotation spectrum which show the normal direction of rotation are found to belong to $P$ branches; those which show the opposite direction, to $R$ branches.Three new series of fluorescent doublets, $\ensuremath{\nu}(29, 45\frac{1}{2})$, $\ensuremath{\nu}(29, 50\frac{1}{2})$ and $\ensuremath{\nu}(29, 51\frac{1}{2})$, extending to the -1 order, are found and formulated, and their relationship to bands (29,1) and (29,0) demonstrated.Revised versions of Mecke's equations for band heads, based on corrected numbering, and of the constants of four red bands, based on new computations, are given; and the apparent occurrence of $Q$ branches in the red bands is shown to be due to the fact that the values of these constants are such as to cause the lines of the $P$ and $R$ branches to coincide.Calculated values of the constants of the fluorescent series, based on the results of the new absorption measurements, agree well with the values of these constants determined empirically from the fluorescent spectrum. Every detail is in agreement with the theory advanced by Lenz to account for the simple fundamental series of doublets excited by the narrow green mercury line.

The refraction and dispersion of gaseous carbon tetrachloride

The refractive index of gaseous carbon tetrachloride has been found for the green mercury line (λ5461), the result being expressed in connection with the density of the gas, that is, so as to show the refractivity of the gas by the same number of molecules as 1 c.c. of hydrogen contains at N.T.P. Adopting the value 1.001799 for the refractive index under these conditions, the dispersion of the gas has been studied over the range λ4800 to λ6700, and is represented by the expression µ - 1 = 13.543 × 1027/(7831.7× 1027 - ν2) ν being the frequency of the light.

The relation between the refractivity and density of carbon dioxide

A number of different experimenters have determined the relation between the refractivity and density of various gases, and, with a fair agreement, they have come to the conclusion that the L. Lorenz and H. A. Lorentz formula ( µ 2 - 1 / µ 2 + 2 . 1/ ρ = constant) is true within the limits of their experimental errors. At small densities this formula will, of course, reduce to either of the other two well-known relations, that of Drude ( µ 2 - 1/ ρ = constant), or the empirical relation of Gladstone and Dale ( µ —1/ ρ = constant). At greater densities the Lorenz and Lorentz formula is distinctly more accurate than the others, Drude’s formula diverging the most rapidly. This is well brought out in an experiment by A. Occhialini, published in ‘II Nuovo Cimento,' August, 1914. Even the Lorenz and Lorentz formula is not accurately true, however, when applied to the large changes of density from a gas to a liquid. For example, for the green mercury line ( λ = 5461 x 10 -7 ) µ 2 - 1 / µ 2 + 2 . 1/ ρ = 0.2065 for water, while its value is 0.2082 for water vapour, a difference of 0.82 per cent. It is thus evident that the densities used in the experiments with gases have not been great enough to exhibit the variations of the Lorenz and Lorentz constant. By experimenting with a gas just above its critical temperature large continuous changes of density may be produced and for this reason this experiment was carried out with carbon dioxide at a temperature of 34° C.

Resonance Radiation and the Quantum Theory

IN the Philosophical Magazine for September, 1916, Dr. Silberstein has made an attempt to explain the resonance radiation of iodine vapour on the basis of classical dynamics by assuming that the resonator is non-Hookean—i.e. that its restitutive elastic force is not simply proportional to the displacement. On this theory, the principal lines in the resonance series should appear at constant frequency-intervals, and to support this view Dr. Silberstein has given a tabular statement of the frequencies and their differences, based upon the work of Prof. R. W. Wood. A critical examination of the figures shows, however, that the frequency-intervals are by no means constant, but have a decided tendency to decrease on the long wave-length side. This has, indeed, been remarked upon by Prof. Wood himself (Phil. Mag., October, 1912). I find on calculation that it is not the frequencies themselves, but their square-roots, that show constant decrements in the series. The following table, prepared from Prof. Wood's data (loc. cit., p. 684) for the mercury green line excitation, demonstrates this clearly:—

On the mercury green line λ = 5461 resolved by glass and quartz lummer plates and on its zeeman constituents

Numerous investigators have studied the structure of some of the finer line in the mercury arc, and other spectra, with ruled gratings, échelon spectroscopes, and Lummer plates; but up to the present when Lummer plates and échelons were used these were invariably made of glass. A short time ago a Lummer plate of crystal quartz was made for the Physical Laboratory at Toronto by the Adam Hilger Company, for the investigation of the structure of some of the finer lines in ultra-violet spectra; but before proceeding to use it for this purpose some measurements were made with it, and with two Lummer plates made of glass, on the wave-lengths of the satellites of the mercury green line λ = 5461 Å. U. At the same time a precise method of measuring up the photographic fringe patterns produced by Lummer plated has been developed in which the geometrically central line of the double fringe pattern is taken as the line of reference in the measurements. This exact formula permits of the use of the fringes that emerge from the plate at nearly grazing direction, for which the dispersion is the greatest. The following paper contains an account of the investigation and includes the values of the wave-lengths of the satellites of the green line as deduced by the application of the method to which reference has just been made. The quartz Lummer plate, it may be added, was cut with the axis of the crystal parallel to the plane refracting surfaces and perpendicular to the length of the plate. The source of the light used in the investigation was one or other of a number of ordinary Cooper-Hewitt mercury-arc lamps. The light was passed through the collimator tube of a spectroscope and then into the plate in the usual manner.

Societies and Academies

LONDON. Royal Society, March 12.—Sir William Crookes, president, in the chair.—Sir James Stirling: Note on a functional equation employed by Sir George Stokes.—Prof. J. C. McLennan and A. R. McLeod: The mercury green line λ = 5461 as resolved by glass and quartz Lummer plates and on its Zeeman components.—H. Hartley: The electrical condition of a gold surface during the absorption of gases and their catalytic combustion. At the suggestion of Prof. W. A. Bone, the author has carried out experiments on the electrical conditions of a gold surface during its absorption of hydrogen, carbon monoxide, and oxygen, respectively, at temperatures between 300° and 400°, in order to establish certain data relative to surface combustion phenomena. The results have proved (1) that the metal acquires a negative charge during the catalytic combustion of gases in contact with it (thus confirming previous unpublished observations by Bone and Makower), which effect is probably antecedent to the actual combustion, and primarily due to “occlusion” phenomena; (2) that the metal becomes negatively charged (0.5 to 1.5 volts) during the occlusion of the combustible gas (hydrogen or carbon monoxide), and positively charged (0.8 volt) during the occlusion of oxygen; and (3) that such electrical effects are probably due to occluded gas which is leaving (rather than entering) the surface. The experiments indirectly lend support to the view that the well-known electronic emission from incandescent solids is probably de pendent upon the occlusion of gas.—J. H. Mackie: The diffusion of electrons through a slit.—Dr. A. Holt: The rate of solution of hydrogen by palladium. The rate of solution of hydrogen at constant (atmospheric) pressure by palladium in the form of black, thin and thick foil has been examined. The rate curves in the case of palladium black are simple and of continuous curvature, but for the foil a more or less pronounced discontinuity of curvature is always observed. The discontinuity is accounted for by considering that the gas is dissolved in two different forms of the metal, the rate of solution being different in the two forms. Palladium black is believed to consist almost wholly of one form, and hence gives a simple rate curve, whilst the foil (which is mainly crystalline) contains both varieties of metal, and so gives two rates, the first rate passing into the second when solution in both forms becomes equally rapid.—Dr. R. A. Hoiistoim The dispersion of a light pulse by a prism. A light pulse of a form giving the Wien energy distribution is incident on a prism, and expressions are derived (1) for the disturbance in the region immediately behind the prism where the different colours overlap; and (2) for the disturbance in the focal plane of the telescope. The first expression holds only for a particular law of dispersion, but the second is for any law of dispersion. They are both in accordance with results obtained by Lord Rayleigh by considerations of stationary phase and hydrodynamical analogy, but they go further. For example, it is definitely stated how the amplitude varies in the front and rear of and throughout the train of waves given rise to by the pulse in the different parts of the spectrum.

On a fluorescence spectrum of iodine vapour

In a number of most interesting papers Prof. R. W. Wood has shown that it is possible to obtain from iodine vapour at ordinary room temperatures, under the stimulation of light from the mercury are, a fluorescence spectrum, consisting of a number of lines ranging from λ = 7005·5 Å. U. to λ = 5337·63 Å. U. Further, he has shown that these lines can be divided into three series, one of which is stimulated by the light from the green line λ = 5460·74 Å. U. another by the light from the yellow line λ = 5769·60 Å. U.., and a third by the light from the yellow line λ = 5790·66 Å. U. Up to the present, he has identified in his photographs some 23 members in the series stimulated by the mercury green line, 10 members in that excited by the yellow line of shorter wave-length, and 13 members in the series arising from the excitation of the yellow line of greater wave-length. Moreover, by using apparatus of high resolving power, he has recently been able to show that in nearly every case the members of the green line series are complex and are in reality close doublets accompanied by a number of fainter companions.

On the constitution of the mercury green line λ = 5461 Å. U., and on the magnetic resolution its satellites by an echelon grating

In a previous communication on the series lines in the arc spectrum of mercury, attention was drawn by the writer to the excellence of the spectrograms obtained when a highly exhausted commercial Cooper Hewitt mercury arc-lamp was used as the source of the light. With this lamp, provided with a side tube carrying a window of thin crystalline quartz, it was found that exceedingly good definition was obtained over the whole range of the spectrum from slightly beyond λ = 7000 down to λ = 2150. When using the lamp at a later period in making some observations with an echelon grating of high resolving power on the structure of some of the finest lines in the visible portion of the spectrum, it was found that the components of a number of these lines also came out with exceedingly good definition.

Societies and Academies

LONDON.Royal Society, June 13.—Sir Archibald Geikie, K.C.B., president, in the chair.-C. T. R. Wilson: An expansion apparatus for making visible the tracks of ionising particles in gases, and some results obtained by its use. The method of making visible and photographing the tracks is essentially that described in a previous communication. The apparatus has been enlarged and otherwise improved. The paths of alpha-particles are generally straight or nearly so until within about a mm. of the end (in air at atmospheric pressure) where they become bent. Portions of the tracks of beta-particles from radium have been photographed, the individual ions set free being made visible by the cloud particles condensed upon them, so that they may readily be counted. The photographs of the clouds formed when a narrow beam of X-rays is sent through the cloud chamber show the tracks of kathode or beta-particles starting within the primary beam and extending for some distance beyond it. There is no indication of any action of the X-rays other than the production of the corpuscular rays. The corpuscular rays appear to start in all directions, showing no preference for that of the primary beam.—Hon. R. J. Strutt: Chemically active modification of nitrogen, produced by the electric discharge. IV. (i) Active nitrogen is a highly endo-thermic body, but its energy is of the same order of magnitude as that of other chemical substances. (2) In the reversion of active to ordinary nitrogen, the number of atoms ionised is a very small fraction of the whole number concerned in the change. The ionisa-tion is a subordinate effect, and may be due to light of very short wave-length emitted in the reaction. (3) Additional experiments are described to prove that the change of active nitrogen is more rapid at low temperatures. This is thought to be connected with the monatomic character of the molecule, and to throw light on the connection between temperature and velocity of reaction in other cases.—Prof. J. C. McLennan: The series lines in the arc spectrum of mercury.-Prof J. C. McLennan: The constitution of the mercury green line = 5461 AU; and on the magnetic resolution of its satellites by an echelon grating. —Prof. W. H. Young: The convergence of certain series involving the Fourier constants of a function.—Prof. W. H. Young: Classes of summable functions and their Fourier series.—H. G. Moseley: The number of particles emitted in the transformation of radium. The number of particles emitted at the disintegration of each atom has been determined by measuring the current carried in vacuo by the radiation from a known quantity of active material. It is found that one atom of radium B and an atom of radium C together emit 2.20 particles on an average; that an atom of radium B emits the same number of particles as an atom of radium C, and that an atom of radium E appears to emit less than one particle. From measurements of the ionisation produced by active deposit of radium emitting a measured number of 0-particles, the number of ions produced by a i3-particle per cm. of path in air has been calculated. This number varies approximately as, where A is the absorption coefficient of the radiation for aluminium.—S. D. Carothers: Portland experiments on the flow of oil. The paper was j primarily the outcome of an attempt to obtain from the results of a series of experiments, which came into the writer's hands, a relation between velocity and resistance for oil. It was seen that a considerable number of the results of the experiments followed the capillary law, and attention was directed to determining where this broke down.—G. B. Jeffery: A form of the solution of Laplace's equation suitable for problems relating to two spheres.—A. LI. Hughes: The emission velocities of photo-electrons. This investigation was undertaken to determine the relations between the maximum velocity with which electrons are emitted from metallic surfaces illuminated by ultra-violet light and (a) the wave-length of the light and (&) the nature of the metal.

On the refraction and dispersion of neon

By the kindness of Sir William Ramsay and Mr. H. E. Watson we have had an opportunity of measuring the refractive index of neon with a large quantity of the gas (300 c. c.) which had been carefully purified by Mr. Watson. Subject to small corrections which he has not yet completed, the weight of 1 litre of the gas was 0·9005 gramme at 0° C. and 760 mm. pressure in London. From 11 experiments which hardly varied by 1 part in 500 we find the refractive index at 0° C. and 760 mm. for the green mercury line (λ = 5461) to be 1·00006716 or, doubling for comparison with diatomic gases, 1·0001343.

XLIV. The echelon spectroscope, its secondary action, and the structure of the green mercury line

(1909). XLIV. The echelon spectroscope, its secondary action, and the structure of the green mercury line. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 18, No. 105, pp. 371-396.

Echelon Spectroscopes and the Green Mercury Line

IT is interesting, in reference to Prof. Nagaoka's letter in NATURE of April 23 (p. 581), to note that I exhibited photographs of the green mercury line, showing a number of new components, at the Leicester meeting of the British Association. I did not publish the number or position of the lines in the report, not being quite satisfied that some of the fainter ones might not be produced in the instrument, and I discovered later (NATURE, vol. lxxvii., pp. 198 and 222) that secondary effects, due to light reflected in the echelon, have to be taken into account. Since then Von Baeyer's measurements with a Lummer and Gehrcke spectroscope and Galitzin's echelon measurements have confirmed two of the lines that were new, and added confirmation to my values for the old ones. A doubt still remains, however, about some of the fainter lines, and as a comparison of the values given by different instruments is the most obvious way of confirming the true components and eliminating false ones, I give my results for comparison below.

The Echelon Spectroscope, its Secondary Action, and the Structure of the Green Mercury Line

(1909). XLIV. The echelon spectroscope, its secondary action, and the structure of the green mercury line. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 18, No. 105, pp. 371-396.