the hydrocarbon to carbon monoxide (e.g. mixtures of two volumes methane with one volume oxygen, or of equal volumes of ethane and oxygen). The lowest temperature at which such mixtures of methane and oxygen interact, when sealed up in a borosilicate glass bulb at atmospheric pressure, and afterwards placed in a constant temperature air-bath, is somewhere about 300; in the case of the mixtures of ethane and oxygen it is about 225°. At all temperatures ethane is oxidised much more rapidly than is methane, other conditions being equal. Under such conditions a portion of the hydrocarbon is burnt to, finally, carbon dioxide, carbon monoxide, and steam, without any liberation of free hydrogen or separation of carbon, while a portion of the original hydrocarbon always remains intact. Below are tabulated the analyses of the products from two typical experi We next devised an apparatus in which the reacting gaseous mixtures can be continuously circulated day and night, at a practically uniform rate, (1) over a surface maintained at a constant temperature; and (2) through suitable washing and cooling arrangements for the removal of soluble or condensable intermediate products. A manometric arrangement enables us to take pressure records of the gas in the apparatus at regular time-intervals throughout a given experiment, which may often extend over many consecutive days and nights. The records so obtained show, in the case of both methane and ethane, a regular and continuous fall of pressure throughout the oxidation. The experiments with methane reveal the fact that formaldehyde plays an important rôle as an intermediate product; that, indeed, the oxidation involves at least two distinct stages, namely:— 1. A primary oxidation to formaldehyde and steam 2. The subsequent further rapid oxidation of the formaldehyde to carbon monoxide, carbon dioxide, and steam. This may best be considered as the result of two simultaneous reactions, namely :— H (a) H·C: 0 + 0 : 0 0 : 0 : 0 + H2O H (b) H·C: 0 + 0 : 0 + H·C: 0 = 200 + 2H ̧O. Possibly the latter may involve the formation and very rapid decomposition of formic acid.. Thus In the case of ethane we are able to distinguish the successive formations of (1) acetaldehyde, and (2) formaldehyde, as intermediate products. The experimental results are consistent with the following view of the case, namely:— 1. That the primary oxidation involves the formation of acetaldehyde and steam CH,ÁCH, + O, = CH,CHO + H,O. 3 2. That the acetaldehyde is further rapidly oxidised to carbon monoxide, steam, and formaldehyde 3. That the formaldehyde suffers further oxidation as indicated above. These views, it may be stated, are supported by experiments on the oxidation of acetaldehyde. I wish it to be understood that I have provisionally adopted the explanations just given of the oxidation stages of methane and ethane as a convenient working hypothesis because they express most simply the observed facts. Professor Armstrong has recently given us a very suggestive general theory of combustion which embodies his dictum that chemical interchange and electrolysis must be regarded as interchangeable equivalent terms. Applied to hydrocarbons (e.g. methane) the theory involves the successive 'hydroxylation' of each hydrogen by an indirect process, the oxygen being transferred electrolytically across 'conducting' water, as indicated by the following scheme : The hydrogen peroxide formed being in part decomposed by heat, and in part acting as depolariser. The hydroxylated molecules thus produced may decompose, as for instance : and then the formaldehyde is further indirectly oxidised to (1) formic acid (2) carbonic acid, thus: (6) 0 : C : H ̧ + OH ̧ +02 => : 0 + H2O2 2 HO H но (7) HO>C : 0 + OH, +02 = HO>C : 0 + H20, 2 The formic and carbonic acids thus produced then decompose, as follows: It does not come within the province of this paper to discuss this electrolytic theory of chemical change; it should, however, be pointed out that Professor Armstrong's views demand the formation of an alcohol in the primary oxidation of a saturated hydrocarbon. Although I have never failed to obtain a marked 1 Trans. Chem. Soc. 1903, 83, 1088. formation of aldehydes in my experiments on methane and ethane, I have so far searched in vain for alcohols; if the latter are produced during the primary oxidation, they are very rapidly further oxidised to the corresponding aldehyde, which must be presumed to be more stable under these conditions. The question now arises whether these reactions which undoubtedly occur at low temperatures also occur at the higher temperatures of hydrocarbon flames. My own view is this: the velocities of these low temperature' reactions will rapidly increase as the temperature rises, and so long as aldehydes can exist, aldehyde formation will occur. But aldehydes themselves decompose at high temperatures; thus acetaldehyde is known to yield carbon monoxide and methane CHỢ-CHO +CH,+CO and similarly formaldehyde yields carbon monoxide and hydrogenH CHO = CO + H and possibly within certain temperature limits these reactions are reversible. The production of formaldehyde in the oxidation of methane, for example, will only be limited by the temperature at which formaldehyde is incapable of existence, whatever that may be. We shall have to take into account similar considerations in discussing other probable changes, as, for example, (1) the further oxidation of aldehydes, and (2) the purely thermal decomposition of hydrocarbons. All these possible reactions call for further careful investigation. As yet we have so few wellestablished data that it seems premature to formulate general theories. The subject is very complex, and is beset with many and great experimental difficulties, but it is surely within our power to overcome them, especially if a sufficient number of workers will co-operate. 2. Fluorescence as related to the Constitution of Organic Substances. By JOHN THEODORE HEWITT. A distinction must be made between substances which are simply coloured and those which exhibit the phenomenon known as fluorescence. Whilst bota classes of substances select radiant energy of certain wave-lengths, the fate of this energy is different in the two cases. A merely coloured substance degrades the energy it absorbs to a confused mixture of relatively slow vibrations, so that the substance or its solution tends to rise in temperature. A fluorescent solution largely transforms the absorbed energy and emits it with an altered frequency, in most cases still sufficiently high for the emitted energy to appear as light. Both the absorption and the fluorescent spectrum are composed of bands which in the fluorescent spectrum are usually broader than in the absorption spectrum. Dark-line absorption spectra or bright-line fluorescent spectra are not to be expected in the case of a solution; the molecules of the solvent must exert an influence on the vibrations of the molecules of dissolved coloured substance, and, this influence not being uniform for all the molecules of dissolved substance, both spectra can only be expected to consist of bands and not of lines. In the case of a gas the emission spectrum varies with the pressure; should the gas be sufficiently rarefied, the molecules perform their vibrations in an unfettered manner and the spectrum consists of bright lines corresponding to definite rates of vibration. But on increasing the pressure of the gas the molecules must mutually influence one another, with the result that their rates of vibration are affected. Since at any instant different molecules will not be affected to the same extent, they will execute their vibrations at somewhat varying rates and the lines in the spectrum will broaden into bands. A fluorescent-line spectrum could only be found in the case of a gas; whether any sufficiently fluorescent rarefied gas exists appears very doubtful. The ultimate cause of fluorescence has naturally attracted attention. Stokes 1 was inclined to attribute a peculiar sensibility to the molecules of substances exhibiting this phenomenon. Lommel started with the assumption that light of a certain frequency may give rise to vibrations of varying amplitudes in the molecules of a substance. If the frequency depends on the amplitude, the emitted light will not be homogeneous and the substance may be considered as fluorescent. Two grave objections to Lommel's theory are, that there seems to be no possibility of a source of light remaining homogeneous whilst it fades in intensity, and that all coloured substances should be fluorescent. Both deductions are at variance with actual facts. Fluorescence must of necessity attract the attention of organic chemists, chiefly on account of the fact that so many fluorescent substances are organic compounds of known constitution. Richard Meyer attempted to connect the fluorescence of organic dyestuffs with the presence of certain atomic groupings which he termed 'fluorophors.' Amongst such fluorophors, the pyridine, pyrone, and paradiazine rings may be mentioned. For fluorescence to be developed it is necessary that the fluorophor be attached to heavy carbon groups, usually aromatic nuclei. Meyer's theory gives no explanation of the influence of solvents and of the differences frequently observed in the case of isomeric compounds. The present author has started from a fundamentally different point of view, which may be stated as follows. If in the case of a tautomeric compound the passage from one to the other configuration can be effected by two equal but opposite atomic displacements, the molecules will vibrate between the two extreme positions of less symmetry, passing through the intermediate more symmetrical configuration. Energy absorbed when the molecules possessed one configuration could then be emitted when they had the other configuration; and as the two configurations would certainly correspond to different vibration frequencies, one has the necessary conditions for the exhibition of fluorescence. Consider the fluorescence phenomena in the case of the following compounds :I. Fluoran, CH120, V. 45-Dinitrofluorescein, C20H16(NO2)2O5. 4 VI. 45-Dinitro-27-dibromofluorescein, CH (NO), Br,O. 7 Of these substances, I. is colourless, and in 'neutral solvents gives colourless, non-fluorescent solutions. It fluoresces, however, if dissolved in strong sulphuric acid. II. III. and IV. all fluoresce, especially in alkaline solution. The alkaline solutions of V. VI. VII. do not fluoresce at all. Meyer's theory gives no explanation of these differences. The theory now brought forward agrees 1 Phil. Trans., 1852, 463. 3 Zeitschr. physikal. Ch. (1897), 24, 468. 2 Wied. Annalen, 3, 268. * Proc. Ch. Soc. (1900), 16, 3; Zeitschr. physikal. Ch. (1900), 34, 1–19. Ibid. (1902), 81, 893. with the observed facts. Fluoran, though not itself tautomeric, might give tautomeric fluorescent oxonium salts; these have been isolated. The non-fluorescence of the nitro- derivatives of fluorescein is readily explained; the nitro- groups enter into the ortho- positions to the hydroxyl groups, and since compounds of the type -C(NO2) = C(OH)-yield sodium salts which are, in all probability, of the general formula-C(NO,Na)-CO-the fluorescence which depends on a doubly symmetrical tautomerism is necessarily inhibited. Whilst in the greater number of cases the theory propounded agrees with the observed facts, exceptions such as the following must not be overlooked. 1. Substances having the necessary constitution, but not exhibiting fluorescence. A secondary tautomerism might inhibit the vibration between two extreme similar configurations; this case has been considered in dealing with the nitroderivatives of fluorescein, In some cases it is possible that fluorescence has not been detected owing to the emitted radiant energy corresponding to an invisible part of the spectrum. Another cause which may preclude the necessary vibration is that the symmetrical intermediate configuration may correspond to more molecular free energy than the extreme unsymmetrical configurations. The molecule would then have no tendency to vibrate regularly, the case being analogous to that of an inverted pendulum. 2. Substances which fluoresce but cannot possess doubly symmetrical tautomeric formula. The author does not think the occurrence of such substances can be taken as a serious argument against his theory, which may be formulated as follows: If the molecules of a tautomeric substance possess such a structure that the passage from the configuration of least free energy to the less stable configuration may be effected by equal and opposite atomic displacements, the molecules will vibrate between the extreme positions and the substance exhibit the phenomenon of fluorescence. That fluorescence may be due to other causes is not negatived by this assertion. 3. Preliminary Note on some Electric Furnace Reactions under High Gaseous Pressures. By J. E. PETAVEL and R. S. HUTTON. The paper gives an account of some work carried out in an inclosed electric furnace constructed to work with gaseous pressures up to 200 atmospheres. The power employed has been usually about 15 kilowatts per hour, the furnace containing a charge of about 20 lb. of material and 1,000 to 2,000 litres of gas. A second furnace of about one-tenth the capacity was used for gas reactions with high-tension current. The reactions at present under investigation include the direct reduction of alumina by carbon, the conditions of formation of calcium carbide, particularly as modified by the change of gaseous atmosphere, and the formation of graphite. With regard to gaseous reactions a study of the production of nitric acid and cyanogen compounds has already been commenced. The preliminary experiments have shown that under pressure alumina is reduced to the metallic condition, but in all cases accompanied by a large amount of aluminium carbide. This reaction is most unfavourably influenced if the carbon monoxide which is formed be retained, whereas it is favoured by the rapid removal of the gaseous products of reaction. So far as calcium carbide is concerned, contrary to expectation, the yield is in no way diminished by the presence of carbon monoxide gas even at high pressures. An important difference in the methods of working is necessary in those cases where it is desired to effect purely gaseous reactions. Here a high-tension current is required. For instance, the formation of nitric acid, even at pressures of 100 atmospheres, is only accomplished in appreciable amount where the electromotive force used is of several thousand volts. The account includes a general description of the plant employed for preparing and compressing the various pure gases required in quantity for this work. |