628 REPORT— 1903. 



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 aldehj^des can exist, aldehyde 

 formation will occur. But aldehydes themselves decompose at high temperatures j 

 thus acetaldehyde is known to yield carbon monoxide and methane — 



CHg-CHO + CH, + CO 



and similarly formaldehyde yields carbon monoxide and hydrogen — 



HCHO = 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 well- 

 established data that it seems premature to formulate general theories. The 

 subject is very complex, and is beset with many and great experimental diflicultieff, 

 but it is surely within our power to overcome them, especially if a sufficient 

 cumber 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 botn 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 trans- 

 forms 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 onlj' 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 aflected. 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 ffuorescent rarefied gas 

 exists appears very doubtful. 



