120 Dr. W. Marshall Watts on the Spectra 



Kayser, in the fifth volume of his great work HandhucJi 

 der Spectroscopie (1910), after describing the experiments of 

 Angstrom and Thalen, says: "I believe that the authority 

 which, with perfect justice, was at that time attributed to 

 the views of Angstrom upon spectroscopic matters is the 

 reason that the Swan spectrum is by many still spoken of as 

 the spectrum of hydrocarbons or of acetylene ; although, in 

 my opinion, this conclusion has been proved to be untenable." 



Other experimenters who expressed the opinion that the 

 " Swan " spectrum must be attributed to carbon were Secchi*, 

 Lecoq de Boisbaudran f, Ciamician J, Deslandres §, and 

 Eder || . Eder H photographed the spectrum of burning 

 hydrocarbons from the yellow into the ultra-violet as far as 

 2449: the five groups of bands in the red, yellow, green, blue, 

 and violet (the " Swan " spectrum) he assigns to carbon, and 

 the very strong bands in the ultra-violet he assigns to water- 

 vapour. 



In a paper on " The Spectra of Carbon Compounds " in 

 the Philosophical Magazine for 1901, Prof. Smithells ** 

 advances a new view of the origin of the " Swan " spectrum 

 and of the spectrum of carbon monoxide or dioxide in a 

 Geissler tube, attributing the first to carbon monoxide and 

 the second to carbon dioxide. Prof. Smithells's defence of 

 his position is based, for the most part, upon a study of the 

 phenomena of flames. He seeks to set aside the natural 

 conclusion to be drawn from the repeated observations of the 

 •'Swan" spectrum in carbon compounds not containing 

 oxygen by the suggestion that it is impossible to free these 

 substances from water, and other impurities containing 

 oxygen, and points to the difficulty of removing films of air 

 or moisture from glass, the occlusion of gases by electrodes, 

 and the fact that glass itself contains oxygen as forming well- 

 recognized difficulties, quite apart from the purely chemical 

 difficulties of obtaining pure materials. 



I have now to describe experiments in which the " Swan " 

 spectrum was observed in the absence of oxygen as far as it 



* Secchi, C. P. lxxvii. p. 173 (1873). 



+ Lecoq de Boisbaudran, Spectres lumineux, p. 43 (1874). 



% Ciamician, Szb. Wien, lxxii. (ii.) p. 425 (1880). 



§ Deslandres, C. R. cvi. p. 842 (1888) ; Ann. Chim. Phys. xv. p. 5. 



|| Eder, Beitriiye zur Photochemie, 1890. 



51 Eder's photograph of the spectrum of the Bunsen flame obtained 

 "by 36 hours' exposure on an Erythrosin plate shows C y , C<j, C e , and /, 

 with " the three " lines, and the " fine-grained " structure from 4315, and 

 the "coarse-grained" structure up to 3873. (See figs. 1 & 4.) 



** SmitheHs, Phil. Mag. i. p. 476 (1901). 



