Spectra of Carbon Compounds. 47$K 



evidence which, 1 think, substantiates the original hypothesis 

 and gives a more acceptable explanation of the source of the 

 Swan spectrum than any hitherto advanced. 



I take this opportunity of acknowledging my great indebt- 

 edness to Sir Gr. G. Stokes for the interest he has taken in 

 the work, and for the invaluable criticism with which he has 

 assisted me throughout. 



The Swan Spectrum from Hydrocarbon Flames. 



As is well known, the Swan spectrum is to be seen in all 

 ordinary hydrocarbon flames. If the hydrocarbon is burnt 

 without previous admixture with air, the region which gives 

 the spectrum is visible as a bright blue sheath investing the 

 lower part of the flame like the calyx of a flower. This part 

 of a flame has often been confused with what is otherwise 

 distinguished from it as the " mantle ;"- but the mantle is 

 really distinct from it. The blue calyx thins off gradually 

 from below upwards, and is no longer visible where the bright 

 yellow glow of the flame is intense, whilst the mantle sui> 

 rounds the calyx and invests the whole flame. 



If a hydrocarbon be mixed with air before burning, as in 

 a Bunsen burner or blow-pipe, the flame consists of two dis- 

 tinct feebly luminous cones, which may be distinguished as the 

 inner and outer cones. The Swan spectrum is given by the 

 inner cone. 



In a paper published in 1892 (Journ. Chem. Soc. lxi. p. 217) 

 I showed, without any regard to spectra, that the blue calyx 

 of a luminous flame corresponded chemically with the inner 

 cone of a Bunsen flame. At the same time I showed that the 

 gases arising from the inner cone of a Bunsen burner con- 

 suming either coal-gas or a single hydrocarbon contained an 

 abundance of carbon monoxide and free hydrogen, and I con- 

 cluded that the combustion of a hydrocarbon with an amount 

 of oxygen insufficient for complete oxidation resulted in a 

 preferential oxidation of the carbon. This conclusion was 

 opposed to the view generally held at that time, according to 

 which hydrogen was the more oxidizable element and should, 

 in competition with carbon for a limited supply of oxygen, be 

 the element preferentially oxidized. 



Earlier and neglected observations had pointed to the 

 same conclusions as my own, and the careful and elaborate 

 researches of Professor H. B. Dixon (see especially u The 

 Rate of Explosions in Gases/' Bakerian Lecture, Phil. Trans, 

 clxxxiv. A, p. 97, 1893) and Mr. Brereton Baker (Phil. 

 Trans, clxxviii. a, p. 571, 1888) may, I think, be held to 

 have finally proved that the first step in the oxidation of a 



