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XLIII. The Spectra of Carbon Compounds. 

 By Akthuk Smithells *. 



Introduction. 



THE chief object of this paper is to give an account of 

 experiments relating to the hydrocarbon flame spectrum 

 and to advance a new view as to its origin. The other 

 spectrum concerned in the paper is that commonly called the 

 carbonic oxide spectrum. 



The hydrocarbon flame spectrum noticed by Wollaston in 

 1802 was first mapped in detail by Swan in 1857, and hence 

 it is often known as the Swan spectrum. In addition to these 

 names the spectrum has also been called the banded, chan- 

 nelled, or fluted spectrum of carbon, the candle spectrum, the 

 carbon spectrum of the first order, or simply the carbon 

 spectrum. Misunderstandings have occasionally arisen from 

 the use of these and other names to indicate one and the same 

 spectrum. 



To avoid confusion I shall adopt the name Sioan spectrum 

 throughout this paper. 



The spectra of carbon compounds have been the subject of 

 a vast amount of research and controversy, and the literature 

 is very voluminous. A history of the subject by Prof. 

 Schuster will be found in the British Association Reports 

 (1880, p. 258), and also in the text-books of Salet, Kayser, 

 and Landauer. I do not propose to deal with the subject as 

 a whole, but shall allude to previous work as occasion requires. 

 It will, however, be convenient to give a list of the recorded 

 spectra of carbon compounds which I deal with in the 

 following pages, together with the names and some of the 

 commonest sources of the spectra. A rough diagrammatic 

 drawing of the chief features of the spectra is given in fig. 1. 



(I.) The Swan Spectrum (synonyms already given). 

 Occurrence : 

 (i.) The blue or greenish blue parts of hydrocarbon flames 



burning in oxygen or gases containing oxygen, 

 (ii.) The flame of cyanogen burning in air or oxygen, 

 (hi.) The ordinary carbon arc in air. 



(iv.) Many carbon compounds in the gaseous state when sub- 

 jected to the electric discharge. ■■<■,- 

 Reputed origin : 

 (i.) Carbon as an element, 

 (ii.) A particular hydrocarbon, especially acetylene or in general 



carbo-hydrogenl 

 (iii.) Carbon as an anion, 

 (iv.) Carbon in a molecular as distinct from an atomic state. 



The most general view is apparently that the spectrum is due 

 to carbon. 



* Communicated by the Author. 



