Spectra of Carbon Compounds, 483 



just quoted may be held to express a valuable scientific opinion 

 in the prima facie aspect of the question. 



The difficulty involved in supposing carbon to exist as 

 vapour in a hydrocarbon flame is, I am aware, an old one. 

 The subject was dealt with by Dibbits in 1863. The explana- 

 tion given by him has apparently been considered satisfactory 

 by many spectroscopists, but I cannot share this view. The 

 following is a translation from the pamphlet of Dibbits (De 

 Spectraal Analyse, p. 179) : — 



" We have already shown that the flames of all hydrocarbon 

 compounds give a common spectrum ; van der Willi gen has 

 pointed out that the spectrum is the same as that of an 

 electric spark which passes between two electrodes of carbon; 

 we are therefore justified in considering this the spectrum of 

 carbon. We remark that this spectrum is only given by the 

 lower part of the flame, that is, only in that part where the 

 decomposition of the volatile hydrocarbon takes place. We 

 can give a satisfactory account of this in the following way : 

 CrH s is dissociated as gas, C is separated, and the separated 

 carbon atoms occur for some time free in the flame ; they are 

 in such vibratory motion that the light emitted produces the 

 spectrum in question. In what state of aggregation the free 

 atoms exist in the flame at the moment of their separation 

 cannot be determined ; solid particles they are not, still less 

 liquid ; perhaps they are gaseous, perhaps they are in a state 

 that is not to be likened to any of the three known states. 

 They do not at any rate remain long in this state ; they com- 

 bine with oxygen to form carbonic oxide or carbonic acid, or 

 if they do not immediately burn they agglomerate to form 

 small solid particles of charcoal, which remain for some time 

 glowing in the flame and are the cause of the bright light ; they 

 give then, like all solid bodies, an uninterrupted spectrum 

 which extends the farther into the violet the higher the 

 temperature. 



" This view that the real carbon spectrum only, occurs 

 when the carbon atoms occur in a free uncombined state 

 gains in probability when we recollect that the carbon bands 

 are not seen in the flame of carbonic oxide, a flame in which 

 no free carbon atoms could occur. It is remarkable that in the 

 spectrum of the flame of CS 2 we see no carbon bands but only 

 the light of glowing C0 2 and of glowing S0 2 ; in this flame 

 therefore there are no free carbon atoms. The burning of 

 CS 2 may be considered to occur in the following way : first, 

 two equivalents of sulphur are replaced by two of oxygen, 

 so that by substitution CS 2 passes into C0 2 , and only then 

 does the liberated sulphur burn. The spectrum of free 



