Spectra of Carbon Compaunds. 495 



It is true that the two points just raised teJl if at all in 

 opposite senses. I do not wish to lay too much stress upon 

 them, but I think that either of them would afford an ex- 

 planation of the fact that the flame of carbon monoxide as 

 ordinarily produced does not give the oxy carbon spectrum. 



I may add that the flame of carbon monoxide burning in 

 oxygen or in nitrous oxide still gives a continuous spectrum, 

 and the same is true when the combustion is inverted and 

 oxygen burnt in carbon monoxide. 



4. Li vein or and Dewar record that the spark-discharge 

 without condenser between poles of purified graphite in car- 

 bon monoxide at atmospheric pressure gives both the oxy- 

 carbon spectrum and the Swan spectrum. As the pressure 

 is increased the oxycarbon spectrum fades, and the Swan 

 spectrum becomes more intense, the carbon line-spectrum 

 being also visible. At higher pressures the Swan spectrum 

 predominates and is very strong. At low pressures the 

 oxycarbon spectrum together with the line-spectra of carbon 

 and oxygen are seen without the Swan spectrum. 



These observations do not appear to throw much light on 

 the origin of the spectra. They do not in any particular 

 degree support the views I have put forward, nor do they 

 contradict these views. I think it only right, however, to 

 quote the evidence, and for the present range it in the category 

 of that which does not confirm my views. 



Electric Spectra of Carbon Compounds not containing Oxygen. 



I have little doubt but that the chief difficulty which will 

 be felt by spectroscopists in accepting the view that the Swan 

 spectrum belongs to carbon monoxide is to be found in 

 frequently recorded observations of the Swan spectrum 

 under conditions which appear to exclude the presence 

 of that gas. Thus it has been found in the electric spectrum 

 of hydrocarbons, of carbon tetrachloride, of cyanogen, and 

 in the spectrum produced when the electric discharge takes 

 place between carbon points in an atmosphere of hydro- 

 gen. In many cases the observations have been made with 

 great care and with elaborate precautions for the removal of 

 water vapour ; less frequently, however, with equal regard 

 to the absence of air or other oxidizing agents. 



I believe that at present many spectroscopists are distrustful 

 of conclusions based upon the supposed purity of the sub- 

 stances submitted to examination in highly exhausted Pliicker 

 tubes. The difficulty of removing films of air or moisture 

 from glass, the occlusion of gases by electrodes, the oxidizing 

 character of glass itself, all form well recognised difficulties 



