the Spectra of Carbon and Hydrocarbon. 549 



Probably the chief interest of the arc-in-flame spectrum 

 lies in the region about X4382 to X4364, and in the hydro- 

 carbon bands. In the former re g ion are the three lines 

 which appear to form part of the u Swan '" spectrum, and to 

 be attributable to carbon. These three lines occur in the 

 flame spectrum, where they are superposed on the first 

 portion of the hydrocarbon "/" group, but are frequently 

 so faint as to be hardly visible amorgst the lines forming 

 the band. Their brightness, however, changes considerably 

 with the conditions of combustion. In a Meeker flame with 

 a rapid flow of gas, the region immediately above the grid 

 is blue and the flame roars, but when the flow is sufficiently 

 reduced it becomes almost silent and the colour changes to 

 yellowish green. 



The spectrum then shows an increase in brilliancy of the 

 "Swan" bands, and simultaneously "the three" appear 

 clearly, standing out on the background of the hydrocarbon 

 band. 



In the normal carbon arc in air these lines are not con- 

 spicuous, but are recorded with suitable conditions and 

 exposure. 



hi the spectrum of the arc-in-flame we find " the three " 

 present with very considerable intensity, and their sym- 

 pathetic variation with the carbon bands lends support to 

 the conclusion that they have the same origin. 



The sources from which the carbon and hydrocarbon 

 spectra were obtained were as follows :— 



1. Flame of coal-gas in air from a Meeker burner. 



2. Carbon arc in air. 



3. Carbon arc in flame of coal-gas in air. 



4. High-tension transformer spark in air between 



carbon electrodes (capacity and self-induction 

 in circuit). 



5. Transformer spark between carbon electrodes in an 



atmosphere of coal-gas (capacity and self-induction 

 in circuit). 



6. The same as No. 5, but in a flame of coal-gas in 



air. 



7. Transformer spark in absolute alcohol, and also 



in glycerine (no capacity or self-inductance in 

 circuit). 



Visual observations of the spectra were made with various 

 spectroscopes, and the enlargements which accompany this 



