of the Flame and Furnace Spectra of Iron. 225 



§ 10. Note on the Carbon Bands observed in the Furnace. 



No special attention was given to these bands, but the 

 few observations made of them en passant are worth re- 

 cording. The bands met with under various furnace con- 

 ditions are those generally attributed to hydrocarbons, 

 cyanogen, and carbon monoxide (Swan spectrum). Of these 

 the last-named bands have been observed only at tempe- 

 ratures above 2500° 0. in the presence of a strong ionization 

 current. No bands were obtained at 1500° C. The relative 

 behaviour of the hydrocarbon and cyanogen bands at various 

 furnace temperatures is seen from the following table. At 

 the lowest temperature, namely 1600° C, the observations 

 were made with a current of hydrogen passing through the 

 furnace. In all the other cases the furnace contained 

 stagnant air. 



Relative Intensity at 



Edge. Wave-length. 1600° 1900° 2100° 2400° 



Red 3871 — — 1 



Red 3883 — | 2 3 



Violet 4241 § — 1 1 



Violet 4260 \ — — £ 



When a current of ammonia is passed through the furnace 

 at 2400° C. the cyanogen bands become most intense and 

 show a high degree of development. With a current of 

 hydrogen at the same temperature they still show plainly, but 

 their tails are imperfectly developed. 



With regard to the origin of these bands, the following 

 observations may possibly provide a clue. It was found 

 that when air, hydrogen, &c. were passed through the carbon 

 tube, the latter burnt through always near the end where the 

 gases entered. This of course indicates a marked wear of 

 the tube at the place upon which the gases impinge first. 

 When no gases are passed through the furnace tube, the latter 

 burns through almost invariably near the middle. There is 

 no doubt that the wear noted in the former case is caused by 

 the gas combining with the carbon at the lower temperature 

 of the tube end. The newly formed compounds then enter 

 the hot central region of the furnace, where they undergo 

 dissociation. It may be the process involved in this dis- 

 sociation which causes the emission of these bands, and the 

 excitation would thus be due, as in the case of iron, to 

 thermo-chemical actions; On the other hand, the Swan 

 spectrum, which appears only at the highest furnace tempe- 

 ratures, seems to owe its emission to electric actions. 



Phil. Mag, S. 6. Vol. 36. No. 213. Sept. 1918. Q 



