TV* 

 vv^ CT23 ^8 v 



LONDON, EDINBURGH, and DUBL^ 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



OCTOBER 1918. 



XXIX. On the Origin of the Line Spectrum emitted by Iron 

 Vapour in an Electric Tube Resistance Furnace at Tempe- 

 ratures above 2500° 0. By Gr. A. Hemsalech, Honorary 

 Research Fellow in the University of Manchester* . 



§ 1. Introduction. 



IT was shown in the preceding communication (this volume 

 page 209) that the spectrum of iron as observed in the 

 carbon tube resistance-furnace up to 2500° 0. and in flames up 

 to 2700° G. is caused by thermal actions on a compound of this 

 metal and not by the direct action of heat on the pure metal. 

 Now, as far as flames are concerned, the character o£ the 

 spectrum changes only slowly, though progressively, as the 

 temperature rises to 2700° C. But in the case o£ the tube 

 furnace a great change is observed soon after the boiling-point 

 of iron has been reached and the gases from the boiling metal 

 have diffused into the interior space of the tube. These facts 

 have led to the conclusion that the mode of excitation under- 

 lying the emission of the high-temperature furnace spectrum 

 of iron is no longer the same as that which prevails in the 

 furnace below 2500° and in flames up to 2700° 0. Further, 

 the appearance, at the high furnace temperature, of lines 

 which are characteristic of the arc and spark, and their 

 absence in flames of the same temperature, has suggested 

 the idea that the spectrum of iron as emitted by the furnace 

 under these conditions is of electric origin. The experiments 

 described in this paper were accordingly based on this idea, 



* Communicated by Sir K Rutherford, F.R S. 

 Phil. Mag. S. 6. Vol. 36. No. 214. Oct. 1918. U 



