234 Mr. Gr. A. Hemsalech on the Line Spectrum of 



through the space enclosed by the lamp chimney and the 

 flame is started in the usual way. 



When the air is not charged the resulting flame is of pale 

 blue colour and presents the shape of a semicircular arc 

 passing parallel to and over the row of holes in the burner. 

 This arc seems to constitute the feeble explosion region. If 

 now the air is charged with iron spray the arc becomes 

 luminous and gives out a continuous spectrum ; further, 

 from each hole of the burner a luminous streamer (though 

 less luminous than the arc) proceeds upwards through 

 the arc. These streamers, which seem to represent the 

 mantle, remain absolutely isolated and do not meet 

 anywhere. 



The spectroscopic observations were made end on, i. e. in 

 a direction parallel to the row of holes in the burner, and 

 that part of the lamp chimney through which the light 

 passed to the spectrograph was kept hot by means of a 

 Bunsen flame in order to prevent the deposit of moisture on 

 the inside. 



The spectrum shows, in spite of an exposure of two hours, 

 only very few lines and a feeble continuous ground in the 

 visible part. The bands of the Swan spectrum are absent. 

 With regard to the iron lines it is interesting to note that 

 only the stronger ones of Class I. are brought out, namely, 

 XX 3856, 3860, 3879, 3886, 3923, 3928, 3930, and traces of 

 a few others. But there is no trace of Class II. triplets at 

 4046 and 4384. Hence there is under these conditions com- 

 plete absence of any reaction between nitrogen and iron. 

 Further, the restricted development of the iron spectrum as 

 emitted by this flame seems to be indicative of a very low 

 temperature. 



§ 9. Spectrum of Iron given by an Air-coal Gas Flame 

 burning in an atmosphere of coal gas. 



The general appearance of the flame is very similar to that 

 given by air burning in coal gas, but it is both larger and 

 brighter. The spectrum, which was again obtained with a 

 two hours' exposure, is of a similar character as that of the 

 air flame, only a little more intense. In addition to the iron 

 lines of Class I. already recorded with the air flame (§ 8), 

 there is also present the quartet at 4376 (group y). This 

 fact is rather remarkable, because this group is not a 

 particularly prominent one under ordinary conditions. A 

 further interesting feature of this spectrum is the presence 

 of Class II. line 4384. It is, however, considerably fainter 



