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



is also emitted in the electric furnace at the highest tempera- 

 ture, Dr. King has suggested that it might be due to barium *. 

 But, according to Mons. de Watteville's observations, barium 

 does not emit a line o£ this wave-length in the flame f, and, 

 further, none of the characteristic flame and cone lines of 

 barium, such as XX 5536, 4554, and 3994 show in our flame- 

 spectrum of iron. It is therefore highly probable that the 

 line X 3936, as emitted by an iron flame, belongs to iron and 

 not to barium. But, although the line has been classed as 

 enhanced by Lockyer, its real character appears to be still 

 doubtful. Its relative intensity is greater in the Bunsen 

 cone than in the self-induction spark. 



The curious behaviour of the cone lines soon convinced us 

 that their emission by the air-coal gas flame is caused by 

 some yet unknown exciting agent, such as some special 

 chemical actions, prevailing in the cone of this flame but 

 absent from all the other, though hotter, flames examined. 



The present research was undertaken with the object of 

 investigating more fully by means of divers experiments the 

 physical and chemical conditions which govern the emission 

 of the cone lines, and also of gaining a clue to the particular 

 chemical actions which underlie their excitation. These 

 experiments were divided into the following four groups : — 



1. Effect produced on the spectrum by varying the com- 



position of the gas-mixture, §§ 3, 4, 7, and 11. 



2. Effect of changing the atmosphere in which combustion 



takes place and of reversal of flames, §§8, 9, and 10. 



3. Effect of heating and cooling the flame, § 12. 



4. Influence of velocity of gas-mixture, § 13. 



The methods of producing and feeding the flames, as also 

 the spectrographic appliances for examining them, were the 

 same as those described in my first paper. 



§ 2. Relative Appearance of Cone and Flame Lines 



in various Flames. 



The gradual development of the various types of lines on 

 passing from the base or origin of the flame upwards is best 

 studied by forming an image of the flame on the spectro- 

 graph-slit in such a way that the latter bisects both cone and 

 mantle, as indicated by the dotted-line in fig. 1. When in- 

 terpreting the spectrograms obtained in this manner, account 



* S. A. King, 'Astrophysical Journal,' vol. xxxvii. p. 239 (1913). 

 t C. de "Watteville, Phil. Trans. A. vol. cciv. p. 153 (1904). 



