242 Line Spectrum of Iron Vapour in Air- Coal Gas Flame. 



other than the formation of nitrides, can play an active part 

 in the excitation of line spectra, is supported by the inter- 

 esting discovery made by Dr. de Watteville, namely, that 

 of the various mercury compounds he has experimented with, 

 only certain organic salts, when fed into the Bunsen flame, 

 will yield a spectrum of the metal *. This spectrum, as 

 is well known, consists of only one very bright line at 

 X2536. 



It is also possible that in some or all of these chemical re- 

 actions in flames the presence of some substance in the role 

 of a catalytic agent is either an essential or, at least, a con- 

 ducive factor. Thus, in the case of mercury this catalytic 

 agent may be contained in the organic compounds employed 

 by Mons. de Watteville. In this connexion it is interesting 

 to note that, in spite of many efforts, no line spectrum of 

 aluminium has ever been observed in the flame. This may 

 be because the catnlytic agent necessary for starting the 

 reaction has not yet been discovered. 



Although it has not been possible for the moment to carry 

 this investigation still farther, the results so far obtained 

 seem, however, to foreshadow a useful application of spectro- 

 scopic methods to the study of chemical reactions at high 

 temperatures in those cases where the usual chemical tests 

 are not easily applicable. 



It is a pleasant duty for me to express my heartiest thanks 

 to Sir Ernest Rutherford for his unfailing sympathy and the 

 kind interest he continues to take in the work. 



Manchester, 



July 1, 1917. 



* C. de Watteville, Comptes JRendus de VAcademie des Sciences, t. 142, 

 p. 269 (1906). This important paper seems to have escaped the attention 

 of Messrs. MacLennon and Thomson (Proc. Roy. Soc. ser. A, vol. xcii. 

 p. 584 (1916)). As evidence of the superiority of the sprayer methods of 

 obtaining flame spectra and in rectification of the statements made by 

 these experimenters, I may be permitted to recall the fact that Mons. de 

 Watteville did observe the magnesium line X 4571 both in cone and 

 flame (Phil. Trans. Roy. Soc. ser. A, vol. cciv. pp. 139-168). Further, 

 he observed the zinc line X3076, in addition to many other lines of 

 this dement, all of which Messrs. MacLennon and Thomson failed to 

 obtain. 



