Line Spectrum emitted by Iron Vapour. 289 



to obtain a spectroscopic reaction with zinc, even by sub- 

 jecting it to furnace temperatures up to 2700° C. The open 

 ends of the furnace were in this case provided with mica 

 windows in order to exclude air, the presence of which 

 caused a blue glow to appear near the opening, due no doubt 

 to oxidation of the metal. This glow emitted only a strong- 

 continuous spectrum. 



When copper was heated in the tube a band spectrum 

 appeared in the blue and green at a temperature of about 

 2000° C. This band spectrum persisted after the boiling- 

 point of the metal had been passed. But at no time was I 

 able to observe or record photographically a line spectrum. 

 The origin of the bands has not yet been investigated, but it 

 may be connected with the formation and subsequent dis- 

 sociation of a compound. Similarly, silver gave no line 

 emission whatever, not even at the highest temperature. On 

 the other hand, both nickel and cobalt emitted line spectra 

 at 2700° C. 



Thus there are, including iron, two groups of metals which, 

 as regards their spectroscopic reaction in the furnace at high 

 temperatures, behave very differently, namely zinc, copper, 

 and silver which show no reaction, and iron, nickel, cobalt 

 which give well-developed line spectra. It is interesting to 

 inquire whether this difference in behaviour is consistent 

 with the idea that the high-temperature furnace spectrum 

 is caused by the passage of an electric current through tho 

 vapours of these metals. It will be remembered that in the 

 course of my researches on the effect of self-induction on 

 the lines emitted by metal vapours in the electric spark, I 

 established the existence of two groups of metals which 

 exhibited striking dissimilarity in so far as the appearance of 

 nitrogen bands in their spectra was concerned *. One group, 

 to which belong zinc, copper, and silver, showed the nitrogen 

 bands very strongly in addition to the lines of the metal, and 

 the other ^roup, which includes iron, cobalt, and nickel, gave 

 h ardly a trace of them. Thus in the case of the former group 

 the electric current in the discharge was partly carried by 

 nitrogen ions, whereas in the second case almost entirely by 

 metal vapour. These facts receive a plausible explanation 

 by supposing that the vapours of iron, cobalt, and nickel 

 are better conductors of electricity than those of the 

 metals of the other group; and, if this were the right inter- 

 pretation in the case of the spark spectra of these metals, it 

 would equally well explain their relative behaviour in the 



* Hemsalech, Theses de Doctorat, p. Ill, Paris, 1901. 



