CHAPTER III. 



INFRA-RED EMISSION SPECTRA OF METALS. 



This work was begun by examining the spark spectra of such metals 

 as Zn, Al, and Cu. An induction coil and condenser were used. No 

 emission Hnes could be detected; instead of lines a weak continuous 

 radiation was detected in the region of 2 /a to 3 yu,, which appeared to be 

 due to the hot particles from the electrodes. The arc between metallic 

 electrodes of Fe, Zn, and Cu was then tried ; but no lines could be 

 detected in the region of i /x, beyond which point the incandescent 

 oxides gave such an intense, continuous, "black body" spectrum that 

 the emission lines would have been obliterated by the radiation from 

 the oxides. The vapors from the copper arc had but little "black body" 

 radiation. No emission lines were detected, however, although several 

 have been predicted in the region of 2.5 fi. 



3 -^ 



Fig. 135. 



7^ 



Copper. 



In figure 135 two sets of curve a are given for the vapors of the Cu 

 arc, while curve h shows the radiation from the hot electrodes. In 

 this figure it will be noticed that the terminals give a more intense 

 radiation than the vapors, in which the density of the oxides is not so 

 great as in the iron arc. 



303 



