76 INFRA-RED EMISSION SPECTRA. 



temperature and the consequent dissociation of C0 2 into CO, the maxi- 

 mum of the emission band of C0 2 will shift toward that of CO. The writer 

 has observed this emission band of C0 2 under various conditions of tem- 

 perature. In the emission spectrum of the Hefner lamp it was found at 

 4.36 fi. In the arc spectra of the salts of the metals previously studied it 

 was found at 4.52 ;x. In the vacuum-tube radiation of CO and CO, the 

 maximum was found at 4.75 /. In the acetylene flame it was found at 

 4.4 ft, while in the present examination it occurs at 4.55 to 4.65 ;i. It has 

 always appeared to the writer that this shift of the emission maximum 

 with rise in temperature is due to dissociation of C0 2 into CO, and no 

 satisfactory data has yet been found to refute this assumption. The 

 vacuum-tube radiation of CO and C0 2 , where the maximum emission 

 occurs at the same place for both gases, seemed to prove the point. The 

 present data furnish further evidence that the cause is due to dissociation. 

 For, using a graphite arc on 4 amperes, when the arc is short, and the 

 hottest, the maximum occurs at 4.65 fi. When the salts of the metals are 

 introduced into the arc they are ionized and the metals carry the greater 

 part of the current. The resistance is reduced, and hence the tempera- 

 ture (and dissociation of C0 2 ) is reduced. Here the maximum is at a 

 shorter wave-length corresponding to less dissociation of C0 2 . While 

 this explains certain points it fails to account for the lack of an emission 

 band when the current is large, 8 to 15 amperes. It is hardly permissible 

 to assume that neither CO or C0 2 is formed at this high temperature and 

 that the electrode disappears in the form of vapor, though the writer 

 made this assumption at the conclusion of his previous examination of 

 the carbon arc. 



The change in density of the gases in the two cases will not account 

 for the observations, for even the smallest amount of CO and C0 2 is capable 

 of emitting perceptible radiation, as was found in the experiments with the 

 vacuum tube. As a whole, the mechanism producing this radiation is not 

 understood and further experiments will be needed to gain insight into 

 this subject. 



THE INVESTIGATIONS OF MOLL. 



While the above experiments on the carbon arc were being concluded 

 the investigations of Moll 1 on infra-red metallic spectra appeared in print. 

 He examined the emission spectra of the salts of the metals of Na, K, Rb, 

 and Cs in the carbon arc, using for the purpose a rock-salt prism, a ther- 

 mopile, and an automatic device for recording the galvanometer deflections. 

 The apparatus was a little more sensitive than the radiometer previously 

 used by the writer, while his dispersion was almost twice as great, and 

 with the automatic device he was able to explore the region beyond 2 /i 

 more thoroughly than was possible by making personal observations. In 



1 Moll: Onderzoek van Ultra-Roode Spectra, by W. J. H. Moll. Dissertation, Utrecht, 

 1907; Proc. Amsterdam Acad., Feb. 21, 1907. 



