700 Spectra of Mercury, Cadmium, and Zinc Vapours. 



was being exhausted some mercury vapour diffused back 

 into it from the Gaede mercury-pump. It will be noted 

 that the mercury absorption band is also shown in fig. 6. 



From these results it will be seen that there is a com- 

 plete analogy, in so far as the first members of the series 

 v=l"5, S — m, P and v = 2, p 2 — m, S are concerned, in the 

 absorption spectra of mercury, cadmium, and zinc vapours. 



In the absorption spectra of cadmium and zinc vapours no 

 absorption was observed corresponding to that obtained with 

 mercury at A = 2338 A.U. It will be remembered, however, 

 that with mercury this absorption band required high vapour 

 density to bring it out clearly. It may very well be that 

 with cadmium and zinc vapours the densities used were not 

 sufficiently high to produce noticeable absorption at points in 

 these spectra corresponding to the band at X = 2338 A.U. in 

 the mercury spectrum. 



IV. Summary of Results. 



1. In the absorption spectrum of non-luminous mercury 

 vapour there has been shown to be a strong symmetrically 

 spaced band at X=1849'6 A.U. , a diffuse complex band at 

 X=2338 A.U., and an asymmetrical band at X = 2536*72 A.U. 

 The complex band at X=2338 A.U. consists of a band 

 extending from X=2313A.U. to X = 2320A.U., one at 

 X = 2322 A.U., another at X = 2326 A.U., and a wider one 

 between X=2330 A.U. and X = 2338 A.U. 



2. The experiments of the writers confirm the findings of 

 Wood and Guthrie in regard to the absorption spectrum 

 of non-luminous cadmium vapour. There is a strong symme- 

 trically spaced absorption band at A, = 2288 A.U. and a narrow 

 sharply defined one at X = 3260'17 A.U. 



3. In the absorption spectrum of non-luminous zinc vapour 

 there is a strong symmetrically spaced absorption band at 

 X= 2139*3 A.U., and a very narrow 7 sharply defined one at 

 X=3075*99A.U. 



4. With the exception of the absorption band at 

 X = 2338A.U., all the absorption bands found for the 

 vapours of mercury, cadmium, and zinc are the first 

 members of either the series represented by ^ = 1*5, S — m, P> 

 or that represented by v = 2,p 2 — m, S. 



We desire to acknowledge our indebtedness to Mr. P. 

 Blackman, who assisted us in taking the photographs. 



The Physical Laboratory, 

 University of Toronto. 

 May 1st, 1915. 



