Section III., 1915 [167] Trans. R.S.C. 



On the Absorption Spectra of Mercury, Cadmium, Zinc and Other 



Metallic Vapours. 



By Professor J. C. McLennan, F.R.S., and Mr. Evan Edwards, 

 M.A., B.Sc. University of Toronto. 



I. Introduction. 



(Read May Meeting, 1915.) 



In 1907 it was pointed out by R. W. Wood^ that in the absorption 

 spectrum of non-luminous mercury vapour there is a heavy band at 

 A = 2536-72 A°.U., and a less sharply-defined one at A = 2350 AMI. 

 In a later paper by Wood and Guthrie- dealing with the same subject, 

 no mention is made of the absorption band at A = 2350 A.°U.; but 

 it is stated that with dense mercury vapour there is a fairly strong 

 band at A = 2338 A°.U. and another very broad one at A = 2140 A°.U. 

 From the work of Kirschbaum^ and others it is known that light of 

 wave-length A = 1849-6 A°.U. is strongly absorbed by mercury 

 vapour. 



The absorption band at A = 2536-72 A°.U. has been shown by 

 Wood to be asymmetrical. It is sharply defined on the shorter 

 wave-length side; but with increasing vapour density it gradually 

 spreads out towards the red end of the spectrum. With low vapour 

 densities it consists of two bands the one at A = 2536 A°.U. and the 

 other at A = 2539 A°.U. The band at A = 2338 A°.U., which is pro- 

 bably the same one as that originally given by Wood at A = 2350 

 A°.U., does not appear to have been examined in detail. In regard 

 to the band noted by Wood at A = 2140 A°.U., especially as it was 

 obtained with high vapour densities, it appeared to the writers that 

 it might be connected with the absorption observed by Kirschbaum 

 at A = 1849-6 A°.U. Some experiments were made by us to test this 

 view and also to study the character of the absorption band at 

 A = 2338 A°.U. and these will be described in what follows. 



II. Absorption Spectrum of Mercury. 



In the first experiments the light from a quartz mercury arc lamp 

 was projected through an evacuated clear fused quartz tube containing 



iR. W. Wood. Ast. Phys. Jl. Vol. XXVI, p. 41. 1907. 



^Wood and Guthrie. Ast. Phys. Jl. Vol. XXIX. No. 1, p. 211, 1909. 



'Kirschbaum. Electrician. Vol. 72, p. 1074, 1914. 



