[mclennan-young-ireton] absorption SPECTRA 11 



arsenic^ it became of great interest to apply various methods of 

 spectrum analysis to identify the predicted series. The resonance 

 potential was found to be 4-7 volts and the ionisation potential 11-5 

 volts. These correspond to the emission of radiation of wave length 

 A = 2620 A.U. and /I = 1070 A.U. As has been pointed out already in 

 the case of mercury, zinc, cadmium and magnesium, the absorption 

 spectrum of the vapour and the Bunsen flame spectrum have been 

 confined to the series v = (1 -5,5) — (m,p2) and v = (1 -5,5) — (m,P) of 

 which the first member of the former and last line of the latter are 

 determined by applying the quantum relation to the resonance and 

 ionising potentials respectively. 



(a) Absorption of Arsenic Vapour 



The same experimental arrangements were used as in the case of 

 aluminium, thallium, tin and lead. Chemically pure metallic arsenic 

 was vaporised from the vertical carbon of an ordinary rectangular 

 arc with a current of 8-10 amperes. No visual absorption was ob- 

 served but the spectrograms revealed strong unilateral band absorp- 

 tions the sharp edges of the bands having the following wave lengths : 

 Head of band extending to approximately, 



A = 2634 . 5 A.U. A = 2624 A.U. 



2570-0 " 2550 « . 



2503-5 « 2483 " 



2437-3 « 2418 " 



The above are recorded as emission bands by Kayser,^ 

 No line reversals were obtained in any part of the spectrum down 

 to A= 1850 A.U. 



(b) Flame Spectrum of Arsenic 



As will be observed the work on absorption spectra was in no way 

 conclusive in determining the series which one would have expected 

 from the work on resonance potential of arsenic vapour^ to have its 

 slowest frequency at about A = 2620 A.U. In a further attempt to 

 locate the series a study of the flame spectrum was undertaken. 



The type of burner employed consisted of a steel annulus around 

 the top of the tube of a Bunsen burner. The annulus was covered 

 with a conical steel cover to direct the arsenic vapour into the Bunsen 

 flame. This type of burner was previously successfully employed by 



^Foote, Rognley & Mohler, Phys. Rev. Vol. XIII, Jan., 1919, p. 59. 

 ^ Kayser — Handbuch der Spectroscopic. 

 ' Foote, Rognley and Mohler, loc. cit. 



