Section III, 1922 [135] Trans. R.S.C. 



Arc, Spark and Absorption Spectra of Argon 



By W. W. Shaver, M.A. 



Presented by Professor J. C. McLennan, F.R.S. 



(Read May Meeting, 1922) 



A. On the Arc and Spark Spectra of Argon 



I. Introduction 



The resonance and ionization potentials of argon have been 

 accurately determined by Rentschler,' Horton and Davies,^ Déjardin^ 

 and others. The spectrum of the radiation produced by the bom- 

 bardment of argon atoms with electrons of various speeds has also 

 been studied by Déjardin,* using the well-known lamp of the three- 

 electrode type with accelerating potentials varying from 16 to 80 

 volts. He found that with potentials from 16 to 33 volts the lines in 

 the spectrum of the radiation produced all belonged to the red spec- 

 trum of argon. The blue spectrum which is due to the excitation of 

 the ionized agron atoms began to appear with a field of 34 volts and 

 the number of lines increased with increasing accelerating potential. 



The author has repeated these experiments using potentials 

 varying from 10.1 to 240 volts. The results obtained for the most 

 part substantiate the work of Déjardin with this one exception. It 

 was found that a visible radiation persisted with a voltage of 10.1 

 volts after the arc had once been struck, whereas Déjardin found that 

 the lowest possible voltage required to excite radiation was between 

 15 and 16 volts and then it was only detected with an exposure of 

 three hours. The production of this radiation with a grid potential 

 of 10.1 volts, which is approximately the resonance potential of argon, 

 required very exacting experimental conditions as to the gas pressure 

 and the proximity of the filament to the grid, but it was found possible 

 to photograph it with an exposure of half an hour. The spectrum 

 obtained consisted of lines belonging to the red spectrum of argon and 

 some bands, which were probably due to traces of gas impurities from 

 the v/ax used with the quartz window. 



iRentschler, Phys. Rev., Vol. 14, p. 503, Dec, 1919. 



2Horton and Davies, Roy. Soc. Proc. A, Vol. 97, p. 1, March 1, 1920. 



«Déjardin, Comptes Rendus, Vol.. 172, 1921, p. 1347. 



^Déjardin, Comptes Rendus, Vol. 172, 1921, p. 1482. 



