814 Dr. Megh Nad Saha on 



Ionization o£ Potassium. 

 Ionization Potential = 4*318 volts = r00x 10 5 calories. 



Pressure 



1. 



10" 1 . 



io- 2 . 



10 -3 . 10 -4 . 



10~ 5 . 



Temp. 













3000 







2-5 



9 28 



66 



4000 





11 



32 



72 97 





5000 



15 



44 



83 



98 | 





6000 



41 



81 

 95 



98 



97-5 



Complete 







70 

 81 





7000 : . . 



7500 







8000 



87 



99 





Ionization. 





9000 



94 











10000 , 



98 











The identification o£ potassium is to be carried by the 

 lines (1, s) — (3, p{), (1, s)~ (3, _p 2 ) which under all circum- 

 stances are likely to be much less intense tban the leading 

 pair (1, s) — [2, p Y ), (1, s) —(2, p 2 ) which lie in the infra red, 

 \ = 7665"3, 7699'3. This fact, combined with the high 

 proportion of ionization, tends to make the identification 

 rather difficult. The lines of the ionized atom lie in the 

 ultra-violet, and so escape detection (Goldstein, Astro. 

 Journal, xxvii. pp. 25-34 (1908) and Ann. d. Pliys. 

 loc. cit.). 



Over the spots, the potassium lines ought to be strengthened, 

 but no observation seems to have been made on this point. 



(c) Rubidium. 



As has been mentioned in the introduction, no lines of 

 Rubidium have been identified in the Fraunhofer spectrum 

 of the sun, though in the usual flame and arc spectrum there 

 are many strong lines within the available range. 



The following table shows the ionization of rubidium. 

 It will be apparent from the tables that in the sun rubi- 

 dium is completely ionized. Consequently, even if it be 

 present, we shall get the lines due to the ionized atoms only, 

 which, according to Goldstein *, lie in the ultra-violet. The 

 spot spectrum should show some faint rubidium lines. But 

 no observation seems to have been made on this point. 



*' Goldstein, loc. cit. 



