478 Dr. Megh Nad Saha on Ionization 



value of U. Here I wish to remark that an element may- 

 have more than one ionization potential, depending upon 

 the successive transfer of the outer electrons one by one to 

 infinity, or the simultaneous existence of* two more con- 

 stitutions of the normal atom (e. g. helium and parhelium). 

 The ionization potential given in the table corresponds to the 

 case when only one electron is transferred to infinity" leaving 

 an excess of unit positive charge in the atom. We have made 

 it clear in the introduction that the high-level alkaline earth- 

 lines are due to the atoms with one plus charge in excess.' 



The cases of hydrogen and helium will be taken up 

 later on. 



§ 3. Equation of the Reaction-isobar for Ionization. 



As mentioned in the introduction, the equation of gaseous 

 equilibrium proceeds according to the equation, 



lo « K =-|jTT + Tr ?logT + 2 '' C ' • • (l) 



where the reaction proceeds according to the scheme, 



V a A + V b B + = VnM + vJX + . . . 



and K is the u Reaction-isobar," 



p v nip v n 



L TVT -L TV 



p?p\ 



'a p "b 



A l B 



P*' m , p v ™. . . being the partial pressures of the reacting sub- 

 stances — M, N, etc. 



In the present cases, viz., for a reaction of the type, 



Ca7""»Ca,+<?--U, (2) 



we have 



%vC p = ( .Cp)ca+ + (Qp)e— (Cp)ca- 



We can take 



(O p )ca=(Cp)ca+, 



and (C p ) e =|R, the electron being supposed to behave like 

 a m on atomic gas. 



