484 Dr. Meo-h Nad Saha on Ionization 



solar chromosphere. We should add to this the fact that 

 hydrogen exists in the Sun only in the atomic state, for, if 

 there were molecular hydrogen in the Sun, we could have 

 detected some at least of the lines of the secondary spec- 

 trum. But this is not the case ; hydrogen enters into 

 chemical combination with calcium and magnesium in the 

 sun-spot, but does not probably form molecules of its own. 



We shall consider in this section whether these facts are 

 reconcilable with our theory. This requires a knowledge 

 -of the heat of molecular combination and the ionization 

 potential of hydrogen. 



These data already lie available in a recent paper by 

 Franck * and others. They find evidences of the following 

 chemical and electronic reactions : — 



H 2 = H + H + 3-5 volts ( = 84,000 calories;, . . (A) 



H 1 = (H s ) + + « + 10-6 volts,. (B) 



H r=H + + <? + 13'6 volts ( = 3'2.10 5 calories), . (C) 



H 2 = H + + H + + 2* + 30-7 volts ( = 7-2. 10 5 ). . (D) 



The first is a purely chemical reaction, and the heat of 

 molecular combination has been directly measured by 

 Langmuir f and found to be 82,000 calories. The ionization 

 voltage 13*6 in (()), can be calculated from the relation 



Y= — -, taking v = convergence frequency of the Lyman 



e r i i "i • 



series v = N -r 2 2 ? l - e -> v = ~N. The actual occurrence 



of this process in the ionization of H 2 is indicated by a 

 sudden increase of ionization at 171 volts (l3"6 + 3"5 volts). 

 The ionization voltage 30'7 in process (D) = 2 . 13*7 + 3*5, 

 corresponding to the complete breaking up of the H 2 - 

 molecule into 2 atoms, and of these again into the core and 

 the electron. 



Let us first consider reaction (A) — dissociation of the 

 molecule into atoms. Taking the equation of the reaction- 

 isobar, 



logK=- | J rr+ ^logT + X,C, 



* Franck and others, Ber. d. J). Phys. Gesellschaft, vol. xxi. 



t Langmuir, Ztits.f. Elektrochemie , vol. xxiii. p. 217 (1917) no. 20. 



