m the Solar Chromosphere. 479 



Eggert calculates the chemical constant from the Sackur- 

 Tetrode-Stern relation, 



3 5 



(^log^— M ^-=-H+flogM, . . . (4) 



where M = molecular weight, the pressure being expressed 

 in atmospheres. 



Now C has the same value for Ca and Ca + . For the 

 electron M = 5"5xl0~ 5 , and C= — 6*5. 



We have thus 



S»0=-r6-5 (5) 



To calculate the " Reaction-isobar " K, let us assume that 

 P is the total pressure, and a traction x of the Ca-atoms is 

 ionized. 



Then we have 



logK = log I ^ ? P=- F5 ^ 1T +2-51ogT-6-5. (1') 



This is the equation of: the " reaction-isobar " which is 

 throughout employed for calculating the " electron-affinity" 

 of the ionized atom. 



Ionization of Calcium, Barium, and Strontium. 



With the aid of formula (1), the degree of ionization for 

 any element, under any temperature and pressure, can be 

 calculated when the ionization potential is known. As a 

 concrete example, we may begin with Calcium, Strontium, 

 and Barium. 



A glance at equation (1') shows that pressure has a very 

 great influence on the degree of ionization, which does not 

 seem to have been anticipated. This is due to the occur- 

 rence of P in the first power in the expression for the 

 " Reaction-isobar." A reduction in the value of P is 

 attended with greatly enhanced ionization. This will 

 become apparent from an inspection of the following tables, 

 which show the ionization of Calcium, Strontium, and 

 Barium under varying conditions of pressure and tem- 

 perature. 



