16 Capt. A. 0. Egerton on the 



If the formula Xt = > H#*963T- ( e£tfT-f aW 2 . . .. is- 



* 'o 



differentiated, it will be seen X is not necessarily a maximum 

 at the absolute zero : 



^ r = 4-963- (c^ + aT 3 / 2 ), 



which becomes a maximum when 



Gv s = 4-963, i. e. Bv/T = 1*95. 

 For mercury, /3v/T = 97/1*95 = 49°'7 abs. 

 „ cadmium, j3v/T = 147/1*95 = 75°*5 abs. 

 „ zinc, fiv/T = 234/1*95 = 120°-0 abs. 



In order to deduce the above results, the theoretical value 

 of the chemical constant is assumed and the same vapour- 

 pressure measurements are employed, thus for zinc : 



\ = 1-92 + 2-881 + 2-5 log 625-^H°--0-0583 



x 5-4 . 10- 5 . 625 + 1-115 ±0-26 

 = 31330 + 750. 



A-M.Pt. = 31330 + 4-963 . 691-5-235 . 691-2/5 .a . (691) 5 / 2 

 = 30871. 



\ max . = 31330 + 4-963. 120-120. 2-684-2/5. a. (120) 5 / 2 

 = 31570. 



The values in the last column of the following table are 

 calculated from Nernst's relation : 



X = Tb 8-5 log T B . 



They agree closely with the values deduced from, the vapour 

 pressure *. 



The values for X , X max ., and XM.Pt. are given in the table 

 below. 



* It may be noted that Nerust's other empirical expression, 

 X B = 9-5 log T B - 0-007 T B , 



does not agree nearly so well. It is obvious it is not applicable to 

 high temperatures. 



