Determination of Chemical Constants. 19 



whence a = 2'32 . 10~ 5 (at 290° abs.). 



At 473°, Konigsberger (I. c.) gives ^^ = 0-207, so that 

 a = 2-01 . 10- 5 , 

 \ = 128000 and - ^° = - 14*000, 



p = 0-0001072 at 2000° C. = -6-851 atmos. 



Inserting these values, as in the above calculation, 

 "C becomes 2*36. 



Apart from the uncertainty in the value for X owing 

 to the change in the specific heat, it appears that further 

 experimental work is required before these measurements 

 of the vapour pressures at high temperatures can be used 

 for evaluating the chemical constants of these metals. 



Determination of Stephans Constant. 



Professor Lindemann, to whom I am indebted for his 



"kindly advice and assistance and the interest he has taken 



in this work, has suggested to me that a value for one of 



the radiation constants might be obtained from the chemical 



2 , R 

 constant. Thus, Stephan's constant cr=--^7r 5 -.- r/t ,,* , 

 r 15 NV/i 



-and . (2tt) 3 < 2 . K 5 '' 2 _, , AAK/ . /ri „ „ . 



logio— ^,2 p— = Co + 6-0056 (C.G.fe.). 



]og 10 «r = C -log 10 -^- 2 — .^+6 0056. 

 Substituting values : 



li = 8'306 . 10 7 , 

 c = 2-9986. 10 10 , 



log w o- = C y -2-6563 + 6-0056. 



If C - -1-622 (seep. 15) 



c- = 5*27 . 10~ 5 erg . cm -2 . deg~ 4 . 



If the value obtained from mercury, only, is employed, 

 viz. 1-633+0-032 : 



a = 5-16.10" 5 ±0-37. 



* If R = 8-306. 10 7 , N = 6-062 ,10 23 , 7i=&57 . 10" 2T . Substituting 

 (2ir) 3 . ;2 R 5/2 

 i n C = — jp^3 = —1-593, this theoretical figure, used to determine a, 



would give 5'64.10~ 5 , but this value is dependent on other deter- 

 minations of li and N. The value — 1*608 (which has been used) is due 

 to slightly different values of the constants. 



2 



