757 



ak - 485,0 X 10' ^ (2) 



Hence almost 500 . 1()—^ and not 300 . 10 '', as we still assumed in 

 1903 also for Tk- The value of bk, however, is not equal to that 

 of h,,. We shall soon see that for a volume of about 2900. lO"*' 

 (which corresponds with the critical volume) the value of 6 is already 

 about 4,4 7o lower than /;,,. Hence in order to calculate b,, at the 

 critical isotherm, we shall have to increase the just found value 

 1184,2 by 4,4%, so that we get: 



(6,Hw,=: 1236,4 - 10-6 (1«) 



If we suppose au = {ag)ic, hence a not dependent on v, we get 

 for 7V. 



(^A =2,545 ,.-...... (3) 



V « Jkrit 



which relation we shall presently find back at the BoYLE-point. 



We assumed above the value 2900 . 10-*^ for vt- This we namely 

 calculate from 



2,0154 2,0154 



vk = - -^- — — = — - = 0,002901 , 



0,0310 X 22412 694,8 



so that Vk ■■ bk would be =: 2,45, which would yield the value 0,69 

 for y with Vk : ''-'A: = (y + 1) : 7- This value seems i-ather high, because 

 a value y = 0,615 (see above) would correspond with a critical 

 temperature of 33° abs. When we take (^4 = 0,030 instead of 0,031, 

 Vk would have become = 2998 . 10-^, hence vk ■ bk = 2,53, y = 0,65. 



Now Kameriingh Onnes (loc. cit. p. 184) found the value 0,000398 

 for the coefficient of direction of the straight diameter. For the 

 reduced value of y follows from this y = 0,000398 X 33,18 : 

 0,031=0,01321: 0,031=0,426, which seems too small to us, 

 seeing that the value of y for an idetil substance is 0,5, and the 

 values for all other substances must lie above this. With r4 = ^.030 

 the only slightly higher value 0,44 would have been obtained. 



The solution of this contradiction will pi-obably lie in this that 

 Kamerlingh Onnks calculated the value of y from the observations 

 between about 20° and 15° abs., the critical temperature lying at 

 33° abs. The extrapolation of 20° (the boiling point) to 33° seems 

 therefore rather hazardous, particularly as often only above the 

 boiling point the tr7f£ direction of the so-called straight diameter 

 manifests itself M. Hence the value of /, calculated from Kamkklingh 

 Onnes' observations at too low temperatures, is not the same as that 



•) We remind only of mercury, water, helium, etc. 



