CALCULATION OF CRITICAL CONSTANTS 21 



For temperatures below A three roots are possible : 



V= V lt V= V 2 , V= V a , 



and the equation becomes 



(V-V l )(V-V 2 )(V-V 3 ) = o. 

 At A the three roots become equal : 

 V V V V, 



y 1 ~~ Y 2 ~ ' 3 "~ '* 



and the equation is 



hence 



so that 



Ft = 36 from (2) and (3) ; 



E a f / \ 



P k = -r 2 rrom (2) ; 



We accordingly find for ethylene 



8 x 0-00786 . 



T k .= - - = 262 absolute, i.e. j i C. 



27 x 0-0024 x 0-0037 



(observed 282 abs., i.e. 9C. 1 ). 



0-00786 

 P t = - - = c;o-^ (observed ^i) ; 



27 X 0-C024 2 



Ffc = 0-0072 (observed 0-006). 



Whilst, therefore, the qualitative behaviour of gases, 

 including condensation up to the critical temperature, and 

 the formation of liquid is in agreement with the equation, 

 the quantitative data as to critical temperature may also to 

 a certain extent be brought into accord with the values 

 of a and 6, determined from the deviations from the laws 

 of Boyle and Gay-Lussac. 



1 Landolt, Bdrnstein, p. 84. 



