( 291 ) 



For ƒ we may now write 



a 

 pr' 



1 



7 ,v-\-l 

 ^ RT 1 



^a— ^)(.'.-+y) 



A- - j- 1 



(10) 



We observe tliat the factor of — according to (d) is also 



V-b (/,i 



' \+.v^ dv' 



Formnla (10) agrees with (28) on p. 42 in Tkylkr Ot'=l). 



We see at once that when ci is near 1 or 0, the factor of 



RT 



will be very small. If now q itself is also still small, as ma}' be 

 assnmed in case of association nnder the inflnence of the molecnlar 

 forces (see also Solid State VII p. 94 at the top and 98 at the bottom), 

 we may safely neglect the correction term L( in 



LA 



(10^) 



and write, jnst as van dkr Waai,s does 



ƒ= 1 



a 



pv- 



at least in the neighbonrhood of the critical point. But we shonld 

 bear in mind that stricth' speaking this can never be quite exact so 

 long as the state of association is also intluenced by the temperature. 



If (10'') should practically be sufüciently accurate, we should of 

 course also be able to calculate the quantity a from it. 



Before proceeding to calculate the quantities ji and <^ from fi and/' 

 at the critical point, we shall first derive the value of a few quan- 

 tities, which are of importance at te critical poijit. We mean the quan- 



db 



vb" 



d'b 



— I' — . It is self-evident that we do not 



dr' 



tities // = — and 



dr 



find the values now, found for this before by van dek Waals and 

 by myself. For if we start from the equation of state 



_ ET a 



without the factor 1 +,'•,■? of RT, we find // from 

 dp _ RT{\—b')^2a__ 

 ^— ~(^-b)' ' T'^ ~ '' 



and //' from - = 0, which after climinalion of d and /i7' yields 



dr' 



