( 127 ) 

 For coexisting phases this equation becomes 



or 



(2) 



For low temperatures this yields : 



a a a(ü, — b) 



T dp v^ b v^b 



p dT RT RT RT 



or 



or 



/ 

 For T = Tk equation (2) yields : 



p dTJk 

 For the highest temperature, therefore, at which the pressure cur^'e 



'7' 



occurs, the coefiicient with which -^ must be multiplied in order to yield 



rp 7 



the value of , does not differ much from that for the lowest 



p dl 



temperature at which the liquid may exist without solidification. 



Here we have one of the striking inslances, how the equation of 



state Avith constant a and f) may represent the general course of a 



quantity just as it is found in reality, though the numei-ical value 



differs considerabl3^ For the real course of the vapour tc]isic)n is at 



least in approximation represented by the formula : 



— log— = t — — -, 



Pl: J 



but tiie value of /' is nol 4 or somewhat less — but for a great many 

 substances a value is found which does not differ much from 7. 



Before discussing tiiis point further, we shall calculate some other 

 quantities whose values for tli(^ brpiid state for low^ temperatures 

 follow from the equation of state when we keep a and constant. 



Proceedings Royal Acad. Amsterdam. Vol. VI. 



