﻿1022 



Prof. A. W. Porter 



equation, be a constant. In fig. 2 are shown two curves - of 

 ft I plotted against the density (1/v) for isopentane de- 

 termined from the experimental values. Curve A is the 

 critical isotherm and B is the isotherm for 503° abs. It 

 will be seen from this figure that instead of being constant 

 it undergoes very considerable variation. Near the critical 

 point the calculated points fluctuate, but a smooth curve 

 drawn amongst them shows that an equation of at feast the 

 second degree is required to represent them. 



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Isopentane. 

 1 T ^ — p J - plotted against Density. 



Curve A, Critical Isothermal, T = 461 abs. C. 

 „ B, Isothermal, T = 503 abs. C. 



If the necessary extra terms are introduced, it becomes 

 possible to bring the equation for the critical isotherm into 

 the form 



a - / ^ri exp - L ft ft 2 ft* j 



The three conditions for the critical point are satisfied if 



\ = 3i a=l-51, 6 = *267, c=-«237. 



It is noteworthy that the negative value of c is required not 

 only from the data of the critical point, but also by the 

 isotherm on fig. 2. 



