526 



Albert P. Mathews 



TABLE 2 

 Pentane 



Benzene 



Table 2 shows that, in pentane, b v is larger than b^ from the 

 critical temperature to about 160. Below this point v v 

 falls rapidly and apparently soon becomes negative. The 

 reason for this apparent fall is undoubtedly the association, 

 or quasi- association, occurring in the vapor as the temperature 

 falls, as van der Waals suggests, the result being that the 

 number of the molecules in the space does not remain con- 

 stant and hence R does not remain constant. The effect 

 of reducing R to its real value, were we able to correct for 

 the association, would be to make b v larger. In benzene 

 b v falls below b l sooner than in pentane, from which we may 

 infer that the association in benzene is a little larger than in 

 pentane. The apparently negative value of b v is found 

 closer to the critical temperature in the esters which are 

 known to associate slightly. Since association produces an 



