The Internal Pressures of Liquids 



617 



(20) N 3 TV 3 = VoKo/3. 



Dividing by T c and remembering that by (8) 



(21) K Vo/ 3 T c = K c R/ 3 Pc. 



As K -= a/Vl, and K c = a/V' and V V C /S 



(22) i/VoTc = R/V^Pc. 

 Therefore 



(23) S - RTc/PcV c . 



Formula 23 is true. 



We may also check our reasoning as follows : From for- 

 mula (6) a = 3MN 1/ 3TV^ /3 (T C /(T C T)) 2 ^/^ <y and from (8) 

 3N^TV' /3 K C R(T C T)/P C we have 



(24) a KcRM(T c T 

 hence 



(25) ^ </ . RM(T C 



The values of Jj -d v computed by (25) for ethyl acetate 

 compare as shown in Table 5 with those found by S. Young. 



TABLE 5 ETHYL ACETATE, d^ do 



At absolute zero (25) becomes d == RMT C /V'P C = Sd c 

 which is correct. 



Substituting this value in (25) we have 

 (26) d, d v = </ ((T e T) /T c ) v.. 



d computed by (26) for normal pentane using Timmerman's 

 data for densities below zero and S. Young's above is as follows : 



