2 THE TRUE VALUE OF a OF VAN DER WAALS* 



Assuming now that ajV c 2 is 6.5 P c we have 



7 5 P V 



-TLn e (dlD) 



1\. 



(8) 



But P c VJT C = JR/S so 



7.5 iZ 

 X= '——TLn e {diD) 

 o 



Therefore 



SL 



ET Ln e {dl D) 



7.5 



(9) 



(10) 



For most substances for gram mol quantities 7.5 P c V c jT c = 

 about 2 R , or since li in calories is about 2 the product would 

 be about 4. Since 7.5/$= V C \{V C — b c ), V c lb e is seen to be equal 

 to 7.5/(7.5 — S). So from this relationship 6 C is easily determined 

 as (7.5 — S) /" r /7.5. Kor most substances, in which S is not far 

 from 3.75, b c will be approximately / 7 ,./2. 



We will now test the relation-. 



SL 



HT Ln [d/D) 



= 7.5 



c 



(10) 



It may be stated at the beginning that Crompton's equation, 

 which we have used as a basis, is only approximately true so that 

 an exact constancy of 7.5 is not to be expected. 



NO P c = 71.66 j T c = 309.5 (Cardoso and Arm); d, = 0.454 



(VlLLARD); S — 3.658. 



T 



253 

 273 

 293 



L 



d 



D 



66.90 



. 998 



. 044 



59.50 



0.890 



.081 



13.25 



!755 



.151 



c 



6.88 

 7.38 

 7.45 



S0 9 (P e , 71.05; T„ 157.15; d c , 49; S, 3.695) 



273 



91.87 



1.4338 



. 0044 



6 . 94 



303 



SO. 5 



1.3520 



.0136 



6.89 



335 



68.4 



1.2425 



. 0364 



6.90 



