34 THE TRUE VALUE OF a OF VAN DER WAALS' 



{b). Surface tension, a = SMN^T c C/d cl . (7=1.92 (Bat, y and 

 Donnan). iV n/3 is 8.463 X 10 7 - T c = 154.25; d is 1.531 computed 

 from dJ{d—D) = {T c jT c —-Tf l ' i i=1.58XW". It may also be 

 calculated from the second formula given in hydrogen. At — 203° 

 s is 18.35 dynes, d is 1.2393; B is 0.0019. The densities are 

 from Baly and Donnan. sV m is 160.3 ergs a = 1.58XI0 12 



Conclusion. The value of 1.58 from the surface tension is cer- 

 tainly a minimum value. The true value is probably higher than 

 this. The value 1.81 is probably not far from right, a computed 

 from the gravitation with 2 valences in the molecule is a = 1.88 X 10 1 2 , 

 a value nearly -4 °/ higher than the figure computed from, the 

 pressure volume formula. Were there 4 valences in the molecule 

 of course the computed value of a would be much higher still. 

 If there are but 2 valences in the molecule, and by valences is 

 probably meant negative electrons, the agreement is fair. The 'value 

 adopted by van Laar is 1.33 X 1 ()12 - This ls from 20—40% 

 too low, showing again that his method of computing a is wrong. 



4. Carbon monoxide. CO. 



(a). a = 2.03 Bl c Fj 1.03- -P ( ./",. 2 . P e = 34.60; <. = 0.311 

 (Cardoso). T c = 134.3 



S= 3.54; M= 28; F c = 90.03 a=1.70X»0 12 



(£)., a = 6.5 P c F, 2 a = 1.85 X 10 12 



(c). a = 3 sv 2l:i /V 1/:î MT^lid—B) ( T—Tf A 



s, the surface tension, by Baly and 

 Donnan at — 203° = 12.84 dynes. 

 d= .8474; D is neglected. T— 2 7 =64.3. 



M= 28. sv*' 3 = 132.26 ergs a = 1.813 X 10 12 



We have then for the value of « 1.70, 1.85, 1.81 X 10 12 . 

 Probably 1.85 is near the true value. If there are two valences in 

 the molecule a computed from the gravitation and valences is 

 1.72 X 10 12 . With four valences it would be 2.73 X 10 12 . Van 

 Laar's value is 1.41 X 10 12 a value whicji, like the others, is at 

 least 20 % too low. 



5. Methane. CU A . 



{a). ö = 6.5P//. P, = 45.6 ; 7 7 c = 190.15; d c = 0.1623; V c 



= 98.58; 8= 3.48 (Cardoso) a = 2.02 X N>' 2 



(Ó). a = 2.03 BT C VJ\, 0.3. --P C F C 2 à = 2.63 X 1<> 12 



