EQUATION AND THE NATURE OF COHESION. 13 



20. Iso-pentane . (' h ll v> . 



(a), a = 2mBT c F c /l.0B—P c V c 2 . M = 72;P c = 25M8mmI{</.; 

 1\. = 460.8 ; tL = . 23 13 ; V c = 307.3 a = 20.00 X Ï0 12 



(b). a = 0.5 PJ'; 1 a = 20.47 X 10'- 



( C ). a = /x'J/ 2 /3 d; 1 '\ p' = 105.5 a = 20.08 X 10' 2 



(<*). a = C'RT C V C . C' = l.OSs a = 19.88 X 10'* 



(e). a=aV 2 (P=b'T—d)d~\§2M0mmMg. a = 20,06 X 10 12 

 The surface tension was not found. The mean value is 20.11 X Ï0 12 . 

 If 20.84 is the value of a for //-pentane and 20.11 for iso-pentane, 

 the mean of the two is 20.47, which is almost exactly the value 

 calculated from the gravitation (molecular weight) and number of 

 valences of 20.52 X 1 ^' 2 ; VAN Laar finds for isopentane the value 

 corresponding to 10.12 which is 5 °/ lower than 20.11. 



21. Benzene. CqII q . 



(a), a = 2m UT.Vjim — P r V,-. P c = 3G.39bmm.H#.; T r = 



501.5 ; d c = 3045 ; V c = 250.1 a = 20.40 X 10 12 



(b). a = 0.5 P,.r; 2 a = 20.15 X »0' 2 



( c ). a = ^Y 2 /3 d;\ M = 78 ; // = 100.23. . . a = 20.48 X N> 12 



(c). a = C'BT C V C . (" = 1.600 a = 19.17 X »0 12 



(d). a = 3 MN*H\C\d . 0= 2.16 (Morgan and Daghlian, correc- 

 ted according to Lohnstein) d =1.1 404 a = 20.95 X 10' 2 

 The mean value is 20.23 X 1<> 12 . Evidently .19.17 is too low. If 

 Ave omit this the value would he 20.49 X 1° 12 > which is probably near 

 the true value. The calculation from the molecular weight and number 

 of valences by the usual formula : a = 1 .1703 X 10 11 (MX Val.f^, 

 with 30 valences in the molecule requires that a should be 

 20.73 X !0 ,2 > which is very close to the mean value when 19.17 is 

 omitted. Van Laar's value is one corresponding to 18.72 X l^ 12 

 which is obviouslv too low. 



22. Ft 'nor- Benzene. C,JF b Fl. 



(.a), a = 2.03 BT c F c /l.QS~P c r 2 . P c = 3SM2mm.Bff.; d r = 

 .3541; T r = 550.5; r. = 271.1.... a = 21.51 X 10 12 



(6). a = 0.5 P C V 2 a = 21.60 X 10' 2 



(c). a = f/M 2 3 <l;\ M = 96 ; fi = 85.65 ... a = 22.00 X l»' 2 

 (d). a = CBT C V C . (" = 1.711 a = 24.18 X »0' 2 



