EQUATION AND THE NATURE OF COHESION. 33 



2. Nitrogen. N 2 . 



{a). From the surface tension, a = SMN il3 T n C/d lt . Or by the 

 formula already given in the case of Hydrogen. C (Balv and Donnai)) 

 is 1.95; M = 28; iV 1 ' 3 = 8.463 X™ 7 ; T c , 125.96 (Abs.); d , 

 calculated by the same formula as used in hydrogen is 1.104. d, of 

 N 2 at 20.5° Abs. is 1.0265 (Dewar). This is the temperature of 

 boiling 1I 2 . For comparison oxygen at 20.5° Abs. has a density 

 of 1.4526. Its density at absolute zero is computed to be 1.531. 

 If the density of N 2 at absolute zero is 1.104 then a = 1.58 X N> 12 



(b). From' «=6.5P c r c 2 . P c = 33,49; d e is 

 0.311; M is 28; V c is 90.03 a=1.74X »0 12 . 



(c). From a = 2 . 3 HT, .F C J 1 . 3 — P C F C 2 a = 1.58 X 10 12 . 



Conclusion. We have the values 1.58, 1.74, 1.58 X 10 12 as the 

 three found values. The surface tension value of 1.58 is certainly, 

 for the reasons already stated in the case of hydrogen, a minimum 

 value. The value of a for nitrogen is certainly higher than 1.58. 

 It may be as high as 1.74. From the gravitational mass and the 

 valences, taking two valences to the molecule, a is computed to 

 be 1.72 X 10' 2 , which' is probably not far from its true value. In 

 assuming nitrogen to be monovalent here, it may be pointed out 

 that as chemists have supposed nitrogen to be monovalent, di, tri, 

 penta, and hepta valent in different compounds, there is as good 

 reason for taking it monovalent as for assuming it to be di, or 

 tri, valent. If it is monovalent, as it appears to be, the agreement 

 between the value of a computed from, the gravitational attrac- 

 tion and that from the pressure volume formula is perfect. Van 

 Laar's value for N 2 is 1.33 X !0 12 - This is certainly 20% too 

 low, if we accept the minimum value computed from the surface 

 tension of 1.58 as correct. If 1.7.2 is the correct value, as I think, 

 then he is '30 °/ o too low. It is clear that computing from the 

 valences and the gravitation we obtain here as in hydrogen a much 

 better agreement with the real value of a than by van Laar's 

 method. The same objection applies to the value of 1.33 for N 2 

 as to the low figure for hydrogen: it makes b c too small. N 2 

 like hydrogen, is more, not less compressible than pentane, and 

 b c must accordingly be larger than Vj% and not smaller. 



3. Oxygen. 2 . 



(a). From the formula: a= (>.öP c F c 2 . P c = 49.71 (Onnes, Dors- 

 man and Holst). d c is 0.4299 (Mathias and Onnes). M is 32. 

 V c = 74.43 a = 1.81 X 10 12 . 



Vei'hand. der Kon. Akad. v. Wetensch. (I e Sectie) Dl. XII N". 4. D 3 



