

l,a i vs of Mo I ecu lav Fo rce. 273 



case of C0 2 , for example, if from Table XXV. we take S 

 as 1*05, then 



1= -00367 and l' = '00206, 



but in the case of ethyl oxide, with S = 4*5, 



/= -00738 and l' = -00491. 



In both cases we see that the pairing of the molecules to 

 form a new chemical compound or polymer is attended 

 with a reduction of the virial constant towards one half, 

 but not exactly to one half of the original value. Now the 

 data given in Tables I. and III. and the form of virial term 

 taken to represent them, l/(v + k), along with the fact that 

 below volume h the form is l/2v, mean that in the limiting 

 gaseous state the virial term is practically l/v, just as below k 

 it is l/2v ; hence we must regard the pairing of the molecules 

 to be such as to cause the virial constant to become one half 

 of its higher limit — in other words, the pairing must be 

 different from polymerization. We are therefore led to 

 differentiate the chemical and physical pairing of molecules 

 by the statement that while chemical pairing alters the virial 

 constant in the ratio 



(6 S + '66 S 2 )/(12S + 2-64 S 2 ) or (l + 'llS)/(2 + -44S), 



physical pairing alters it in the ratio 



6S/12S or 1/2. 



The term 'Q6 S 2 would thus appear to have a certain chemical 

 significance. 



And now as to the form l/(v + k) connecting the two ex- 

 treme cases. We can explain it in the following manner : — 

 It will be shown when we come to treat of solutions that if a 

 salt having a parameter of molecular force 3 A (proportional 

 to its virial constant I) is dissolved in a solvent with parameter 

 3 W so that there are n molecules of salt to one of solvent, 

 then the solution behaves as if it consisted of molecules 

 having a parameter 3 X given by the singular relation 



X- 1 = (W- ] +nA- 1 )/(l + ? i). 



Now, in a gas being compressed towards the volume k, let us 

 assume that there are a number of pairs of molecules propor- 

 tional to k and a number of single molecules proportional to 

 v— k, and that the same relation applies to the mixture of 

 paired and single molecules as to the solvent and salt in a 

 solution, then, replacing W by I and A by 1/2 and ?i by 



