110 



Dr. R. D. Kleeman on the Kinetic 



molecular path l l . The viscosity ?/ is equal to this gain of 

 momentum, and hence r) = n l (v 1 m a — v 2 m)=n 1 l l m a . Now the 

 value of rii is given by the equation rc 1 A = P»-Hj0, and the 

 foregoing equation becomes 





m 



The equation is perfectly general. In the case of a perfect 



ffas P„ = 0, p= , and u 2 = ' : — • , which reduce the equa- 



tion to the well-known form rj = ^pvli. It is of interest to 

 note that it follows from the above equation that the viscosity 

 of a liquid might in some cases be greatly increased by 

 increasing the external pressure without necessarily pro- 

 ducing anv appreciable change in density. 



Table III. contains the values of /,, calculated by means 

 of equation (4) for three liquids, using the values of P„ given 



Table III. 



1 



Substance. 



t°. 



p. 



(Liquid). 



L. 



100 

 62-45 



82-5 



(Liquid). 



(Gas). 



Benzene 





 



18-12 



•9001 

 1-5264 



•8891 



•009025 

 •00700 



•005299 



7-02xl0" 8 cm. 

 414 



459 



8-0xl0~ 9 cm. 

 9-96 



9-1 



Chloroform 



1 Methvl- 



1 Isobutyrate... 



by the equation V n = L l p. The table also contains the values 

 of li calculated by means of the equation 7) = ^pvl^ which 

 supposes that the liquid behaves as a perfect gas. It will bo 

 seen that the former values are larger than the latter. This 

 can be easily explained if the interaction of the molecules 

 during " collision " is largely due to the field of force sur- 

 rounding them. The amount a molecule gets deflected when 

 it flies past another molecule in that caso depends on the 

 vicinity of other molecules. Thus, if a molecule a flies 

 between two molecules b and c some distance apart, the 

 deflexion of a caused by b will be smaller than when c is 

 absent, the attraction of b being partly neutralized by that 

 of c. It will be evident therefore that the " radius of the sphere 

 of action of a molecule " in a substance will decrease with 

 its density. The mean free path will therefore not vary 

 inversely as the density over all ranges of densities, but less 

 rapidly with an increase of density when this has reached a 



