and Two New Types of Viscosity. 27 



Hence by definition of D the coefficient of diffusion with 

 7 i / 6 = 0'001035/10 11 . 



2A 01 A n2 0-001035 2 



Aoi + A 02 ' 10 Tl * 



But in C.G.S. units R for a gram-molecule is 10 s X226/273. 



. D= 2^2T 2A 01 A 02 10 _ 7 

 273 A 01 + A 02 



This is the relation which Nernst showed to be well verified 

 by the experimental values of D for electrolytes. It shows 

 the connexion between diffusion velocities and ionic velocities 

 without going into the dynamical details of either. Thus, by 

 means of the theory of the present paper and Nemst's- 

 relation between the two sorts of velocity, we can give a 

 complete dynamical theory of the diffusion of electrolytes. 



But in the case of non-electrolytic solutions we must build 

 up the theory of diffusion from dynamical first principles. 

 As we have to do with electrically neutral molecules, we do 

 not need to take account of our two new types of viscosity of 

 electric origin. The investigation has been given already 

 (PhiL Mag. [6] ix. p. 781, and Austr. Assoc, for the Adv. 

 of Sci. 1904). The result is that for a solute of molecular 

 radius a 



D _™\i±Mg (27) 



Since this equation was published Thovert has shown for 

 12 liquids, from ethyl oxide to glycerol mixed with 

 20 °/o water, which has a viscosity 300 times as great, that 

 the velocity of diffusion of phenol dissolved in them, multi- 

 plied by the viscosity, that is D77, is constant, the range of 

 variation in arbitrary units being from 92 to 100. This 

 verifies (27) in one important particular. As regards the 

 theoretical result that for different solutes at a given tem- 

 perature Da should be approximately a constant with a 

 certain variation due to the theoretical factor 



(l + 3 v //3a)/(l + 2 v /f3a) 



for slipping, I showed from experimental data that with 

 Bi representing a, when B is the limiting minimum volume 

 of a gram-molecule of the diffusing solute, 



10 G B*D = b + k/B^ (28) 



where h and k are constants for a given solvent at a given 



