142 
Walter Stiles 
There seems thus good reason for concluding that the coefficient 
of diffusion is related in inverse fashion to the complexity and 
magnitude of the molecule. 
With regard to the connection between coefficient of diffusion and 
electrical conductivity, Nernst (1888) put forward the following 
equation to express the relation between diffusivity and ionic 
mobilities: 
D = RT. - UV — ■ 
u + v 
where u and v are the ionic mobilities of anion and kation, and the 
other symbols have the same signification as before. Nernst himself 
realised that this formula could only be approximately correct as 
the diffusivity varies with concentration, nor does the formula take 
into account the diffusion of the undissociated part of the molecule. 
To allow for the influence of concentration on diffusion, Wieder- 
burg (1899) modified Nernst’s formula as follows: 
where D is the coefficient of diffusion at a concentration c, K the 
dissociation concentration at the concentration and temperature in 
question, and w the molecular mobility. 
Arrhenius (1892) obtained good agreement between experiment 
and the equation 
where is the coefficient of diffusion at infinite dilution, a a 
constant depending on the viscosity, and B a constant. 
Arrhenius found the coefficient of diffusion of hydrochloric acid 
and of potassium hydroxide increased with increasing concentration, 
but that the reverse was the case with acetic acid, sodium hydroxide 
and sucrose. Scheffer also found an increase of diffusivity with 
increasing concentration in the case of hydrochloric acid; with 
sodium and potassium chlorides he found no notable change, while 
with sodium nitrate, sodium thiosulphate and silver nitrate the 
diffusivity diminishes with increasing concentration. A careful 
investigation of the influence of concentration on diffusivity of a 
number of electrolytes has been made by Oholm (1905); the data in 
Table V are taken from among his results. Data with regard to the 
influence of concentration on diffusion of glycerin, urea, sodium 
chloride and hydrochloric acid are given by Heimbrodt (1903, 1904). 
