Walter Stiles 
146 
which represents the distribution of the solute between solvent and 
adsorbent. The similarity of this equation to that of the partition 
law is obvious. 
The principle involved in the partition law has been applied with 
great success to the separation of substances which otherwise have 
so far been found inseparable, or are only separable with great 
difficulty. The separation of the four pigments of the green leaf by 
Wilistatter (1913) is almost entirely based on the different partition 
coefficients of the four pigments and the substances with them, in 
the commoner organic solvents. 
It is now necessary to consider how far the laws governing the 
rate of diffusion are modified in more complex systems. 
The case of an electrolyte diffusing in a solution of another 
substance instead of in pure water has been investigated by Oholm 
(1912). He found that the presence of a non-electrolyte such as 
glycerin or sugar appreciably reduces the rate of diffusion. In the 
following table are given the values obtained by Oholm for the 
coefficients of diffusion of potassium chloride in solutions of non¬ 
electrolytes of different concentrations. 
Table VIII 
Diffusion of Potassium Chloride in Solutions of Sucrose and 
Glycerin of Various Concentrations 
(Data from Oholm) 
Coefficient of Diffusion 
at 18° C. in 
Concentration in 
Substance 
gram-mols. per litre 
# sec. 
Sucrose 
o-o 
1-535 
,, 
i -5 
0-486 
,, 
2'0 
o -255 
Glycerin 
5-0 
0-501 
,, 
7-48 
0-201 
We now come to the important question of the diffusion of 
substances in colloidal systems. The diffusion of various substances 
in gels has received a considerable amount of attention, partly 
because of its obvious bearing on physiological problems (cf. Chapter 
II), and also because it lends itself more readily in some ways to 
investigation than diffusion in free liquids. 
It was concluded by Graham (1861) that sodium chloride diffused 
as rapidly through gelatine as through water. De Vries (1884) on 
the other hand concluded from observations of the colour that 
