24 



COLLOIDS IN BIOLOGY AND MEDICINE 



Fig. 4 shows the line passing through the logarithms of these data 

 and it should be observed that all logarithms less than unity are 

 negative. 



The tangents to the angle of inclination between the elements of 



FIG. 4. (After H. Freundlich.) 



the curve (acetic acid, propionic acid and succinic acid) and the 



i " 



abscissa (log c) is the exponent -. The distance on the ordinate 



IV 



(log ) from the zero point (origin of co-ordinates) to the point inter- 

 m/ 



secting the uniting lines is log k. They have these values: 



Acetic acid - = 0.425, k = 2.606. 

 n 



Propionic acid - = 0.354, k = 3.463. 



Succinic acid - = 0.274, k = 4.426. 

 n 



Since the values observed do not lie all in the same line, as is shown 

 in Fig. 4, a mean value for the angle whose tangent is n may be de- 

 rived by means of a protractor. In the same way, log k is not de- 

 rived from the intersection of the last element of the curve, but 

 from the mean value. 



The exponent - conditions the shape of the curve, and varies 



within moderate limits. Though marked exceptions have been ob- 

 served, it fluctuates usually between 0.5 and 0.8 as H. FREUNDLICH 

 has shown in his numerous experiments. 



The constant k in the adsorption formula is, in an ideal case, a 

 natural constant which may be as characteristic for the adsorbed 

 substance as k is in the distribution between two solvents. 



The great difficulty lies in the fact that, in the case of the dispersed 

 adsorbing phase, we do not consider the mass, which may be easily 



