PHYSICAL FORCES INVOLVED IN BIOLOGICAL ACTIVITIES l8l 



the anode, they are negatively charged, if toward the cathode positively 

 charged. The significance of this movement of the particles of different 

 colloids in response to an electric current passed through a solution does 

 not seem to be clearly understood. 



The size of the particles existing in a suspensoid or an emulsoid or 

 even in a molecular solution is of considerable importance from the 

 standpoint of stability, reaction to light and many other phenomena. 

 Ostwald* presents the matter very tersely in the following diagram 

 which has been slightly modified by the writers. 



Dispersoids 



True or coarse 



dispersions 



(suspensions, emulsions, 

 etc.) 



Size of the particles of 



disperse phase greater 



than O.IM 



Colloidal solutions 



(Suspensoids, emulsoids, 



etc.) 



Size of particles of the 



disperse phase between 



o.ifj, and i fin 



\ 



Molecular or 

 supermolecular 

 dispersoids 



Size of particles of the 



disperse phase about 



i nn or less 



Colloidality decreases 



Degree of dispersion increases. 

 FIG. 107. An arrangement of dispersoids. (After Ostwald.) 



This graphic presentation can be still better understood by giving also 

 the illustration provided on page 30 of the same publication (Fig. 8) 

 of this publication (Fig. 108). 



By use of the ultramicroscope developed by Siedentopf and Zsig- 

 mondy it has been possible to employ Tyndall's phenomenon which 

 makes the visibility of rays of light passing through a medium depend- 

 ent upon solid particles as dust in the air of a room. The light must 

 enter into a dark room as a ray from one side only to illuminate the 

 particles and render the demonstration successful. In the same man- 

 ner particles suspended in a transparent medium may also be illumin- 



* Ostwald, Wolfgang. Handbook of Colloid Chemistry, p. 33. 



