I ORGANIZATION OF SOLS I5 



o-eneity requires that they shall be oi submicroscopic dh/iens'ions .Y\xQ.vc\X&t- 

 nal structure, therefore, refers to the arrangement ot atoms, ions and 

 molecules, which in Figs. 3-7 have been indicated by points or arrows. 



It follows from this definition that sols cannot be homogeneous. 

 For, if in a sol we consider submicroscopic volumes of sufficiently 

 small size, the one may contain a colloid particle, while the other may 

 merely contain the solvent, i.e., the dispersing medium. In contrast to 

 sols, not only are all pure substances homogeneous, whether in the 

 solid, liquid or gaseous state (Figs. 8-10), but so also are real solutions, 

 provided the solute consists of amicroscopic particles (Fig. 11). If, 

 however, differences in the concentration, for instance concentration 

 gradients, occur in the solution, it is heterogeneous. Similarly, either 

 homogeneous or heterogeneous mixed crystals can originate from a 

 solution or melt, according as the two components can unite to a 

 crystal lattice in a regular or in an irregular distribution (Figs, iz 

 and 15). 



Colloid solution having been recognized as heterogeneous, the 

 further question arises whether the colloid particles themselves may be 

 considered as homogeneous. To answer this question we must deal 

 shortly with the phase theory, which treats of relations between 

 homogeneous states. 



c. Concept of Phase in Colloids 



According to the thermodynamical definition, any homogeneous state 

 is called a phase. Figs. 8-12 thus picture the structure of phases. Fig. 13 

 representing not a homogeneous phase but a heterogeneous system of 

 AB2 and EBg. 



The colloid particles were formerly believed to be homogeneous 

 and the dispersed particles were therefore designated as dispersed phase 

 and the surrounding liquid as dispersing medium (Fig. 14). Thus a sol 

 represents a two-phase system. The study of the structure of colloids 

 need not, of course, be confined to the liquid state. Dispersions of 

 liquid or solid particles in liquid or solid media (emulsions, suspen- 

 sions, etc.) are known in the microscopic domain. We may also expect 

 to find them in the submicroscopic world. Since, however, the par- 

 ticles in such dispersions are no longer visible, colloid systems were 

 designated as dispersoids. In this way an attempt was made to charac- 

 terize, not only the organization of sols, but in the most general sense 



