l6 FUNDAMENTALS OF SUBMICROSCOPI C MORPHOLOGY I 



that of all colloids, as will be clear from the following system (Wo. 

 OsTWALD, 1909). 



Systematics of dispersoids. According to the theory of dispersions, 

 each of the three states of matter, solid, liquid or gas, can occur either 

 as dispersing medium or as dispersed particles (Fig. 14), so that 3^ = 9 

 combinations are possible (Table II). Fig. 14 shows how in these 

 systems the dispersed part I is distributed in the dispersing phase 11. 



TABLE II 

 DISPERSOID SYSTEMS, ACCORDING TO WO. OSTWALD, 1909 



On the strenght of the definition of phases it was originally believed 

 that the dispersed part I was homogeneous. In the dispersoids, how- 

 ever, this leads to difficulties. Often it was doubtful whether a 

 dispersed phase was liquid or soHd. For, suppose the dispersoid 

 particles become smaller and smaller until they contain only a few 

 molecules, then it would be difficult to decide whether they are solid 

 or liquid. Liquid drops may be taken to be homogeneous, whereas it is 

 very difficult to prove this of solid suspended particles. It was only 

 by the introduction of X-ray iiiethods in colloid chemistry that the 

 particles of certain dispersoids, for instance gold and silver sols, 

 could be proved to possess a crystal lattice and, therefore, to be really 

 homogeneous. With increasing degree of dispersion, however, the 

 homogeneity of a crystal lattice also becomes questionable. For, the 

 energy ot the points lying at its surface is different from that of the 

 points inside the lattice, because they are no longer surrounded on all 

 sides by equivalent fields of force (Fig. i6). In the case of liquids this 

 sives rise to surface tension. For instance, in the smallest gold particles 



