THE COLLOIDAL MATTER OF SOILS 155 



suspension. While this method of comparison fails to 

 recognize the various phases that colloidal materials 

 may exhibit and is therefore faulty in this regard, it 

 does lay emphasis on the differences as to size of par- 

 ticle that exist between colloidal bodies and materials 

 as they are ordinarily recognized. ^This relationship 

 is shown by the following diagram : — 



ORDINARY SUSPENSION | COLLOIDAL STATE I TRUE SOLUTION 



MOLECULAR COMPLEX 



Fig. 22. — Diagram showing the relationship of the colloidal state 

 (molecular complex) to ordinary suspensions and true solution^. 



Since colloidal particles vary in size from .005 of a 

 micron to a molecule, the range must be very great. 

 Just how great cannot be very accurately stated. It 

 is interesting to note, however, that this range is much 

 greater in proportion than is exhibited between the fine 

 gravel and the ordinary clay particles found in soil. With 

 this possible difference, it is no great wonder that the 

 various colloids exhibit with different intensities the 

 characteristics so peculiar to them and of such great im- 

 portance in everyday life. The particles in the upper 

 range of the colloidal field can be seen with the ordinary 

 microscope. As such particles become smaller they cease 

 to be visible under the ordinary microscope and can be 

 detected only by the ultramicroscope. It is probably 

 true that by far the greater proportion of the particles 

 of material in a colloidal state cannot be detected by 

 microscopic means. This gradation of colloidal materials 

 and the extreme fineness of the particles is well illus- 

 trated by the following diagram (Fig. 23), although it 

 fails to convey any idea regarding the various phases 

 that colloids may occupy. 



