COLLOIDS 



9 



colloidal matter has been the subject of very interesting 

 researches by Zsigmondy and Siedentopf. Fig. 2 clearly 

 illustrates the principle of the ultramicroscope. The solution 

 to be examined is placed in the glass cell at b and is strongly 

 illuminated by a converging beam of light. On observing 

 the lighted-up solution by the microscope at right angles to the 

 path of the beam the colloid substance present in the solution 

 is visible as brightly illuminated particles. The methods of 



FIG. 2. THE PRINCIPLE OF THE ULTRAMICROSCOPE. 1 



producing a brilliant converging beam of light, and the 

 construction of the observation cell have in practice been 

 improved and rendered more compact and precise, but Fig. 2 

 sufficiently illustrates the principle employed. 



By means of the ultramicroscope particles are rendered 

 visible which are far smaller than any that can be seen under 

 the ordinary microscope. Thus, for example, if an ordinary 

 blood-corpuscle be represented by a circle three inches in 



1 Reproduced by permission from Zsigmondy's wcrk, Zur Erkennt- 



niss der Kolloide. 



