114 
ELEMENTARY CHEMICAL MICROSCOPY 
edge h, the beam of light must be lowered below h. If this 
is done, the beam of light R will lie too low to be focused, even 
if the lower lens of the objective is brought into actual contact 
with the upper surface of the object. 
In this case the beam lies beyond 
the working distance of the objec¬ 
tive. Should we attempt to bring 
R within the range W, as indicated 
in the lowest diagram, diffraction, 
refractions, reflections and disper¬ 
sions take place of such characters 
and to such degrees as to render 
the detection of micellae impossible. 
No suggestions as to optical com¬ 
binations or size and intensity of 
the illuminating light beam may be 
given which will be applicable to all 
materials. As in all other cases 
of microscopic investigation, the 
proper conditions must be experi¬ 
mentally ascertained for each prep¬ 
aration examined, but it is a safe 
rule to always avoid too large a 
slit and too high a magnification. 
For the slit ultramicroscope as 
. made by Zeiss two objectives are 
Fig. so. The Necessity of having • n 
Two Sides at Right Angles in the specially constructed^ a dry 7 milli- 
Object for Ultramicroscopic Study, meter, 0.4 N.A. achromatic objec¬ 
tive for the study of solids, and a 
4.4 millimeter water immersion of 0.75 N.A., for use with cells 
containing solutions. A good general outfit should include 
oculars, i, 6, 8, 12 and 18. 
When polarized light is necessary in the study of colloidal 
reactions ^ a nicol prism as polarizer mounted upon a saddle 
stand is placed between the lens Ci and the slit S. The ana- 
1 For a discussion and explanation of the behavior of colloidal particles in polar¬ 
ized light see: Garnett, Trans. Roy. Soc. Lond. (A) 203 (1904) 385. 
