ULTRAMICROSCOPES 
113 
with a proper solvent and long washing is imperative. Before 
introducing a liquid for examination it is always best to pour a 
little alcohol through the cell and to follow this with the alco¬ 
holic solution to be studied, or if aqueous suspensions are to be 
employed, displace the alcohol with distilled water free from all 
fatty or greasy matter and then introduce the colloidal solution. 
This process is usually essential in order that the liquid to be 
examined shall come into perfect contact with the windows of 
the cell with no interfering film and no air bubbles. 
A much cheaper and simpler cell is shown in Fig. 55.^ It 
consists of a tube of black glass with central swelling and win¬ 
dows at right angles to 
each other. These win¬ 
dows are either of glass 
or of quartz, the latter 
being preferable, since 
glass is slightly fluores¬ 
cent . For use, two pieces 
of rubber tube are at¬ 
tached as shown by the 
dotted lines. These little 
cells give excellent results with gases and vapors and may also be 
employed for the study of such solutions as will not be affected 
by contact with rubber. For preliminary examinations they 
are far more convenient than the Biltz cell and like it can 
easily be held in place on the type of stage shown in Fig. 51 by 
thin metal clamps or rubber bands. Moreover, these cells are 
more easily cleaned and are relatively inexpensive.^ 
When solids are to be examined, as, for example, specimens 
of glass, it is important that there be two sides of the preparation 
which meet at as nearly right angles in as sharp an edge as is 
possible. The reason for this will readily be understood by 
referring to the diagram, Fig. 56. If the sides do not meet in a 
sharp edge as shown at a, but form an obtuse angle or rounded 
^ Made by E. Leitz, Wetzlar. 
2 A simple, easily constructed cell has been devised by Kiplinger, J. Amer. Chem. 
Soc. 1917, 1616. 
Fig. 55. 
Simple Cell for Use with Slit 
Ultramicroscopes. 
