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. 1 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. 2 



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 



1 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. 



