Specifications include, but are not limited to: Equipment Required: 1. Microscope (minimum 100X magnification) 2. Light source - preferably sodium light or other monochromatic source, but not absolutely essential 3. Refractive index liquids* 4. Microscope slide and slide cover 5. Mortar and pestle *Available from R.P. Cargille Laboratories, Inc., Cedar Grove, NJ. Procedure: 1. Using the mortar and pestle, crush a few representative beads and place a few of these crushed particles on a microscope slide. 2. Place a drop of a refractive index liquid, with an index as close to that of the glass as can be estimated, on the particles. 3. Cover the slide with a microscope slide cover and view the crushed particles by transmitted light normal to the slide surface (illuminated from the bottom). 4. Adjust the microscope mirror to allow a minimum light intensity for viewing. This is particularly important if sodium light is not used. 5 Bring a relatively flat and transparent particle into focus. 6. By slightly raising and lowering the objective (microscope tube), look for one or both of the following: a. Becke Line - This light line will appear to move either into the particle or away from it. In general, if the objective is raised, the line will move toward the material of higher refractive index; if the objective is lowered, the line will move toward the material of lower index. b. Variation in Particle Brightness - When raising the object from a sharp focus, the particle will appear to get brighter or darker than the surrounding field. If it becomes brighter, the glass has a higher refractive index than the liquid. If it becomes darker, the glass has a lower refractive index than the liquid. In both cases, the opposite will be true if the object is lowered.
