PREPARATION METHODS 



175 



a cover glass. A cover glass will give clearer results with a regular 8-mm 

 objective. 



Since concentration gradients differ in refractive index, they may be 

 seen with the phase microscope (Section 3.2). Other technics that may 



a 



MWOHtrtifcnMMMIiMP^ilNMI 



Fig. IV.2. Replica of piston ring surface, 150 X. vl, brightfield. jB, dark-contrast 



phase. C, bright-contrast phase. 



Fig. IV.3. Chromium shadowcast silica repUca of martensitic steel, 230 X. A, 

 brightfield. B, dark-contrast phase. C, bright-contrast phase. 



be helpful in the examination of materials with the phase microscope 

 are: differential swelling (such as cellulosics with cuprammonium), 

 stepwise dehydration with isopropyl or higher alcohols, incomplete 

 salting out, and isothermal distillation. Reactions in capillary tubes 

 may be watched if the tube is immersed in a drop of fluid of the same 



