CHAPTER VI 



INDUSTRIAL APPLICATIONS OF PHASE 



MICROSCOPY 



The technics and materials of industry no longer are separated from 

 those in other fields. Although this chapter concerns materials from an 

 industrial viewpoint much of it will he of interest to others; likewise, 

 parts of the previous two chapters will be useful to industrial micros- 

 copists. All three chapters should be read for a complete understanding. 



The visualization of transparent materials with small differences in 

 refractive index, or of slight absorption or pigmentation, is helpful in 

 industrial microscopy for the identification of materials and impurities 

 therein, for the control of processing, such as salting-out, homogenization, 

 solution, dispersion, polishing, and for the examination of surfaces and 

 changes in them from weathering and abrasion. 



1. CHEMICALS, CRYSTALS, AND MINERALS 



Transparent, uncolored crystals having a slight difference in refractive 

 index from their surround, or mother lic[uor, may be seen clearly with 

 the phase microscope when they are too transparent for bright field 

 microscopy. Because of the increased \'isibility, form and size may be 

 determined to a degree of smallness beyond the capability of the bright- 

 field microscope. Larger crystals show better with low-contrast 

 (0.2A±0.25A) and the smallest visible ones with high-contrast 

 (0.07A±0.25X) diffraction plates. Both bright and dark contrast are 

 useful, and the choice usually depends on the conditions and needs of 

 the examination (see the suggestions in Chapter R^). 



Microcrystals of parafhn from isopropyl alcohol (Fig. VI.l, E and F) 

 are of interest. Since the crystals are very small, only the rolled edges 

 show with polarized light, and these were mistakenly interpreted to be 

 acicular crystals. With phase they appear as thin plaques with a 

 hexagonal symmetry, which is more suitable for waxing paper and other 

 materials. The thin plates of |S-naphthol are readily seen (Bennett, 

 1946), and stereophasephotomicrographs of them showed small spicules 

 of interest in filtration procedures (Fig. IV.6-B). 



Emulsions of other than densely pigmented materials show well with 



223 



