MICROSPECTROSCOPY AND MICROSPECTROPHOTOMETRY 



263 



microscope-illuminating source S radiates light in the plastic-material 

 rod T. The light travels in the rod owing to full reflections against 

 its walls. Bending the rod does not alter the phenomena. The com- 



FiG. 10.19. Photometric device using a plastic-material rod (Frangon). 



parison surface of the cube M is thus readily illuminated. Photometric 

 balance or measurement is made by means of a device, such as neutral 

 wedge or polaroid element. Monochromatic filters can be used. 



7. FLUORESCENCE MICROSPECTROPHOTOMETRY 



Under ultra-violet radiation, some substances radiate visible light 

 (primary fluorescence) whose constitution may provide valuable in- 

 formation regarding the details of the investigated specimen. Other 

 substances treated with fluorescent materials radiate a fluorescence 

 of different spectral constitution (secondary fluorescence) which is well 

 worth investigating. 



A monochromatic incident ultra-violet radiation gives rise to 

 fluorescence comprising several types of radiation. The spectral in- 

 vestigation of the fluorescence is made setting the spectrograph next 

 to the microscope in accordance with a layout similar to the one 

 shown in Fig. 10.11. 



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