RAW QUARTZ, ITS DEFECTS AND INSPECTION 



349 



fluid to be examined, is mounted in an adjustable-height stand, the optical 

 system lowered into the test tube until the flat bottom surface of the lens 

 contacts the fluid, and the stand is placed in an inspecloscope, conoscope, 

 or in front of a lamp (the stand being adjusted to proper height for good il- 

 lumination). The optical system comprises a lens L (for magnification and 

 elimination of ripples on the liquid surface), a thin Z-cut quartz prism Q,^ 

 and a narrow slit diaphragm 5. When the slit is viewed simultaneously 

 through, and at the sides of the prism, a view similar to one of those shown 



GLASS. 



TEST TUBE 



DRAW 

 TUBE " 



An = .02 I 



U=OH |e 



004 1 



|000 



"TOI 



INDEX 

 HIGH 



INDEX 

 LOW 



Uu=.( 



Fig. 4.4 — The immersion REFRACTOSCOPE may be used in conjunction with an 

 inspectoscope or conoscope for determining the degree of refractive index match (or mis- 

 match) of the immersion fluid relative to quartz. At the right is shown the manner of 

 reading the instrument. 



in the figure may be seen. The two short lines are always the same distance 

 apart and are used as a unit of index mismatch, the unit being u = .009 == 

 .01. The left-hand short line is the one to be aligned with the long line for 

 perfect match, and the actual mismatch An, is measured by the separation of 

 these two lines. The remainder tab is added to remind the operator which 

 indications represent perfect match, too high and too low fluid index. Since 

 the indices of both quartz and fluid vary with temperature and with color 

 of light used, the refractoscope was especially designed for immersion directly 



^ The larger the prism angle the greater will be the sensitivity of reading, and the smaller 

 will be the readable range of mismatch. 



