8o 



INFRA-RED REFLECTION SPECTRA. 



from 9.4 to 10.3 p,, with maxima at 9.45, 9.8, and 10.2 p,. The region 

 from 12 to 13 /A is complex, with a maximum at 12.8 p. In addition to 

 this are sharp maxima at 8.55, 13.8, and 14.6 /A. 



QUARTZ (SiO 2 ). 

 (Curve b, fig. 64.) 



Section cut perpendicular to optic axis. The examination was made 

 to compare the maxima of the silicates studied. The maxima (at 8.48 

 and 9.02/1,) agree well with those found by Rubens and Nichols, using 

 a wire grating. The enormous reflecting power of 95 per cent at 9 /* 



1 00 of c 



3 9 10 II I 



FIG. 64. Diaspore (a); Quartz. 



a 



is 



16JU. 



has been found only in quartz, and is slightly higher than found by 

 others. In the silicates to be noticed presently it will be found that the 

 bands found in quartz are shifted to new positions for each new com- 

 pound examined. 



A new band which is unusually sharp and narrow was found at 

 12.5 p.. It is so very narrow that it seems more appropriate to call it a 

 line instead of a band. 



Trowbridge measured the reflecting power of quartz at 9, 10, II, 12, 

 and 12.78 ju,, and found a rapid decrease to 12 /*, while the last reading is 

 much higher, which increase he interpreted as being due to the band at 



