32 



INFRA-RED REFLECTION SPECTRA. 



have properties similar to fluorite. That the expectations were not ful- 

 filled is perhaps to be attributed to the fact that the specimen was an 

 hydrated alteration product, as will be noticed from its transmission 

 spectrum (fig. 26) , which shows that the mineral contained water. 



In fig. 23 is given the reflection curve of cryolite, four large, well-polished 

 surfaces being used. The central image was quite strong. The first-order 



-2 -/ / 



Fig. 23. Cryolite. 



diffraction band to the right and to the left is quite strong, being measured 

 in centimeters instead of millimeters. This, of course, is partly due to the 

 coarser grating. The mean angular position of the maximum is 2 43'. 

 From the calibration curve the wave-length of this maximum is 15.1 /'., 

 which is just half the value of the most intense band of fluorite. 



RESIDUAL RAYS FROM OTHER MINERALS. 



Diaspore [AIO(OH)]. 



In examining the following minerals grating No. 1 was used in order 

 to obtain an intense spectrum. The slits were 4 mm., which is a little 

 smaller than those used by others. In Carnegie Publication No. 65 the 

 reflection spectrum of an intense double band was found at 14 to 15 ft. 

 From its general trend it was hoped to find the reflection spectrum to con- 

 tain further bands. Only two reflecting surfaces were available. With 

 these, the maxima at 15 ;>. in the rock-salt spectrum were verified, but no 

 bands were detected beyond this point. 



