CHAPTER II. 



INFRA-RED REFLECTION SPECTRA OF VARIOUS SUBSTANCES. 



SULPHATES. 



(CaSO*+H 2 O). 



Cleavage piece 1 cut parallel to b axis. The curve a, fig. 60, shows a 

 uniform decrease in reflection to 7 ju., then an abnormal decrease to 7.8 /*. 

 The maximum occurs at 8.7^ (Aschkinass, 8.69 /A), and from its lack 

 of symmetry may be complex. In fact, from what follows one would 



70% 



6 7 a 9 IO 



FIG. 60. Selenite (a); Barite. 



12 



expect another band at 9.1 ;,, which is of frequent occurrence, and is 

 harmonic with the SO 4 band at 4.5 /*. 



In a recent research by Koch, 2 who used a reflection band as a source 

 of energy in an interferometer, there are indications that the band of 

 selenite at 8.7 ju is complex. 



1 In the present discussion "cleavage piece" signifies that the natural unpolished 

 surface was used. 



'Koch: Ann. der Phys. (4), 17, p. 658, 1905. 



77 



