42 



INFRA-RED TRANSMISSION SPECTRA. 



ing part of the spectrum the absorption coefficient is very small, and the loss 

 of energy is due to the high reflecting power, which is about 40 per cent. 

 Molybdenite differs from stibnite in that it is very opaque throughout 

 the spectrum, examined to 15 p.. The two specimens examined were thin 

 folia, only 0.05 and 0.31 mm. in thickness (curves a and b, fig. 25). From 

 the greatly decreased transmission of the thicker piece, it will be noticed 

 that the loss of energy is due to absorption rather than reflection. The 

 absorption coefficient has not been computed, but an inspection of the 

 curves shows that it must be large. By increasing the thickness six times 

 the transmission is decreased 18 per cent, while in stibnite, by increasing 

 the thickness five times, the transmission is reduced only about 5 per cent, 

 in the region of general absorption. 



90% 



0/2345675 

 Fig. 26. Kuntzite (a); Cryolite (6); Carborundum (c); Nitrocellulose. 



(From Pala, California. 



Kuntzite [LiAI(Si0 3 )2]. 



Cleavage piece, parallel to m; transparent; ^ = 1.05 mm. 

 Curve a, fig. 26.) 



This mineral, which is violet spodumene, is obtainable in large speci- 

 mens, hence it was of interest to determine its transparency to infra-red 

 radiation. It is lacking in the small band of Si0 2 at 2.95 /* and is more 

 opaque than quartz in the region of 1 //, so that it would not be more 

 serviceable than the latter in optical work. 



