OXIDES. 



!7 



maxima, at 11.75 an ^ I 3- 1 , u > respectively. The reflecting power decreases 

 uniformly from 12 per cent at 4 t a to 10 per cent at 8 p, passes through a 

 minimum of 4 per cent at 10.8 /<, then suddenly rises to 78 per cent at 

 11.75//. 



Rutile (TiO,). 

 (Graves Mountain, Lincoln County, Georgia. Curve b, fig. 9.) 



The surface of the specimen examined was a natural crystal face, area 

 about 1.4 by 1.8 cm., having a high polish, but uneven and containing cracks. 



The reflection curve is the most unusual of all examined in that the 

 band of selective reflection occurs almost at the working limit of a rock- 

 salt prism. The maximum is broad and is fairly well defined at 13.6 ft. 



80% 



3 4 5 6 7 8 9 10 II 12 13 



Fig. 9. Wulfenite (a); Rutile (6); Zincite. 



14 ISfl 



Zincite (ZnO). 

 (From Franklin, New Jersey. Curve c, fig. 9.) 



The specimen examined was massive, having a red color and a dull 

 polish. The surface was full of cracks, which would materially reduce 

 the reflecting power. The reflecting power is low and uniform throughout 

 the region of the spectrum examined. No bands of selective reflection 

 were found. In this respect zincite is similar to iron oxide, but, on account 

 of its low reflecting power, it is to be classed with the " insulators," and 

 hence one would expect to find bands of selective reflection in the infra-red. 



Corundum (AI2O3). 

 (Craigmont, Renfrew County, Ontario. Curve b, fig. 10.) 



This specimen was an opaque crystal, of which a cleavage surface, 

 about 2 by 3 cm. in area, was examined. The surface contained striae, 

 but otherwise had a high polish. The reflecting power is unusually low, 

 except in the region of selective reflection, when it is quite high. The 

 region of selective reflection is wide with maxima at n.o, n.8, and 13.5 fi. 



