94 



INFRA-RED REFLECTION SPECTRA. 



CARBORUNDUM (SiuciuM CARBIDE) (SiC). 

 (Large hexagonal plate, naturally highly polished. Curve a, fig. 81.) 



This is an artificial product obtained from a carborundum furnace. 



The reflection curve is the most remarkable one yet discovered. The 

 selective reflection bands of quartz at 8.5 to 9.03 ^ stand second in the 

 order of intensity. 



Since absorption, reflection, and refraction are intimately connected, 

 the reflection curve gives us an idea, qualitatively, of the dispersion of 

 this mineral. It will be noticed that the reflection curve drops abruptly 

 from a fairly constant value at 9 p, to a very low value at 10 /x, while 

 beyond 13 /j. it remains abnormally high. This is exactly what is found 

 for the refraction curve, in the region of anomalous dispersion, and to 

 illustrate this point the carborundum curve is the best example yet 

 observed. In this connection it will be noticed the reflection curve of 

 quartz decreases more uniformly throughout this whole region. 



FIG. 81. Carborundum (a) ; Sulphur (b] ; Graphite (e). 



GRAPHITE (C). 

 (Natural mineral from Siberia. Curve c, fig. 81.) 



The reflecting power of various forms of carbon, such as "gas- 

 carbon" and anthracite, have been examined by Aschkinass, 1 who found 

 the reflection to increase from 30 per cent at 8 p. to 53 per cent at 26 ft 

 for the former, and a uniform reflection of about 13 per cent throughout 

 this same region for the latter. 



Aschkinass: Ann. der Phys. (4), 18, p. 373, 1905. 



