14 



INFRA-RED REFLECTION SPECTRA. 



Pyrrhotite [(Fe, Ni)S]. 

 (Massive. From Sudbury, Ontario. Curve b, fig. 6.) 



The specimen examined did not appear so highly polished as molyb- 

 denite. It is composed of a bright metal and a darker background. The 

 reflecting power is higher than that of MoS, and increases rapidly with 

 wave-length through the spectrum of 14 /i. 



Chalcocite (Cu 2 S). 

 (Curve c, fig. 6.) 



The reflecting power rises rapidly from 15 per cent at 1 /z to 45 per 

 cent at 4 /*, while beyond 7 /j. the reflecting power has a fairly constant 



2 3 4 5 6 7 a 9 10 11 12 13 



Fig. 6. Molybdenite (a); Pyrrhotite (ft); Chalcocite (c); CoveUite. 



/4/Z 



value of 55 per cent. This substance is black, not unlike magnetite and 

 the Siberian graphite previously described. The polish was higher than 

 in pyrrhotite. 



CJ COVELLITE (CuS). 



(From Anaconda Mine, Butte, Montana. Curve d, fig. 6.) 



This mineral is of a steel-blue color, and appears as compact as steel. 

 The reflecting power rises rapidly at 1 and 2 // and then more slowly to 

 14 p., where it amounts to 75 per cent. 



As a whole, the examination of the sulphides shows that the sulphur 

 atom has merely reduced the reflecting power of the metal, but has not 

 brought about any bands of selective reflection in the region examined. 

 In the case of sphalerite (ZnS) the sulphur atom has introduced into the 

 metal a property which is to be found only in non-metals, viz, low re- 

 flecting power and selective absorption in the infra-red. Of the elements 

 which are on the border line between metals and non-metals, selenium 

 behaves like a metal in its high reflecting power (see fig. 7) and absence 

 of infra-red absorption bands, while iodine and sulphur (non-metals) have 

 absorption bands in this region. 



