SILICATES. 



IO7 



Apatite [Ca 5 F(P0 4 )3]. 



(Rod 12 by 1.5 mm. Energy supplied, 9.3 and 11.8 watts. Curves a and b, fig. 75. 



Transmission, Carnegie Publication No. 65, p. 58.) 



The emission spectrum shows emission bands at 2.9 and 4.5 fx. The 

 rod was made from a dark massive specimen which may have contained 

 silica, whence the band at 2.9 /j. in both the emission and absorption spec- 



345 



Fig. 75. Apatite. 



8JU. 



trum. On the other hand, many oxides, known to be free from silica, 

 have a strong emission band in this region, from which it would appear 

 that this band is characteristic of the oxides. 



Aluminum Oxide (AI2O3). 

 (Rod 14 mm. long, tapering from 2.5 to 3 mm. in diameter. Energy supplied, 0.025 and 



0.115 ampere. Curves a and b, fig. 76.) 



The rod was built up from the pure powder in an oxy-hydrogen flame. 

 The emission curve is conspicuous for the great variation in intensity of 

 its emission bands which occur at 1.4, 2, 3.1, 4.7, 5.2, and 7-5(?) /* The 

 emission curve differs but little from the one of topaz except that the latter 

 has the silicate band at 2.85 11. In fig. 65, curve c shows the radiation 

 from a rod made from alumina and 1 per cent of feldspar, and curve b, 

 fig. 65, gives the radiation from a rod made of alumina and 1 per cent of 

 silica. In both cases the silica band at 2.87 fi is superposed upon the 

 spectrum of the aluminum oxide. 



