RESIDUAL RAYS; SILICATES. $$ 



Stibnite (Sb 2 S 3 ). 



Stibnite was previously found to have a high reflecting power up to 

 15 /, where it seemed to decrease. In the present examination, using 

 three reflecting surfaces, this high reflecting power was found to continue 

 throughout the infra-red. A small maximum was found at 2 /1, which no 

 doubt belonged to the third-order diffraction band. When using alumi- 

 num mirrors a similar band was found at this point. 



Spodumene [LiAl(Si0 3 )2]. 



Three large reflecting surfaces were used. The galvanometer was 

 perfectly steady, so that 0.2 mm. deflections could have been read, but no 

 radiation was detected beyond that due to the reflection bands at 9 to 10 / 

 previously examined with the rock-salt prism. 



Celestite (SrSCX,). Selenite (CaS0 4 +2H 2 0). 



Three large cleavage specimens of each of these were examined, using 

 slits 4 mm. wide. In the case of celestite the central image gave a deflec- 

 tion of 50 + cm., but nowhere could radiation be detected except in the 

 region of 9 to 10 / previously studied. Aschkinass (Joe. cit.) has predicted 

 a band in the region of 50 jx for the sulphates. 



Apatite [Ca 6 F(P0 4 ) 3 ]. 



Three large ground and polished surfaces were used in this examina- 

 tion. No reflection bands were observed except at 9 ft, where an exami- 

 nation with a rock-salt prism showed a weak (20 per cent) double band. 

 Apparently the phosphates have no strong reflection bands throughout the 

 infra-red spectrum. This is just the opposite of what has been described 

 in Chapter II on the oxides, where very intense bands were frequently 

 observed. 



CYANINE (C29H35N2I). 



(Grating No. 2; slits 4 mm.) 



This substance was melted between glass plates, which were then split 

 apart, thus leaving plane smooth surfaces. Three such films on glass were 

 examined. It was previously found (see Carnegie Publication No. 35, 

 p. 82) that cyanine is very opaque at 6 to 8 //. The central image gave 

 a deflection of 50 + cm., and there was still a little reflected energy to be 

 detected at 25 (i, indicating a high reflecting power, but no reflection bands 

 could be detected throughout the spectrum. 



SILICATES. 



The reflection curve of mica has already been described in connection 

 with the calibration of the instrument. This examination included also 

 serpentine, albite, and microcline. The grating spectrum showed the 

 reflection bands at 9 ji, but beyond this no appreciable radiation could be 

 detected. This, of course, was to be expected for serpentine, for which 



