CHAPTER III. 



MINUTE EXAMINATION OF THE REFLECTION BANDS OF QUARTZ 



AND OF THE CARBONATES. 



Having assembled a fluorite prism and bolometer for radiation work, 

 it seemed worth while to spend some time on the examination of the reflec- 

 tion bands at 6 to 7 p. in the carbonates, and at 8.5 to 9 /< in quartz. The 

 fluorite prism had a circular aperture of 3.3 cm., angle 6o, and was per- 

 fectly clear. It was mounted on the spectrometer used in the previous 

 work and, for the regions of the spectrum examined, the dispersion was 

 from 4 to 6 times that of rock salt. On account of the large dispersion 

 and the small prism face, the deflections were only about one-tenth that 

 previously used. The glower of the Nernst lamp was used in order to 

 obtain a sufficiently strong source of radiation. The main objection in 

 using a glower is its narrowness, which requires greater care in maintaining 

 a constant adjustment. The bolometer strip was about 0.5 mm. or 4' of 

 arc, while the temperature sensibility was 1 mm. = 5 X io~ 5 C. A radi- 

 ometer would have been more satisfactory, but the bolometer was con- 

 veniently at hand. With this greater dispersion it was found that the 

 reflection bands of some of the carbonates are quite complex, while in 

 others there is but one band. 



Quartz. 1 



(Crystal cut perpendicular to optic axis. Curve b, perfectly clear specimen of 



quartz glass, fig. 14.) 



It has repeatedly been noticed that the various silicates have quite 

 different reflection spectra, while in the carbonates and in the sulphates 

 the spectra show great similarity. It was therefore assumed that the 

 silicon oxide radical is differently united in the different silicates. All the 

 evidence obtainable, without exception, of substances in the solid or liquid 

 (crystalline or amorphous) condition, shows that crystallographic form 

 does not explain these anomalies; neither will the slight impurities present 

 in many of the silicates explain them. 



Pfund 2 found identical reflection bands of sodium-potassium tartrate 

 (C 8 H 4 K Na0 6 + 4H 2 0) in the form of a polished crystal, and also in the 

 molten condition. His reflection maxima of molten nitroso-dimethylani- 



1 The writer is indebted to Dr. Day and Mr. Sheppard, of the Geophysical Laboratory of 

 the Carnegie Institution of Washington, for the sample of quartz glass. 



2 Pfund, Astrophys. Jour., 24, p. 31, 1906. 



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