WATER OF CONSTITUTION. 



49 



H or OH. There is no deep, wide absorption band at 3 p., so that, 

 judging by the present method of examination, there can not be any 

 hydroxyl groups present. 



Muscovite has a deep, narrow band at 2.85 /*, and smaller bands at 

 J -9> 3-6, 5-6, 5.9, 6.3, and 7.1 /*. Biotite has small bands at 2.8, 5.9, 6.2, 

 and 6.7 /z, and indications of bands at 5.6 and 7 to 8 ju,. It has also a 

 band in the visible spectrum. 



Both micas have a large opaque region at 9 to n, followed by a 

 transparent region at 12 p, beyond which there is again complete opac- 

 ity. Rubens and Nichols 1 have found metallic reflection bands at 8.32, 



J 4 5 6 9 9 10 II 



FIG. 35. Muscovite (a) ; Biotite (b) ; Tourmaline (c). 



a 



9.38, 18.40, and 21.25 p. It will thus be noticed that the bands located 

 by reflection and by transmission do not coincide, as is to be expected, 

 since we are in regions of anomalous dispersion. 



The spectrum energy curves, found by the writer 2 using a rock-salt 

 prism, and a radiometer having windows of the same material, never 

 showed a sharp depression at 2.8 p., while those found by Stewart, 8 

 using a fluorite prism and a radiometer having an inner window of 

 muscovite mica and an outer one of fluorite, contained a conspicuous 

 depression in this region. The discrepancy was explained on the 



Rubens and Nichols: Ann. der Phys. (3), 60, p. 418, 1897. 

 - Nichols and Coblentz : Phys. Rev., 17, p. 267, 1903. 

 8 Stewart : Phys. Rev. 13, p. 261, 1901. 



4 c 



