3 



INFRA-RED REFLECTION SPECTRA. 



image A is plotted to one-fifth the scale of B x and B 2 , while the scale of 

 C\, C' 2 and D\, D' 2 is five times that of B u B 2 . The sharp maxima at 

 B 1 B 2 are due to the complex reflection band at 6.7 /x, previously studied. 

 In the present case the maximum occurs at i4o/, which corresponds to 

 6.78//. The wave-length of the maximum at 5 45', D u D 2 is 29.4 ix as 

 determined by Aschkinass (loc. ciL). He located the maximum at C 1} C 2 

 at 1 1.4 /1 in the rock-salt spectrum, but did not find it in the grating spec- 

 trum. From his observations he predicted a weak band in the region of 

 15 to 20//. The asymmetrical part of the reflection curve at +4 indi- 

 cates a possible band at 14 to 16 jx, beginning also in the transmission curve 



2 10/ 



Fig. 21. Calcite. 



of calcite, previously studied (see Carnegie Publication No. 65, p. 70), where 

 the substance becomes entirely opaque at 14 [x. 



The band at 11.4 ;x deserves further study because of the possibility of 

 its being dependent upon the direction of polarization of the incident 

 energy. 1 In the transmission curve of calcite previously studied (see Car- 

 negie Publication No. 65, p. 70) it was found that the region of 9 to 14 it 

 is quite transparent. A small absorption band was found at 11.3 jx, which 

 is so inconspicuous that it would appear impossible for it to give rise to 

 selective reflection. Of all the substances examined this is the first example 

 (see, however, nitrosodimethyl aniline) where a small absorption band 

 apparently coincides with, or gives rise to, a reflecting band. In all other 



1 While this paper is in press, Nyswander (Phys. Rev., 26, p. 539, 1908), using polarized 

 light, found that the band at 11. 3 n is due to the complete absorption (reflection) of the 

 extraordinary ray, the ordinary ray showing no trace of an absorption band in this region. 

 At 14. 1 M is a band due almost entirely to the complete absorption of the ordinary ray. 



