54 



INFRA-RED TRANSMISSION SPECTRA. 



GROUP IV: TRANSMISSION SPECTRA OF COLORED GLASSES. 



Cobalt Glass. 

 (Fig. 37. Thickness, 2.43 mm.) 



Colored glasses have been but little studied. Nichols 1 examined cobalt 

 glass, and found an absorption band at 1.4 ;i. This is one of the few 

 substances having a prominent band near the visible spectrum. Garnett 

 (loc. cit.) concludes that the deep blue color of cobalt glass can not be 

 due to small diffused spheres of metallic cobalt, which would give a reddish 

 color to transmitted light, but that the metal is in the form of discrete 

 molecules (amorphous). 



For the present work a fluorite prism and bolometer were used (see 

 Appendix II). 



2 3 



Fig. 37. Cobalt blue glass. 



In fig. 37 is given the transmission curve of a cobalt blue glass which 

 showed three weak absorption bands in the visible spectrum. In the 

 infra-red there is a larger absorption band at 1.5 p., a smaller band at 

 2.1 fi, and second large band at 3.5 p. The small band at 3 /i is due to 

 the glass itself, and is also found in quartz. Beyond 4 p. the opacity is 

 due to the glass, as found in clear specimens. 



The behavior of this glass is entirely different from the red glasses to 

 be noticed on a following page. It is not like an optically turbid medium, 

 unless we consider it to have more than one region of selective absorption, 

 which is in line with the conclusion arrived at by Garnett {loc. cit.). 



"Nichols, E. F.: Phys. Rev., 1, p. 1, 1893. 



