122 



INFRA-RED EMISSION SPECTRA. 



which is not unlike that of cerium and thorium oxides, observed by Rubens. 

 Smaller bands appear at 2.4, 3.3, and 4 fx. The calcium oxide was heated 

 to a bright red before mounting it upon the heater-tube, and was apparently- 

 free from the carbonate (fig. 92). Since there are no emission bands 

 belonging to that substance, it appears that the water used in making the 

 CaO into a paste was entirely expelled. 



0/234567 

 Fig. 91. Calcium oxide (a); (6); Tricalcium phosphate. 



The tricalcium phosphate has two marked emission bands, at 2.85 and 

 4.75 li, respectively, and smaller bands at 2 /x and 6.2 /. The emission 

 spectrum is unusually similar to that of apatite (fig. 75). 



A chemical analysis of calcium oxide, by Dr. H. C. P. Weber, showed 

 no weighable amount of silica. This shows that the band at 2.8 11 is not 

 due to silica. 



Calcite (CaCOs). 

 (Curves a and b, fig. 92. Transmission, Carnegie Publication No. 65, p. 70.) 



The sample examined was a layer of finely ground white marble. The 

 surface color in the two cases corresponded to about 900 and 1000 , re- 

 spectively. The emission curve is of interest on account of the two types 

 of emission it contains. In the region of 6.7 / calcite has a band of strong 

 selective, "metallic," reflection. In this region of the spectrum the emis- 

 sivity is proportional to the reflecting power, thus placing in the class with 



