CALCIUM SULPHATE. 



121 



pression at 3.3 /j. is very marked, while at the lower temperatures it is 

 not so deep. 



The calcium sulphate used was a thick, smooth layer of "plaster of 

 paris," which dehydrated (at least in part) at the red heat used. The 

 emission bands at 2, 3.2, 4.65, and 6.3 jx coincide in intensity and position 

 with the absorption bands found in previous work (see Carnegie Publica- 

 tion No. 65, fig. 4). The band at 4.65 / is shifted from its position at 



/ 2 3 4 5 6 7 



Fig. 90. Nickel oxide (a), (b), (c); Calcium sulphate. 



8M 



4.55 fi in anhydrite (CaSOJ, but coincides with the partially dehydrated 

 selenite (CaS0 4 +2H 2 0) given in Carnegie Publication No. 65, figs. 3 and 4. 

 The absence of the band usually found at 2.8 it may indicate that it is 

 not due to water. Paschen found an emission band of water at 2.83 // in 

 the Bunsen flame. 



Calcium Oxide (CaO); Tricalcium Phosphate [Ca 3 (PO) 2 ]. 

 (Curves a and 6 = CaO; curve c = Ca 3 (P0 4 )2; fig. 91.) 



The surfaces of these two substances were at a dull red heat. The 

 calcium-oxide layer was somewhat cracked, but not sufficient to interfere 

 with the radiation. The layer of oxide in each case was about 1.2 mm. 



The calcium-oxide emission curve is conspicuous for its two sharp 

 maxima, at 2.8 /x and at 4.75 ;i, respectively, and a high emissivity at 8 ll, 



