OXIDES. 



II 9 



from an unmelted surface. The depression at 3.3 // is marked, and at 

 5.5 ; there is a possible emission band. The thickness of the layer was at 

 least 1.2 mm. 



Curves e and /show the emission of a strip of platinum. No depression 

 appears at ^ n, from which it would appear that the depression at 3.$ n 

 is a characteristic of the oxides and not due to absorption in the instrument. 



/ 2 3 4 5 6 7 8JU 



Fig. 87. Zinc oxide (a); Lead oxide (6), (c); Platinum. 



Iron Oxide (Fe 2 3 ); Copper Oxide (CuO). 

 (Curves a and b, Fe 2 3 ; curves c, d e, CuO; fig. 88.) 



The iron oxide used was red hematite, or "rouge." The layer on the 

 heater-tube was 1.5 mm., heated to redness, 8oo. The energy curve is 

 smooth, except a depression at 3.2 /<. The copper-oxide layer was 1.5 mm., 

 heated to a deep red. The energy curve is smooth, except the slight 

 depression at 3.2 /*. 



Cobalt Oxide (C02O3); Chromium Oxide (Cr 2 3 ); Stannic Acid (Sn0 2 ). 

 (Curve a = Co 2 3 ; curves b and c, Cr 2 3 ; curve d, Sn0 2 ; fig. 89. Sensibility 80, 85, 

 and 73, respectively. Temperature 8oo to 900 ). 



The cobalt-oxide curve is smooth throughout, except the depression at 



Chromium oxide is green in color, and emits a fairly smooth spectrum 

 with a possible maximum at 5 [i. The depression at 3.2 fx is prominent. 

 Stannic acid is grayish-white in color, but, unlike many of the white 



