JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. V ■ JUNE 4, 1915 No. 11 



PHYSICS. — The emissivity of metals and oxides. IV. Iro7i oxide.^ 

 George K. Burgess and Paul D. Foote, Bureau of 

 Standards. 



This paper is a continuation of the study of the radiometric 

 properties of metals and oxides. By the use of radiation py- 

 rometers and the method of microscopic melts described in 

 the earlier papers, the total and monochromatic emissivity 

 (X = 0.65 yu) of iron oxide formed by heating iron in air has 

 been determined at high temperatures. 



Iron oxide in the spectral region X = 0.65 ^ is almost ''black," 

 having an emissivity varying from 0.98 to 0.92 in the range 800° 

 to 1200°C. The corrections necessary to apply to the readings 

 of an optical pyrometer in this temperature range vary from 0° 

 to 10°C. The total emissivity of iron oxide increases from 

 0.85 at 500°C. to 0.89 at 1200°C. The corrections necessary to 

 apply to the readmgs of a radiation pyrometer in this tempera- 

 ture range vary from 30° to 50°C. 



The temperature of the outside of the oxide layer is consid- 

 erably different from that of the inside in contact with the metal, 

 as a result, in part, of the low thermal conductivity of the oxide 

 and, in part, undoubtedly, of the actual separation of the outside 

 oxide layer from the metal, thus forming an air gap between the 

 two surfaces or between two surfaces of oxide, the outer one 

 thick and the inner one thin. The drop in temperature through 



1 To appear in full in the Bulletin of the Bureau of Standards. 



377 



