TABLES 277-278. 



RADIATION EMISSIVITIES- 



TABLE 277. Relative Emissive Powers for Total Radiation. 



249 



Emissive 

 600 + C. Ka 



of black body = i. Receiving surface platinum black at 25 C; oxidized surfaces oxidized at 

 1 and Overholzer, Phys. Review, 2, p. 144, 1913. 



Remark: For radiation properties of bodies at temperatures so low that the radiations of wave-length greater than 

 20 n or thereabouts are important, doubt must exist because of the possible and perhaps probable lack of blackness of 

 the receiving body to radiations of those wave-lengths or greater. For instance, see Table 379 for the transparency 

 of soot. 



TABLE 278. Emissivities of Metals and Oxides. 



Emissivities for radiation of wave-length 0.55 and 0.65 ft. Burgess and Wallenberg, Bui. Bureau of Standards, 

 n, 591, 1914. 



In the solid state practically all the metals examined appear to have a negligible or very small temperature coeffi- 

 cient of emission for X = 0.55 and 0.65 /j, within the temperature range 20 C to melting point. Nickel oxide has a 

 well-defined negative coefficient, at least to the melting point. There is a discontinuity in emissivity, for X = 0.65 p 

 at the melting point for some but not all the metals and oxides. This effect is most marked for gold, copper, and 

 silver, and is appreciable for platinum and palladium. Palladium, in addition, possesses for radiation a property 

 analogous to suffusion, in that the value of emissivity (X = 0.65 /*) natural to the liquid state may persist for a time 

 after solidification of the metal. The Violle unit of light does not appear to define a constant standard. Article con- 

 tains bibliography. 



SMITHSONIAN TABLES. 



