Total emissivities have been obtained for various metal, carbon, paint-coated, and glass samples. The carbon and glass samples were measured at about 500, 320, and 100°C; the others only at 100°C. The equipment consisted of a thermopile, three diaphragms, and three shutters, all at 0°C, and suitable heaters. For calibration, a special blackbody at 100°C was used. Its principal feature was a polished conical brass mirror, also at 100°C, for reflecting blackbody radiation to the thermopile.
The emissivity data for glass were corrected for radiation transmitted through the sample from the blackened heater surface, and for the temperature gradient in the sample. The resulting emissivity values ranged from 0.82 to 0.91 for two glass samples and from 0.67 to 0.775 for fused quartz. For pressed carbon plates, the range was 0.71 to 0.77; for radiator paints, 0.29 to 0.84; for well polished metals, 0.05 to 0.135.
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