Total radiation from polished and from soot-covered nickel
B. T. Barnes
Total radiation data were obtained on polished nickel and on the same metal when covered with soot. Temperatures below the range of an optical pyrometer were determined from a log-resistance vs log-temperature curve obtained from resistance measurements on the wire mounted in a lamp in a furnace at known temperatures and extended up to the points obtained when using a pyrometer. The log-resistance vs log-temperature curve had a sharp break at the magnetic transformation point just as noted by previous investigators. This break occurred at about 360°C. In the region from 800 to 900° the total radiation values for unpolished nickel deviated somewhat from a smooth curve through the values at lower and higher temperatures. This may be due to an error in drawing the log-resistance vs log-temperature curve since there were no resistance temperature measurements from 500 to 725°C between the range of the furnace readings and that of the pyrometer. Total emissivity values for soot-covered nickel range from 0.92 at 400°K to a mimimum value of 0.81 at 800°K, then rise to 0.86 at 1100A°K. The total emissivity of polished nickel was found to be 0.205 at 1400°K. At 400°K it was 0.087 before heating to incandescence and 0.063 afterwards. At intermediate temperatures there were similar differences due to surface changes during the initial heating. © 1929 The American Physical Society.
