The emissivity of hot metals in the infra-red

A specially designed vacuum-tight, water-jacketed furnace has been used in the measurement of the emissivity of incandescent metals for wave-lengths of 1.0 to 4.5 μ. Results have been given for pure platinum, iron, molybdenum, copper and nickel. A "split cylinder" type of comparison black-body has been used and its efficiency has been compared with a spherical standard. This calibration has suggested a correction to be applied to Ives' standard of visible radiation. From the present emissivity values, and from those given by other workers, it appears that for a wave-length (usually in the near infra-red) peculiar to each metal the emissivity is constant over a large range of temperature. Such X-points have been observed in the case of iron and molybdenum, but not with platinum or copper.