Abstract The melting temperature of platinum can be measured by using pure platinum ribbons, heated by a modulated direct electric current. The modulation of the emitted radiation shows a sharply increasing distortion when the current is raised to a value whereby in each period the maximum of the temperature reaches the melting point. During a fraction of the period a small center dot of the ribbon melts, causing a rise in emissivity of the center. It has been found that the radiance temperature at which the melting starts can be measured with a sensitivity of 0.02 K. Furthermore, using an opto-electronic stabilization, platinum ribbons in free air can be kept within 0.2 K at a constant mean temperature close to the melting point for one hour or more. From measurements of the radiance temperature and the spectral emissivity the melting temperature of platinum on the IPTS-68 was found to be 2041.0 ± 0.5 K.
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