The Optical Properties of Molten Metals

Abstract

Optical Properties of Molten Bi, Pb, Sn, and Wood's Alloy to 500\ifmmode^\circ\else\textdegree\fi{} and of Hg to 345\ifmmode^\circ\else\textdegree\fi{} C.---While there is considerable evidence that the optical properties of metals in the solid state do not vary with temperature, the question has not yet been investigated for molten metals. A vacuum tight furnace enabled a nitrogen atmosphere to be used so that surfaces free from oxidation could be studied. The optical properties were determined by letting plane polarized light of wave-length about 6020 \AA{}.U. fall at an angle of 45\ifmmode^\circ\else\textdegree\fi{} upon the metal surface, and analyzing the reflected light with the help of a Jellet split nichol having a Brace elliptic half-shade mounted just before it. The method of calibration and use of the apparatus is described. The optical properties were found to be independent of the temperature for all the metals tried. The mean values, correct to better than one per cent., are as follows: for Bi, $\ensuremath{\nu}=0.493$, $k=1.32$; for Hg, $\ensuremath{\nu}=0.442$, $k=1.43$; for Pb, $\ensuremath{\nu}=0.415$, $k=1.76$; for Sn, $\ensuremath{\nu}=0.398$, $k=1.46$; for Wood's alloy, $\ensuremath{\nu}=0.397$, $k=1.78$. From a discussion it appears that the constancy of the optical properties is not consistent with Drude's equations.