A Precise Method of Measuring Heat Conductivity Applicable to Either Molten or Solid Metals. Thermal Conductivity of Zinc

Abstract

A metal rod or a hollow vertical graphite cylinder containing molten metal is packed in silocel contained in an outer iron cylinder. Downward heat flow is established, and vertical gradients are measured differentially by thermojunctions in quartz tubes as are also radial temperature drops across the silocel at all levels. At low temperatures the iron cylinder is surrounded by constant temperature baths, at high temperatures by additional silocel contained in magnesia pipe lagging. The differential junction measurements were obtained by raising one junction progressively while the other was left at the bottom. High temperatures were obtained by a heater winding placed directly on the specimen or graphite cylinder but insulated electrically. For either low or high temperature arrangements the gradient down the specimen is found to change with distance at a constant rate. This means that radial temperature drops across the silocel are constant from bottom to top. This was checked experimentally. Previously published values for solid zinc are verified and extended through the melting point to 730°. The drop in conductivity at the melting point agrees with data of Konno (the only data found in the literature). The values in the liquid state decrease slightly with rise of temperature. Konno's data suggested this but did not extend far enough to prove it.