A Vacuum Apparatus for Measuring Thermal Expansion at Elevated Temperatures, with Measurements on Platinum, Gold, Magnesium and Zinc

An apparatus for measuring linear thermal expansion between room temperature and 950°C in vacuo by an interference method has been developed and tested on platinum, gold, magnesium and single-crystal zinc. Although designed primarily for metals which oxidize readily it seems to give excellent results for all metals in the temperature ranges through which their vapor pressure is low. Under conditions such that a metal has a high vapor pressure the performance is not quite so satisfactory because of the deposition of metallic films on some of the cooler parts of the optical train. The refractive index of fused silica for the helium line λ=5877.2 has been calculated for the temperature range 18° to 950°C. A study of the dilatation of single-crystal zinc yields no evidence for the existence of more than one form between 20° and 350°C.