Reanalysis of Possible effects due to Gold-plating on the Thermal Expansion of Copper on Constant-volume Gas Thermometry at Low Temperatures

Constant-volume gas thermometry below the triple point of water (TPW) with reference to TPW gives temperature values higher than the correct ones when the thermal expansion coefficient of the bulb assumed in the calculation is smaller than the real one. Therefore, in order to attribute this temperature difference to a change in the thermal expansion coefficient of copper due to gold-plating, it is necessary that gold-plating increases the thermal expansion coefficient of copper even though that of gold is smaller than that of copper.