THE REPRODUCIBILITY OF THE STEAM POINT

Abstract

A steam-point apparatus and precision manometer have been constructed in connection with the realization of the International Temperature Scale at the National Research Council. By means of this apparatus the steam point may be realized to 0.0002 °C. with a reproducibility of 0.0001 °C; the difference is due to uncertainties in the physical constants involved.The manometer is capable of measuring pressures of from 0 to 85 cm. of Hg with a precision of 1 micron, using electrostatic capacitance detection of the mercury surfaces and end standards to determine the height. The steam boiler gives constant results for a wide variety of operating conditions and has been used to show the increase of temperature with increasing head of water vapor.The triple-point cells used in these experiments show a similar temperature change with change of immersion. It has been shown that a period of 1 to 3 days is required for them to establish temperature equilibrium, after which they are constant to within 0.0001 °C. The resistance thermometer used is extremely stable at the steam and triple points if it is carefully handled.