THE MELTING POINT OF TIN

摘要

The benefits of using the melting point of tin (MPT) rather than its freezing point as a temperature fixed point are discussed. A procedure for the realization of the MPT with high accuracy was developed. An improved procedure for inducing the freeze by using outside-gas-flow cooling is also described. The calibration data obtained from the MPT are compared with that from the freezing point of tin. Thirteen SPRTs were calibrated on eighteen pairs of freezing curves and melting curves. The average difference between the melting point and freezing point was found to be -0.33 mK. The MPT can, therefore, be used to calibrate SPRTs instead of the freezing point of tin in the situations where an expanded uncertainty (k=2) of about 1.5 mK or larger is acceptable, which satisfies most requirements for SPRT calibrations.