Abstract
The study aimed at realizing a stable freezing point of tin and to utilize the freezing point in the practical appratus for calibration of a thermometer.
The apparatus features a stable super-cool which takes place in tin filled in a graphite crucible without an excessive falling rate of temperature by means of moderate cooling effect of circulating air in the copper pipe surrounding the crucible.
Two measuring wells of the crucible allow the accurate measurement of freezing point or the concurrent inspection of two resistance thermometers.
In case of 1.5kg of tin molten in the crucible, the temperature of freezing point of 99.9999% tin is 231.9681±0.001°C, which is higher than that of 99.999% tin by 1mK, and has a good agreement with that in IPTS-68.
