ijspunten

Ijspunten are reference temperatures used in the field of thermometry. The term is Dutch for “ice points” and refers to temperatures at which ice and water are in equilibrium under standard atmospheric conditions. The most widely used ijspunt is the ice point of pure water at one atmosphere, defined as 0.00°C (273.15 K). This fixed point provides a simple, reproducible reference for calibrating thermometers and for defining temperature scales. Historically, fixed points like the ijspunt were realized by preparing an ice–water bath and ensuring uniform temperature; thermometers are adjusted to read 0°C in this bath.

Other ijspunten were used in the development of metrology, such as fixed points realized in specialized equipment based on the melting points of pure metals. In modern metrology, the fixed points used for calibration have shifted toward more stable and precise references, including the triple point of water (0.01°C at 611.657 pascal) and metal fixed points such as gallium. The ijspunt concept remains a teaching tool to illustrate how thermometers are calibrated and how temperature scales are anchored.

In Dutch usage, ijspunten may appear in discussions of the history of thermometry, calibration practices, and temperature standards. See also thermometry, fixed point, melting point, triple point of water, calibration.