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Silver Facts

Freezing Silver Helps Labs Check Thermometers

When very pure silver changes from liquid to solid, its temperature holds nearly steady. Laboratories use that pause as a reference for high-temperature measurements.

A useful pause in the cooling

Freezing silver gives laboratories a reliable reference for checking thermometers. As very pure molten silver turns solid under controlled conditions, its temperature stays nearly steady for part of the freeze. This flat stretch in the cooling curve is called a plateau.

Here, “freezing” means turning solid, not becoming cold. Silver’s reference freezing point is assigned 961.78 °C on the International Temperature Scale of 1990, usually shortened to ITS-90.

A shared reference for a hot measurement

Calibration means comparing an instrument’s readings with a known reference. Instead of simply trusting a furnace’s temperature setting, a laboratory can compare a thermometer with the physical change happening in the silver.

The silver sits in a purpose-built fixed-point cell: a carefully prepared container and sample used to reproduce that reference. The assigned temperature applies to specified conditions, including pressure. Impurities and uneven heating can change the result, so laboratories estimate and report the remaining uncertainty.

A silver coin or bar cannot substitute for this equipment. Other metals in an alloy, contamination and the measurement setup all matter.

A reference on the temperature scale

The kelvin is the scientific unit of temperature. Its modern definition uses the Boltzmann constant, a constant of nature that relates temperature to energy. Silver’s freezing point instead belongs to a practical scale that helps laboratories make comparable measurements.

That is silver’s unusual job here: a repeatable change of state helps people judge how well a thermometer is reading. It is specialist laboratory work, not a home heating experiment.

About this edition

Original source and editorial notes
An edited, source-checked edition

Adapted from original material by Rich Silver. Original source card: Silver fact: supplied original card (publication date not established).

Reviewed 2026-11-05. Clarified that 961.78 °C is the assigned silver freezing-point value on ITS-90 under specified reference conditions, not an exact universal temperature for any silver object. Distinguished practical scale realization from the modern SI kelvin definition and removed unqualified precision claims. The source card has no verified publication date or public URL; none has been inferred from file metadata. No source-card graphics are reproduced. Reader-first revision leads with the freezing plateau and explains calibration, fixed-point cell and kelvin in plain language. Retains assigned-value/reference-condition and measurement-uncertainty distinctions. Existing section-2 and section-1 anchors follow their matching explanations after reordering.

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