Field of Science

Weird Words of Chemistry: Frigorific

I ran across this word when my youngest, who I'm coaching for the thermodynamics event for Science Olympiad,asked me why the freezing point of water was 32o on the Fahrenheit scale. The Celsius/centigrade scale was originally pinned to the freezing point and boiling point of pure water at 1 atmosphere of pressure. (Now it's pinned to absolute zero and the triple point of water.) What physical property was 0o linked to? The freezing point of something other than water? I had to admit I didn't know and now that my curiosity was piqued, went off to hunt it down.

The zero of Fahrenheit's temperature scale was essentially pinned to the temperature of a "frigorific" mixture of ice, water and solid ammonium chloride in a 1:1:1 ratio, along with the freezing point of water and the temperature of the human body. Frigorific seems to have been coined by Robert Boyle to describe particles of cold that were transferred from body to body, and ultimately got attached to mixtures that achieved a particular temperature regardless of the starting temperatures of the materials. Wandering through the old chemistry literature, I found this table of frigorific mixtures "sufficient for all practical and philosophical purposes, in any part of the world in any season," useful in the days before refrigerators, still useful for those who need a constant temperature bath at low temperatures.

The size of a degree was set by bisecting the difference between the point at which ice and water were in equilibrium and body temperature six times, or 64 degrees (26). Binary was easier to use when you had to make your own instrument than decimal.

Frigorific has essentially vanished from the chemist's vocabulary, though it's still apparently alive and well in the engineering literature. As words of science go, it sounds awkward to my ears — as roughly sharp as heaved Arctic ice.

Nova has an excellent piece on the hunt for absolute zero. Thanks, Kathryn J for the reference!

For more on what I think about well-formed science words, you can read "Neolexia" at Nature Chemistry.


  1. Definition of FRIGORIFIC IMerriumIWebster)

    : causing cold : chilling
    Origin of FRIGORIFIC

    Latin frigorificus, from frigor-, frigus frost
    First Known Use: 1667

  2. Very interesting! We still use it in French (as well as "réfrigéré") - "camion frigorifique" or "wagon frigorifique" for refrigerated lorry or cold-storage wagon.

  3. That is a weird word! But I think there are quite a few of those in chemistry. Ununpentium, anyone?

  4. For additional information on the history of the Fahrenheit/Celsius/Rømer scale, see episode 45 of the Mechanical Universe Videos, available at
    The discussion of temperature scales comes near the end of the 30 minute video.


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