Fahrenheit scale Frigorific mixture Recalibration Commentary

Daniel Gabriel Fahrenheit thermometry

Fahrenheit scale

• In 1701, Isaac Newton described a temperature scale
• in which zero was the freezing point of water
• and twelve was the human body temperature.
• Daniel Gabriel Fahrenheit was a glassblower
• who made barometers, altimeters, and thermometers.
• He invented the mercury-in-glass thermometer in 1714.
• He met and took ideas from Ole Rømer for his own scale.
• Fahrenheit originally established
• three calibration points for his scale.
• He set ninety six at the human body temperature;
• he set thirty two at the freezing point of water;
• and he set zero at the temperature of a mixture
• of ice, water, and ammonium chloride.

Frigorific mixture

• A mixture of equal amounts
• of ice, water, and ammonium chloride
• is a frigorific mixture. Together, these ingredients
• reach a stable temperature
• regardless of their initial temperatures.
• But something was wrong with Fahrenheit’s mixture;
• maybe the salts were impure or poorly dissolved;
• it didn’t work quite right.

Recalibration

• Fahrenheit chose ninety six for body temperature
• to improve the simplicity of his scale.
• He started with Ole Rømer’s scale,
• but he didn’t like that water freezes at 7.5 °Rø
• or that body temperature is 22.5 °Rø.
• He multiplied Rømer’s degree by four,
• separating the freezing and boiling points by sixty degrees,
• but he wanted a difference of sixty four
• to make it easy to mark out the degrees
• using a compass to bisect the distances,
• so freezing became thirty two
• and body temperature became ninety six.
• Today the Fahrenheit scale
• is defined in reference to the Celsius scale,
• which is calibrated by any two of sixteen
• reference points—the vapor point of helium,
• the melting point of gallium,
• the triple or freezing points of various elements,
• and the triple point of Vienna Standard Mean Ocean Water.
• Water freezes at 0 °C or 32 °F,
• and boils at 100 °C or 212 °F.
• Today the United States
• is the only English-speaking country
• for whom the majority of citizens
• a balmy temperature of 25 °C doesn’t signify.