Answers to Go with Susan Smith

Q. Why is the Fahrenheit temperature for freezing 32 degrees? Is that just a random number?

A. Let’s turn to “The Gale Encyclopedia of Science” for information on Mr. Fahrenheit and his efforts to measure temperature.

Gabriel Daniel Fahrenheit had no formal education. He was the eldest son of a wealthy German merchant. When Fahrenheit’s parents died suddenly, his guardian sent him to Amsterdam to learn a trade. While there, he became intrigued with the making of scientific instruments. Although the manufacture of these instruments was a small, specialized profession at that time, he chose it as his life’s work.

Early thermometers held water or water-alcohol mixtures. Unfortunately for its use in thermometers, the volume of water does not change uniformly with changes in temperature. When cooled, liquid water contracts. Then as the water approaches its freezing point, it expands. This unusual property of expansion upon cooling means that a water thermometer not only goes down as the temperature falls, but it sometimes goes up.

In 1714, Fahrenheit experimented with liquid mercury for thermometers. Mercury has a uniform volume change with temperature, a lower freezing point and higher boiling point than water, and does not wet glass.

Fahrenheit’s mercury thermometers made possible the development of reproducible temperature scales and quantitative temperature measurement.

To fix the size of a degree, Fahrenheit decided that there should be exactly 180 degrees between the temperature at which water freezes and the temperature at which water boils.

Fahrenheit chose 180 because it is divisible by one and by 16 other whole numbers. Similarly, 360 – 180 times 2 – was set as the number of degrees in a circle by ancient mathematicians.

Fahrenheit now had to choose standard reference values. Should the freezing point and boiling points of water be set as zero and 180?

He eventually decided to fix zero at the coldest temperature that he could make in his laboratory. Salts, when mixed with ice, lower the melting point of ice. Fahrenheit established the lower defining point, 0 degrees, at the temperature of a solution of brine made from equal parts of ice and salt.

With zero at the salty, icy brine temperature, the freezing point of pure water was 32 degrees. He added 32 and 180 to set 212 as the boiling point of water.

In 1742, the noted Swedish astronomer Anders Celsius, professor of astronomy at the University of Uppsala, proposed the temperature scale that was first known as centigrade – now Celsius.

Celsius set the freezing and boiling points of water at 100 degrees apart. His system set boiling at zero and freezing at 100, but this was reversed in 1750 by Martin Stromer, Celsius’ successor at Uppsala.

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