What's going on? Is the "-21" a typo, or is rock salt somehow different from what Fahrenheit used, or is there some transient effect not reflected in Fahrenheit's procedure, or is it something else I have not thought of?
Rik Littlefield, Senior Research Scientist, Pacific Northwest National Laboratory 4/22/01
freezing point depression
He eventually replaced the upper calibration point at blood temperature with the boiling point of water. He discovered that the boiling point of water could be reliably used as a calibration point if atmospheric pressure was fixed, a fact that earlier temperature scale architects had overlooked. The boiling point at normal atmospheric pressure was set to 212°F, exactly 180 degrees between the freezing point of water and the boiling point of water, perhaps because 180 degrees is the number of degrees between opposite poles.
It always takes longer than you think it's going to take, even when you take into account Hofstadter's Law.
|Phase map for salt water. Drawn from a diagram by R. E. Dickerson (Note 3)|
By mixing salt, ice, and water so that at least 23.3% of the mixture was salt, Fahrenheit should have reached the eutectic point- in theory. But in practice:
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