Technology
The Historical Calibration of the Fahrenheit Temperature Scale
The Historical Calibration of the Fahrenheit Temperature Scale
The Fahrenheit temperature scale, developed by Daniel Gabriel Fahrenheit in the early 18th century, has its origins rooted in practical applications and human experience rather than the precise calibration points used in today's systems like Celsius. This article delves into the history and rationale behind the calibration of this temperature scale, focusing on the specific points that were chosen and how they compare to modern scales.
Introduction to the Fahrenheit Scale
Developed in the early 18th century by Daniel Gabriel Fahrenheit, the Fahrenheit temperature scale was initially used for a wide range of practical applications. Unlike the Celsius scale, which is calibrated based on the freezing and boiling points of water, the Fahrenheit scale has meaningful reference points that were more aligned with the temperature extremes and human body temperature of the time.
Zero Degrees Fahrenheit (0°F)
0°F was set by Fahrenheit based on a mixture of ice water and salt brine. This mixture could produce temperatures colder than any that he expected to encounter in practical use. The primary intention behind this calibration was to establish a temperature that could be reliably reached in laboratory settings without the need for specific equipment. This point was not an arbitrary choice but rather a result of the available materials and technologies of the time.
One Hundred Degrees Fahrenheit (100°F)
100°F was a surprisingly high value compared to the freezing point of water. This point was initially set to represent the approximate human body temperature, which was then considered to be around 100°F. As medical science advanced and more accurate body temperature measurements were made, it became known that the average body temperature is around 98.6°F. This point, while based on an approximation, provided a practical and relatable reference point for people of the time.
Historical Calibration Points of Fahrenheit
According to a paper submitted by Fahrenheit to the Royal Society, he identified three points for calibrating his thermometers:
First Point (0°F): This was determined by placing a thermometer in a mixture of ice water and ammonium chloride or sea salt. The liquid in the thermometer would drop to the point marked with a zero. Second Point (32°F): This was based on the freezing point of water when mixed with ice and without any salts. This point was later standardized as the freezing point of pure water. Third Point (96°F): This was calibrated based on the temperature of a healthy human body when alcohol was introduced under the arm or in the mouth. This point was set to 96°F, which is a round number that is easily remembered.Transition to Modern Calibration Points
As Anders Celsius refined his temperature scale, he fixed the boiling and freezing points of water at 100°C and 0°C, respectively. Fahrenheit adjusted his scale to fit these points, making the boiling point of water 212°F and the freezing point 32°F. This adjustment resulted in a more intuitive and evenly spaced scale with a 180° range between the two points.
Conclusion
The Fahrenheit temperature scale, while rooted in practical applications, was calibrated based on the temperatures that were easily achievable and relatable to the time it was developed. Despite the initial points being based on practical and not scientific measures, the scale has stood the test of time and continues to be used in various applications, particularly in the United States. Understanding the historical context and rationale behind the calibration points helps us appreciate the evolution of our temperature measurement systems.