Thermometers were once ubiquitous in old thermometers households. A variety of large beverage, food, automobile, tobacco, and electrical companies as well as a host of small local businesses manufactured them in glass, plastic, and metal. Some of the larger manufacturers also produced thermometers that were sold through drug stores and pharmacies.

The first thermometers were glass tubes that contained alcohol or mercury and depended on expansion with changes in temperature. In the 1700s a German instrument-maker named Gabriel Fahrenheit invented a thermometer with an inscribed scale that was more reproducible. He calibrated his thermometers using ice and salt water (which has a lower freezing point than fresh water) as zero points and the boiling and normal body temperatures of 96 and 98 degrees respectively.

Measuring Time: The Charm and Utility of Old Thermometers

This new numerical scale became known as the Fahrenheit and Celsius scales. While it is not clear who devised the Celsius scale, a number of people including Linnaeus and the Swedish instrument-maker Anders Celsius are given credit for establishing this system of measurement.

Today, most thermometers used in medical practice are electronic and use an infrared sensor to measure the temperature of a human or liquid. However, old thermometers containing mercury still exist in many homes and are considered hazardous waste. When broken, these mercury thermometers can be dangerous to children and adults. If the mercury inside a thermometer breaks, the glass should be sealed and the spilled liquid mercury should be cleaned up immediately. It is important to ventilate the room for a few hours after a spill as mercury vapors can be toxic.

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