What is Mercury-in-glass thermometer?
[[Image:Mercury Thermometer.jpg|thumb|upright|Mercury-in-glass thermometer for measurement of room temperature.]] The '''mercury-in-glass thermometer''' was invented by [[Daniel Gabriel Fahrenheit]] in [[Amsterdam]] (1714). It is a bulb containing [[Mercury (element)|Mercury]] attached to a glass tube of narrow diameter. The [[volume]] of mercury in the tube is much less than the volume in the bulb. The volume of mercury changes slightly with temperature. The small change in volume drives the narrow mercury column up the tube. The space above the mercury may be filled with nitrogen or it may be at less than [[atmospheric pressure]], a partial [[vacuum]]. Mercury cannot be used to measure temperatures lower than -39˚C (as mercury freezes at that point) or temperature higher than 356.7˚C (the boiling point of mercury). Mercury has been replaced largely by [[alcohol]] for use in thermometers. [[Ethanol]] is cheaper and safer than mercury and can be used as low as -80˚C. However, ethanol boils at 78°C (172.4°F), which means its upper limit is much lower than mercury thermometers. {{science-stub}} [[Category:Medical equipment]] [[Category:Measuring tools]] [[Category:Thermometers]]