Humans are already prone and exposed to the changing temperatures present on Earth. How we react to certain temperatures clearly signifies that we are still alive. Moreover, every thing under the sun- be it living or non-living has its own way of reacting to certain temperatures. Even so, in determining temperatures we used the thermometer to know precisely the temperature reading in a much clearer sense. Thermometers are simple scientific instruments based on the idea that metals change their behavior in a very precise way as they get hotter (gain more heat energy). We already know since our childhood that the red liquid which is actually put inside a thermometer, rises when its hot but tends to drop when its cold.
But how does that red liquid react to temperatures? What's really the phenomenon behind?
During elementary classes, we were already taught that metals are conductive- reactive too. Yes! When applied with varying temperatures, they tend to react in such a way that their molecules move apart or closely which causes vibration due to expansion. One of such phenomenon is called thermal expansion which will be discussed on the proceeding topics. This blog offers you an insight about how that red liquid Mercury (Hg) reacts to certain temperatures; what's the reason why of all liquids, it's used to be put inside a thermometer; why when heated it goes up and when cold goes down.
Mercury is a chemical element with symbol Hg and atomic number 80 and atomic mass of 200.59. It is commonly known as quicksilver and was formerly named hydrargyrum. A heavy, silvery d-block element, mercury is the only metallic element that is liquid at standard conditions for temperature and pressure; the only other element that is liquid under these conditions is bromine, though metals such as caesium, gallium, and rubidium melt just above room temperature. It reacts as temperature increases by expanding to a predictable amount; this property made it useful in thermometers until they were phased out in favor of less toxic alternatives.
Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide). The red pigment vermilion is obtained by grinding natural cinnabar or synthetic mercuric sulfide.
Mercury is used in thermometers because it has high coefficient of expansion. Hence, the slightest change in temperature is notable when it's used in a thermometer. Also, mercury has a freezing point of -38.83 °C and boiling point at 356.7 °C, this gives a very big range to measure temperatures for may general purposes, also it does not stick to (wet) the capillary wall of the thermometers, and its easy to obtain in its elemental form.
Mercury’s volume coefficient of expansion is 0.00018, so it expands by .018 percent in volume for every degree of temperature increase. To make the difference easier to see, a mercury thermometer contains a reservoir of the metal and a thin glass capillary into which it can expand. The mercury in the reservoir grows in volume as temperatures rise, but the walls of the reservoir constrain the mercury; it has nowhere to go but into the thin column, which converts the slight volume change into a more noticeable linear change.
In addition to its expanding and contracting with temperature, liquid mercury freezes solid at -38.83 °C (-37.89 °F). Because of this, mercury thermometers have limited utility in very cold places where temperatures dip to below mercury’s freezing point. Alcohol thermometers, which freeze at much lower temperatures, are used instead.
Liquid mercury responds to very high temperatures by boiling into a vapor; this occurs at 356.73 °C (674.11 °F). As with most liquids, reduced pressures lower mercury’s boiling point. To circumvent the limitations of mercury, high-temperature thermometers use thermocouples, infrared light sensors and other ways of measuring hot objects.
Websites:
Author/Books:
Introduction
Liquid Mercury
Element in Peiodic table
Vermilion
Mercury
Thermal Expansion
Mercury Expansion
