Mercury expands and shrinks at a more steady pace than most other substances when heated or cooled. It also has a large temperature range between its boiling and freezing points. Liquid mercury is an extremely toxic substance and should be handled by trained personnel.
When mercury freezes it becomes solid metal. Before it can be worked with, it must be melted back down again. This process of melting and then refreezing mercury is called "quenching". When quenched, the mercury becomes a glass. The color of the glass depends on how it was treated during processing - blue-gray for untreated material, green-black for treated with zinc, white for tin-plated specimens.
As mercury heats up it becomes a liquid. At 38.9 degrees Celsius (101.3 degrees Fahrenheit) it starts to boil and vaporize. Above 485 degrees Celsius (900 degrees Fahrenheit), it begins to burn. Vaporized mercury forms bubbles when it is illuminated with light from an electric bulb or candle flame. These bubbles expand rapidly and disappear, leaving small holes in the glass surface.
The term "vapor pressure" is used to describe the amount of vapor that is present in relation to temperature. At standard conditions (0 degrees Celsius, or 32 degrees Fahrenheit), the vapor pressure of mercury is very high (about 1 atmosphere).
Mercury is stable (it does not react) in air, water, acids, and alkalis. When mercury is exposed to air, it will gradually lose weight because oxygen takes away some of its electrons.
When mercury is hot, it can be toxic. When mercury is cold, it can be brittle and break easily. Below -58 degrees F (–50 degrees C), mercury becomes a liquid. At that point, it is extremely dangerous because there is less chance that you would feel the heat from the element if it were liquid. The chemical symbol for mercury is Hg. It has an atomic number of 80 and a mass equal to 198.91."
Hg is a poisonous substance that can cause brain damage and death if it enters your body through the mouth, nose, or lungs. Small amounts are found in almost all foods. The only way to be sure you do not eat any dangerous levels of mercury is by not eating fish or other marine animals that contain high levels of this element. Scientists think that the slow release of mercury into the environment may be responsible for a growing number of severe allergies among children. These discoveries have led many people to avoid mercury-containing dental fillings and other products.
Gabriel Daniel Fahrenheit, a German-Dutch scientist, invented the mercury thermometer in 1714. Before that time, people used ice baths to measure body temperatures. The mercury thermometer is still used today in hospitals all over the world.
When mercury freezes, it takes on a hexagonal shape and can be broken off into thin sheets called cryolite. This is what gives glass its color: red for ruby, white for silver, and blue for azurite.
As mercury melts, it takes on a liquid form that is almost as dense as water. This makes mercury useful for plumbing and electronics where weight matters. If you put a lump of solid mercury in your pocket, it will stay there until you melt it down and use it again.
People have used mercury thermometers for medicine as well as science. Doctors once thought that if you added heat to a body part that had been injured in some way, it would help heal the injury faster. This practice continues today in acupuncture treatments. Warm needles are inserted into specific points on the body to relieve pain and treat diseases.
The first known reference to using mercury thermometers to measure body temperatures occurred in 1648.
Even at low temperatures, mercury does not evaporate quickly. Because it is a metal, it conducts heat well. This implies that it responds swiftly to temperature fluctuations. Except for the actual peak temperature, the rise in mercury is continuous or linear to increases in heat. Other metals have less ability to conduct heat so they must be heated more thoroughly to raise their temperature.
Because of its property of conducting heat well, mercury is useful for making high-resolution thermometers capable of detecting small changes in temperature. When used in conjunction with a glass tube, mercury thermometers are sensitive enough to measure temperatures as low as -150 degrees C. By comparison, most metal thermometers break down below -40 degrees C.
Metal thermometers need to be extremely thin and flat to show an accurate reading. This is difficult if not impossible to do with metal because even gold has a certain thickness that makes it impractical to use for thermometers.
Mercury's ability to smoothly and consistently transmit heat enables it to be used in automatic devices such as alarm clocks and kitchen timers. These devices require a stable constant temperature environment in order to function properly. Other components within these devices may fail if exposed to sudden large changes in temperature.
Metal components would have to be removed and replaced whenever the device is turned on or off which would be inconvenient for the user.