Mercury has more meanings than you can shake a stick at. Here are some of the more relevant and major examples.
 The god
The original use of "Mercury" as a name was for the Roman version of the Greek god Hermes, who was the "Messenger of the Gods" and known for his great speed. Both the planet and the element (and, most likely, the make of Ford automobile) are named after the Roman god Mercury.
 The planet
Mercury is the planet that is closest to the Sun. It is also the smallest planet in the Solar System, now that Pluto has been
demoted to reclassified as a "dwarf planet". Since it is the innermost planet, it has the quickest orbital period (88 days), and its surface temperature ranges between boiling and freezing; the former is due to the planet's close proximity to the sun and the latter is due to the thin atmosphere letting heat escape, in contrast to Venus's very thick atmosphere which keeps much of the heat in. Most importantly, the orbit of Mercury cannot be accurately predicted using the laws of mechanics derived by Newton and it wasn't until Einstein's general relativity, which explains gravity as distortions in spacetime, that the orbit could be predicted accurately. Scientists have attributed a partially molten core to be the source of the anomaly in Mercury's orbit.
 The music
Mercury, the Winged Messenger is the scherzo section of Gustav Holst's suite of tone poems, "The Planets".
 The element
The metallic element mercury - also known as quicksilver ("quick" in the sense of "living") - is unique in being a liquid metal at room temperature, which is defined as somewhere in the region of 295°K. What makes this trait truly unique is not merely that it is a metal that is liquid at room temperature, but also that it does not "wet" glass (meaning it doesn't stick to glass like water does). Gallium is a metal whose melting point is almost exactly room temperature, allowing one to melt it with one's own hand's body-heat, but it does wet glass, and it tends to supercool; also, like water, gallium expands slightly when it is solidified. Caesium will be liquid on a hot day or at body temperature above 301°K, but reacts quite violently with water; bromine is also a liquid at room temperature but it is a halogen, not a metal. Mercury's atomic number is 80 and symbol is Hg after its Latin name of hydrargyrum, meaning "watery" (i.e. liquid) silver. It has been used extensively in thermometers, manometers (hence the pressure measurement of "millimetres of mercury" or "mmHg") and electrical switches. With moderate exposure it is also a neurotoxin, particularly when organic mercury compounds like methylmercury are formed. Historically, mercury compounds were used in hat making; the neurological effects of mercury exposure may have resulted in the expression "mad as a hatter".
 The mercury militia (or, actual dangers vs. woo)
The "mercury militia" is a term coined by Orac of Respectful Insolence to describe a collective of quacks and their supporters who believe just about anything containing the slightest bit of mercury is toxic or deadly. Mercury is, of course, dangerous in certain doses. The operative word being "doses." Different chemical forms of mercury also have different levels of toxicity; elemental mercury is pretty toxic, and dimethylmercury is gram-for-gram one of the most poisonous substances known, but the mercury in thimerosal is relatively harmless.
The general logic of the "mercury militia" types is that mercury can be dangerous, therefore anything containing mercury is dangerous. If you grew up in a house with a mercury thermometer in the window, it's probably time to start guzzling chlorella supplements! This is generally a failure to understand the golden rule of toxicology: "The dose makes the poison" (or the dose-response curve, to be technically correct). This line of reasoning is common to many types of "chemophobia." Here is a brief overview of real dangers versus fear-mongering:
- Shattering mercury thermometers. Don't try this at home, kids.
- Mercury emissions from power plants.
- Mercury in fish. However, this is often blown out of proportion by quacks who insist nearly any consumption of fish will lead to mercury poisoning. In reality, the danger is related to what kind of fish you eat and how much of it you eat (see the FDA guidelines below).
- Broken CFL light bulbs. Another favorite of quacks, who will claim that using fluorescent bulbs will lead to mercury poisoning. This is false — the CFLs are only dangerous when broken, although as in many cases, the danger is in the dose, and the dose of mercury vapor from one or two broken CFLs really isn't enough to panic about most of the time. Fluorescent lights rely on a tiny amount of ionized mercury to conduct electricity through their tubes, although even in large, commercial-sized bulbs it's only a milligram amount.
- Batteries, certain electronic equipment, and certain antique devices.
- Dimethylmercury[wp] is staggeringly toxic and can diffuse with ease through rubber gloves. Incredibly, it was considered as a possible rocket propellant in the 1950s, but its true danger wasn't revealed until the 1997 death of chemist Karen Wetterhahn from a tiny drop of the stuff. Fortunately, you're not likely to run into the stuff outside of chem labs.
- The Mercury Maze. A freaking toy!
- Its use in a compound used to preserve vaccines, thiomersal, has led to one common element of vaccine hysteria, even though the compound has been shown not to be bioaccumulative and isn't used as extensively as anti-vax campaigners lead people to think.
- Mercury amalgam fillings are the basis for most dental woo.
- Mercury as a quack cure has been consigned to the dustbin of history for the most part, but it's still used in traditional Chinese and Ayurvedic medicine.
- Mercury as a mainstream medical treatment for 2nd-stage syphilis, popular when syphillis was first introduced to the Old World near the end of the Renaissance. The cautionary saying went: "A night with Venus, a lifetime with Mercury."
 Mercury and crankery
The mercury militia is responsible for a wide range of crank ideas purporting to diagnose and cure mercury poisoning. These include:
- Filling extraction kits and methods (again, see dental woo).
- Autism as a symptom of mercury poisoning.
- Use of chelation for conditions that are not mercury poisoning, e.g. autism.
- Use of hair analysis for diagnosing mercury poisoning.
- Use of a "provoking agent" prior to urine testing to discover "hidden body stores". This temporarily raises heavy metals in the urine and jeopardizes the results of legitimate urine tests. .
- "Cleansing" methods such as colonic irrigation and detox diets. These diets often include algal supplements such as chlorella and spirulina or are a form of liquid fast such as the lemonade diet.
- Lupron therapy (see also the Geier family).
There's also "red mercury", which is claimed to be a code name for a substance used in triggering compact nuclear devices. In actuality, it probably doesn't exist and was probably made up as bait to track people trying to obtain nuclear weapons materials on the black market. The name may have been inspired by mercury-containing substances like mercury fulminate, a contact explosive used in ammunition cartridges, and mercury (II) thiocyanate or "Pharaoh's Serpent", a substance with similar but more dramatic properties to black snake fireworks, which are generally considered a safer alternative. Whether the probably fictional "red mercury" is actually supposed to be a mercury compound is anyone's guess.
- What Is Mercury Poisoning? Scientific American
- Here, have some mercury pills for your insomnia…, Doubtful News.
- March of the Mercury Militia, Lafayette Skeptics
- That Quacking Sound in Colonial America, Colonial Williamsburg Journal
Red mercury may well mean mercury oxide, which is red and formed by heating mercury above 350C.
- ↑ Isao Tomita's 1976 electronic version of Mercury, the Winged Messenger
- ↑ Queen: The Ultimate Illustrated History of the Crown Kings of Rock, page 22 (and who clearly know nothing about astrology - houses (ie constellations) rise, planets are in the houses.
- ↑ http://news.bbc.co.uk/earth/hi/earth_news/newsid_9243000/9243902.stm
- ↑ See the copious number of his posts on the mercury militia.
- ↑ And Joseph Mercola can sell you some for a one-time low price!
- ↑ What to do if a thermometer breaks, EPA
- ↑ Controlling Power Plant Emissions: Overview, EPA
- ↑ The FDA publishes guidelines for mercury in fish and shellfish and mercury levels in commercial fish and shellfish.
- ↑ Cleaning up a broken CFL, EPA
- ↑ Which is not to say that one should go breaking fluorescent lights for fun, but a broken bulb in a well-ventilated area isn't exactly cause for a Superfund project.
- ↑ See the EPA's list of Consumer and Commercial Products containing mercury.
- ↑ No, really!
- ↑ Mercury and Chinese herbal medicine,Issue: BCMJ, Vol. 46, No. 9, November 2004, page(s) 442 Letters H.C. George Wong, MD.
- ↑ Mercury in Traditional Medicines: Is Cinnabar Toxicologically Similar to Common Mercurials?, doi: 10.3181/0712-MR-336 Exp Biol Med (Maywood) July 2008 vol. 233 no. 7 810-817.
- ↑  How the "Urine Toxic Metals" Test Is Used to Defraud Patients
- ↑ In the real, non-conspiracy world, nuclear warheads usually use some form of polymer-bonded explosive, i.e. a solid explosive like TNT or RDX bound into a solid plastic matrix, that starts a fission explosion, which is used to fire a secondary charge that contains the fusion fuel. Red mercury is supposed to be substantially more powerful, capable of triggering a supercritical state without a fission explosion. Needless to say, it's not necessarily impossible to do so with a chemical reaction, but it's very unlikely *cough*cold fusion*cough*.