Quicksilver, formally known as the element mercury (chemical symbol Hg), is recognized for its unique physical properties. It is the only metal that exists as a liquid at standard room temperature, presenting as a heavy, silvery-white, and highly dense fluid. This exceptional characteristic led to its ancient recognition across many cultures. For centuries, this dual nature—a captivating element with later-recognized toxicity—has shaped its vast and often contradictory applications.
Historical Applications of Quicksilver
Before the 20th century, mercury’s toxicity was not fully understood, leading to its widespread use in numerous historical applications. A primary industrial use was the extraction of gold and silver through the amalgamation process. Mercury readily binds with these precious metals, forming an amalgam that was heated to evaporate the mercury, leaving the purified metal behind. This method was widely employed during the Gold Rush eras and remains a concern in artisanal mining today.
In medicine, mercury compounds were used extensively, notably in the treatment of syphilis from the 16th to the 20th century, often with devastating side effects. Traditional Chinese and Ayurvedic medicines also utilized mercury derivatives for various ailments.
A famous application involved the felt-making industry, where mercuric nitrate was used to process animal furs for hats. Workers exposed to the mercury vapor developed neurological symptoms, which gave rise to the phrase “mad as a hatter.” Furthermore, the compound cinnabar, or mercuric sulfide, was used as a brilliant red pigment in cosmetics and art, and elemental mercury was used in the production of mirrors.
Essential Industrial Uses
Despite its decline in consumer products, mercury’s unique properties—such as high conductivity and consistent volume expansion—make it difficult to replace in certain industrial processes and specialized equipment. One of the largest historical industrial uses is the chlor-alkali process, which uses mercury cells to produce chlorine gas and caustic soda (sodium hydroxide). While this process is being phased out globally due to environmental concerns, many facilities still rely on this method.
Mercury is also used to ensure high performance and reliability in certain electrical components, particularly in switches and relays. Specialized devices, like mercury displacement relays, utilize the liquid metal to complete a circuit, offering advantages such as low contact resistance and non-eroding contacts in industrial controls. High-efficiency lighting, such as compact fluorescent lamps (CFLs) and high-intensity discharge lamps, also contain small amounts of mercury vapor. When electricity passes through, the mercury atom is ionized, producing ultraviolet light that excites the phosphors coating the inside of the bulb to create visible light.
Artisanal gold mining continues to rely on mercury amalgamation because it is inexpensive and simple to perform. This largely unregulated practice results in significant environmental release of the element, contributing substantially to global mercury pollution. In most other industrial applications, the element is contained within sealed or regulated systems to minimize the risk of human exposure and environmental release.
Presence in Consumer and Medical Items
The average person is most likely to encounter quicksilver in specific medical and measurement devices, though its use has been drastically reduced. Historically, elemental mercury was the core component in fever thermometers, barometers, and sphygmomanometers (blood pressure cuffs) due to its precise and stable volume changes. Although these devices are mostly replaced by digital or non-mercury alternatives, they can still be found in specialized hospital settings.
In dentistry, mercury is a primary component of dental amalgams, or silver fillings, which are alloys composed of about 50% elemental mercury mixed with silver, tin, and copper. When mixed, the mercury reacts with the other metals to form a durable, stable filling material. While regulatory bodies affirm that the small amount of mercury vapor released from these fillings is safe for most adults, many countries are actively working to phase down their use.
In the pharmaceutical sector, an organic mercury compound called Thimerosal has been used as a preservative in multi-dose vaccine vials since the 1930s. Thimerosal is metabolized to ethylmercury, which is distinct from the more toxic methylmercury found in fish and is cleared from the body more quickly. As a precautionary measure, thimerosal has been removed from nearly all childhood vaccines in the United States and Europe, though it remains in some multi-dose influenza vaccine formulations.
Global Efforts to Eliminate Mercury Use
The continued use of quicksilver is constrained by its proven toxicity, which affects the central nervous system and is particularly dangerous to developing fetuses and young children. Mercury is a potent neurotoxin that accumulates in the food chain through bioaccumulation, with the organic form, methylmercury, posing the greatest threat via the consumption of contaminated fish. The recognition of these global health risks has led to significant international regulatory action.
The primary framework for reduction is the Minamata Convention on Mercury, a global treaty that entered into force in 2017. This international cooperation aims to protect human health and the environment by controlling the entire lifecycle of mercury.
Key Requirements of the Minamata Convention
The agreement mandates several actions, including:
- The phase-out of the manufacture, import, and export of many mercury-added products (e.g., thermometers, specific batteries, and some fluorescent lamps).
- The control and reduction of mercury use in industrial processes like chlor-alkali production.
- The control and reduction of mercury use in artisanal gold mining.
- Controlling the entire lifecycle of mercury, from mining to waste disposal.