What’s Formalin?

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Formalin is a solution of the gas formaldehyde (CH2O) in water. A saturated solution contains about 40% by volume – or 37% by weight – of the gas, plus a small amount of a stabilizer, usually 10-12% methanol; this prevents polymerization. The liquid is used as an embalming fluid and for preserving animal specimens and tissue samples. It is also used, generally in a much more diluted form, as a disinfectant, antibacterial cleaner and in aquariums for the treatment of parasitic fish infections. The disinfectant properties of the solution are due to the presence of formaldehyde, which also gives it a pungent and irritating smell.

Production

Formaldehyde is produced industrially by the oxidation of methanol. Large quantities of the chemical are produced this way for use in the production of plastics and resins. Formalin is produced by dissolving the gas in water until the desired concentration is reached, up to a maximum of 40%. Since water is the other product of the reaction, the process can produce formalin directly. Formaldehyde in aqueous solution is unstable and tends to polymerize into larger molecules which are insoluble and therefore precipitate out of solution. For this reason, methanol is added to the solution, which prevents polymerization.

Property

Formalin is a colorless liquid with a strong, irritating odor, due to the release of formaldehyde gas. It is this compound that is primarily responsible for the chemical properties of the solution. The solution is neutral in terms of acidity and alkalinity, but can be oxidized to produce formic acid. Because it can be easily oxidized, it is a reducing agent. Strong formalin solutions are flammable and burn to produce carbon dioxide and water.

it is used

Formaldehyde solutions can be used as disinfectants and germicides, as they quickly kill potentially harmful bacteria and other microorganisms. They have a dehydrating effect and also combine with proteins, inactivating them and killing cells. Because of these properties, formalin is commonly used in aquariums to kill parasites that live on fish. It is used for this purpose only in very diluted solutions to avoid damaging the fish.

In histology and related disciplines, formalin is used extensively to preserve tissue specimens, a process known as fixation. The compound binds protein molecules together, increasing the stiffness of the sample and facilitating the preparation of thin slices for microscopic examination. It also prevents decay. Normally a 10% solution is used; as this is prepared with standard 40% formalin, the resulting liquid contains 4% formaldehyde.

The preservative properties of this solution make it suitable for long-term storage of animal and organ specimens, which can be stored in large glass jars filled with formalin. It is also used as a preservative in vaccines. One of the best known uses of this solution has been as an embalming agent. It is able to penetrate deep into the tissues, not only killing bacteria, but also helping the body structures to keep their shape. Cells altered by formaldehyde also resist future attack by bacteria and other microorganisms. However, it is no longer widely used for this purpose, due to health and safety concerns.
Another use is as a treatment for warts. It can be applied, heavily diluted, as a gel or solution. The compound appears to work by damaging the skin cells of the warts and possibly killing the virus responsible. It can, however, cause an allergic reaction in some people.

Health and safety issues
There are a number of risks associated with the use of formalin. Easily releases formaldehyde gas, which is both toxic and highly flammable. Accidental release of the solution can rapidly bring the concentration of this gas to dangerous levels, posing a direct threat to health and the risk of fire or explosion.
If swallowed, the solution has a corrosive effect on the mouth, tongue and oesophagus, causing pain, vomiting and bleeding. Other symptoms include kidney failure, central nervous system effects, and coma. The lethal dose for humans can be about 1 ml.

People are more likely to experience ill effects through inhaling the vapor. At low levels, it is irritating to the eyes and nose and can cause headaches. At higher levels, inhalation can lead to bronchitis and fluid buildup in the lungs. Contact with skin may cause irritation or dermatitis. Eye contact with very dilute solutions will cause irritation, but higher concentrations can damage the cornea and cause loss of vision.

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