This substance is an aqueous (liquid) form of the gas formaldehyde. In most applications, the ratio of water to formaldehyde is approximately forty percent by volume or thirty-seven percent by weight. Additionally, Formalin usually has a stabilizer, such as methanol to prevent the substance from hardening into a polymer. The stabilizer makes up another ten to twelve percent of the solution. In fact, Formalin is usually produced in large quantities by oxidizing methanol, as this produces the proper ratio of formaldehyde and water. The substance has a strong, off-putting odor.
Applications of Formalin are usually as a means of embalming and preserving tissue. For the most part, Formalin is used to embalm animals as well as tissue samples, rather than humans. If the solution is diluted to a sufficiently low amount, it can even be applied as a disinfectant or an antibacterial wash. Formalin is sometimes used in aquariums to kill parasites that feed on fish.