formaldehyde (fôrmălˈdəhĪdˌ) [key], HCHO, the simplest aldehyde. It melts at - 92°C, boils at - 21°C, and is soluble in water, alcohol, and ether; at STP, it is a flammable, poisonous, colorless gas with a suffocating odor. Formaldehyde is used in the preparation of dyes, in the production of Bakelite and other plastics and synthetic resins, and for several other purposes. Pure gaseous formaldehyde is uncommon, since it readily polymerizes into paraformaldehyde, a white crystalline solid. Paraformaldehyde in the form of candles has been used for fumigating rooms, since it yields formaldehyde when heated. Formalin is a 40% by volume solution of formaldehyde in water, usually with a small amount of methanol (methyl alcohol) added to prevent polymerization; it is used as an antiseptic, disinfectant, and preservative for biological materials. Formaldehyde is prepared commercially by passing methanol vapor mixed with air over a catalyst, e.g., hot copper, to cause oxidation of the methanol; it is also prepared by the oxidation of natural gas. It forms formic acid when it is oxidized. The IUPAC name for formaldehyde is methanal.