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methanal (formaldehyde, HCHO) Colourless, inflammable, poisonous gas with a penetrating odour. It is the simplest aldehyde and is produced by the oxidation of methanol by air. German chemist August von Hofmann (1818–92) discovered it in 1867. Most methanal is in the form of formalin. Methanal is used in the manufacture of dyes and plastics. Chief properties: r.d. 0.82; m.p. −92°C (−133.6°F); b.p. −19°C (−2.2°F).