Methanal. Computer illustration of a molecule of methanal, or formaldehyde (formula HCHO). Atoms are depicted as cylinders and are colour-coded: carbon (yellow), hydrogen (white) and oxygen (red). Methanal is a colourless gas with a pungent odour. It is soluble in water up to 52%. A commercial solution, formalin, contains about 37% methanal, and is used for sterilisation and the preservation of biological specimens. Methanal is also used in the manufacture of urea, phenol, and poly-formaldehyde resins.