Formaldehyde. Computer graphic representation of a molecule of formaldehyde (methanal). Its molecular formula is HCHO. Atoms are depicted as spheres and colour- coded: carbon (grey), hydrogen (green), oxygen (red). Formaldehyde is a colourless gas with a pungent odour. It is soluble in water up to 52%; the commercial solution is known as formalin" and contains about 37% formaldehyde. It is a powerful germicide used for sterilization and for preserving pathological specimens. It is also used in the manufacture of urea, phenol, and poly- formaldehyde resins."