Formalin is a water solution of formaldehyde (HCHO). Its appearance is colorless, transparent and corrosive. Because of the strong volatility of formaldehyde, it will emit a strong pungent odor immediately after opening the bottle.

Formaldehyde is a compound of carbon, hydrogen and oxygen. It is in a gas state under normal conditions and has the characteristics of strong irritation to the eyes and respiratory organs [1].

Formaldehyde content is 35% to 40% (usually 37%) in aqueous solution, and 10% - 15% methanol is added to prevent polymerization. It has the functions of antisepsis, disinfection and bleaching. Different fields have different roles.