Formaldehyde (molecular formula H2-C=O; CAS number 50-00-0) is a colourless gas, flammable and highly reactive at room temperature. Formaldehyde can also be obtained commercially as a 30–50% (by weight) aqueous solution, known as formalin. In ambient air, formaldehyde is quickly photo-oxidized in carbon dioxide.
Formaldehyde has various applications in science and preservation including biological research, histological exams/microscopy, vaccine production, disinfection and sterilization, taxidermy, anatomical and forensic studies, funeral services, and the preservation of zoology and botany specimens in museums.