formaalein

Formaalein, more commonly called formalin, is a solution of formaldehyde in water, typically containing about 37% formaldehyde by weight and small amounts of a stabilizer such as methanol to reduce polymerization. It is widely used as a preservative, fixative, and disinfectant in medical, laboratory, and industrial settings. In solution, formaldehyde exists in equilibrium with methylene glycol, and the active species are responsible for its preservative and crosslinking properties.

Common uses include tissue fixation in histology and pathology, embalming, and surface disinfection. Formalin’s rapid penetration and ability to form crosslinks with proteins make it effective for preserving biological specimens and preparing slides for microscopic examination. It is also used in some industrial processes and as a biocide in certain water treatment contexts.

Safety and handling are important considerations. Formaldehyde is a recognized occupational exposure hazard and is classified as a human carcinogen by major health authorities. Inhalation or skin contact can cause irritation and more serious health effects with sufficient exposure. Work with formalin requires appropriate engineering controls, such as a fume hood, and personal protective equipment, including gloves and eye protection. Containers should be kept tightly closed, protected from heat, and stored in a well-ventilated area away from incompatibles.

Disposal of formalin must follow local regulations for hazardous chemical waste. Spills should be contained and cleaned up with absorbent material, with proper ventilation and disposal as hazardous waste.