FORMALIN, an agneous solution containing 4o% of for maldehyde (q.v.), is a commercial product. After dilution this solution is used as a disinfectant, for the preservation of anatomi cal specimens, etc. It possesses the property of converting protein substances (q.v.) into a hard elastic mass insoluble in water. It is also used in photography. A photographic film with a gelatin basis is immersed in a dilute formalin solution for a short time to render the gelatin insoluble.