What will happen to formalin when evaporated to dryness on a water bath?

When formalin is evaporated to dryness on a water bath, the water content will gradually evaporate, leaving behind a residue of formaldehyde and other components present in the solution. The formaldehyde may polymerize into paraformaldehyde, a solid polymer, upon concentration. This process can release vapors of formaldehyde, which are hazardous and require proper ventilation. Care should be taken to avoid overheating, as it can lead to decomposition and the release of toxic gases.