Formaldehyde is a gas at room temperature and is commercially available as a 37% solution in water, which is called formalin. As a gas, it polymerizes into a white powder called Paraformaldehyde.
Explanation:
Para-formaldehyde (PFA) is the product of formaldehyde formed by a polymerization degree of 8–100 units. Due to decomposition, it has the smell of formaldehyde.
Para-formaldehyde forms white precipitate, if it is stored in the cold. Formalin contains little monomeric formaldehyde and mostly it forms a short chain of poly formaldehyde.
To limit the excess of polymerization, a small quantity of methanol is used.
